NCERT Solutions for Class 10 Science Ch 1: Chemical Reactions and Equations, is given below.
You will get solutions for;
- In-text questions as well as,
- Exercises questions.
So let’s dive into it!
In-text Questions Set-1
1) Why should a magnesium ribbon be cleaned before burning in the air?
Solution:
Before burning, magnesium ribbon should be cleaned because it reacts with oxygen in the air, forming a stable layer of magnesium oxide (MgO). This layer prevents further reaction with oxygen, so it needs to be removed by cleaning the ribbon.
2) Write a balanced equation for the following chemical reactions.
i) Hydrogen + Chloride → Hydrogen chloride
ii) Barium chloride + Aluminium sulfate → Barium sulfate + Aluminium chloride
iii) Sodium + Water → Sodium hydroxide + Hydrogen
Solution:
i) H2 + Cl2→ 2HCl
ii) 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3
iii) 2Na + 2H2O → 2NaOH + H2
3) Write a balanced chemical equation with state symbols for the following reactions.
i) Solutions of Barium chloride and Sodium sulfate in water react to give insoluble Barium sulfate and solution of Sodium chloride.
ii) Sodium hydroxide solution in water reacts with the hydrochloric acid solution to produce Sodium chloride solution and water.
Solution:
i) BaCl2 + Na2SO4 → BaSO4 + 2NaCl
ii) NaOH + HCl → NaCl + H2O
In-text Questions Set-2
1) A solution of a substance, ‘X,’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Solution:
i) The substance ‘X’ which is used in whitewashing is Calcium Oxide (or quicklime) and its formula is CaO.
ii) CaO + H2O → Ca(OH)2
2) Why is the amount of gas collected in one of the test tubes in Activity 1.7 double the amount collected in the other? Name this gas.
Solution:
In activity 1.7, the gas collected in one of the test tubes is double the amount collected in the other because water undergoes electrolysis, producing hydrogen and oxygen gases.
During this process, two molecules of hydrogen gas and one molecule of oxygen gas are released, so the amount of hydrogen collected is twice that of oxygen.
In-text Questions Set-3
1) Why does the color of copper sulfate solution change when an iron nail is dipped in it?
Solution:
When an iron nail is dipped in copper sulfate solution, iron displaces copper from the solution because iron is more reactive. As a result, the color of the copper sulfate solution changes.
The reaction is:
Fe + CuSO4 → FeSO4 + Cu
2) Give an example of a double displacement reaction other than the one given in Activity 1.10.
Solution:
The reaction between silver nitrate (AgNO3) and sodium chloride (NaCl) is a double displacement reaction. In this reaction, the positive and negative ions switch places, forming a white precipitate of silver chloride (AgCl).
The chemical equation is:
AgNO3 + NaCl → AgCl + NaNO3
3) Identify the substances that are oxidized and that are reduced in the following equation.
i) 4Na(s) + O2(g) → 2Na2O(s)
ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
Solution:
In the first equation, sodium (Na) is oxidized by gaining oxygen (O2). In the second equation, copper (Cu) is reduced by gaining hydrogen (H2).
Exercise Questions
1) Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced
(b) Carbon Dioxide is getting oxidized
(c) Carbon is getting oxidized
(d) Lead oxide is getting reduced
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all the above
Solution:
(i) (a) and (b)
Explanation: (a) Oxygen is removed, and (b) the removed oxygen from lead is added to the carbon.
2) Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
1. Combination reaction
2. Double displacement reaction
3. Decomposition reaction
4. Displacement reaction
Solution:
The answer is 4. Displacement reaction.
Explanation: In this reaction, aluminum displaces iron from its oxide to form aluminum oxide. Since aluminum is more reactive than iron, it replaces iron in the compound. This type of reaction, where one element replaces another, is called a displacement reaction. Specifically, it’s a single displacement reaction because only one element is displaced.
3) What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
1. Hydrogen gas and Iron chloride are produced.
2. Chlorine gas and Iron hydroxide are produced.
3. No reaction takes place.
4. Iron salt and water are produced.
Solution:
Option 1: Hydrogen gas and iron chloride are produced.
Explanation: Iron displaces chlorine from hydrogen chloride in the following reaction:
2HCl + Fe → FeCl2 + H2
4) What is a balanced chemical equation? Why should a chemical equation be balanced?
Solution:
A balanced equation has the same number of each type of atom on both sides of the reaction. Balancing equations is important because it follows the Law of Conservation of Mass. There is no set method for balancing equations; it usually involves trial and error.
5) Translate the following statements into chemical equations and balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulfide gas burns in the air to give water and sulfur dioxide.
(c) Barium chloride reacts with aluminum sulfate to give Aluminum chloride and a precipitate of barium sulfate.
(d) Potassium metal reacts with water to give potassium hydroxide and Hydrogen gas.
Solution:
(a) Unbalanced: H2 + N2→ NH3
Balanced: 3H2 + N2 → 2NH3
(b) Unbalanced: H2S + O2→ H2O + SO2
Balanced: 2H2S + 3O2 → 2H2O + 2SO2
(c) Unbalanced: BaCl2 + Al2(SO4)3 → AlCl3 + BaSO4
Balanced: 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
(d) Unbalanced: K + H2O → KOH + H2
Balanced: 2K + 2H2O → 2KOH + H2
6) Balance the following chemical equations.
(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Solution:
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
7) Write the balanced chemical equation for the following reactions.
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Zinc + Silver nitrate → Zinc nitrate + Silver
Aluminum + Copper chloride → Aluminum chloride + Copper
Barium chloride + Potassium sulfate → Barium sulfate + Potassium chloride
Solution:
2Ca(OH)2 + 2CO2 → 2CaCO3 + 2H2O
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
2Al + 3CuCl2 → 2AlCl3 + 3Cu
BaCl2 + K2SO4 → BaSO4 + 2KCl
8) Write a balanced chemical equation for the following and identify the type of reaction of each case.
KBr + BaI2 → KI + BaBr2
ZnCO3 → ZnO + CO2
H2+ Cl → HCl
Mg + HCl → MgCl2+ H2
Solution:
2KBr + BaI2 → 2KI + BaBr2 (Double Displacement Reaction)
ZnCO3 → ZnO + CO2 (Decomposition Reaction)
H2 + Cl → 2HCl (Combination Reaction)
Mg + 2HCl → MgCl2 + H2 (Displacement Reaction)
9) What is meant by exothermic and endothermic reactions? Give examples.
Solution:
An endothermic reaction absorbs heat from the surroundings (e.g., photosynthesis, melting ice, evaporation). In contrast, an exothermic reaction releases energy into the surroundings (e.g., explosions, setting concrete, nuclear fission and fusion).
10) Why is respiration considered to be an exothermic reaction?
Solution:
We need energy to survive, which we get from the food we eat. During digestion, food is broken down into simpler molecules like glucose.
These molecules then react with oxygen in our cells to produce carbon dioxide, water, and energy (a process called respiration).
This energy, which is in the form of heat and helps maintain our body temperature, makes respiration an exothermic reaction.
The reaction is:
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
11) Why are decomposition reactions called the opposite of Combination reactions? Write equations for decomposition reactions.
Solution:
A combination reaction occurs when two or more molecules combine to form a larger molecule. In contrast, a decomposition reaction involves breaking a larger molecule into two or more smaller molecules. Essentially, decomposition is the opposite of combination.
Decomposition reactions are usually endothermic, meaning they absorb heat from the surroundings or an external source to break the bonds in the larger molecule.
Here are a few examples of decomposition reactions:
ZnCO3 → ZnO + CO2
CaCO3 + Energy → CaO + CO2
2HgO → 2Hg + O2
12) Write one equation each for decomposition reactions in which energy is supplied in the form of heat, light or electricity.
Solution:
(a) Thermal Decomposition (Thermolysis)
When potassium chlorate is heated, it breaks down into potassium chloride and oxygen. This reaction is commonly used to produce oxygen.
Equation: 2KClO3 + Heat → 2KCl + 3O2
(b) Electrolytic Decomposition (Electrolysis)
When electricity is passed through molten sodium chloride, it decomposes into sodium and chlorine.
Equation: 2NaCl + Electricity → 2Na + Cl2
(c) Photolytic Decomposition (Photolysis)
In the presence of light, hydrogen peroxide decomposes into water and oxygen.
Equation: 2H2O2 + Light → 2H2O
13) What is the difference between displacement and double displacement reactions? Write relevant equations for the above.
Solution:
A displacement reaction occurs when a more reactive substance displaces a less reactive one from its salt solution. In contrast, a double displacement reaction involves the exchange of ions between two compounds. In a displacement reaction, only one element is replaced, while in a double displacement reaction, two elements or groups are exchanged.
Example:
Displacement reaction:
Mg + 2HCl → MgCl2 + H2
Double displacement reaction:
2KBr + BaI2 → 2KI + BaBr2
14) In the refining of Silver, the recovery of silver from Silver nitrate solution involves displacement reaction by Copper metal. Write down the reaction involved.
Solution:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
15) What do you mean by a precipitation reaction? Explain by giving examples.
Solution:
When two solutions containing soluble salts are mixed, a double displacement reaction occurs where the ions exchange between the compounds. If one of the resulting compounds is insoluble in water, it forms a solid that settles at the bottom of the container. This solid is called a precipitate, and the reaction is known as a precipitation reaction.
Examples of precipitation reactions include:
CdSO4(aq) + K2S(aq) → CdS(s) + K2SO4(aq)
2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)
16) Explain the following in terms of the gain of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Solution:
(a) In a chemical reaction, when oxygen is added to an element to form its oxide, the element is said to be oxidized. For example:
4Na(s) + O2(g) → 2Na2O(s)
H2S + O2 → H2O + SO2
(b) In a chemical reaction, when oxygen is removed from a compound, the compound is said to be reduced. For example:
CuO(s) + H2(g) → Cu(s) + H2O(l)
2HgO → 2Hg + O2
17) A shiny brown coloured element ‘X’ on heating in the air becomes black in color. Name the element ‘X’ and the black-coloured compound formed.
Solution:
The shiny, brown metal is copper (Cu). When heated in air, copper reacts with oxygen to form copper oxide, which is a black compound.
2Cu(s) + O2(g) → 2CuO(s)
18) Why do we apply paint on iron articles?
Solution:
Iron articles are painted to prevent rusting. Without paint, the metal surface reacts with oxygen in the air and moisture to form iron(III) oxide, also known as rust. Painting the surface keeps out air and moisture, preventing rusting.
19) Oil and Fat containing food items are flushed with Nitrogen. Why?
Solution:
Nitrogen is flushed into food packets containing oil and fat to prevent rancidity. Rancidity happens when oil or fat reacts with oxygen, causing an unpleasant smell and taste. Nitrogen creates an unreactive environment, preventing this reaction and keeping the food fresh.
20) Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Solution:
(a) Corrosion is when a refined metal reacts with oxygen in the air to form a more stable compound, like an oxide. This process causes the metal to gradually degrade. A common example is the rusting of iron, where iron turns into iron oxide.
(b) Rancidity occurs when oils and fats in food react with air, causing an unpleasant taste and smell. Keeping food in the refrigerator slows down rancidity because the low temperature reduces the rate of oxidation.