CBSE Class 10 Science 2023 Outside Delhi Set 3

Question : 9

Total: 12

(a) (i) What property do acids and bases have in common? Explain it with an example.
(ii) A compound which is prepared from gypsum has the property of hardening when mixed with water.
Identify the compound and write its formula. How is this compound prepared? Describe it in the form of a chemical equation only.
OR
(b) (i) Write the chemical name and Molecular formula of tooth enamel.
(ii) How does it get corroded? What is the preventive measure for this?

Solution:

(a) (i) Both acids and bases are electrolytes which means that they are good conductors of electricity. Acids and bases both produce ions in aqueous solution. Acids release hydrogen ions (H+)whereas Bases release hydroxide ions (OH−). The process of mixing acid or a base in water is exothermic in nature.
(ii) The compound which is prepared from gypsum which has the property of hardening when mixed with proper quantity of water is called plaster of Paris having the formulaCaSO4⋅H2O. Its chemical name is calcium sulphate hemihydrate CaSO4⋅1∕2H2O. Plaster of Paris is prepared by heating gypsum at 373K. When gypsum is heated it loses three-Fourths of its water of crystallisation and forms Plaster of Paris.

CaSO4⋅2H2O

Gypsum

373K

→

CaSO4⋅‌

H2O+‌

H2O

Plaster of Paris

(b) (i) Tooth enamel is calcium phosphate, Ca3(PO4)2 which is a very hard substance.
(ii) Tooth enamel gets affected when the pH of our mouth falls below 5.5 . This happens because the bacteria present in our mouth breaks down the sugar and food particles to acids which damage our teeth by corroding them. To cure this, we should clean our mouth after eating with toothpaste which is basic in nature and will neutralize the effect, thereby keeping our teeth fit and fine.

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