Frank Brothers Solutions for ICSE Class 9 Chemistry Chapter 4 The Language Of Chemistry

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Solution 1:
Symbol - It is the short form or abbreviation used for the name of an element. It represents one atom of that element.
Formula - Formula of a compound represents the composition of a molecule of the substance in terms of the symbols of the elements present in the molecule.
A symbol is like a unique nickname that helps scientists identify an element quickly without writing the full name. A chemical formula acts like a recipe, showing exactly which atoms are combined to create a specific substance.
Teacher's Tip: Think of a symbol as a single letter and a formula as a complete word in the language of chemistry.
Exam Tip: Always capitalize the first letter of a chemical symbol and keep the second letter lowercase to avoid confusion with other elements.

Solution 2:
1. CaCO₃
2. MgSO₄
3. Fe₂ (SO₄)₃
4. CaHCO₃
5. CuI
6. K₂Cr₂O₇
7. KMnO₄
8. Na₂SO₄
9. Mg (NO₃)₂
10. Ca3 (PO₄)₂
These chemical formulas use subscripts to show the fixed ratio of different atoms within a single molecule. By looking at these formulas, you can identify every element that makes up the compound and how many atoms of each are present.
Teacher's Tip: The small number (subscript) belongs only to the element written immediately before it.
Exam Tip: When writing formulas with brackets, like Mg(NO₃)₂, remember that the subscript outside the bracket multiplies everything inside it.

Solution 3:
1. Valency - The combining capacity of an element is called its valency.
2. Helium < Sodium < Magnesium < Carbon < Phosphorous
Valency describes the "hooking power" of an atom, telling us how many bonds it can form with others. This ordered list ranks elements from those that do not want to bond at all to those that can form many connections.
Teacher's Tip: Imagine valency as the number of hands an atom has available to hold onto other atoms.
Exam Tip: Elements in the same group of the periodic table usually have the same valency, which is a great way to remember them.

Solution 4:
Law of conservation of matter governs a completely balanced equation. It states that “matter can neither be created nor destroyed.”
This scientific law means that in a chemical reaction, atoms are simply rearranged into new patterns rather than disappearing. Because of this, the total mass of the materials you start with must equal the total mass of what you produce.
Teacher's Tip: Think of balancing equations like a seesaw; both sides must have the exact same number of "blocks" to stay level.
Exam Tip: State the law exactly within quotation marks to show the examiner you have memorized the standard scientific definition.

Solution 5:
A symbol signifies one atom of that element.
The symbol identifies the specific element and represents its presence as a single unit in a chemical equation. It also stands for a specific amount of the element known as its atomic mass.
Teacher's Tip: A chemical symbol is like the ID card for an individual atom.
Exam Tip: Do not confuse a symbol (O) with a molecule (O₂); the symbol represents only one individual atom.

Solution 6:
Latin names of the following compounds are -
Iron - Ferrum
Tin - Stannum
Lead - Plumbum
Sodium - Natrium
Potassium - Kalium
Mercury - Hydragyrum
Many elements have symbols that do not match their English names because they were discovered long ago and given Latin titles. This explains why we use Fe for Iron and Na for Sodium instead of letters from their English names.
Teacher's Tip: To remember Potassium's symbol (K), think of its Latin name "Kalium."
Exam Tip: Learning these Latin names helps you understand why some symbols in the periodic table seem unusual or hard to remember.

Solution 7:
The equation in which the total number of atoms of each element in the reactants, on the left side of the equation is same as the number of atoms in the products formed, on the right side of the equation is called as balanced chemical equation.
A balanced equation provides a mathematically accurate way to describe how substances change during a reaction. It ensures that every single atom that enters the reaction is accounted for in the final result.
Teacher's Tip: Balancing is like checking your receipt after shopping; every penny spent must match the items you bought.
Exam Tip: Always double-check your atom counts for every element on both sides of the arrow before moving to the next question.

Solution 8:
(a) 3Mg + N₂ → Mg₃N₂
(b) 2K + 2H₂O → 2KOH + H₂
These balanced equations show how magnesium and potassium react with nitrogen and water respectively. The large numbers at the beginning (coefficients) are added to make sure the number of atoms is equal on both sides of the arrow.
Teacher's Tip: Coefficients represent the number of whole molecules, while subscripts represent the atoms inside a molecule.
Exam Tip: When balancing, only change the large numbers (coefficients) in front; never change the small subscripts within a formula.

Solution 9:
A chemical equation gives information about -
1. What substances enter into a given reaction (reactants) and what products are formed as a result of the reaction.
2. The quantities of the reactants and the product formed.
3. The optimum conditions of temperature and pressure.
An equation acts as a complete summary of a chemical event in a very small space. It tells us exactly "who" is involved, "how much" is used, and "how" the experiment should be conducted.
Teacher's Tip: Read a chemical equation from left to right, just like a sentence in an English book.
Exam Tip: If a reaction requires heat or a specific temperature, remember to mention it above the reaction arrow for a complete answer.

Solution 10:
(a) FeCl₃ + 3NaOH → Fe(OH)₃ + 3NaCl
(b) 4NH₃ + 5O₂ → 4NO + 6H₂O
(c) P₂O₅ + 3H₂O → 2H₃PO₄
(d) 2H₂S + SO₂ → 3S + 2H₂O
(e) 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂
These examples show complex reactions where multiple molecules break apart and combine to form new substances. Balancing them requires a systematic approach to ensure every element follows the law of conservation of mass.
Teacher's Tip: Start balancing with the most complex molecule or the element that appears in only one place on each side.
Exam Tip: For large equations like (e), create a small tally chart to keep track of your atom counts as you adjust the coefficients.

Solution 11:
H₂ means hydrogen, O₄ means oxygen and S means sulphur in the formula of H₂SO₄
This formula specifically indicates that a single molecule of sulfuric acid contains two hydrogen atoms, one sulfur atom, and four oxygen atoms. The subscripts are used to define the exact chemical structure of this particular acid.
Teacher's Tip: If an element symbol like S has no number written after it, it means there is exactly one atom of that element.
Exam Tip: When asked what a formula "means," always list the names of the elements and the number of atoms for each one clearly.

Solution 12:
1. The highest valency of the element Z is six.
2. The formula of the fluoride of Z will be ZF₆
Since each fluorine atom has a valency of one, it requires six of them to match the high valency of element Z. This relationship is determined using the criss-cross method where valencies are swapped to become subscripts.
Teacher's Tip: A valency of six is quite high and is often found in elements like Sulfur when they react with Fluorine.
Exam Tip: If valencies can be simplified (like 2 and 4 becoming 1 and 2), always use the simplest ratio for your final formula.

Solution 13:
The three valencies of element are -
1. Two - Since the element X combines with two hydrogen to form H₂ and two atoms of X combines with one carbon to form CX₂.
2. Four - Since the element X combines with two oxygen to form XO₂.
3. Six - Since the element X combines with three oxygen to form XO₃.
This example shows that some elements are flexible and can bond in different ways depending on their environment. By observing the ratios in these formulas, we can work backward to figure out the bonding strength of the unknown element X.
Teacher's Tip: Use the known valencies of Hydrogen (1) and Oxygen (2) to solve the mystery of an unknown element's valency.
Exam Tip: When a question gives multiple formulas for the same element, it is testing your knowledge of "variable valency."

Solution 14:
Variable valency - Some elements are capable of showing more than one valency in their compounds called variable valency. Some elements show variable valency i.e. more than one valency since these elements have more than one common valency state.
This happens because certain atoms can use different numbers of electrons for bonding depending on how much energy is available. Common metals like Iron and Copper frequently exhibit this behavior by forming different types of salts.
Teacher's Tip: Think of variable valency like a person having different "levels of energy" for making friends on different days.
Exam Tip: When naming compounds with variable valency, use Roman numerals in brackets, like Iron(II) Chloride, to be precise.

Solution 15:
Chemical formula - It represents the composition of a molecule of the substance in terms of the symbols of the elements present in the molecule. The rule for writing the formula is criss-cross method.
1. The positive and negative radicals are represented by their symbols and written side by side with the correct valency written below each.
2. The valencies are divided by their highest common factor if any to get the simplest ratio.
3. These numbers are then interchanged and written as subscripts.
The criss-cross method is a helpful tool that makes it easy to balance the electrical charges of different ions. It turns the theoretical "bonding capacity" of elements into a practical blueprint for building a chemical molecule.
Teacher's Tip: Always write the positive part (the metal or cation) on the left and the negative part on the right.
Exam Tip: If you are working with a group of atoms (a radical), put brackets around it before adding a subscript outside.

Solution 16:
(a) Fe + H₂SO₄ → FeSO₄ + H₂
(b) 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O
(c) 2NH₃ + O₂ → 2NO + 3H₂O
(d) ZnS + O₂ → ZnO + SO₂
(e) 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂
These reactions illustrate how acids, metals, and bases interact to form entirely new compounds like salts and gases. Following the rules of balancing ensures that these equations correctly represent the real-world chemistry taking place in a lab.
Teacher's Tip: Oxygen is often found in many parts of a reaction, so it is usually best to balance it at the very end.
Exam Tip: If you find it hard to balance an equation with an odd number of atoms, try doubling all your coefficients to make them even.

Solution 17:
1. Sodium hydrogencarbonate
2. Sodium hexacyanoferrate(III)
3. Manganese(II) borate
4. Calcium phosphate
5. Potassium manganate(VI)
These chemical names follow a standardized system that helps scientists communicate clearly about specific substances. The numbers in brackets indicate the specific valency of the metal in that particular compound.
Teacher's Tip: If a chemical name ends in "-ate," it is a big clue that the compound contains Oxygen atoms.
Exam Tip: Pay close attention to spelling, as changing just one letter can often describe a completely different chemical compound.

Solution 18:
Co stands for cobalt which is an element while CO stands for carbon monoxide which is a compound.
The lowercase letter in 'Co' indicates that it is a single element from the periodic table with its own properties. When both letters are capitalized as 'CO', it shows that Carbon and Oxygen atoms have bonded together to form a molecule.
Teacher's Tip: One capital letter = one element. Two capital letters = a compound made of two different elements.
Exam Tip: Always write the second letter of an element's symbol clearly smaller than the first to avoid confusing the examiner.

Solution 19:
Radical - A radical is an atom or a group of atoms of same or different elements that behaves in the manner of positive or negative ion. Radicals have their own combining power(valency) and chemical formulae.
Examples -
Monovalent radicals -H^–,OH^–,Cl^–,NO₃^–,H⁺,Na⁺,K⁺,NH₄⁺
Trivalent radicals-PO^₄3- ,Fe(CN)₆^3-,AsO₃ ^3-,N^3-,Fe³⁺,Al³⁺,Bi³⁺,Au³⁺
Radicals act as a single, unbreakable unit during most chemical reactions, almost like they are a single atom. They carry a charge which determines how they will attract or repel other parts of a chemical compound.
Teacher's Tip: Think of a radical as a "team" of atoms that always sticks together when moving from one compound to another.
Exam Tip: Memorize common radicals like Sulfate (SO₄^2-) and Nitrate (NO₃^-) as they appear very frequently in exams.

Solution 20:
The modifications made in a chemical equation to overcome the limitations of it in providing information are -
(i)Physical states of the reactants and products are abbreviated and written after the substance in brackets .Ex solid(s),liquid(l),gas(g), aqueous(aq), dilute(dil.), concentrated(conc.).
(ii) Substances evolving as gases in the products are shown by the upward arrow (↑), ex-H₂(↑).The substances precipitating down in reaction are shown by downward arrow (↓), ex-BaSO₄(↓)
(iii)Condition of temperature, pressure or catalyst are written above and below the horizontal arrow mark (→) after the reactants.
N₂ (g) + 3H₂(g) → (Fe + Mo), 200atm ]{ 770K } 2NH₃g
(iv)When a reaction does not proceed to completion, it is indicated by a double arrow mark (rightleftharpoons).
Ex PCl₅ ⇔ PCl₃ + Cl₂
These extra symbols turn a basic chemical equation into a detailed set of instructions for a laboratory experiment. They help chemists understand if a substance will float away as gas or sink to the bottom as a solid precipitate.
Teacher's Tip: (aq) stands for "aqueous," which simply means the substance is dissolved in a container of water.
Exam Tip: When representing a reversible reaction, ensure you draw two half-arrows pointing in opposite directions to show the reaction goes both ways.

Solution 21:
1. Anion - Negatively charged radicals are termed as anions.
2. Cation - Positively charged radicals are termed as cations.
Anions have extra electrons which give them a negative pull, while cations have lost electrons, giving them a positive charge. Because opposites attract, these two types of ions often come together to form strong chemical bonds.
Teacher's Tip: Remember: **Ca+ion** has a "plus" sign (t) in its name, so it is always the positive one!
Exam Tip: In any chemical formula, the cation is always written first, followed by the anion on the right.

Solution 22:
Disadvantages associated with hit and trial method of balancing of equations -
1. It is tedious and takes a long time.
2. The method is rather difficult for balancing such equations which contain the same element being repeated in a number of compounds.
3. It does not give any information regarding the mechanism of the reaction.
This method can be frustrating because it relies on guessing rather than following a direct mathematical formula. For very complex reactions, it can take many attempts to find the correct numbers that make both sides equal.
Teacher's Tip: If you get stuck using this method, erase your numbers and try starting with a completely different element first.
Exam Tip: Practice balancing equations every day to build your speed so that this "tedious" method becomes second nature during a test.