NCERT Solutions For Class 10 Science chapter 1 Chemical Reactions and Equations

NCERT Books Solutions For Class 10 Science chapter 1 Chemical Reactions and Equations

NCERT Solutions For Class 10 Science chapter 1 Chemical Reactions and Equations is the first stepping stone for a student in the competitive world. With the introduction of the CBSE Board Exam for class 10 a few years back, this has become an important gateway for a student as based on the results of class 10th a student selects his future stream of Science, Commerce, or Arts.

Takshila Learning provides you with detailed and well explained NCERT Solutions for Class 10 of each chapter of each subject for NCERT Class 10. These NCERT Solutions help you to easily understand every concept so that you can score high in your CBSE Class 10 Board Exams.

Below you can find the NCERT solution for Class 10 Science. You can get a Solution for the all-important question of “Class 10 Science CH 1 Chemical Reactions and Equations”

Ques 1: Why should a magnesium ribbon be cleaned before burning in air?

Soln: Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with the atmospheric oxygen and forms Magnesium Oxide (MgO) layer which is a very stable compound. In order to prevent further reactions with Oxygen, it is therefore necessary to clean the ribbon by to remove the layer of MgO.

 

Ques 2: Write balanced equations for the following chemical reactions.

1. i) Hydrogen + Chloride → Hydrogen chloride
2. ii) Barium chloride + Aluminium Sulphate → Barium sulphate + Aluminium chloride

iii) Sodium + Water → Sodium hydroxide + Hydrogen

Soln:

1. i) H2+Cl2→2HCl
2. ii) 3BaCl2+Al2(SO4)3→2AlCl3+3BaSO4

iii) 2Na+2H2O→2NaOH+H2

 

Ques 3: Write a balanced chemical equation with state symbols for the following reactions

1. i) Solutions of Barium chloride and Sodium Sulphate in water react to give insoluble Barium Sulphate and solution of Sodium chloride.
2. ii) Sodium hydroxide solution in water reacts with hydrochloric acid solution to produce Sodium chloride solution and water.

Soln:

1. i) BaCl2+Na2SO4→BaSO4+2NaCl
2. ii) NaOH+HCl→NaCl+H2O

 

 Pg. No. 10

Ques 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.

Soln:

1. i) The substance ‘X’ which is used in whitewashing is quick lime or Calcium Oxide and its formula is CaO.
2. ii) CaO+ H2O → Ca(OH)₂

 

Ques 2: Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas

Soln: In activity 1.7, gas collected in one of the test tubes is double of the amount collected in the other because water gets hydrolysed to release H2 and O2 gas. Here, after electrolysis two molecules of Hydrogen and one molecule of oxygen gas is released, hence the amount of Hydrogen collected would be double than that of oxygen.

Pg. No. 13

Ques 1: Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Soln: When an iron nail dipped in the copper Sulphate solution, iron displaces copper from the copper Sulphate because iron is more reactive than copper, therefore the colour of the Copper Sulphate solution changes. The reaction is:

Fe+CuSO4 → FeSO4 +Cu

 

Ques 2: Give an example of a double displacement reaction other than the one given in Activity 1.10.

Soln: Reaction Between silver nitrate (AgNO3) and Sodium chloride (NACl) is an example of double displacement reaction. Here Silver donates its ion to Sodium chloride ion and pick up Nitarate ion to form silver chloride and sodium Nitrate

AgNO3 + NaCl → AgCl + NaNO3

 

Ques 3: Identify the substances that are oxidized and that are reduced in the following equation.

1. i) 4Na(s)+O2(g) → 2Na2O(s)
2. ii) CuO(s)+H2(g) → Cu(s)+H2O(l)

Soln: The Sodium (Na) in the first equation is getting oxidized with the addition of Oxygen (O2) and the Copper (Cu) in the second equation is reduced due to the addition of Hydrogen (H2)

 

 

EXERCISE –

Ques 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 oxidised

(c) Carbon is getting oxidised

(d) Lead oxide is getting reduced

(i) (a) and (b)

(ii) (a) and (c)

(iii) (a), (b) and (c)

(iv) all

Soln: (i) (a) and (b)

Explanation: (a) because Oxygen is being removed and (b) because the removed oxygen from Lead is added to the elemental Carbon.

 

Ques 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.

Soln: Answer is 4 – Displacement reaction.

Explanation: Ferrous oxide displaces oxygen from aluminum metal to form aluminum oxide. Aluminum is a more reactive metal than LA in this reaction. Therefore Al will displace Fe from its oxide. This type of chemical reactions in which one element displaces another is called displacement reaction. Here the less reactive metal is displaced by the more reactive metal. Since a one-time displacement is occurring, it is called a single displacement reaction.

Ques 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.

Soln: 1 – Hydrogen gas and Iron chloride are produced.

Explanation: The Chlorine from Hydrogen chloride is displaced by the Iron fillings to undergo the following reaction.

2HCl+Fe→FeCl₂+H₂

 

Ques 4: What is a balanced chemical equation? Why should a chemical equation be balanced?

Soln: A balanced equation is one in which the number of different atoms on both the reactant and the product side are equal. It is necessary to balance the chemical equation. The reaction must follow the law of conservation of energy. Balancing the chemical equation is not a defined method and is purely a trial and error attempt.

 

Ques 5:  Translate the following statements into chemical equations and balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.

(b) Hydrogen Sulphide gas burns in air to give water and sulphur dioxide.

(c) Barium chloride reacts with aluminium sulphate to give Aluminium chloride and a precipitate of barium sulphate.

(d) Potassium metal reacts with water to give potassium hydroxide and Hydrogen gas.

Soln:

(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

 

Ques 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

Soln:

(a)2HNO₃+2Ca(OH)2→2Ca(NO3)₂+2H2O

(b)6NaOH+3H₂SO4→H₂SO4+6H₂O

(c)NaCl+AgNO₃→AgCl+NaNO₃

(d)BaCl₂+H2SO₄→BaSO₄+2HCl

 

Ques 7: Write the balanced chemical equation for the following reactions.

1. Calcium hydroxide + Carbon dioxide —-> Calcium carbonate + Water
2. Zinc + Silver nitrate —-> Zinc nitrate + Silver

• Aluminium + Copper chloride —-> Aluminium chloride + Copper

1. Barium chloride + Potassium sulphate —-> Barium sulphate + Potassium chloride

Soln:

1. 2Ca(OH)₂+2CO₂→2CaCO₃+2H₂O
2. Zn+2AgNO₃→Zn(NO₃)₂+2Ag

• 2Al+3CuCl₃→2AlCl₃+3Cu

1. BaCl₂+K₂SO₄→BaSO₄+2KCl

 

Ques 8: Write a balanced chemical equation for the following and identify the type of reaction of each case

1. KBr+BaI₂→KI+BaBr₂
2. ZnCO₃→ZnO+CO₂

• H₂+Cl→HCl

1. Mg+HCl→MgCl₂+H₂

Soln:

1. 2KBr+BaI₂→2KI+BaBr₂ (Double Displacement Reaction)
2. ZnCO₃→ZnO+CO₂ (Decomposition Reaction)

• H₂+Cl→2HCl  (Combination Reaction)

1. Mg+2HCl→MgCl₂+H₂ (Displacement Reaction)

 

Ques 9:  What is meant by exothermic and endothermic reactions? Give examples.

Solution: An endothermic reaction occurs when energy is absorbed as heat from the surroundings. (Example: photosynthesis, melting of ice, evaporation). In contrast, an exothermic reaction is one in which energy is released from the system into the atmosphere. (Examples: explosion, solid setting, nuclear fission and fusion).

 

Ques 10: Why is respiration considered to be an exothermic reaction?

Solution: For life to exist, we need energy. We get this energy from the food we eat. Through the process of digestion, food molecules break down into simple molecules like glucose. These substances with a certain amount of energy (respiratory process) are exposed to the oxygen present in the cells of our body to form carbon dioxide and water. Since energy is in the form of heat (which maintains our body temperature) respiration is considered an exothermic reaction. Reaction:

                               C₆H₁₂O₆+6O₂→6CO₂+6H₂O+Energy

 

Ques 11: Why are decomposition reactions called the opposite of Combination reactions? Write equations for decomposition reactions.

Solution: A combination reaction is called a reaction between two or more molecules to form a large molecule; whereas the decomposition reaction is defined as the division of larger molecules into two or more small molecules. This essentially explains that the decomposition reaction is the opposite of the combination reaction.

In most cases the decomposition reaction is endothermic because heat from the surrounding or induced heat is used to break the bond of the larger molecule. Some examples of dissolution reactions are: ZnCO₃→ZnO+CO₂

CaCO₃+Energy→CaO+CO₂

2HgO→2Hg+O₂

 

Ques 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 reaction (Thermolysis)

Decomposition of potassium chlorate: When heated strongly, potassium chlorate decomposes into potassium chloride and oxygen. This reaction is used for the preparation of oxygen.

2KClO₃+Heat→2KCl+3O₂

 

(b) Electrolytic decomposition reaction (Electrolysis)

Decomposition of sodium chloride: On passing electricity through molten sodium chloride, it decomposes into sodium and chlorine.

2NaCl→electricity 2Na+Cl₂

 

(c) Photodecomposition reaction (Photolysis)

Decomposition of hydrogen peroxide: In the presence of light, hydrogen peroxide decomposes into water and oxygen

2H₂O₂ (light) → 2H₂O+O₂

 

Ques 13:  What is the difference between displacement and double displacement reactions? Write relevant equations for the above.

Solution: A displacement reaction is when a more reactive substance displaces a less reactive than its salt solution while a double displacement reaction is one where there is a mutual exchange of ions between two compounds.

In the displacement reaction, there is only one displacement while in the double displacement reaction, as the name suggests, there is two displacements between the molecules.

Example: Displacement reaction – Mg+2HCl→MgCl₂+H₂

Double displacement reaction – 2KBr+BaI₂→2KI+BaBr₂

 

Ques 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)

 

Ques 15: What do you mean by a precipitation reaction? Explain by giving examples.

Solution: When two solutions containing soluble salts are combined, a double displacement reaction occurs in which ions are exchanged between the compounds. When one of such compounds formed is in solid form (which is insoluble in aqua) it settles at the bottom of the container. This solid is known as precipitate and the associated reaction is called precipitation reaction. Some examples of precipitation reactions are:

CdSO₄(aq)+K₂S(aq)→CdS(s)+K₂SO₄(aq)

2NaOH(aq)+MgCl₂(aq)→2NaCl(aq)+Mg(OH)₂(s)

 

Ques 16: Explain the following in terms of gain of oxygen with two examples each.

(a) Oxidation

(b) Reduction

Solution:

(a) In a chemical reaction, when the oxygen is added to the element to form its respective oxide it is the element being oxidised. Example:

4Na(s)+O₂(g)→2Na₂O(s) H₂S+O₂→H₂O+SO₂

(b) In a chemical reaction, when the oxygen is being removed from the compound then it is said to be reduced. Example:

CuO(s)+H2(g)→Cu(s)+H₂O(l) 2HgO→2Hg+O₂

 

Ques 17: A shiny brown coloured element ‘X’ on heating in the air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Solution: The bright brown color element is copper metal (Cu). When the metal is heated in air, it reacts with atmospheric oxygen to form copper oxide. Hence the black colored compound is copper oxide.

2Cu(s)+O₂(g)→2CuO(s)

 

Ques 18: Why do we apply paint on iron articles?

Solution: Iron articles are painted to prevent them from rusting. When left unaffected, the metal surface is exposed to atmospheric oxygen and in the presence of moisture from iron (III) oxide. But if the surface is painted it is not exposed to moisture and air thus preventing rust.

 

Ques 19: Oil and Fat containing food items are flushed with Nitrogen. Why?

Solution: The main purpose of transporting nitrogen into food packets that contain oils and fats is to prevent the rancidity that occurs when oils or fats react with oxygen, leaving an unpleasant odor and taste. Therefore by flushing nitrogen, an ineffective surrounding is created, thus preventing stiffness.

 

Ques 20: Explain the following terms with one example each.

(a) Corrosion

(b) Rancidity

Solution:

(a) Corrosion is a process in which a refined metal is oxidized by atmospheric oxygen to form a more stable compound in the form of oxidation. The metal slowly deteriorates during the corrosion process. Corrosion of iron is a good example of rust where iron is converted into iron oxide. Millions of dollars are spent annually to prevent corrosion from bridges and other monuments.

(b) A condition caused by aerial oxidation of oils and fats present in food ingredients causing an unpleasant taste and smell. The oxidation does not promote the reaction after low temperatures, when the food is kept inside the refrigerator, the hardness is retarded.

 

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