Important Questions – 2012
Class – X
Subject – Science (Acids, Bases and Salts)

1. During summer season, a milkman usually adds a very small amount of baking soda to milk. Why?

2. Tooth enamel is one of the hardest substances in our body. How does it undergo damage due to eating chocolates and sweets? How do toothpastes prevent this damage?

3. How are all the acids and bases similar? Explain.

4. Baking soda is used in small amounts in making breads and cakes. It helps to make thes4e soft and spongy. An aqueous solution of baking soda turns red litmus blue. It is also used in soda acid fire extinguisher. Use this information to answer the following questions –
i. How does baking soda help to make cakes and breads soft and spongy?
ii. How does it help in extinguishing fire?
iii. Is the pH value of baking soda solution lower than or higher than 7?

5. Dry HCl gas does not turn blue litmus red whereas hydrochloric acid does. Give one reason.

6. A student drooped few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was passed through lime water. What change would be observed in lime water? Write balanced chemical equation when (i) gas was evolved (ii) gas was passed through lime water.

7. Answer the following questions –
i. Why is the formula of Plaster of Paris written as CaSO4.½H2O? How is it possible to have half of water molecule attached to CaSO4?
ii. Why is sodium bicarbonate an essential ingredient of most antacids?
iii. Sodium bicarbonate is an essential ingredient of baking powder. What is the function of it?
iv. When electricity is passed through aqueous solution of NaCl, three products are obtained. Why this process is called chlor-alkali process?

8. Fresh milk has a pH of 6. When it changes into curd, will its pH value increase or decrease? Why?

9. A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound. Write the chemical equation for its preparation. For what purpose it is used in hospitals?

10. Why does tooth decay start when the pH of mouth is lower than 5.5?