Chapter 01 : Chemical Reactions and Equations

Class 10 Chapter 1 : Chemical Reactions and Equations Internal Questions and Answers :

Internal Questions :

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

Answer : A magnesium ribbon should be cleaned before burning in air to remove any impurities or oxide layers that may prevent it from reacting fully and producing a bright and vigorous flame. Cleaning the magnesium ribbon ensures a more effective and reliable reaction, allowing it to burn brightly and completely in the presence of air.
2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen

Answer : (i) 

(ii) 

(iii) 

3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water .

Answer : (i)

(ii)

Internal Questions :

1. A solution of a substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Answer : (i) The substance 'X' used for white washing is calcium oxide (CaO).

(ii)  Chemical equation: 

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.

Answer : The amount of gas collected in one of the test tubes is double that of the other because water () consists of two hydrogen atoms and one oxygen atom. During the activity, the water molecule breaks down into hydrogen gas () and oxygen gas () using electricity. Since the ratio of hydrogen atoms to oxygen atoms in water is 2:1, the amount of hydrogen gas collected is double that of the oxygen gas. So, the gas collected is hydrogen gas.

Internal Questions :

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

Answer : The color of the copper sulphate solution changes when an iron nail is dipped in it because the iron nails more reactive than copper . So,the iron reacts with the copper ions in the solution, causing the copper to be displaced and form a new compound. This results in a color change from blue (copper sulphate) to greenish-brown (iron compounds).
2. Give an example of a double displacement reaction other than the one given in Activity 1.10.

Answer : An example of a double displacement reaction is the reaction between potassium iodide () and lead(II) nitrate () to form lead(II) iodide () and potassium nitrate ():

       

In this reaction, the potassium and lead ions switch places to form the new compounds, lead(II) iodide and potassium nitrate.

3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) 
(ii)   

Answer : (i)

(ii)

  

 Class 10 Chapter 01 : Chemical Reactions and Equations Exercises :    

1. Which of the statements about the reaction below are incorrect?
       
(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

Answer : (i) (a) and (b)  .

2.    
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.

(c) decomposition reaction.
(d) displacement reaction.

Answer : (d) displacement reaction.

3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.

Answer : (a) Hydrogen gas and iron chloride are produced.

4. What is a balanced chemical equation ?  Why should chemical equations be balanced ?

Answer : The number of atoms of each element remains the same, before and after a chemical reaction ,then the reaction is called a balanced chemical equation.We know that mass can neither be created nor destroyed in a chemical reaction.

Chemical equations should be balanced to ensure that the same amount of each type of atom is present before and after the reaction. This is important because it helps us understand how substances react with each other and the exact amounts of reactants and products involved in the chemical reaction.So, chemical equations Should be balanced.

5. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur 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.

Answer :  (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.

        

6. Balance the following chemical equations.
(a)  
(b)  
(c)    
(d)  

Answer : W have,

(a) 
(b)
(c)   
(d) 

7. Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer : The balanced chemical equations are :

 (a)

(b)

(c)

(d) 

8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

Answer : The balanced chemical equation are :

(a)

      Double displacement reaction .

(b)

    Decomposition reaction .

(c) 

        Combination reaction .

(d) 

     Combination reaction  (Exothermic reaction) .

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

Answer :  Exothermic reactions : Reaction in which heat is released along with the formation of products are called exothermic chemical reactions.

Example: 

Endothermic reactions : Reaction in which energy is absorbed are known as endothermic reactions.

Example:  Melting ice , Dry ice

10. Why is respiration considered an exothermic reaction? Explain.

Answer : We all know that we need energy to stay alive. We get this energy from the food we eat. During digestion, food is broken down into simpler substances. For example, rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen , then produced water , carbon dioxide , energy and also provides heat . So, the respiration is considered an exothermic reaction . The chemical reaction of respiration is given below :

11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Answer :  In a decomposition reaction, a single substance decomposes to give two or more substances.

For example :

In a combination reaction,  two or more substances combine to form a new single substance.

 

So, decomposition reactions are called the opposite of combination reactions .

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

Answer :  For heat : When limestone heated , then produce quick lime and carbon dioxide .

             

For Light : When silver chloride react at present of light, then produces silver and chlorine .

                       

For electricity : When electricity is passed through acidified water (dilute  and water) , then produced hydrogen and oxygen .

      

13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Answer :  For displacement  reaction:  When an element displaces another element from its compound, a displacement reaction occurs.

 

For double displacement reaction : Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.

    

14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Answer :   The chemical equation is :

 

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

Answer :  When the reactant  produce a precipitate in the reaction , then it is called a precipitation reaction.

Example : When sodium sulphate react with barium chloride, then produced barium sulphate and sodium chloride .

              

16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction

Answer :  (a) Oxidation : If a substance gains oxygen during a reaction , then it is called oxidation .
(b) Reduction : If a substance loss oxygen during a reaction , then it is called reduction .

Example : (i)

    

(ii)

    

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

Answer :  The name the element ‘X’ is Cu and the name  black coloured compound is CuO .

When copper heating in air then produce black copper oxide . The chemical reaction is :

 

18. Why do we apply paint on iron articles?

Answer :  We apply paint on iron articles to protect them from rusting. Rusting is a chemical reaction between iron and oxygen in the presence of water or moisture. The paint forms a protective layer over the iron surface, preventing it from coming into contact with water and oxygen, thus stopping the rusting process.

19. Oil and fat containing food items are flushed with nitrogen. Why?

Answer : Oil and fat-containing food items are flushed with nitrogen to prevent oxidation. When these foods come into contact with oxygen in the air, they can undergo oxidation, which leads to rancidity and a deterioration of taste and quality. Nitrogen helps create an oxygen-free environment, reducing the chances of oxidation and keeping the food fresher for a longer time.

20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity

Answer : (a) Corrosion : When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. The black coating on silver and the green coating on copper are other examples of corrosion.

Corrosion causes damage to car bodies, bridges, iron railings, ships and to all objects made of metals, specially those of iron. Corrosion of iron is a serious problem. Every year an enormous amount of money is spent to replace damaged iron.
(b) Rancidity : When fats and oils are oxidized , they become rancid and their smell and taste change. Usually some substances which prevent oxidation (antioxidants) are added to foods containing fats and oil. So, Keeping food in air tight containers helps to slow down oxidation.

For example : The chip manufacturers usually do flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidized .