CBSE Class 10 Science HOTs Chemical Reactions and Equations

Please refer to CBSE Class 10 Science HOTs Chemical Reactions and Equations. Download HOTS questions and answers for Class 10 Science. Read CBSE Class 10 Science HOTs for Chapter 1 Chemical Reactions and Equations below and download in pdf. High Order Thinking Skills questions come in exams for Science in Class 10 and if prepared properly can help you to score more marks. You can refer to more chapter wise Class 10 Science HOTS Questions with solutions and also get latest topic wise important study material as per NCERT book for Class 10 Science and all other subjects for free on Studiestoday designed as per latest CBSE, NCERT and KVS syllabus and pattern for Class 10

Chapter 1 Chemical Reactions and Equations Class 10 Science HOTS

Class 10 Science students should refer to the following high order thinking skills questions with answers for Chapter 1 Chemical Reactions and Equations in Class 10. These HOTS questions with answers for Class 10 Science will come in exams and help you to score good marks

HOTS Questions Chapter 1 Chemical Reactions and Equations Class 10 Science with Answers

Question. Zinc reacts with silver nitrate to form which compounds?
(a) Zn (NO3)2 + Ag
(b) ZnNO3 + Ag
(c) AgNO3 + Zn (NO3)2
(d) Ag + Zn (NO3)3
Answer : A

Question. Which of the following statements about the given reaction are correct?
3Fe(s) + 4H2O(g) → Fe3O4(g) + 4H2(g)
(i) Iron metal is getting oxidised
(ii) Water is getting reduced
(iii) Water is acting as reducing agent
(iv) Water is acting as an oxidising agent
(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)
Answer : C

Question. When green coloured ferrous sulphate crystals are heated, the colour of the crystal changes because
(a) it is decomposed to ferric oxide
(b) it loses water of crystallisation
(c) it forms SO2
(d) it forms SO3
Answer : B

Question. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) only
(b) (ii) only
(c) (iv) only
(d) (ii) and (iv)
Answer : D

Question. What is observed when a solution of potassium iodide is added to silver nitrate solution?
(a) No reaction takes place
(b) White precipitate of silver iodide is formed
(c) yellow precipitate of Agl is formed
(d) Agl is soluble in water.
Answer : C

Question. Which of the following is redox reaction ?
(a) NaOH + HCl → NaCl + H2O
(b) AgNO3 + KI → AgI + KNO3
(c) BaO2 + H2SO4 → BaSO4 + H2O2
(d) SnCI2 + HgCI2 → SnCI4 + Hg

Answer : D

Question. The reaction between aqueous solutions of sodium chloride and silver nitrate is -
(a) displacement reaction
(b) synthesis reaction
(c) double displacement reaction
(d) analysis reaction

Answer : C

Question. CH4 + Cl2 → CH3 Cl + HCl reaction is an example of - 
(a) Synthetic
(b) Analytical
(c) Displacement
(d) Neutralisation

Answer : C

Question. A Brown and bright element “x” when heated in presence of air turns into black substance “y”. If Hydrogen gas is passed over this heating material again “x” is obtained. “x” and “y” are –
(a) Cu & CuO
(b) S & SO2
(c) C & CO2
(d) Na & NaH

Answer : A

Question. Which of the following statements is correct for oxidation reaction ?
(a) Gain or addition of electronegative radical or element
(b) Removal of hydrogen atom
(c) Removal or loss of electropositive radical or element
(d) All the above statements are correct.

Answer : D

Question. Oxidation is defined as : 
(a) loss of electron
(b) gain of electron
(c) loss of proton
(d) gain of proton

Answer : A

Question. From the following metals whose nitrate produces NO2 gas on heating [West Bengal NTSE Stage-I/13]
(a) Na
(b) K
(c) Pb
(d) None of these

Answer : C

Question. When FeSO4 crystals are heated in a test tube, the pale green colour of FeSO4 fades away, due to :
(a) loss of electrons
(b) loss of dye
(c) Oxidation is the gain of oxygen.
(d) loss of water of crystallization

Answer : D

Question. Four students recorded their respective observations after performing the reaction for double displacement as :
(i) The reactants are barium chloride and sodium sulphate
(ii) A white precipitate is formed
(iii) The white precipitate is barium sulphate
(iv) A yellow precipitate is formed
The correct statements are :
(a) (i), (iii), (iv)
(b) (ii), (iii), (iv)
(c) (i), (ii), (iii)
(d) (i), (ii), (iv)

Answer : C

Question. Precipitate formation during chemical reaction is indicated by this arrow : 
(a) ↑
(b) →
(c) ↓
(d) ←

Answer : C

Question. BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq) 
The types of reaction are :
(a) Displacement (b) Precipitation (c) Combination (d) Double displacement
(A) (a) & (C)
(B) (a), (B), & (C)
(C) (B) & (C)
(D) (B) & (D)

Answer : D

Question. The chemical reaction HNO3 + KOH → KNO3 + H2O is an example of
(a) neutralization
(b) double displacement
(c) neutralization and double displacement
(d) combination

Answer : C

Question. Hydrolysis of water is which type of following reactions? 
(a) Endothermic
(b) Decomposition
(c) Both A and B
(d) Combination

Answer : C

Question. When a burning splinter is brought near the gas jar containing hydrogen gas a popping sound is observed. It is due to 
(a) exothermic
(b) endothermic
(c) exothermic and endothermic
(d) none of these

Answer : A

Question. On heating ferrous sulphate crystal, one would get :
(a) sweet smell
(b) rotten egg smell
(c) smell of burning sulphur
(d) no solid residue

Answer : C

Question. When Anupreeta heated ferrous sulphate crystals in a test tube, she observed :
(i) green colour changes to yellow
(ii) green colour changes to reddish brown
(iii) blue colour changes to brownish colour
(iv) smell of burning sulphur is obtained
(a) (i) and (iv)
(b) (ii) and (iv)
(c) (ii) and (iii)
(d) (i) and (iii)

Answer : B

Question. Four students A, B, C and D were asked to carry out a decomposition reaction. Each one followed different method as mentioned :
1 : Heated aqueous solution of iron sulphate in a test tube.
2 : Added Zn granules to iron sulphate in a test tube and then heated the mixture.
3 : Heated crystals of iron sulphate in a test tube.
4 : Heated crystals of iron sulphate along with copper sulphate crystals in a china dish. The student whoadopted the correct method is :
(a) 1
(b) 2
(c) 3
(d) 4

Answer : C

Question. The correct pair of salt solutions to demonstrate double displacement reaction is :
(a) barium sulphate and sodium sulphate
(b) barium chloride and sodium chloride
(c) barium chloride and barium sulphate
(d) barium chloride and sodium sulphate

Answer : D

Question. Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) is an example of -
(a) precipitation reaction
(b) endothermic reaction
(c) evolution of gas
(d) change in colour

Answer : C

Question. Diplacement reaction is : 
(a) CaO (s) + H2O(l) → Ca(OH)2 (aq)
(b) Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)
(c) MnO2(s) + 4HCl(l) → MnCl2\(s) + 2H2O(l) + Cl2(g)
(d) C6H12O6 + 6O2 → 6CO2 + 6H2O

Answer : B

Question. When quicklime is added to water in a Jar , what happens chemically?
Answer :
 Quicklime (calcium oxide) forms into slaked lime (calcium hydroxide) and heat is generated, indicating that reaction is exothermic.

Question. Why hydrogen peroxide is kept in colored bottles?
Answer :
 Light decomposes hydrogen peroxide into water and oxygen.

Question. During electrolysis of water a few drops of sulphuric acid is added into water. Why?
Answer :
 Pure water is a bad conductor of electricity. By adding few drops of sulphuric acid, we make it a good conductor of electricity.

Question. A white salt on heating decomposes to give brown fumes and yellow residue is left behind. Name the salt and write the  eaction involved.

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Question. A reddish brown vessel developed a green colored solid X when left open in air for a long time. When reacted with dil H2SO4 , it forms a blue colored solution along with brisk effervescence due to colourless & odourless gas Z. X decomposes to form black colored oxide Y of a  eddish brown metal along with gas Z, Identify X, Y, & Z.
Answer :
 X = CuCO3. Cu (OH)2, Y= CuO, Z= CO2

Question. A student has mixed the solutions of lead (II) nitrate and potassium iodide.
(i)What was the colour of the precipitate formed? Can you name the compound precipitated?
(ii) Write the balanced chemical equation for this reaction.
(iii) What type of reaction is it?
Answer : (i). Yellow, Lead iodide
(ii) Pb (NO3)2 + KI --> PbI2 + 2KNO3
(iii) Double displacement reaction
 
Question. A reddish brown metal X when heated in presence of oxygen forms a black compound Y which is basic in nature when heated with hydrogen gas gives back X. Identify X & Y.Write the chemical reaction between Y & H 2. Identify the substance being oxidized & reduced.
Answer : Oxygen reacts with copper to form copper oxides which has black colour
2 Cu(s) + O (g)           2 Cuo(s )
The copper (II) oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidized.
 
Question. Why do fireflies glow at night?
Answer : Fire flies have a special kind of substance that is duciferin that undergoes oxidation ( in the presence of air) in the presence of an enzyme . This reaction is accompanied by the emission of light. Their fore fire flies glow at night.
 
Question. A student dropped few pieces of marble in dilute HCl contained in a test tube. The gas evolved was passed through lime water. What change would be observed in lime water? Write chemical reactions for both the changes observed.
Answer : Ca (OH) 2(aq) + CO2 (g) - CaCO3(s) + H2O (l)
 
Question. Astha has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings
Answer : Corrosion is responsible for this coating. Black coating is due to formation of Ag2S and green coating is due to formation of CuCO3.Cu (OH)2.
 
GISTS OF THE LESSON
 
1 Chemical reaction— Chemical changes or chemical reactions are the changes in which one or more new substances are formed.
 
2 Chemical Equations – Representation of a chemical reaction in terms of symbols and formulae of the reactants and products is known as chemical equation.
 
3 Balanced Chemical equations – The chemical equation in which the no. of atoms of different elements is same on both sides of the arrow is called balanced chemical equation.
 
4 The chemical reactions can be classified into different types such as—
a) Combination reaction – The reactions in which two or more substances combine to form a new substance are called combination reaction. For example,
2Mg(s) + O2 (g)  2 MgO (s)
 
b) Decomposition reaction - The reaction in which a single compound breaks up into two or more simpler substances are called decomposition reactions. For example,
2Pb (NO3)2 (s)  2PbO (s) + 4NO2 (g) +O2 (g)
 
The decomposition of a substance by passing electric current through it is known as electrolysis.
The decomposition of a substance on heating is known as thermal decomposition.
The decomposition of a substance by absorbing light energy is called photochemical decomposition.
 
c) Displacement reactions -The chemical reactions in which a more reactive element displaces a less reactive element from a compound are known as displacement reactions. For example,
i) Zn (s) + CuSO4 (aq)  ZnSO4 (aq) + Cu (s).
ii) Cu (s) + 2AgNO3 (aq)  Cu (NO3)2 (aq) +2Ag (s).
 
d) Double Displacement Reactions - The chemical reactions in which compounds react to form two different compounds by mutual exchange of ions are called double displacement reactions.
These reactions take place in solution two common types of this reaction are precipitation reactions and neutralization reactions
 
i) Precipitation reaction : In this reactions, aqueous solution of two salts are mixed whereby
Some salts precipitate due to mutual exchange of ions between the two salts. For example
AgNO3 (aq) + NaCI (aq) -----> AgCl(s) + NaNO3.
 
ii) Neutralization reaction: In this type of reaction an acid reacts with a base to form salt and water by exchange of ions.
NaOH (aq) + HCl (aq)  NaCl (aq) + H2O.
 
e) Redox reaction: Chemical reaction which shows both oxidation and reduction reaction.
 
Oxidation: Reaction that involves the gain of oxygen or loss of hydrogen.
 
Reduction: Reaction that shows the loss of oxygen or gain of hydrogen.
 
Both oxidation and reduction take place simultaneously and hence called redox reaction.
ZnO + C  Zn + CO
ZnO reduc`e to Zn ---- reduction
C oxidize to CO ------oxidation
f) Exothermic reaction and endothermic reaction: On the basis of energy changes during chemical reaction, they can be classified as
 
i) Exothermic reaction: A chemical reaction in which heat energy is produced.
C + O2  CO2 (g) + heat
 
ii) Endothermic reaction: A chemical reaction in which heat energy is absorbed.
CaCO3 + Heat →  CaO + CO2
 
5 Corrosion – The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases etc. present in the atmosphere is called corrosion. Rusting – Iron when reacts with oxygen and moisture forms red substance called rust.
 
6 Rancidity – The taste and odour of food materials containing fat and oil changes when they are left exposed to air for long time. This is called rancidity. It is caused due to oxidation of fat and oil present in food material.
It can be prevented by using various methods such as by adding antioxidants to the food materials,
Storing food in air tight container and by flushing out air with nitrogen.
 
SUGGESTED ACTIVITIES
1. Burning of a magnesium ribbon in air and collection of magnesium oxide.
 
2. Formation of hydrogen gas by the action of dilute sulphuric acid on zinc
 
3. i) Combination reaction Formation of slaked lime by the reaction of calcium oxide with water
 
   ii) Decomposition reaction Heating of lead nitrate and emission of nitrogen dioxide Electrolysis of water
 
  iii) Displacement reaction Iron nails dipped in copper sulphate solution.
 
  iv) Double displacement reaction Formation of barium sulphate and sodium chloride.
 
  v) Oxidation reaction Oxidation of copper to copper oxide.
 
HOTS QUESTIONS (SOLVED)
 
Question. A water insoluble substance ' X' on reacting with dilute H2SO4 released a colourless and odourless gas accompanied by brisk effervescence. When the gas was passed through water, the solution obtained turned blue litmus red. On bubbling the gas through lime water, it initially became milky and milkyness disappeared when the gas was passed in excess.
Identify the substance  'X' rite its chemical equations of the reactions involved.
Answer : The water insoluble substance ‗↓‘ is metal carbonate CaCO3.
CaCO3 (S) + H2SO4 (Aq)  CaSO4(Aq) + H2O (Aq) + O2 (G)
Ca(OH)2 + CO2 (G)  →  CaCO3 (S) + H2O (L) (milky)
CaCO3 (S) + CO2 (G)+ H2O (Aq)Ca(OH)(milkiness)
 
Question. Ahmad took a magnesium ribbon (cleaned) and burned it on a flame. The white powder formed was taken in a test tube and water was added to it. He then tested the solution formed with red and blue litmus paper. What change was seen? Why?
Answer : Red litmus paper turned blue.
Blue litmus paper remained blue.
This is because the magnesium ribbon on burning in air forms the white magnesium oxide. Which dissolved in water, it forms magnesium hydroxide, which is Basic in nature.

Question. What happens when a chemical reaction occurs?
Answer : When a chemical reaction occurs:
i. New substances are formed by breaking and making of new bonds.
ii. Some gases may evolve during the reaction.
iii. Change in smell.
iv. Change in colour.
v. Change in state (liquid, solid or gaseous)
vi. Change in temperature.

Question. What happens when hydrogen combines with oxygen in the presence of an electric current?
Answer : When hydrogen reacts with oxygen in the presence of an electric current, formation of water takes place which conducts electricity.
At the cathode, the electrons and the hydrogen ions combine with oxygen to make water.
The reaction takes place is given as:
2H2 + O2→ 2H2O

Question. Give an example of a double displacement reaction.
Answer : The reaction in which there is an exchange of ions between the reactant takes place is called double displacement reaction.

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For example:
Na2SO4 + BaCl→ BaSO4 + 2NaCl
Sodium Barium Barium Sodium sulphate chloride sulphate chloride
In the above reaction, the exchange of ions (SO42- and Ba2+) takes place. The white precipitate of BaSO4 is formed by the reaction of SO42- and Ba2+. The other product formed NaCl remains in the solution.

Question. “We need to balance a skeletal chemical equation.” Give reason to justify this statement.
Answer : Balanced chemical equation: A chemical equation in which the number of atoms of reactants are equal to the number of atoms of products is called a balanced equation.
We need to balance a skeletal chemical equation because:
i. According to the law of conservation of mass, mass (or atoms) are neither created nor destroyed in chemical reactions.
ii. It means the total mass of the products formed in chemical reaction must be equal to the mass of reactants consumed.

Question. Giving an example list two information which make a chemical equation more useful (informative).
Answer : Chemical equations can be made more informative by the following characteristics:
Physical state
There are three different states which are solid, liquid and gaseous. If the substance exists in solid state, it is represented by (s).
If the substance exists in aqueous state, it is represented by (aq).
If the substance exists in gaseous state, it is represented by (g).
For example:

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Evolution of gas
If the gas is liberated in a reaction, it is indicated by an arrow upward and its physical state is shown by (g).
For example:
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)↑

Question. Write a balanced chemical equation for process of photosynthesis.
Answer : Photosynthesis reaction: CO2 + H2O → C6H12O6 + O2 + H2O
Balanced equation: 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O
Step 1: Write the unbalanced equation
CO2 + H2O → C6H12O6 + O2 + H2O
Step 2: Compare the number of atoms of reactants with the number of atoms of products.

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Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, first let us consider carbon atom. If we multiply 6 in the reactant (in CO2), we will get the equal number of atoms as in product (in C6H12O6)

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Step 4: Write the resulting equation:
6CO2 + H2O → C6H12O6 + O2 + H2O
Step 5: Now check whether the equation is balanced or not by comparing the atoms

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We find that the equation is not balanced yet. As the number of
Hydrogen and oxygen atoms are unequal on the two sides.
First balance the hydrogen atom.
Step 6: If we multiply 12 in the reactant (in H2O) and 6 in the product (in H2O), we will get the equal number of hydrogen atoms both sides.

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Step 7: Write the resulting equation:
6CO2 + 12H2O → C6H12O6 + O2 + 6H2O
Step 8: Now check whether the equation is balanced or not by comparing the atoms.

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We find that the equation is not balanced yet. As the number of oxygen atoms are unequal on the two sides
Step 9: Now, we consider oxygen atoms. If we multiply 6 in the product (in O2), we will get the equal number of atoms as in reactants (in 6CO2 and 12H2O)

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Step 10: Write the resulting equation:
6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O
We find that the equation is balanced now.
Step 11: Write down the final balanced equation:
6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O

Question. When do desert plants take up carbon dioxide and perform photosynthesis?
Answer :
In deserts, the weather is very hot and the amount of rainfall is very low. Hence, if desert plants take CO2 during day, large amount of water can be lost. To avoid this water loss, some of the desert plants take CO2 during night.

Question. Zinc liberated hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?
Answer :

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As you can observe in the above series that zinc is more reactive than the hydrogen whereas copper is less reactive than hydrogen.
More reactive the metal is, more easily it will displace hydrogen atoms. Hence,
i. When zinc reacts with hydrochloric acid, it liberates hydrogen gas (hydrogen is displaced)
Zn + HCl → ZnCl2 + H2
ii. On the other hand, when copper reacts with hydrochloric acid, it is unable to displace the hydrogen gas. As a result, no hydrogen gas is liberated.
Cu + HCl → No reaction

Question. Identify the reducing agent in the following reactions:
(a) 4NH3 + 5O2→ 4NO + 6H2O
(b) H2O + F2→ HF + HOF
(c) Fe2O3 + 3CO → 2Fe + 3CO2
(d) 2H2 + O2→ 2H2O
Answer :
Reducing agent: A reducing agent is an element that loses electrons.
The reducing agent means to loose electrons; it is said to have been oxidized.
The element which undergoes oxidation (gets oxidized) is called reducing agent.
a) NH3 is reducing agent
4NH3 + 5O2→ 4NO + 6H2O
In the given reaction, nitrogen is oxidized to NO by gaining oxygen atom. Thus, NH3 is reducing agent as it undergoes oxidation.
b) F2 is reducing agent
H2O + F2→ HF + HOF
In the given reaction, F2 is oxidized to HOF by gaining hydrogen atom. Thus, F2 is reducing agent as it undergoes oxidation.
(c) CO is reducing agent
Fe2O3 + 3CO → 2Fe + 3CO2
In the given reaction, CO is oxidized to CO2 by gaining oxygen atom. Thus, CO is reducing agent as it undergoes oxidation.
(d) H2 is reducing agent
2H2 + O2→ 2H2O
In the given reaction, 2H2 is oxidized to 2H2O by gaining oxygen atom. Thus, 2H2 is reducing agent as it undergoes oxidation.

Question. You might have noted that when copper powder is heated in a china dish, the surface of copper powder becomes coated with a black colour substance.
(a) How has this black coloured substance formed? (b) What is that black substance? (c) Write the chemical equation of the reaction that takes place.
Answer :
(a) When copper powder is heated in the presence of air (oxygen), cooper reacts with oxygen to form copper oxide. The copper oxide formed is black in colour. The black colour is formed because the oxidation of copper takes place.
(b) The black substance formed is copper oxide.
(c) The chemical equation of the reaction that takes place is given below:
2Cu + O2→ 2CuO

Question. Identify the oxidising agent (oxidant) in the following reactions:
(a) Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O
(b) 2Mg + O2→ 2MgO
(c) CuSO4 + Zn → Cu + ZnSO4
(d) V2O5 + 5Ca → 2V + 5CaO
(e) 3Fe + 4H2O → Fe3O4 + 4H2
(f) CuO + H2→ Cu + H2O
Answer : Oxidizing agent: An oxidizing agent is an element that gains electrons. Since, the oxidizing agent means to gain electrons; it is said to have been reduced.
The element which undergoes reduction (gets reduced) is called oxidizing agent.
(a) Pb3O4 is reducing agent
Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O
In the given reaction, Pb3O4 loses oxygen and reduces to PbCl2
Thus, Pb3O4 is an oxidizing agent as it undergoes reduction.
(b) O2 is oxidizing agent
2Mg + O2→ 2MgO
In the given reaction, O2 is reduced by losing oxygen atoms. Thus, O2 is an oxidizing agent as it undergoes reduction.
(c) CuSO4 is oxidizing agent
CuSO4 + Zn → Cu + ZnSO4
In the given reaction, CuSO4 is reduced to Cu by losing oxygen atoms. Thus, CuSO4 is an oxidizing agent as it undergoes reduction.
(d) V2O5 is oxidizing agent
V2O5 + 5Ca → 2V + 5CaO
In the given reaction, V2O5 is reduced to V by losing oxygen atoms. Thus, V2O5 is an oxidizing agent as it undergoes reduction.
(e) H2O is oxidizing agent
3Fe + 4H2O → Fe3O4 + 4H2
In the given reaction, H2O is reduced to H2 by losing oxygen atoms. Thus, H2O is an oxidizing agent as it undergoes reduction.
(f) CuO is oxidizing agent
CuO + H2→ Cu + H2O
In the given reaction, Cu is reduced to Cu by losing oxygen atom. Thus, CuO is an oxidizing agent as it undergoes reduction.

Question. Write the balanced chemical equation for the following equations for the following reaction and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in presence of conc. H2SO4.
(d) Ethene is burnt in presence of oxygen to form carbon dioxide, water and releases heat and light.
Answer :
(a) When nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas. The following reaction takes place

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The above reaction is a type of combination reaction.
Combination reaction is reaction in which two reactants combined together to form a product.
(b) When sodium hydroxide solution is treated with acetic acid to form sodium acetate and water. The following reaction takes place:
NaOH + CH3COOH → CH3COONa + H2O
The above reaction is a type of neutralization reaction/ double displacement reaction.
A neutralization reaction is a reaction in which base (NaOH) and acid (CH3COOH) react together to form a salt (CH3COONa) and water.
(c) When ethanol is warmed with ethanoic acid to form ethyl acetate in presence of conc. H2SO4. The following reaction takes place:

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An esterification reaction is a reaction in which alcohol (C2H5OH) and Carboxylic acid (CH3COOH) react together to form a sweet-smelling substance called ester (CH3COOC2H5)
(d) When ethene is burnt in presence of oxygen to form carbon dioxide, water and releases heat and light. The following reaction takes place:
C2H4 + 3O→ 2CO2 + 2H2O + heat + light
The above reaction is a type of combustion reaction.
Combustion reaction is a reaction which takes place in the presence of oxygen to form carbon dioxide.

Question. Complete the missing components/variables given as x and y in the following reactions:
(a) Pb(NO3)2(aq) + 2Kl(aq) → PbI2(x) + 2KNO3(y)
(b) Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + x
(c) Zn(s) + H2SO4(aq) → ZnSO4(x) + H2(y)

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Answer : (a) Pb(NO3)2(aq) + 2Kl(aq) → PbI2(s) + 2KNO3(aq)
Hence, x is (s) and y is (aq) (s) means PbI2 exists in solid state and (y) means that KNO3 exists in aqueous/liquid state.
(b) Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
Hence, x is Ag(s) In the above reaction, Ag gets replaced by Cu.
(c) Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
Hence, x is (aq) and y is (g) (aq) means copper sulphate formed exists in aqueous state. (g) Means hydrogen gas is liberating.

""CBSE-Class-10-Science-HOTs-Chemical-Reactions-and-Equations-6

Hence x is heat
When CaCO3 is heated in the presence of oxygen, it forms calcium oxide (CaO) and carbon dioxide.

Question. Identify the type of chemical reaction taking place in each of the following:
(a) Barium chloride solution is mixed with a copper sulphate solution and a white precipitate is observed.
(b) On heating copper powder in the air in a china dish, the surface of copper powder turns black.
(c) On heating, green coloured ferrous sulphate crystals, reddish brown solid is left and a smell of a gas having an odour of burning sulphate is experienced.
(d) Iron nails when left dipped in blue copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.
(e) Quick lime reacts vigorously with water releasing a large amount of heat.
Answer : (a) Double displacement and precipitation reaction
When barium chloride solution is mixed with copper sulphate solution and a white precipitate is observed.
In double displacement reaction, a precipitate is formed which settles down at the bottom. Any reaction that produces a precipitate is called a precipitation reaction.
BaCl2 + CuSO→ BaSO4 (↓) + NaCl White ppt.
Note: A precipitate is a substance which is insoluble in water.
(b) Oxidation reaction
On heating copper powder in air in a china dish, the surface of copper powder turns black because copper undergoes oxidation in the presence of air.
2Cu +O2→ 2CuO Black
(c) Thermal decomposition
On heating green coloured ferrous sulphate crystals, reddish brown solid is left and smell of a gas having odour of burning sulphate is experienced.

""CBSE-Class-10-Science-HOTs-Chemical-Reactions-and-Equations-2

In the above reaction, ferrous sulphate (FeSO4) decomposes to ferric oxide (Fe2O3)
(d) Displacement reaction
Iron nails when left dipped in blue copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.
Fe + CuSO→ FeSO4 + Cu
As we know that displacement reaction is a reaction in which one element displaces other element from its compound and takes its place there in.
In the above reaction Fe replaces Cu and form a new compound.
(e) Exothermic reaction
Quick lime reacts vigorously with water releasing a large amount of heat:
CaO + H2O → Ca(OH)2 + heat
In the above reaction, the heat is released. Hence, it is an exothermic reaction.
Exothermic reaction is a reaction in which heat is released when reactants changes into products.

Question. Seema likes sugar apple which is a multipurpose, an all-rounder fruit. It can be used by athletes as high calorie fruit for high energy. The powdered of its seeds is an effective pesticide in agriculture and horticulture and also used to remove head lice. Its leaves have anti-diabetic properties. The alcoholic extract of its leaves and stems can treat tumours. This extract is an antidepressant. Fruits are sweet and increase the haemoglobin, cooling and act as sedative. Seeds are insecticides. Its roots are powerful purgatives and used in dysentery.
(a) Why is sugar apple used by athletes?
(b) Why should we use it as a pesticides and insecticides instead of chemicals? Which value is associated with its use?
(c) Which metal is present in haemoglobin?
Name one more fruit which is rich in iron?
(d) Why should people take fruits rich in iron?
(e) What values are possessed by Seema who uses this multipurpose fruit instead of junk food?
Answer :
(a) Sugar is used by athletes because:
i. It is a multipurpose, an all-rounder fruit.
ii. It can be used by athletes as high calorie fruit for high energy.
iii. It increases the flow of blood in the whole body.
iv. It increases haemoglobin too.
(b) We should use sugar apple as a pesticides and insecticides instead of chemicals because:
i. Chemicals can harm plants and can stop their growth.
ii. On the other hand, the powdered seeds of sugar apple do not cause any harm to plants as they are purely natural.
(c) Iron is present in our haemoglobin. Iron is an important element for the formation of blood in the body. The lack of iron in body can cause too many problems. The other fruits which is rich in iron is banana.
(d) People take fruits rich in iron because iron increases the production of blood in the body. It increases the haemoglobin which keeps us fit from top to bottom
(e) Seema is health-conscious, aware and knowledgeable too.

Chapter 01 Chemical Reactions and Equations
CBSE Class 10 Science HOTs Chemical Reactions and Equations
Chapter 03 Metals and Non-Metals
CBSE Class 10 Science HOTs Metals and Non Metals
Chapter 05 Periodic Classification of Elements
CBSE Class 10 Science HOTs Periodic Classification of Elements
Chapter 08 How do the Organisms Reproduce
CBSE Class 10 Science HOTs Question How Do Organisms Reproduce
Chapter 10 Light Reflection and Refraction
CBSE Class 10 Science HOTs Reflection and Refraction
Chapter 13 Magnetic Effect of Electric Current
CBSE Class 10 Science HOTs Magnetic Effects of Electric Current
Chapter 16 Sustainable Management of Natural Resources
CBSE Class 10 Science HOTs Question Management of Natural Resources
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CBSE Class 10 Science HOTs Question Bank

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