Question

(a) Define catalyst.

(b) What are (i) positive catalysts and

(ii) negative cata lysts ? Support your answer wit h one example for each of them.

(c) Name three biochemical catalyst found in the human body.

Answer 1

(a) Catalyst: A catalyst is a substance that either increases or decreases the rate of a chemical
reaction without itself undergoing any chemical change during the reaction.(b) (i) Positive catalyst: When a catalyst increases the rate of chemical reaction, it is called positive
catalyst.
e.g. when potassium chlorate heated to 700°C decomposes to evolve oxygen gas, when MnO 2 is
added the decomposition takes place at 300°C
(ii) Negative catalyst: When a catalyst decreases the rate of chemical reaction it is called negative
catalyst.
Example. Phosphoric acid acts as a negative catalyst to decrease the rate of the decomposition of
hydrogen peroxide. Alcohol too acts as a negative catalyst in certain chemical reactions.
(c) Biochemical catalysts found in human body:
1. Pepsin
2. Tryspin
3. lipase.