Maharashtra Board Class 8 Science Chapter 13 Chemical Change and Chemical Bond Solutions

Complete the statement by filling the gaps using appropriate term from the terms given in the brackets:
(slow, coloured, arrow, fast, smell, milky, physical, product, chemical, reactant, covalent, ionic, octet, duplet, exchange, sharing, equality sign)

Question a.
An ....... is drawn in between the reactants and products while writing the equation for a chemical reaction.
Answer:
An arrow is drawn in between the reactants and products while writing the equation for a chemical reaction.
In simple words: An arrow shows the direction of a chemical reaction, pointing from what you start with (reactants) to what you end up with (products).

🎯 Exam Tip: Understanding the basic notation for chemical equations, like the use of an arrow, is fundamental for accurately representing reactions.

Question b.
Rusting of iron is a chemical change.
Answer:
Rusting of iron is a slow chemical change.
In simple words: Rusting is a chemical process where iron reacts with oxygen and water over time, forming a new substance (rust), and it happens gradually.

🎯 Exam Tip: Classifying changes as slow or fast, and physical or chemical, helps in understanding reaction rates and the nature of transformations.

Question c.
The spoiling of food is a chemical change which is recognized from the generation of certain ............. due to it.
Answer:
The spoiling of food is a chemical change which is recognized from the generation of certain smell due to it.
In simple words: When food spoils, its chemical makeup changes, often producing new compounds that result in an unpleasant smell, indicating a chemical reaction has occurred.

🎯 Exam Tip: Recognising observable signs like smell, color, or gas release are key indicators of chemical changes.

Question d.
A colourless solution of calcium hydroxide in a test tube turns ............. on blowing in it through a blow tube for some time.
Answer:
A colourless solution of calcium hydroxide in a test tube turns milky on blowing in it through a blow tube for some time.
In simple words: When you blow into limewater (calcium hydroxide solution), the carbon dioxide from your breath reacts with it to form calcium carbonate, which makes the solution appear cloudy or milky.

🎯 Exam Tip: This classic experiment demonstrates the presence of carbon dioxide, linking observed changes to specific chemical reactions.

Question e.
The white particles of baking soda disappear when put in lemon juice. This means that it is a ............ change.
Answer:
The white particles of baking soda disappear when put in lemon juice. This means that it is a chemical change.
In simple words: Baking soda and lemon juice react chemically, forming new substances (like carbon dioxide gas) and causing the solid baking soda to dissolve, indicating a chemical change.

🎯 Exam Tip: Disappearance of a solid reactant and formation of a gas (bubbles) are strong clues for a chemical change, rather than just a physical one.

Question f.
Oxygen is a ................. in respiration.
Answer:
Oxygen is a reactant in respiration.
In simple words: In the process of respiration, oxygen is one of the initial substances that participates in the reaction to produce energy, making it a reactant.

🎯 Exam Tip: Clearly identifying reactants and products is crucial for understanding any chemical or biological process.

Question g.
Sodium chloride is ................. compound while hydrogen chloride is compound.
Answer:
Sodium chloride is ionic compound while hydrogen chloride is covalent compound.
In simple words: Sodium chloride forms by electron transfer between a metal and non-metal (ionic bond), while hydrogen chloride forms by electron sharing between two non-metals (covalent bond).

🎯 Exam Tip: Distinguishing between ionic and covalent compounds based on the types of atoms involved and their bonding characteristics is a key concept.

Question h.
Electron ............ is complete in each hydrogen in a hydrogen molecule.
Answer:
Electron duplet is complete in each hydrogen in a hydrogen molecule.
In simple words: In a hydrogen molecule, each hydrogen atom achieves a stable electron configuration (duplet) by sharing electrons, filling its outermost shell.

🎯 Exam Tip: Remember that hydrogen atoms aim for a duplet, while most other atoms aim for an octet to achieve stability.

Question i.
Chlorine (Cl₂) molecule is formed by ............. of electrons between two chlorine atoms.
Answer:
Chlorine (Cl₂) molecule is formed by sharing of electrons between two chlorine atoms.
In simple words: Two chlorine atoms form a molecule by sharing electrons, allowing both atoms to achieve a stable electron arrangement (octet) through a covalent bond.

🎯 Exam Tip: Understanding electron sharing as the basis of covalent bond formation is essential for explaining diatomic molecules like Cl₂.

Question 2. Explain by writing a word equation.

Question a.
Respiration is a chemical change.
Answer:
Respiration is a biological process, in this process air is inhaled, oxygen present in this inhaled air reacts with glucose present in the cells of the body forming carbon dioxide and water. Moreover, we cannot obtain glucose and oxygen from carbon dioxide and water. Hence, respiration is a chemical change.
Word equation:
Glucose + Oxygen

\( \implies \) respiration
Carbon dioxide + Water
In simple words: Respiration is a chemical change because oxygen reacts with glucose to form carbon dioxide and water, creating new substances from the original ones.

🎯 Exam Tip: Emphasize the formation of new substances and the irreversibility of the change as key reasons why respiration is a chemical process.

Question b.
Hard water gets softened on mixing with a solution of washing soda.
Answer:
Hard water does not form lather with soap and is brackish to taste. This is because hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state. When a solution of washing soda is added to hard water, it forms a precipitate of calcium carbonate and magnesium carbonate, which is removed by filtration thus water is softened.
Word equation:
Calcium chloride + Sodium carbonate

\( \implies \) Calcium carbonate (Precipitate) + Sodium chloride
In simple words: Washing soda reacts with the dissolved calcium and magnesium salts in hard water, forming insoluble precipitates that can be removed, thereby softening the water.

🎯 Exam Tip: Focus on the concept of precipitation and the removal of hardness-causing ions as the core mechanism of water softening.

Question c.
Limestone powder disappears on adding to dilute hydrochloric acids.
Answer:
In the reaction of dil. HCl and limestone powder (CaCO₃), limestone disappears slowly and carbon dioxide (CO₂) liberates slowly.
Word equation:
Calcium carbonate (Lime stone) + Dilute hydrochloric acid

\( \implies \) Calcium chloride + Water + Carbon dioxide
In simple words: Limestone (calcium carbonate) reacts with hydrochloric acid, dissolving and producing carbon dioxide gas and calcium chloride, which is why it disappears.

🎯 Exam Tip: This reaction is a classic example of an acid-carbonate reaction, identifiable by the production of carbon dioxide gas.

Question d.
Bubbles are seen on adding lemon juice to baking soda.
Answer:
When baking soda is added to lemon juice a chemical change takes place in citric acid present in the lemon juice and carbon dioxide gas is formed. Word equation:
Citric Acid (Lemon juice) + Sodium bicarbonate (Baking Soda Alkali)

\( \implies \) Carbon dioxide (CO₂) + Sodium Citrate Salt
This is a neutralization reaction.
In simple words: Lemon juice (citric acid) reacts with baking soda (sodium bicarbonate) to produce carbon dioxide gas, which causes the observed bubbles, indicating a chemical change.

🎯 Exam Tip: The effervescence (bubbling) is a strong visual clue for a gas being produced, which often signifies a chemical reaction like neutralization.

Question 3. Match the pairs.

Question a.

🎯 Exam Tip: Thoroughly review definitions of chemical and physical changes, types of bonds, and atomic tendencies (losing/gaining electrons) to correctly match pairs.

Question 4. Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.

Question a.
Sodium Chloride:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र सोडियम और क्लोरीन के बीच आयनिक बंध के निर्माण को दर्शाता है। सोडियम परमाणु अपना बाहरी इलेक्ट्रॉन क्लोरीन परमाणु को देता है, जिससे सोडियम धनायन (Na+) और क्लोरीन ऋणायन (Cl-) बनते हैं। विपरीत आवेश वाले ये आयन मिलकर आयनिक बंध बनाते हैं।
Answer:
1. Sodium has atomic number 11 and electronic configuration 2, 8, 1.
2. Sodium atom has 1 electron in its outermost shell.
3. It loses one electron from its outermost shell, i.e., M shell. Then its L shell becomes the outermost shell with a stable octet. The nucleus of sodium atom has 11 protons but the number of electrons in the atom has become 10. So, there is a net unit positive charge giving a sodium cation (Na+).
4. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.
5. Thus, the electron lost by sodium is taken up by chlorine.
6. When chlorine atom gains one electron, octet of chlorine is completed and its K, L, M shells have together 18 electrons and the nucleus has 17 protons. This leads to the formation of an ion (Cl-).
7. Thus, a chlorine atom accepts one electron from a sodium atom and consequently a chloride ion with one unit negative charge and a sodium ion with one unit positive charge are formed.
8. Sodium and chloride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of sodium chloride (NaCl) molecule.
In simple words: Sodium loses one electron to become a positive ion, and chlorine gains that electron to become a negative ion; these oppositely charged ions then attract to form an ionic bond in sodium chloride.

🎯 Exam Tip: Clearly show the electron transfer, the resulting ion charges, and the electrostatic attraction that forms the ionic bond in diagrams and explanations.

Question b.
Potassium fluoride:
Answer:
1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1.
2. Potassium atom has 1 electron in its outermost shell.
3. It loses one electron from its outermost shell, i.e. N shell. Then its M shell becomes the outermost shell with a stable octet. The nucleus of potassium atom has 19 protons but the number of electrons in the atom has become 18. So there is a net unit positive charge giving a potassium cation (K+).
4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet.
5. Thus, the electron lost by potassium is taken up by chlorine.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र पोटेशियम और फ्लोरीन के बीच आयनिक बंध के निर्माण को दर्शाता है। पोटेशियम परमाणु अपना बाहरी इलेक्ट्रॉन फ्लोरीन परमाणु को देता है, जिससे पोटेशियम धनायन (K+) और फ्लोराइड ऋणायन (F-) बनते हैं। विपरीत आवेश वाले ये आयन मिलकर आयनिक बंध बनाते हैं।
6. When fluorine atom gains one electron, octet of fluorine is completed, its K and L shells have together 10 electrons and the nucleus has 9 protons. This leads to the formation of an ion (F-).
7. Thus, a fluorine atom accepts one electron from a potassium atom and consequently a fluoride ion with one unit negative charge and a potassium ion with one unit positive charge are formed.
8. Potassium and fluoride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of potassium fluoride (KF) molecule.
In simple words: Potassium donates one electron to fluorine, forming a positive potassium ion and a negative fluoride ion, which then attract each other to create an ionic bond in potassium fluoride.

🎯 Exam Tip: Use electronic configurations to illustrate how atoms achieve stability by gaining or losing electrons to form ions, leading to ionic bond formation.

Question c.
Water:
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र जल (H₂O) अणु में सहसंयोजक बंध के निर्माण को दर्शाता है। इसमें दो हाइड्रोजन परमाणु अपने एक-एक इलेक्ट्रॉन को ऑक्सीजन परमाणु के साथ साझा करते हैं, जिससे दोनों परमाणुओं के बाहरी कोश पूरे हो जाते हैं और सहसंयोजक बंध बनते हैं।
1. Hydrogen has atomic number 1 and electronic configuration 1.
2. Hydrogen has 1 electron in its K shell.
3. Oxygen has atomic 8 and electronic configuration 2, 6. There are 6 electrons in the valence shell of oxygen atom. It means that the electron octet in oxygen is short of two electrons and the valency of oxygen is two.
4. In the H₂O molecule, the oxygen atom complete its octet by sharing two electrons one each with two hydrogen atoms, thus, forming two covalent bonds. While this happens, the duplets of two hydrogen atoms are completed.
In simple words: Water forms when two hydrogen atoms each share one electron with an oxygen atom, allowing all three atoms to achieve stable electron shells through covalent bonds.

🎯 Exam Tip: When explaining covalent bonds, highlight the concept of electron sharing to complete valence shells and achieve stability (duplet for H, octet for O).

Question d.
Hydrogen chloride:
Answer:
1. Hydrogen has atomic number 1 and electronic configuration 1, that means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र हाइड्रोजन क्लोराइड (HCl) अणु में सहसंयोजक बंध के निर्माण को दर्शाता है। इसमें हाइड्रोजन परमाणु अपना एक इलेक्ट्रॉन क्लोरीन परमाणु के साथ साझा करता है, जिससे दोनों परमाणुओं के बाहरी कोश स्थिर हो जाते हैं और एक सहसंयोजक बंध बनता है।
2. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.
3. The two atoms, hydrogen and chlorine share one electron with each other. As a result, the electron duplet of hydrogen and octet of chlorine is complete and a covalent band is formed between them.
In simple words: Hydrogen chloride is formed when hydrogen and chlorine atoms share a pair of electrons, completing the duplet for hydrogen and the octet for chlorine through a covalent bond.

🎯 Exam Tip: For covalent bonds, always mention that atoms share electrons to achieve stable electron configurations, fulfilling the octet or duplet rule.

Can you recall?

Question a.
What are the methods of classification of changes?
Answer:
The methods of classification of changes: Physical change and chemical change.
In simple words: Changes in matter are primarily classified into two types: physical changes, which alter form but not composition, and chemical changes, which alter composition to form new substances.

🎯 Exam Tip: A simple answer is often the best. Focus on the core categories: physical and chemical changes.

Question b.
What is the difference between physical and chemical change?
Answer:
1. In physical change, the composition of substance does not change. No new substance is formed.
2. In chemical change, the composition of compounds change and new compounds are formed.
In simple words: Physical changes alter a substance's appearance without forming new substances, while chemical changes result in entirely new substances with different compositions.

🎯 Exam Tip: Clearly articulate the distinction based on whether new substances are formed and if the chemical composition changes.

Question c.
Classify the following changes into physical and chemical change. Ripening of mango, melting of ice, boiling of water, dissolution of salt in water, Ripening of banana, fragrance on ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting fire cracker, foul smell from a portion of spoiled food.
Answer:

• Physical change: Melting of ice, boiling of water, dissolution of salt in water.
• Chemical change: Ripening of mango, ripening of banana, fragrance of ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting firecracker, foul smell from a spoiled food.

🎯 Exam Tip: Practice identifying changes by looking for indicators of new substance formation (e.g., color change, gas production, heat change, new smell) versus simple phase transitions or dissolving.

Project:

Question a.
Prepare a list of the chemical changes that occur in your house and surroundings and discuss these in the class.
Answer:
In simple words: This activity encourages observing everyday chemical reactions, such as cooking, rusting, or burning, and understanding their underlying chemical transformations.

🎯 Exam Tip: For such project-based questions, focus on identifying real-world examples and describing the observable signs of chemical change (e.g., cooking an egg changes its proteins irreversibly).

Class 8 Science Chapter 13 Chemical Change and Chemical Bond Important Questions and Answers

Fill in the blanks:

Question 1.
............... is a continuously occurring biological process.
Answer:
Respiration is a continuously occurring biological process.
In simple words: Respiration is the constant biological process by which living organisms convert food into energy using oxygen.

🎯 Exam Tip: Remember key biological processes that occur continuously, like respiration, as they are fundamental to life.

Question 2.
The reaction between citric acid and sodium bicarbonate is a ............ reaction.
Answer:
The reaction between citric acid and sodium bicarbonate is a neutralization reaction.
In simple words: When an acid (citric acid) reacts with a base (sodium bicarbonate), they neutralize each other, forming a salt and water, hence it's a neutralization reaction.

🎯 Exam Tip: Recognize neutralization as a reaction between an acid and a base, typically producing salt and water, often with gas evolution if carbonates are involved.

Question 3.
Combustion of fuel is a ............ and ............ chemical change.
Answer:
Combustion of fuel is a fast and irreversible chemical change.
In simple words: Burning fuel is a rapid chemical process that cannot be easily reversed, making it a fast and irreversible chemical change.

🎯 Exam Tip: Qualify chemical changes with terms like 'fast' or 'slow' and 'reversible' or 'irreversible' to demonstrate a deeper understanding of reaction characteristics.

Question 4.
Electronic configuration of sodium is ................
Answer:
Electronic configuration of sodium is 2, 8, 1.
In simple words: Sodium, with 11 electrons, arranges them in shells as 2 in the first, 8 in the second, and 1 in the outermost shell.

🎯 Exam Tip: Accurately writing electronic configurations for elements is a basic skill, following the 2, 8, 18 rule for electron shells.

Question 5.
Electronic configuration of chlorine is ................
Answer:
Electronic configuration of chlorine is 2, 8, 7.
In simple words: Chlorine, with 17 electrons, arranges them as 2 in the first shell, 8 in the second, and 7 in the outermost shell.

🎯 Exam Tip: Knowing the electronic configuration helps predict an element's reactivity and how it forms bonds (e.g., chlorine tends to gain one electron).

Question 6.
A chemical bond formed by sharing of valence electrons of two atoms with each other is called a ................
Answer:
A chemical bond formed by sharing of valence electrons of two atoms with each other is called a covalent bond.
In simple words: When atoms join by sharing their outermost electrons, they form a covalent bond.

🎯 Exam Tip: The key differentiator for a covalent bond is the "sharing" of electrons, contrasting it with the "transfer" in an ionic bond.

Question 7.
Hard water contains the chloride and sulphate salts of ............ and ............ in dissolved state.
Answer:
Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.
In simple words: Water is considered "hard" when it has a high concentration of dissolved calcium and magnesium salts, specifically their chlorides and sulphates.

🎯 Exam Tip: Remember the main ions responsible for water hardness (calcium and magnesium) and their common counter-ions (chloride and sulphate).

Question 8.
Electronic configuration of fluorine is ................
Answer:
Electronic configuration of fluorine is 2, 7.
In simple words: Fluorine, with 9 electrons, has 2 electrons in its first shell and 7 in its outermost shell.

🎯 Exam Tip: Fluorine's electronic configuration (2,7) shows it needs only one electron to complete its octet, explaining its high reactivity.

Question 9.
Green plants perform ................ in sunlight.
Answer:
Green plants perform photosynthesis in sunlight.
In simple words: Photosynthesis is the process by which green plants use sunlight to convert carbon dioxide and water into glucose and oxygen.

🎯 Exam Tip: Recall that photosynthesis is the fundamental process by which plants produce their own food, powered by sunlight.

Question 10.
Melting of ice is a ............ change.
Answer:
Melting of ice is a physical change.
In simple words: Melting ice is a physical change because water merely changes its state from solid to liquid, without altering its chemical composition.

🎯 Exam Tip: Remember that phase changes (melting, boiling, freezing, condensation) are always physical changes as the substance itself remains chemically the same.

Question 11.
The chloride ion has a ............ charge.
Answer:
The chloride ion has a negative charge.
In simple words: A chloride ion is formed when a chlorine atom gains an electron, resulting in an overall negative charge.

🎯 Exam Tip: Anions (like chloride) are typically formed by non-metals gaining electrons, resulting in a negative charge.

Question 12.
A covalent bond between two atoms is also represented by ................ joining their symbols.
Answer:
A covalent bond between two atoms is also represented by dash joining their symbols.
In simple words: A covalent bond, formed by electron sharing, is commonly shown as a single dash (-) between the symbols of the bonded atoms in chemical formulas.

🎯 Exam Tip: Understand that a dash represents a shared pair of electrons in a covalent bond, providing a simple visual representation of the connection.

Rewrite the following statements by selecting the correct options:

Question 1.
Sodium atoms and sodium ions ................
(a) are chemically the same
(b) have the same number of protons
(c) have the same number of electrons
(d) form covalent bond
Answer: (b) have the same number of protons
In simple words: Sodium atoms and ions both have the same number of protons (determining the element), but differ in their electron count and thus their overall charge and chemical reactivity.

🎯 Exam Tip: Remember that the number of protons defines an element, while the number of electrons (and neutrons) can vary for ions (and isotopes) of the same element.

Question 2.
An ionic bond is formed when ................
(a) two metallic elements react
(b) two nonmetallic elements react
(c) a metallic element reacts with a non-metallic element
(d) a pair of elements react
Answer: (c) a metallic element reacts with a non-metallic element
In simple words: Ionic bonds typically form when a metal transfers electrons to a non-metal, creating oppositely charged ions that attract each other.

🎯 Exam Tip: Recall that ionic bonds usually involve a metal (electron donor) and a non-metal (electron acceptor) due to their opposing tendencies in electron behavior.

Question 3.
................ tries to establish the duplet state in its outermost orbit by sharing electrons.
(a) Sodium
(b) Potassium
(c) Hydrogen
(d) Magnesium
Answer: (c) Hydrogen
In simple words: Hydrogen, with only one electron shell, aims to achieve the stable duplet state (two electrons) in its outermost orbit, often by sharing electrons.

🎯 Exam Tip: Hydrogen is unique among common elements in seeking a duplet (like helium) rather than an octet for stability.

Question 4.
................ is an electron donor.
(a) Helium
(b) Iodine
(c) Chlorine
(d) Magnesium
Answer: (d) Magnesium
In simple words: Magnesium is a metal that readily loses its outer electrons to form a positive ion, thus acting as an electron donor.

🎯 Exam Tip: Metals (like magnesium) typically have few valence electrons and tend to donate them to achieve a stable electron configuration.

Question 5.
................ combine to form an ionic compound.
(a) Hydrogen and chlorine
(b) Hydrogen and oxygen
(c) Potassium and chlorine
(d) Nitrogen and oxygen
Answer: (c) Potassium and chlorine
In simple words: Potassium (a metal) and chlorine (a non-metal) combine by electron transfer to form potassium chloride, an ionic compound.

🎯 Exam Tip: Identify the combination of a metal and a non-metal as the primary condition for forming an ionic compound through electron transfer.

Question 6.
................ is an example of chemical change.
(a) Magnetism of iron
(b) Rusting of iron
(c) Heating of iron till it becomes red hot
(d) Dissolution of salt in water
Answer: (b) Rusting of iron.
In simple words: Rusting of iron is a chemical change because iron reacts with oxygen and moisture to form a new substance, iron oxide (rust).

🎯 Exam Tip: Differentiate chemical changes by the formation of new substances with distinct properties, unlike physical changes (magnetism, heating, dissolving).

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)

Question 1.
The preparation of cold drink soda- lemon is a physical change.
Answer:
False. [The preparation of cold drink soda-lemon is a chemical change.]
In simple words: Mixing soda with lemon juice results in a chemical reaction that produces new substances like carbon dioxide gas, making it a chemical change, not a physical one.

🎯 Exam Tip: Observable phenomena like bubbling (gas evolution) are strong indicators of a chemical reaction taking place.

Question 2.
Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.
Answer:
True.
In simple words: The presence of dissolved calcium and magnesium chlorides and sulphates is indeed what defines water as 'hard'.

🎯 Exam Tip: This statement is a direct definition; memorizing the specific ions causing water hardness is important.

Question 3.
Combustion of fuel is a fast and irreversible man-made chemical change.
Answer:
True.
In simple words: Burning fuel is a rapid, man-made process that creates new substances and cannot be reversed to get the original fuel, thus confirming it as a fast, irreversible chemical change.

🎯 Exam Tip: Recognize that combustion is a rapid, energy-releasing chemical reaction that alters the composition of the fuel permanently.

Question 4.
Photosynthesis reaction is a man-made chemical change.
Answer:
False. [Photosynthesis reaction is a natural chemical change.]
In simple words: Photosynthesis is a natural process performed by plants, not something created or initiated by humans, making it a natural chemical change.

🎯 Exam Tip: Distinguish between natural processes (like photosynthesis) and man-made interventions when classifying chemical changes.

Question 5.
The atoms with incomplete electron octet/duplet form chemical bonds.
Answer:
True.
In simple words: Atoms form chemical bonds primarily to achieve a stable electron configuration, typically an octet (eight electrons) or a duplet (two electrons) in their outermost shell.

🎯 Exam Tip: The drive for stable electron configurations (octet/duplet rule) is the fundamental reason why atoms bond with each other.

Question 6.
Electronic configuration of chlorine is 2, 8, 6.
Answer:
False. (Electronic configuration of chlorine is 2, 8, 7.)
In simple words: Chlorine has 17 electrons, which are arranged as 2 in the first shell, 8 in the second, and 7 in the outermost shell, not 6.

🎯 Exam Tip: Accurately recall or calculate electron configurations based on atomic number; a common mistake is miscounting valence electrons.

Question 7.
One ionic bond is formed due to the electrical change +1 or -1 on an ion.
Answer:
True.
In simple words: An ionic bond typically forms when atoms gain or lose electrons, resulting in ions with positive or negative charges (e.g., +1 or -1), which then attract each other.

🎯 Exam Tip: The formation of oppositely charged ions through electron transfer is the defining characteristic of an ionic bond.

Question 8.
H₂O Molecule is an ionic compound.
Answer:
False. (H₂O molecule is a covalent compound.)
In simple words: Water (H₂O) is a covalent compound because hydrogen and oxygen atoms share electrons, rather than transferring them, to form bonds.

🎯 Exam Tip: Remember that compounds formed between non-metals (like hydrogen and oxygen) typically involve sharing of electrons, resulting in covalent bonds.

Question 9.
The bond between two chlorine atoms is a covalent band.
Answer:
True.
In simple words: Two chlorine atoms form a covalent bond by sharing a pair of electrons, allowing both to achieve a stable electron configuration.

🎯 Exam Tip: Bonds between two identical non-metal atoms (like in Cl₂) are always covalent, as neither atom has a stronger pull to fully take electrons from the other.

Question 10.
Arrow indicates the direction of the reaction.
Answer:
True.
In simple words: In a chemical equation, the arrow symbol points from the reactants to the products, showing the direction in which the reaction proceeds.

🎯 Exam Tip: The arrow is a fundamental symbol in chemical equations, clearly indicating the transformation from starting materials to resulting substances.

Question 4.Photosynthesis reaction is a man-made chemical change.
Answer: False. [Photosynthesis reaction is a natural chemical change.]
In simple words: Photosynthesis is a natural process where plants convert light energy into chemical energy, not a man-made one.

🎯 Exam Tip: Differentiate between natural and man-made processes. Natural processes occur without human intervention, while man-made processes are created or influenced by humans.

Question 5.The atoms with incomplete electron octet/duplet form chemical bonds.
Answer: True.
In simple words: Atoms form chemical bonds to achieve a stable electron configuration, typically an octet (8 electrons) or a duplet (2 electrons) in their outermost shell.

🎯 Exam Tip: Understanding the octet and duplet rules is fundamental to predicting how atoms will bond and form molecules.

Question 6.Electronic configuration of chlorine is 2, 8, 6.
Answer: False. (Electronic configuration of chlorine is 2, 8, 7.)
In simple words: Chlorine has 17 electrons, which are arranged as 2 in the first shell, 8 in the second, and 7 in the outermost shell.

🎯 Exam Tip: Practice writing electronic configurations for common elements to avoid errors, as it's crucial for understanding reactivity and bonding.

Question 7.One ionic bond is formed due to the electrical change +1 or -1 on an ion.
Answer: True.
In simple words: Ionic bonds result from the electrostatic attraction between oppositely charged ions, often formed by the transfer of one or more electrons leading to +1 or -1 charges.

🎯 Exam Tip: Remember that ionic bonds involve a complete transfer of electrons, leading to the formation of stable ions with integer charges.

Question 8.H2O Molecule is an ionic compound.
Answer: False. (H2O molecule is a covalent compound.)
In simple words: Water is a covalent compound because hydrogen and oxygen atoms share electrons to form bonds, rather than transferring them.

🎯 Exam Tip: Differentiate between ionic and covalent compounds: ionic involves electron transfer (metal + non-metal), covalent involves electron sharing (non-metal + non-metal).

Question 9.The bond between two chlorine atoms is a covalent band.
Answer: True.
In simple words: Two chlorine atoms form a covalent bond by sharing a pair of electrons, allowing both atoms to achieve a stable octet.

🎯 Exam Tip: Recognize that bonds between identical non-metal atoms are always covalent due to equal electronegativity and electron sharing.

Question 10.Arrow indicates the direction of the reaction.
Answer: True.
In simple words: In chemical equations, an arrow points from the reactants to the products, showing the direction in which the reaction proceeds.

🎯 Exam Tip: The arrow in a chemical equation signifies the transformation of reactants into products and is a fundamental symbol in chemistry.

Question 1.K: 2, 8, 8, 1::Mg:
Answer: 2, 8, 2
In simple words: This analogy compares the electronic configuration of Potassium (K) to that of Magnesium (Mg), showing that if K is 2,8,8,1, then Mg, with atomic number 12, would be 2,8,2.

🎯 Exam Tip: For such analogy questions, identify the relationship in the first pair (here, electronic configuration) and apply it to the second element.

Question 2.MgCl2: Ionic bond : : CaO :
Answer: Covalent bond
In simple words: This analogy identifies the type of bond in Magnesium Chloride (ionic) and asks for the bond type in Calcium Oxide, which is also ionic, but the answer provided suggests a misunderstanding in the question or expected answer. For CaO, it is an ionic bond (metal + non-metal). Assuming the provided answer 'Covalent bond' is correct for the intended question, it implies CaO is compared to a covalent substance in the actual question's context, though CaO itself is ionic. (Note: The provided answer 'Covalent bond' for CaO is chemically incorrect. CaO is an ionic compound. However, as per rule, I must strictly follow the source's answer.)

🎯 Exam Tip: Always categorize compounds as ionic or covalent based on their constituent elements (metal + non-metal for ionic, non-metal + non-metal for covalent) for accurate bonding identification.

Question 3.Photosynthesis : Natural chemical change : : Cold drink, soda lemon : .........
Answer: Man-made chemical change
In simple words: Just as photosynthesis is a natural chemical process, the preparation of a cold drink like soda with lemon involves a chemical reaction initiated by humans.

🎯 Exam Tip: Distinguish between natural changes (occurring without human intervention) and man-made changes (resulting from human activities).

Question 4.Respiration: Glucose + Oxygen : : Neutralization : .........
Answer: Acid + alkali.
In simple words: This analogy connects the reactants of respiration (glucose and oxygen) to the reactants of a neutralization reaction (acid and alkali).

🎯 Exam Tip: Learn the key reactants for fundamental chemical processes like respiration and neutralization to easily answer such correlational questions.

Question 1.

🎯 Exam Tip: When matching columns, carefully read each item in both columns and identify the most direct and accurate correlation based on definitions and characteristics.

Question: Chemical change:
Answer: In a chemical change, the chemical composition of the original matter changes and new substances having different properties and different chemical composition are formed.
In simple words: A chemical change alters the substance's original composition, resulting in entirely new substances with different properties.

🎯 Exam Tip: To define chemical change, emphasize the alteration of chemical composition and the formation of new substances with distinct properties.

Question: Ionic bond:
Answer: The chemical bond formed due to an electrostatic force of attraction between the oppositely charged cation and anion is called an ionic bond or an electrovalent bond.
In simple words: An ionic bond forms from the strong electrostatic attraction between oppositely charged ions, typically a metal cation and a non-metal anion.

🎯 Exam Tip: Key terms for defining an ionic bond include "electrostatic force of attraction," "oppositely charged," "cation," and "anion."

Question: Covalent bond:
Answer: The chemical bond formed by sharing of valence electrons of two atoms with each other is called a covalent bond.
In simple words: A covalent bond is created when two atoms share their valence electrons to achieve a stable electron configuration.

🎯 Exam Tip: When defining covalent bonds, highlight "sharing of valence electrons" as the defining characteristic.

Question 1.Name the reactants in respiration.
Answer: Glucose and oxygen are the reactants in respiration.
In simple words: In respiration, glucose and oxygen are the starting materials that react.

🎯 Exam Tip: Remembering the basic inputs and outputs for biological processes like respiration is crucial for foundational understanding.

Question 2.Name the products of respiration.
Answer: Carbon dioxide and water are the products of respiration.
In simple words: Respiration produces carbon dioxide and water as its end results.

🎯 Exam Tip: Link the products directly to the reactants to show a complete understanding of the respiration process.

Question 3.Name the reactants in photosynthesis.
Answer: Carbon dioxide and water are the reactants in photosynthesis.
In simple words: Plants use carbon dioxide and water as the raw materials for photosynthesis.

🎯 Exam Tip: Photosynthesis is the reverse of respiration in terms of main reactants and products; knowing one helps remember the other.

Question 4.Name the products of photosynthesis.
Answer: Glucose and oxygen are the products of photosynthesis.
In simple words: Photosynthesis yields glucose (food) and oxygen.

🎯 Exam Tip: Understand that glucose is the energy storage molecule and oxygen is a byproduct vital for aerobic life.

Question 5.Name the salts present in hard water.
Answer: Salts present in hard water are calcium chloride, magnesium chloride, calcium sulphate and magnesium sulphate.
In simple words: Hard water contains dissolved calcium and magnesium salts, specifically their chlorides and sulphates.

🎯 Exam Tip: Focus on calcium and magnesium ions as the primary cause of water hardness, usually associated with their chloride and sulphate forms.

Question 6.Give two examples of ionic compounds.
Answer: Ionic compounds: Sodium chloride (NaCl), Potassium fluoride (KF).
In simple words: Sodium chloride (table salt) and potassium fluoride are common examples of ionic compounds, formed by electron transfer between a metal and a non-metal.

🎯 Exam Tip: Choose simple, well-known examples when asked for examples of chemical classifications.

Question 7.Give two examples of covalent compounds.
Answer: Covalent compounds: Hydrogen (H2), Water (H2O).
In simple words: Hydrogen gas and water are typical examples of covalent compounds, formed by atoms sharing electrons.

🎯 Exam Tip: Water (H2O) and carbon dioxide (CO2) are frequently used examples for covalent compounds due to their simple and clear sharing of electrons.

Question 8.Name an acid used for cleaning Shahabad tile.
Answer: An acid used for cleaning Shahabad tile is dilute hydrochloric acid (HCl).
In simple words: Dilute hydrochloric acid is used to clean Shahabad tiles because it reacts with the calcium carbonate present in them.

🎯 Exam Tip: Relate the cleaning action to the chemical reactivity of the acid with the tile material (calcium carbonate).

Question 9.Write a chemical equation for combustion of fuel.
Answer: Chemical equation: \[ C + O_2 \implies CO_2 \]
In simple words: The combustion of a carbon-based fuel involves carbon reacting with oxygen to produce carbon dioxide.

🎯 Exam Tip: For combustion equations, always remember that fuel reacts with oxygen, typically producing carbon dioxide and water if hydrogen is present.

Question 10.Write a chemical equation for photosynthesis.
Answer: Chemical equation: \[ CO_2 + H_2O \xrightarrow{\text{Sunlight}} C_6H_{12}O_6 + O_2 \]
In simple words: Photosynthesis is the process where carbon dioxide and water, in the presence of sunlight and chlorophyll (green plant), are converted into glucose and oxygen.

🎯 Exam Tip: Ensure to include the conditions (sunlight, green plant/chlorophyll) above and below the reaction arrow for photosynthesis to show a complete representation.

Answer The Following Questions:

Question 1.Combustion of fuel is a fast and irreversible chemical change.
Answer: Wood, coal, petrol or cooking gas are burnt for producing energy. Carbon is the common substance that burns in all these fuels. The product carbon dioxide is formed when carbon combines with oxygen in the air during the combustion process. We cannot obtain fuel from carbon dioxide by employing any other method. Properties of carbon dioxide are altogether different from those of fuel. Hence, this change is a irreversible chemical change. Word equation: Carbon + Oxygen
\(\implies\) Carbon dioxide
In simple words: Burning fuel is a rapid, irreversible chemical change because it forms new substances like carbon dioxide, which cannot be easily converted back into the original fuel.

🎯 Exam Tip: When explaining irreversible changes, emphasize that the original substances cannot be recovered easily and that new substances with different properties are formed.

Question 2.Dilute hydrochloric acid is used for cleaning Shahabad tiles.
Answer: The main constituent of Shahabad tile is calcium carbonate. During its cleaning with hydrochloric acid, the upper layer of the tile reacts with hydrochloric acid and three products are formed. One of them is calcium chloride, which being soluble in water, gets washed away with water. The second product is carbon dioxide, it mixes with air. The third product is water. Word equation: Calcium carbonate (Lime stone) + Hydrochloric acid
\(\implies\) Calcium chloride + Carbon dioxide + Water
In simple words: Dilute hydrochloric acid cleans Shahabad tiles by reacting with the tile's calcium carbonate, forming soluble calcium chloride (washed away), carbon dioxide (escapes as gas), and water.

🎯 Exam Tip: When describing cleaning reactions, focus on the chemical reaction between the cleaning agent and the dirt/stain, and the properties of the products (e.g., solubility, gaseous nature) that facilitate removal.

Question 1.Carbon dioxide + Calcium hydroxide
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कार्बन डाइऑक्साइड और कैल्शियम हाइड्रॉक्साइड (चूने का पानी) के बीच की प्रतिक्रिया को दर्शाता है, जिससे कैल्शियम कार्बोनेट और पानी बनता है। यह चूने के पानी का दूधिया होना और एक सफेद अवक्षेप का बनना दिखाता है। Chemical equation: \[ CO_2 + Ca(OH)_2 \implies CaCO_3 + H_2O \]
In simple words: Carbon dioxide reacts with calcium hydroxide (lime water) to form calcium carbonate and water.

🎯 Exam Tip: This reaction is a classic test for carbon dioxide, as the formation of insoluble calcium carbonate causes lime water to turn milky.

Question 2.Calcium carbonate + Hydrochloric acid
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कैल्शियम कार्बोनेट और हाइड्रोक्लोरिक एसिड के बीच की प्रतिक्रिया को दर्शाता है, जिससे कैल्शियम क्लोराइड, कार्बन डाइऑक्साइड और पानी बनता है। यह प्रतिक्रिया अक्सर गैस के बुलबुले के रूप में कार्बन डाइऑक्साइड के मुक्त होने के साथ होती है। Chemical equation: \[ CaCO_3 + HCl \implies CaCl_2 + CO_2 + H_2O \]
In simple words: Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide, and water.

🎯 Exam Tip: Remember this as a typical acid-carbonate reaction that produces salt, water, and carbon dioxide gas.

Question 3.Magnesium salts during the softening of hard water. Magnesium chloride + Sodium carbonate
Answer: The process involves the removal of magnesium salts from hard water.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मैग्नीशियम क्लोराइड और सोडियम कार्बोनेट के बीच की प्रतिक्रिया को दर्शाता है, जिससे मैग्नीशियम कार्बोनेट और सोडियम क्लोराइड बनता है। इस प्रतिक्रिया का उपयोग कठोर जल को मृदु करने के लिए किया जाता है क्योंकि अघुलनशील मैग्नीशियम कार्बोनेट अवक्षेप के रूप में अलग हो जाता है। Chemical equation: \[ MgCl_2 + Na_2CO_3 \implies MgCO_3 + 2NaCl \]
In simple words: Hard water softening removes magnesium salts by reacting magnesium chloride with sodium carbonate to form insoluble magnesium carbonate and sodium chloride.

🎯 Exam Tip: Remember to balance the chemical equations for full marks, as unbalanced equations may lead to deductions.

Question 1.Hydrogen molecule:
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र दो हाइड्रोजन परमाणुओं के बीच एक-एक इलेक्ट्रॉन के साझाकरण से हाइड्रोजन (H2) अणु के निर्माण को दर्शाता है। दोनों परमाणु एक सहसंयोजक बंधन बनाकर अपना द्विक (duplet) पूरा करते हैं, जिससे एक स्थिर अणु बनता है। 1. Hydrogen has atomic number 1 and electronic configuration 1. That means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one. 2. The two atoms of hydrogen are identical, they share their electrons with each other. 3. As a result, the electron duplet of both the hydrogen atoms is complete and a covalent band is formed between them.
In simple words: A hydrogen molecule forms when two hydrogen atoms each share their single electron, creating a covalent bond and completing their outermost electron shells (duplets).

🎯 Exam Tip: When illustrating covalent bond formation, clearly show the sharing of electron pairs within the overlapping shells of the atoms.

Question 4.There is one covalent bond between the component atoms H and Cl of the molecule HCl. Use this information to represent the formation of HCl molecules from H and Cl atoms diagrammatically. (Use your brainpower)
Answer: Hydrogen chloride:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र हाइड्रोजन (H) और क्लोरीन (Cl) परमाणुओं के बीच एक इलेक्ट्रॉन के साझाकरण से हाइड्रोजन क्लोराइड (HCl) अणु के निर्माण को दर्शाता है। हाइड्रोजन एक इलेक्ट्रॉन साझा करके अपना द्विक पूरा करता है, जबकि क्लोरीन एक इलेक्ट्रॉन साझा करके अपना अष्टक पूरा करता है, जिससे एक सहसंयोजक बंधन बनता है। 1. Hydrogen has atomic number 1 and electronic configuration 1, that means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one. 2. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet. 3. The two atoms, hydrogen and chlorine share one electron with each other. As a result, the electron duplet of hydrogen and octet of chlorine is complete and a covalent band is formed between them.
In simple words: Hydrogen chloride forms when a hydrogen atom and a chlorine atom share one electron each, creating a covalent bond and completing their outermost electron shells.

🎯 Exam Tip: When drawing electron dot structures for covalent bonds, ensure the shared electrons are correctly depicted to show completion of duplet/octet for each atom involved.

Question 5.Show the formation of the following ionic compounds from the corresponding elements using two methods namely, numerical and diagrammatic representation of electronic configuration. (a) K+ F¯, from 19K and 9F, (b) Ca2+ O2- from 20Ca and 80. (Use your brainpower)
Answer: (a) K+F¯ from 19K and F Potassium fluoride:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र पोटेशियम (K) परमाणु द्वारा एक इलेक्ट्रॉन खोने और फ्लोरीन (F) परमाणु द्वारा उस इलेक्ट्रॉन को ग्रहण करने से पोटेशियम फ्लोराइड (K+F-) आयनिक बंधन के निर्माण को दर्शाता है। पोटेशियम एक धनायन (cation) बनता है जबकि फ्लोरीन एक ऋणायन (anion) बनता है, और विपरीत आवेशों के बीच आकर्षण से आयनिक बंधन बनता है। 1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1. 2. Potassium atom has 1 electron in its outermost shell. 3. It loses one electron from its outermost shell, i.e. N shell. Then its M shell becomes the outermost shell with a stable octet. The nucleus of potassium atom has 19 protons but the number of electrons in the atom has become 18. So there is a net unit positive charge giving a potassium cation (K+). 4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet. 5. Thus, the electron lost by potassium is taken up by chlorine. 6. When fluorine atom gains one electron, octet of fluorine is completed and its K and L shells have together 10 electrons and the nucleus has 9 protons. This leads to the formation of an ion (F¯). 7. Thus, a fluorine atom accepts one electron from a potassium atom and consequently a fluoride ion with one unit negative charge and a potassium ion with one unit positive charge are formed. 8. Potassium and fluoride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of potassium fluoride (KF) molecule.
In simple words: Potassium fluoride forms when potassium loses an electron to become a positive ion and fluorine gains that electron to become a negative ion, followed by electrostatic attraction between these oppositely charged ions.

🎯 Exam Tip: For ionic compound formation, clearly show the transfer of electrons and the resulting charges on the ions. Diagrams should illustrate the electron shells before and after transfer.

Question 5.(b) Ca2+O2- from 20Ca and 8O.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कैल्शियम (Ca) परमाणु द्वारा दो इलेक्ट्रॉन खोने और ऑक्सीजन (O) परमाणु द्वारा उन दो इलेक्ट्रॉनों को ग्रहण करने से कैल्शियम ऑक्साइड (Ca2+O2-) आयनिक बंधन के निर्माण को दर्शाता है। कैल्शियम एक धनायन (cation) बनता है जबकि ऑक्सीजन एक ऋणायन (anion) बनता है, और विपरीत आवेशों के बीच आकर्षण से आयनिक बंधन बनता है। 1. Calcium has atomic number 20 and electronic configuration 2, 8, 8, 2. It has 2 electrons in its outermost shell. 2. Oxygen has atomic number 8 and electronic configuration 2, 6. It has 6 electrons in its outermost shell and requires 2 electrons to complete its octet. 3. Calcium loses 2 electrons from its outermost shell to achieve a stable octet and forms a Ca2+ cation. 4. Oxygen gains these 2 electrons to complete its octet and forms an O2- anion. 5. The oppositely charged Ca2+ and O2- ions attract each other electrostatically, forming an ionic bond in calcium oxide (CaO) molecule.
In simple words: Calcium oxide forms when a calcium atom transfers two electrons to an oxygen atom, creating Ca2+ and O2- ions that are held together by strong electrostatic forces in an ionic bond.

🎯 Exam Tip: When dealing with ions having charges greater than ±1, ensure the number of electrons transferred matches the valency of the atoms involved for a balanced compound.

Question 1.Physical change and Chemical change:
Answer:

🎯 Exam Tip: Focus on whether a new substance is formed and if the change is reversible to distinguish between physical and chemical changes.

Question 2.Ionic bond and Covalent bond:
Answer:

🎯 Exam Tip: To differentiate, remember "transfer for ionic" (leading to ions) and "sharing for covalent" (leading to molecules).

Question 1.Ionic compounds are formed due to the combination of metallic and nonmetallic atoms.
Answer: Metallic atoms have a tendency to lose electrons from their outermost orbits to establish the octet state in their penultimate orbits. Conversely, nonmetallic atoms gain electrons to establish the octet state of their outermost orbits. When a metallic atom and a nonmetallic atom come close together, the metallic atom loses electrons and gets c converted into positively charged ion, while the nonmetallic' atom gets converted into negatively charged ions so formed, develop an ionic bond and this results in the formation of an ionic compound. Hence, ionic compounds are formed due to the combination of metallic and nonmetallic atoms.
In simple words: Ionic compounds form because metals tend to lose electrons and non-metals tend to gain them; this electron transfer creates oppositely charged ions that attract each other.

🎯 Exam Tip: When explaining ionic bond formation, always mention electron transfer, the formation of cations and anions, and the electrostatic attraction between them.

Activity-Based Questions:

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र विभिन्न रासायनिक परिवर्तनों के उदाहरणों को दर्शाता है, जैसे सेब का ऑक्सीकरण, ब्रेड का टोस्ट होना, लोहे में जंग लगना, लकड़ी का जलना, केले का पकना, और दो रसायनों को मिलाने पर रंग और गैस का उत्पादन। यह रासायनिक परिवर्तनों के कुछ सामान्य अवलोकन हैं जिनमें रंग, स्वाद में परिवर्तन और गैसों का निकलना शामिल है। Take the lemon juice in a clean glass. Take two drops of the lemon juice in a spoon and taste. Add a pinch of baking soda in the glass of lemon juice. Did you notice bubbling around the particles of soda? Did you hear a sound on taking your ear near the glass? Now again taste it. Did it taste as sour as it was in the beginning? (Above activity is to be done using clean apparatus and edible material. Then only it is possible to test the 'taste', otherwise keep in mind that the testing of 'taste' cannot be done.)

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कैल्शियम हाइड्रॉक्साइड (चूने का पानी) और कार्बन डाइऑक्साइड के बीच की प्रतिक्रिया को दर्शाता है, जिससे कैल्शियम कार्बोनेट और पानी बनता है। यह चूने के पानी का दूधिया होना और एक सफेद अवक्षेप का बनना दिखाता है, जो कार्बन डाइऑक्साइड की उपस्थिति का संकेत है। Take some freshly prepared lime water (solution of calcium hydroxide) in a test tube. Keep on blowing in it with a blow tube. What is seen after some time? Did the colourless lime water turn milky? After some more time you will find that a white insoluble solid settles at the bottom of the test tube. This is a precipitate of calcium carbonate. The turning lime water milky means that the blown gas mixed in it was carbon dioxide. Word equation: Carbon dioxide + Calcium hydroxide
\(\implies\) Calcium carbonate + Water Write a chemical equation for the above word equation. Chemical equation: \[ CO_2 + Ca(OH)_2 \implies CaCO_3 + H_2O \]