Chemical reactions and equations

Concepts

Chemical Equations
Balanced Chemical equation
Combination Reaction
Decomposition reaction
Displacement Reaction
Double displacement reaction
Precipitation Reaction
Oxidation Reaction
Reduction Reaction
Redox Reaction or Oxidation-Reduction reaction
Corrosion
Rancidity 

In text questions page number 6

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

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.

In text questions page number 10

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.

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.

In text questions page number 13

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

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

3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.

Text Book Exercise

Question 1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO 
(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

 
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction. 
(c) decomposition reaction.
(d) displacement reaction.

Question 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.

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

Question 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.

Question 6. Balance the following chemical equations. 
 

Question 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

Question 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)

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

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

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

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

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

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

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

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

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

Question 18. Why do we apply paint on iron articles?

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

Question 20. Explain the following terms with one example each.