Question 6

Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turn red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. (T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
(v) Tooth decay is caused by the presence of a base. (T/F)


(i) Answer: False
Nitric acid is not right to turn the red litmus paper into blue. The explanation is that the colour of the paper does not change when an acid comes into contact with a red litmus paper. Only if an acid comes into contact with blue litmus paper will the colour of the litmus paper change into red. Nitric acid is an acid so it does not turns the litmus paper into blue.

(ii) Answer: False
This statement is false because sodium hydroxide is not an acid, it is base which turns red litmus to blue.

(iii) Answer: True
When acid and base reacts with each other, they form an neutral substance, this process is called neutralisation. When the solution of sodium hydroxide (a base) and hydrochloric acid (an acid) is mixed in test tube in proper ratio, both neutralize each other.

(iv) Answer: True
This statement is true because different solution show different colours in acidic or basic medium. Indicators are chemical compounds that change Colour according to pH of the solution they are put in. They are used to determine pH of the body (acidity/basicity).

(v) Answer: False
This statement is false because tooth decay is caused by acids which is formed in our mouth when the food particles left over all night. They constantly damage tooth enamel and thus cause tooth decay.

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