NCERT Solutions For Class 10 Science Chapter 1 Chemical Reactions And Equations

NCERT Solutions For Class 10 Science Chapter 1 Chemical Reactions And Equations Long Question And Answers

Question 1.

1. What is rancidity? Mention any two ways by which rancidity can be prevented.

2.

1. Why is respiration considered an exothermic reaction?
2. Define the terms—oxidation and reduction.
3. Identify the substance that is oxidised and reduced in the reaction:

CuO(s) + Zn(s) → Cu(s) + ZnO(s)

Answer:

1. The process in which the taste and smell of food get spoiled is called rancidity. It happens due to oxidation.

Prevention from rancidity:

• Antioxidants are added to fatty acids to prevent oxidation, e.g., chips are packed in the presence of nitrogen gas which prevents spoilage by oxidation.
• Food should be kept in an airtight container in the refrigerator.

2.

1. This is because heat is evolved during respiration.
2. Oxidation is a process in which O₂ is added or H₂ is removed or loss of electrons takes place.  Reduction is a process in which H₂ is added or O₂ is removed or a gain of electrons takes place.
3. Zn is getting oxidised, and CuO is getting reduced.

Chemical Reactions and Equations NCERT Class 10 Science Solutions

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Question 2.

1. 2 g of ferrous sulphate crystals are heated in a boiling tube.

1. State the colour of ferrous sulphate crystals both before heating and after heating.
2. Name the gases produced during heating.

2.  Give reasons for the following:

1. All decomposition reactions are endothermic reactions.
2. The colour of copper sulphate solution changes when an iron nail is dipped in it.
3. Respiration is an exothermic reaction.

Answer:

1.

1. Before heating- Pale green. After heating- Brown or reddish brown.
2. SO₂ and SO₃

2.

1. Decomposition reactions require energy either in the form of heat, light or
   electricity for breaking down the reactants or energy is absorbed.
2. Iron has displaced copper from the copper sulphate solution to form iron sulphate
   which is light green. Fe is more reactive than copper.
3. During digestion, food (rice, potatoes etc.) containing carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. Since energy is given so it is an exothermic.

Question 3.

1. Write one example for each decomposition reaction

1. Electricity
2. Heat
3. Light

2. Which of the following statements is correct and why copper can displace silver from silver nitrate and silver can displace copper from copper sulphate solution

Answer:

1.

1. 2H₂O  → (Electricities)→ 2H₂(g) +O₂
2. CaCO₃ → (Heat) → CaO+CO₂
3. 2AgBr → (Sunlight) → 2Ag +Br₂

2. Copper can displace silver from AgNO₃ because copper is more reactive than Ag,

Example: Cu + 2AgNO₃(aq)→ Cu(NO₃)₂ (aq) + 2Ag (s)

NCERT Class 10 Science Chapter 1: Chemical Reactions and Equations Summary

Question 4.

1. Define corrosion.
2. What is corrosion of iron called?
3. How will you recognise the corrosion of silver?
4. Why corrosion of iron is a serious problem?
5. How can we prevent corrosion?

Answer:

1. Define Corrosion:  The process in which metals break down gradually by the action of air, moisture or a chemical on their surface.
2. Rusting of iron.
3. By the development of a black coating on silver.
4. Even- year enormous amount of money is spent to replace damaged iron.
5. Paint, or galvanisation, or electroplating.

Question 5. A metal nitrate ‘A’ on heating gives yellowish brown coloured metal oxide along with brown gas ‘B ‘and a colourless gas ‘C’ Aqueous solution of ‘A’ on reaction with potassium iodide forms a yellow precipitate of compound ‘D’. Identify ‘A, B, C, and D Also identify the types of h reactions. The metal present in ‘A’ is used in the alloy which is used for soldering purposes.
Answer:

Metal nitrate A is Pb(NO₃)₂.

A’ is lead nitrate, ‘B’ is nitrogen dioxide, ‘C’ is oxygen and ‘D’ is lead.

• Is decomposition reaction and
• Is a double displacement reaction (Precipitation reaction

NCERT Solutions Chapter 1: Chemical Reactions and Equations Questions and Answers

Question 6. Translate the following statement into chemical equations and then balance them.

1. Hydrogen gas combines with nitrogen to form ammonia.
2. Hydrogen sulphide gas burns in the air to give water and sulphur dioxide.
3. Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
4. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
5. Aluminium chloride reacts with ammonium hydroxide to form a gelatinous white precipitate of aluminium hydroxide and a salt of ammonium chloride.

Answer:

1. \(3 \mathrm{H}_2(g)+\mathrm{N}_2(g) \Longrightarrow 2 \mathrm{NH}_3(g)\)

2. \(2 \mathrm{H}_2 \mathrm{~S}(g)+3 \mathrm{O}_2(g) \longrightarrow 2 \mathrm{SO}_2(g)+2 \mathrm{H}_2 \mathrm{O}(g)\)

3. \(3 \mathrm{BaCl}_2(a q)+\mathrm{Al}_2\left(\mathrm{SO}_4\right)_3(a q) \longrightarrow 2 \mathrm{AlCl}_3(a q)+3 \mathrm{BaSO}_4(s) \)

4. \(2 \mathrm{~K}(s)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow 2 \mathrm{KOH}(a q)+\mathrm{H}_2(g) \)

5. \( \mathrm{AlCl}_3(a q)+3 \mathrm{NH}_4 \mathrm{OH}(a q) \longrightarrow \mathrm{Al}(\mathrm{OH})_3(s) \downarrow+2 \mathrm{NH}_4 \mathrm{Cl}(a q)\)

Question 7. Give reasons why:

1. Sodium acts as a reducing agent while chlorine acts as an oxidising agent in the following reactions: 2Na(s)+Cl₂ (g)→ 2 NaCl(s)
2. White-coloured silver chloride turns grey when kept in sunlight.
3.  Why is the decomposition reaction called the opposite combination reaction?

Answer:

1. Sodium reduces chlorine atoms to chloride ions, therefore it acts as a reducing agent while chlorine oxidises sodium atoms to sodium ions, therefore, it acts as an oxidising agent

2. This is due to the decomposition of silver chloride into silver and chlorine by light.

3. In a decomposition reaction, one substance [compound] splits to give two or more simpler substances [elements or compounds] whereas in a combination reaction, two or more substances [elements or compounds] combine to form a single substance. Due to this reason, a decomposition reaction is called the opposite of a combination reaction.

Question 8. Observe the given figure and answer the following questions:

1. Write the complete balanced reaction for the above.
2. Write the type of reaction involved.
3. Is there any precipitate formed?
4. If any precipitate formed, write the colour of the precipitate.

Answer:

1. Na₂SO₄(ag) + BaCl₂(aq) →2NaCl(aq) + BaSO₄(s)↓ (White precipitate)

2. Double displacement reaction

3. Yes.

4. White precipitates of barium sulphate is formed.

NCERT Solutions Chapter 1: Chemical Reactions and Equations Questions and Answers

Question 9. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.

1. Nitrogen gas is treated with hydrogen gas in the presence ofa catalyst at 773K to form ammonia gas.
2. Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
3. Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of
   concentrated H₂SO₄
4. Ethene is burnt in the presence ofoxygen to form carbon dioxide, and water and releases heat and light.

Answer:

Example of a combination reaction.

2. NaOH(aq) + CH₃COOH(aq) → CH₃COOH(aq) + H₂O(l)

Example of neutralisation reaction as well as double displacement reaction.

3. C₂H₅OH(l) + CH₃COOH(Z) → H⁺  → CH₃COOC₂H₅ (l) + H₂O(Z)

Example of displacement reaction/Esterification

4. 2CH₃– CH₃(g) + 7O₂→ 4CO₂ + 6H₂O + Heat

Example of combustion reaction.

Question 10. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.

1. In thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
2. Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
3. Chlorine gas is passed in an aqueous potassium iodide solution to form a potassium chloride solution and solid iodine.
4. Ethanol is burnt in the air to form carbon dioxide, water and releases heat.

Answer:

1. Fe₂O₃(s) + 2Al(s)- Al₂O₃(S) + 2Fe(Z) + Heat

Displacement reaction/Redox reaction

2. 3Mg(s) + N₂(g) – Mg₃N₂(s)

Combination reaction

3. 2KI(aq) + Cl₂(g) – 2KCl(aq) + I₂(s)

Displacement reaction

4. C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l) + Heat

Redox reaction/Combustion reaction

NCERT Class 10 Science Chapter 1: Chemical Reactions and Equations Key Concepts

Question 11. During the reaction of some metals with dilute, hydrochloric acid following changes were made:

1. Silver metal does not show any change.
2. The temperature of the reaction mixture rises when aluminium (Al) is added.
3. The reaction of sodium metal is found to be highly explosive.
4. Some bubbles ofa gas are seen when lead (Pb) is reacted with the acid.
5. Explain these observations giving suitable reasons.

Answer:

1. Silver is below hydrogen in the reactivity series so it cannot displace hydrogen when reacted with acid.

2. The reaction of Al with dilute HC1 is exothermic

2Al + 6 HCl→ 2AlCl₃ + 3H₂ + Heat

3. Sodium is a very reactive metal. It reacts with hydrochloric acid to form NaCl and H₂ with the evolution of heat too. H₂ gas produced catches fire immediately.

4. Lead is slightly more reactive and displaces hydrogen from acid very slowly and to a small extent. Hence, only bubbles of H₂ can be seen

PbCl₂ + 2HCl → PbCl₂ + H₂ (g)

Question 12. Write a balanced chemical equation for each ofthe following reactions and also classify them.

1. Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
2. Ca(OH)₂(aq)
3. A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
4. Iron (3) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
5. Hydrogen sulphidegas reacts with oxygen gas to form solid sulphur and liquid water.

Answer:

Pb (CH₃COO)₂ + 2HCl→PbCl₂ + CH₃ COOH; Double displacement reaction

2Na + 2C₂H₅OH→ 2C₂H₅ONa + H₂; Displacement reaction

Fe₂O₃ + 3CO → 2Fe + 3CO₂ ; Redox reaction

2H₂ S + O₂ – 2S + 2H₂O; Redox reaction

Question 13. Balance the following chemical equations and identify the type of chemical reaction.

1. \(\mathrm{Mg}(s)+\mathrm{Cl}_2(g) \longrightarrow \mathrm{MgCl}_2(s) \)

2. HgO(s)→ (Heat)→  Hg(l)+O₂(g)

3. Na(s)+S(s)→ (Fuse)→ Na₂S(s)

4. \( \mathrm{TiCl}_4(l)+\mathrm{Mg}(s) \longrightarrow \mathrm{Ti}(s)+\mathrm{MgCl}_2(s)\)

5. \(\left(\text { e) } \mathrm{CaO}(s)+\mathrm{SiO}_2(s) \longrightarrow \mathrm{CaSiO}_3(s)\right. \)

6. H₂O₂(l)→(UV) → HO₂(l)+O₂(g)

Answer:

1. \(\mathrm{Mg}(s)+\mathrm{Cl}_2(g) \longrightarrow \mathrm{MgCl}_2(s)\)(Balanced) – Combination reaction

2. 2HgO(s)→ (Heat)→  2Hg(l)+O₂(g)- Decomposition reaction

3. 2Na(s)+S(s)→ (Fuse)→ Na₂S(s) – Combination reaction

4. \(\mathrm{TiCl}_4(l)+2 \mathrm{Mg}(s) \longrightarrow \mathrm{Ti}(s)+2 \mathrm{MgCl}_2\) – Displacement reaction

5.\(\mathrm{CaO}(\mathrm{s})+\mathrm{SiO}_2(\mathrm{~s}) \longrightarrow \mathrm{CaSiO}_3(\mathrm{~s})\) – Combination reaction

6. 2H₂O₂(l)→(UV) → 2HO₂(l)+O₂(g) – Decomposition reaction

Chemical Reactions and Equations NCERT Class 10 Science Explanation and Notes

Question 14. On heating a blue-coloured powder of copper (II) nitrate in a boiling tube, copper oxide(black), oxygen gas and a brown gas X are formed.

1. Write a balanced chemical equation ofthe reaction.
2. Identify the brown gas X evolved.
3. Identify the type ofreaction.
4. What could be the pH range of the aqueous solution ofthe gas X?

Answer:

1. Balanced chemical equation

2Cu(NO₃)₂(s) →(Heat) → 2CuO (s) + O₂(g) + 4NO₂(g)

2. The brown pas X evolved is nitrogen dioxide (NO₂).

3. This is a decomposition reaction.

4. Nitrogen dioxide dissolves in water to form an acidic solution because it is an oxide of non-metal. Therefore, pH of this solution is less than 7.

Question 15. Give the characteristic tests for the following gases

1. CO₂
2. SO₂
3. O₂
4. H₂

Answer:

1. CO₂ gas turns lime water milky when passed through.
2. SO₂ gas when passed through an acidic KMnO₄ solution (purple) turns
   colourless.
3. The evolution of oxygen (O₂) gas during a reaction can be confirmed by bringing a burning candle near the mouth ofthe test tube containing the reaction mixture.The intensity of the flame increases because oxygen supports burning.
4. H₂ gas burns with a pop sound when a burning candle is brought near it.

Chemical Reactions and Equations NCERT Class 10 Science Explanation and Notes

Question 16. What happens when a piece of

1. Zinc metal is added to copper sulphate solution1?
2. Aluminium metal is added to dilute hydrochloric acid.
3. Silver metal is added to copper sulphate solution?

Also, write the balanced chemical equation if the reaction occurs.

Answer:

1. Zinc being more reactive than copper displaces copper from its solution and a solution of zinc sulphate is obtained

⇒ \(\underset{\text { Zinc }}{\mathrm{Zn}(s)}+\underset{\text { Copper sulphate(Blue) }}{\mathrm{CuSO}_4(a q)} \longrightarrow \underset{\text { Zinc sulphate(Colourless) }}{\mathrm{ZnSO}_4(a q)}+\underset{\text { Copper }}{\mathrm{Cu}(s)}\)

2. Aluminium being more reactive displaces hydrogen from dilute hydrochloric acid solution and hydrogen gas is evolved.

⇒ \(\underset{\text { Aluminium }}{2 \mathrm{Al}(s)}+\underset{\text { Hydrochloric acid}}{6 \mathrm{HCl}(a q)} \longrightarrow \underset{\text { Aluminium chloride}}{2 \mathrm{AlCl}_3(a q)}+\underset{\text { Hydrogen }}{3 \mathrm{H}_2(g)}\)

3. Silver metal being less reactive than copper cannot displace copper from its salt solution. Therefore, no reaction occurs

⇒ \(\underset{\text { Silver }}{\mathrm{Ag}(s)}+\underset{\text { Copper sulphate }}{\mathrm{CuSO}_4(a q)}\) → No reaction

Question 17. What happens when zinc granules are treated with a dilute solution of H₂SO₄, HCl, HNO₃, NaCl and NaOH? Also, write the chemical equations if a reaction occurs.
Answer:

The reaction of Zn granules with

1. Dilute H₂SO₄

Zn(s) + H₂SO₄(aq)→ ZnSO₄(aq) + H₂(g)

2. Dilute HCl

Zn(s) + 2HCl(aq)→ ZnCl₂(aq) + H₂(g)

3. Dilute HNO₃

4 Zn(s) + 10HNO₃ (aq) → 4Zn(NO₃)₂(aq) + 5 H₂O(l) + N₂O(g)

4. NaCl solution

Zn(s) + NaCl (aq ) → No reaction

5. NaOH solution

Zn(s) + 2NaOH(ag)→ Na₂ZnO₂(aq)( Sodium zincate) + H₂(g)

NCERT Solutions for Chemical Reactions and Equations Class 10 Science

Question 18. On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, a white precipitate is obtained

1. Write a balanced chemical equation of the reaction involved.
2. What other name can be given to this precipitation reaction?
3. On adding dilute HCl to the reaction mixture, the white precipitate disappears. Why?

Answer:

1. Balanced chemical equation

⇒ \(\underset{\text { Sodium sulphate }}{\mathrm{Na}_2 \mathrm{SO}_3(a q)}+\underset{\text { Barium chloride }}{\mathrm{BaCl}_2(a q)} \longrightarrow \underset{\text { Barium sulphite }}{\mathrm{BaSO}_3(s)}+\underset{\text { Sodium chloride }}{2 \mathrm{NaCl}(a q)}\)

2. This reaction is also known as a double displacement reaction.

3. BaSO₃ is a salt ofa weak acid (H₂SO₃), therefore dilute acids such as HCl decompose barium sulphite to produce sulphur dioxide gas which has the smell of burning sulphur

⇒ \(\underset{\text { Barium sulphite }}{\mathrm{BaSO}_3(s)}+\underset{\begin{array}{c}
\text { Hydrochloric } \\
\text { acid }
\end{array}}{2 \mathrm{HCl}(a q)} \longrightarrow \underset{\begin{array}{c}
\text { Barium } \\
\text { chloride }
\end{array}}{\mathrm{BaCl}_2}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}}+\underset{\begin{array}{c}
\text { Sulphur } \\
\text { dioxide }
\end{array}}{\mathrm{SO}_2(g)}\)

BaCl₂ is soluble in water, hence white precipitate disappears.

Question 19. You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO₃, ZnCl₂, and H₂O. In which of the above containers these solutions can be kept?

Answer:

1. When solutions are kept in a copper container

⇒ Dilute HCl

Copper does not react with dilute HCl. Therefore, it can be kept.

⇒  Dilute HNO₃

Nitric acid acts as a strong oxidising agent and reacts with copper vessels, therefore cannot be kept.

⇒  ZnCl₂

Zinc is more reactive than copper (Cu) therefore, no displacement reaction occurs and hence can be kept.

⇒  H₂O

Copper does not react with water. Therefore, can be kept.

2. When solutions are kept in aluminium containers

⇒  Dilute HCl

Aluminium reacts with dilute HCl to form its salt and hydrogen is evolved.

Therefore, if cannot be kept.

2Al + 6HCl→ 2 AlCl₃ + 3H₂

⇒ Dilute HNO₃

Aluminium gets oxidised by dilute HN03 to form a layer of A1203 and can be kept

⇒ ZnCl₂

Aluminium being more reactive than zinc can displace zinc ions from tho solution.

Therefore, the solution cannot ho kept.

2Al + 3ZnCl₂→ 2AlCl₃ + 3Zn

⇒ H₂O

Aluminium does not react with cold or hot water. Therefore, water can be kept.

Aluminium is attacked by steam to form aluminium oxide and hydrogen

2Al(s) + 3H₂O →Al₂O₃(s) + 3H₂(g)

NCERT Solutions for Chemical Reactions and Equations Class 10 Science

Question 20. Translate the following statement into a chemical equation and then balance the equation: Hydrogen sulphide gas burns in the air to give water and sulphur dioxide.
Answer:

By observing the products, water (H₂O) and sulphur dioxide (SO₂), we can conclude that only oxygen from the air reacts with hydrogen sulphide (H₂S).

Hydrogen sulphide + Oxygen

The skeletal equation for the reaction is:

⇒ \(\mathrm{H}_2 \mathrm{~S}+\mathrm{O}_2 \longrightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{SO}_2\)

If we observe the equation we find that H and S atoms are equal on both sides of the equation. To balance O atoms multiply O₂ by \(\frac{3}{2}\) becomes 3 on each side of the equation.

⇒  \(\mathrm{H}_2 \mathrm{~S}+\frac{3}{2} \mathrm{O}_2 \longrightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{SO}_2\)

To make the coefficients whole numbers, multiply the above equation by 2.

⇒ \(2 \times \mathrm{H}_2 \mathrm{~S}+\frac{3}{2} 3 \mathrm{O}_2 \longrightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{SO}_2\)

⇒ \(2 \mathrm{H}_2 \mathrm{~S}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{H}_2 \mathrm{O}+2 \mathrm{SO}_2\)

In the above equation, there are 4 atoms of hydrogen, 2 atoms of sulphur and 6 atoms of oxygen on each side of the equation. Hence, the equation is balanced.

Question 21. The equation for the oxidation of ammonia is: NH₃ + O₂ →  N+ H₂O, Rewrite the equation in a balanced form.

Answer:

The skeletal equation is

NH₃ + O₂ → N₂ + H₂O

NH₃ contains a maximum number of atoms, so the atoms present in it are balanced first.

Multiply NH₃ by 2 to balance N atoms.

2NH₃ + O₂ →N₂ + H₂O

Multiply H₂O by 3 to balance H atoms.

2NH₃ + O₂ → N₂ + 3H₂O

Oxygen is balanced last of all. To balance oxygen atoms multiply O₂ by \(\frac{3}{2}\)

⇒ \(2 \mathrm{NH}_3+\frac{3}{2} \mathrm{O}_2 \longrightarrow \mathrm{N}_2+3 \mathrm{H}_2 \mathrm{O}\)

Since all the coefficients should be whole numbers, multiply the above equation by 2 in order to convert all the coefficients to whole numbers.

⇒ \(2 \times 2 \mathrm{NH}_3+\frac{3}{2} \mathrm{O}_2 \longrightarrow \mathrm{N}_2+3 \mathrm{H}_2 \mathrm{O}\)

4NH₃ + 3O₂ →  2N₂ + 6H₂O

This is a balanced equation. There are 4 nitrogen atoms, 12 hydrogen atoms and 6 oxygen atoms on each side of the equation.

Question 22. Translate the following statement into a chemical equation and then balance the equation: Carbon disulphide burns in air to give carbon dioxide and sulphur dioxide.
Answer:

Carbon disulphide + Oxygen (from air)-» Carbon dioxide + Sulphur dioxide

The skeletal equation for the reaction is

CS₂ +O₂→ CO₂+ SO₂

Multiply SO₂ by 2 to balance sulphur atoms.

CS₂ +O₂ →CO₂ + 2SO₂

Carbon atoms are already balanced.

To balance oxygen atoms multiply O₂ by 3 so that each side of the equation has 6 oxygen atoms.

CS₂ + 3O₂ → CO₂ + 2SO₂

This is a balanced equation. It has 2 sulphur atoms, 6 oxygen, atoms and 1 carbon atom on each side of the equation

Question 23. When copper (2) oxide is heated with hydrogen, copper metal and water are according to the equation: CuO + H₂ →Cu + H₂O

In this reaction, identify:

1. The substance which undergoes oxidation
2. The substance which undergoes reduction
3. The oxidising agent
4. The reducing agent

Answer:

1. Here, H₂ changes to H₂O This involves addition ofoxygen. Hence, H2 is oxidised to water.

2. In this reaction, CuO changes to Cu. This involves the removal of oxygen i.e., reduction.

Thus, Copper(2) oxide, CuO is reduced to Cu.

3. Here, CuO brings about the oxidation of H₂ by supplying oxygen. Hence, CuO is, an oxidising agent.

4. H₂ brings about a reduction of CuO. Hence, H₂ is, a reducing agent.

Class 10 Science Chapter 1: Chemical Reactions and Equations Practice Questions

Question 24. Give differences between displacement and double displacement reactions.
Answer:

Displacement reactions:

1. In these reactions, a more reactive element displaces a less reactive element from its salt solution.

In these reactions, a more reactive element displaces a less reactive element from its salt solution.

2. These reactions are usually slow and take longer time for their completion.

3. During these reactions usually change of colour takes place. e.g.,

⇒ \(\mathrm{Fe}(s)+\underset{\text { Blue }}{\mathrm{CuSO}_4(a q)} \longrightarrow \underset{\text { Light green }}{\mathrm{FeSO}_4(a q)}+\mathrm{Cu}(s)\)

Double displacement reactions:

In these reactions, there is an exchange of ions between two reactants.

These reactions are usually fast and take place instantaneously.

During these reactions usually, precipitates are formed, e.g.,

AgNO₃(aq) + NaCl(aq)→  AgCl(s)(White Precipitate)↓+ NaNO₃(aq)

Question 25. Translate the following statements into chemical equations and then balance them.

1. Hydrogen gas combines with nitrogen to form ammonia.
2. Hydrogen sulphide gas burns in the air to give water and sulphur dioxide.
3. Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
4. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas

Answer:

1. H₂(g) + N₂(g) → NH₃(g)

Balanced equation: 3H₂ (g) + N₂(g)- 2NH₃(g)

2.  H₂S(g) + O₂(g) →  2H₂O(l) +2 SO₂(g)

Balanced equation: 2H₂S(g) + 3O₂(g) →  2H₂O(l) +2 SO₂(g)

3. BaCl₂(aq) + Al₂(SO₄)₃(aq)→AlCl₃ (aq) +  3 BaSO₄(s)

Balanced equation: 3BaCl₂(aq) + Al(SO₄)₃(aq)→  2AlCl₃(aq) + 3BaSO₄(s)

4. K(s) + H₂O(l) → KOH(aq) + H₂(g)

Balanced equation: 2K(s) + 2H₂O(l) — 2KOH(aq) + H₂(g)

Question 26. Balance the following chemical equations:

1. \(\mathrm{HNO}_3+\mathrm{Ca}(\mathrm{OH})_2 \longrightarrow \mathrm{Ca}\left(\mathrm{NO}_3\right)_2+\mathrm{H}_2 \mathrm{O}\)

2. \(\mathrm{NaOH}+\mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{Na}_2 \mathrm{SO}_4+\mathrm{H}_2 \mathrm{O}\)

3. \(\mathrm{NaCl}+\mathrm{AgNO}_3 \longrightarrow \mathrm{AgCl}+\mathrm{NaNO}_3\)

4. \(\mathrm{BaCl}_2+\mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{BaSO}_4+\mathrm{HCl}\)

Answer:

Balanced equations are as follows:

1. \( 2 \mathrm{HNO}_3+\mathrm{Ca}(\mathrm{OH})_2 \longrightarrow \mathrm{Ca}\left(\mathrm{NO}_3\right)_2+2 \mathrm{H}_2 \mathrm{O} \)

2. \(2 \mathrm{NaOH}+\mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{Na}_2 \mathrm{SO}_4+2 \mathrm{H}_2 \mathrm{O}\)

3. \(\mathrm{NaCl}+\mathrm{AgNO}_3 \longrightarrow \mathrm{AgCl}^2+\mathrm{NaNO}_3 \text { (already balanced) } \)

4. \(\mathrm{BaCl}_2+\mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{BaSO}_4+2 \mathrm{HCl}\)

Question 27. Write the balanced chemical equation for the following and identify the type of reaction in each case.

1. Potassium bromide (aq) + Barium iodide (aq) → Potassium iodidei (aq) + Barium, bromides)

2. Zinc carbonate(s)→ Zinc oxide (s) + Carbon dioxide

3. Hydrogen (aq)+ Chlorine→ Hydrogen chloride(aq)

4. Magnesium(s) + Hydrochloric acid (aq)

Magnesium chloride(aq) + Hydrogen(aq)

Answer:

1. 2KBr(aq) + Bal₂(aq)→ 2KI(aq) + BaBr₂(s)

Type of Reaction: Double displacement reaction

2. ZnCOg(s)→ ZnO(s) + CO2(g)

Type of Reaction: Decomposition reaction

3. H₂(g) + Cl₂(g) — 2HCl(g)

Type of Reaction: Combination reaction

4. Mg(s) + 2HCl(aq)→ MgCl₂(aq) + H₂(g)

Type of Reaction: Displacement reaction

Chemical Reactions and Equations: NCERT Class 10 Science Solutions

Question 28.

1. Write the essential condition for the following reaction to take place:

2AgBr → 2Ag + Br₂ Write one application of this reaction.

2. Complete the following chemical equation of a chemical reaction:

2FeSO₄ →  (Heat)→  Fe₂O₃+……….+……….

3. What happens when water is added to quick lime? Write chemical equation

Answer:

1. 2 AgBr →  (Sunlight)→ 2Ag+Br

This reaction is used in photography

2. 2 FeSO₄ →(Heat) → FeO+SO₂+SO₃

Slaked lime is formed with a hissing sound and a lot of heat is evolved.

⇒ \(\mathrm{CaO}+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{Ca}(\mathrm{OH})_2+\text { Heat }\)

Question 29. A zinc plate was put into a solution of copper sulphate kept in a glass container. It was found that the blue colour of the solution gets fader and fader with time. After a few days when the zinc plate was taken out of the solution, several holes were observed in it

1. State the reason for changes observed on the zinc plate.
2. Write the chemical equation for the reaction involved.

Answer:

1. This is because zinc has displaced copper from CuSO₄. Zinc metal has been used to form zinc sulphate, therefore, a number of holes were observed.

2. \(\mathrm{Zn}(s)+\underset{\text { Blue }}{\mathrm{CuSO}_4(a q)} \longrightarrow \underset{\text { Colourless }}{\mathrm{ZnSO}_4(a q)}+\mathrm{Cu}(s)\)

Question 30. The following diagram displays a chemical reaction. Observe and answer the following questions:

1. Identify the type of chemical reaction that will take place and define it. How will the colour ofthe salt change?
2. Write the chemical equation ofthe reaction that takes place.
3. Mention one commercial use of this salt.

Answer:

1. Photochemical decomposition reaction. The reaction in which a compound breaks down into simple substances in the presence of light is called a photochemical decomposition reaction. The colour of salt will change from white to grey.

2. 2AgCl(s) → (Sunlight) → 2Ag(s)+Cl(g)

3. Silver chloride is used in photography

Question 31. A, B, and C are are three elements which undergo chemical reactions according to the following equation:

A₂O₃ + 2B→ B₂O₃ + 2A

3CSO₄ + 2B→ B₂(SO₄ )₃ + 3C

3CO + 2A → A₂O₃ + 3C

Answer the following questions with reasons:

1. Which element is the most reactive?
2. Which element is the least reactive1?
3. What are the types of reactions listed above?

Answer:

1. B as B displaces both A and C from their solution.
2. C as C, is displaced by both A and B.
3. Displacement reactions

Question 32. Observe the following diagram and answer the following questions that follow:

1. Identify the gases that evolved at the anode and cathode.
2. Why are the amounts ofgases collected in the two test tubes not the same volume?
3. What type ofreaction is this?

Answer:

1.

1. At the anode, oxygen gas is evolved.
2. At the cathode, hydrogen gas is evolved.

2. The amounts of gases collected in the two test tubes are of not the same volume because in water, hydrogen and oxygen are present in the ratio of 2: 1 by mass.

3. This reaction is a decomposition reaction.

Question 33. Write the chemical equation of the reaction in which the following changes have taken place with an example of each:

1. Change in colour
2. Change in temperature
3. Formation of precipitate

Answer:

1. Cu(s) + 2AgNO₃(aq)→ Cu(NO₃)₂(aq) + 2Ag

The solution will become blue in colour and shiny silver metal will be deposited.

2. NaOH + HCl → NaCl + H₂O + Heat

The temperature will increase because heat will evolve.

3. Pb(NO₃)₂ (aq) + 2KI (aq)→ Pbl₂(s) + 2KNO₃(aq)

A yellow precipitate of Pbl₂ will be formed.

NCERT Class 10 Science: Chemical Reactions and Equations Detailed Solutions

Question 34. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer:

A decomposition reaction is considered as the opposite of a combination reaction because in a decomposition reaction, a single substance decomposes to produce two or more substances; whereas in a combination reaction, two or more substances combine to give a single substance.

Examples of decomposition reaction

1. \(\mathrm{NH}_4 \mathrm{Cl}(\mathrm{s}) \longrightarrow \mathrm{HCl}(\mathrm{g})+\mathrm{NH}_3(g)\)

2. \(\mathrm{CaCO}_3(\mathrm{~s}) \longrightarrow \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g})\)

Examples of combination reaction

1. \(\mathrm{NH}_3($ g $)+\mathrm{HCl}(\mathrm{g}) \longrightarrow \mathrm{NH}_4 \mathrm{Cl}(\mathrm{s})\)

2. \(\mathrm{CO}_2(\mathrm{~g})+\mathrm{CaO}(\mathrm{s}) \longrightarrow \mathrm{CaCO}_3(\mathrm{~s})\)

Question 35. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer:

Examples of decomposition reaction

1. Decomposition by the use of heat

⇒ \(\mathrm{CaCO}_3(a) → {\text { (Heat) }}→ \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g}) \text {, }\)

2. Decomposition by the use of electricity

⇒ \(2 \mathrm{H}_2 \mathrm{O}(\mathrm{l})→{\text { (Electricity) }} → 2 \mathrm{H}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g})\)

3. Decomposition by the use of light

⇒ \(2 \mathrm{AgCl}(\mathrm{s}) → {\text { (Sunlight) }} → 2 \mathrm{Ag}(\mathrm{s})+\mathrm{Cl}_2(g)\)

Question 36. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer:

In displacement reactions, an element displaces or removes another element, whereas in double displacement reactions exchange of ions between the reactants takes place.

Example of displacement reaction:

1. \(\underset{\text { Iron }}{\mathrm{Fe}(s)}+\underset{\text { Copper sulphate }}{\mathrm{CuSO}_4(a q)} \longrightarrow \underset{\text { Iron sulphate }}{\mathrm{FeSO}_4(a q)}+\underset{\text { Copper }}{\mathrm{Cu}(s)}\)

In this, the element iron has displaced copper from its salt solution (copper sulphate).

Example of double displacement reaction:

2.  \(\underset{\text { Sodium sulphate }}{\mathrm{Na}_2 \mathrm{SO}_4(a q)}+\underset{\text { Barium chloride }}{\mathrm{BaCl}_2(a q)} \longrightarrow \underset{\text { Barium sulphate }}{\mathrm{BaSO}_4(s)}+\underset{\text { Sodium chloride }}{2 \mathrm{NaCl}(a q)}\)

In the above reaction, the exchange of ions has taken place, i.e., Na+ ion has replaced Ba²⁺ and vice versa.

Question 37. Explain the following in terms of gain or loss of oxygen with two examples each.

1. Oxidation
2. Reduction

Answer:

1. Oxidation: A chemical reaction in which a substance gains oxygen is called oxidation.

For example:

1. 2 Cu +O → (Heat)  → 2 CuO

Cu is oxidised to CuO

2.  2 Mg +O →  (Burn)→  2MgO

Mg is oxidised to MgO

2. Reduction: A chemical reaction in which a substance loses oxygen is called reduction.

For examples:

1.  ZnO+ C → Zn +CO

ZnO is reduced to Zn

2. CuO +H₂ → Cu +H₂O

CuO is reduced to MgO

NCERT Class 10 Science: Chemical Reactions and Equations Detailed Solutions

Question 38. Explain the following terms with one example each.

1. Corrosion
2. Rancidity

Or

What is rancidity? What is corrosion? Mention any two ways by which they can be prevented.
Answer:

1. Corrosion:

Due to the effect of moisture and acids, metals get corroded, i.e., metals particularly iron form a porous layer on the surface and thus get damaged. This effect is called corrosion. Corrosion causes damage to metal articles like car bodies, bridges, iron railings, ships and other substances of daily use. To prevent corrosion iron articles should be regularly painted, done oiling, etc.

2. Rancidity:

Fats and oils in food kept for a long time get oxidised and become rancid and the taste of food changes and causes infection upon eating. This is called rancidity.

To prevent rancidity, antioxidants (which prevent oxidation) are added to foods containing fats and oils. Rancidity can also be prevented by flushing out oxygen with an inert gas like nitrogen.

For example, Packets of food items like chips are flushed with nitrogen so that these can be used even after a long duration.

Question 39. What does one mean by exothermic and endothermic reactions? Give examples.

Or

Differentiate between exothermic and endothermic reactions? Write one example for each of these reactions in the form of a balanced chemical equation.
Answer:

Exothermic reactions: Chemical reactions in which energy is evolved (or given out) are known as exothermic reactions.

For example:

CO₂(s) + O(g) → CO₂(g) + 393.7 kJ (ΔH =- 393.7 kJ)

Endothermic reactions:

Reactions in which energy is absorbed are called endothermic reactions. For example.

C(s) + 2S(s) → + CS₂ – 92 kJ (ΔH = + 92 kJ)

Question 40. A shiny brown-coloured element ‘X’ on heating in air becomes black. Name the element ‘X and the black-coloured compound formed. (PBQ)

Or

A reddish-brown coloured metal, used in electrical wires, when powdered and heated strongly in an open china dish, its colour turns black. When hydrogen gas is passed over this black substance, it regains its original colour. Based on the above information, answer the following questions:
Answer:

1. Name the metal and black-coloured substance formed.
2. Write balanced chemical equations for both reactions.

Answer:

Element ‘X’ = Copper (Cu)

Compound = Copper oxide (CuO)

⇒ \(\underset{\text { Brown }}{2 \mathrm{Cu}(s)}+\underset{\text { (from air) }}{\mathrm{O}_2} \longrightarrow \underset{\text { Black }}{2 \mathrm{CuO}}\)

Question 41. Complete the missing components/variables given as x and y in the following reactions.

1. Pb(NO₃)₂(aq) + 2KI(aq)→ Pbl₂(x) + 2KNO₃(y)

2. Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂ (aq)+ x(s)

3. Zn(s) + H₂SO₄(aq)→ ZnSO₄(x) + H₂(y)

4. CaCO₃(s)→  (x) →  CaO(s)+CO₂(g)

Answer: 

1. x → Solid(s), y → aqueous (aq)

2. x → 2Ag

3. x → Aqueous(aq) y gas (g)

4. x → heat

NCERT Solutions for Class 10 Science Chapter 1: Chemical Reactions and Equations

Question 42. Which among the following changes are exothermic or endothermic?

1. Decomposition of ferrous sulphate
2. Dilution of sulphuric acid
3. Dissolution of sodium hydroxide in water
4. Dissolution of ammonium chloride in water

Answer:

1. Endothermic reaction
2. Exothermic reaction
3. Exothermic reaction
4. Endothermic reaction

Question 43. Identify the reducing agent in the following reactions.

1. 4NH₃ + 5O₂ → 4NO + 6H₂O
2. H₂O + F₂→ HF +HOF
3. Fe₂O₃ + 3CO → 2Fe + 3CO₂
4. 2H₂+ O₂ → 2H₂O

Answer:

1. Ammonia (NH₃)
2. Water (H₂O) as F₂ is getting reduced to HF
3. Carbon monoxide (CO)
4. Hydrogen

Question 44. Identify the oxidising agent (oxidant) in the following reactions.

1. 2Mg +O₂→ 2MgO
2. CuSO₄ + Zn → Cu + ZnSO₄
3. V₂O₅ + 5Ca- →2V + 5CaO
4. 3Fe + 4H₂O
5. CuO + H₂→ Cu + H₂O
6. Pb₃O₄ + 8HCl 3PbCl₂ + Cl₂ + 4H₂O

Answer:

1. O₂
2. CuSO₄
3. V₂O₅
4. H₂O
5. CuO
6. Pb₃O₄

Question 45. A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by the emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.

1. Write the chemical formulae of X and Y.
2. Write a balanced chemical equation, whenX is dissolved in water.

Answer:

2Mg + O₂ →  2MgO

3Mg + N₂→ Mg₃N₂

X is MgO; Y is Mg₃N₂

MgO + H₂O → Mg(OH)₂

Question 46. Tarun visited a government hospital to meet his cousin. He saw the medicines in dark bottles were not stored properly. They were not kept away from light and heat. Tarun reported the issue to the medical doctor and was satisfied that all medicines are stored properly.

1. Why are some medicines stored in cool places in dark bottles?
2. Why do some medicines need cool place1?
3. What can we get from this act?

Answer:

1. Medicines when kept in sunlight or in high temperatures lose its chemical identity.
2. Some medicines if not stored at an appropriate temperature show chemical changes and become dangerous for health.
3. Tarun showed his responsibility of well-being.

Question 47. Hunny a student of class 10 visited the house of his uncle Mohit during the summer holidays. He found that all the water taps were rusted. Hunny suggested Uncle to use either chrome-plated or nickel plated taps in place of iron taps. Mohit accepted his suggestion for the future.

1. Why did iron taps get rusted?
2. Name an antirust solution.
3. Name the process involved in the chrome plating or nickel plating.
4. Mention the values associated with the above act.

Answer:

1. Articles made up of iron readily get rusted when kept in moisture or water.
2. Bisphenol
3. Electroplating
4. Use of scientific knowledge, and help of others.

NCERT Solutions for Class 10 Science Chapter 1: Chemical Reactions and Equations

Question  48.

1. Write one example for each ofthe decomposition reactions carried out with the help of:

1. Electricity
2. Heat 
3. Sunlight

Give balanced chemical equations in each case.

2. Which of the following statements is correct and why? Copper can displace silver from the solution of silver nitrate and silver can displace copper from the solution of copper sulphate.

Answer:

1.

1. Electricity: 2H₂O(g)→ (Electric/current )→ 2H₂(g) + O₂(g)
2. Heat: CaCO₃(s) → (Heat) → CaO(s) + CO₂
3.  Sunlight:  2AgCl(s) → (Sunlight)→ 2 Ag(s)+Cl₂(g)

2. Copper can displace silver from silver nitrate solution because it is more reactive than silver.

Cu(s) + 2AgNO₃(aq)→ Cu(NO₃)₂(aq) + 2Ag(s)