Question

A group of students measured the pH of some substances they found in their homes. Their results are given in the following table:

Substance	pH	Substance	pH
Apples	3.0	Salt	7.0
Baking soda	8.5	Sugar	7.0
Black coffee	5.0	Toothpaste	9.0
Household ammonia	12.0	Vinegar	3.0
Lemon juice	2.5	Washing soda	11.5
Milk	6.5

(a) What would the students have used to measure the pH?
(b) Which solution is the most acidic?
(c) Which solution is the most alkaline?
(d) Which solutions are neutral?
(e) Which solution can be used to treat wasp stings?
(f) Which solutions can be used to treat bee stings?

Answer 1

(a) The students would have used universal indicator paper to measure the pH values of the substances. Universal indicator paper indicates different pH values of solutions with different colour changes. The strength of an acid or a base is known with the help of different colours.
(b) Lemon juice, with pH 2.5, is most acidic.
(c) Household ammonia, with pH 12.0, is most alkaline.
(d) Salt and sugar, with pH 7, are neutral.
(e) Vinegar, with pH 3, can be used to treat wasp stings. As a wasp sting is alkaline (pH > 7), an acid, such as vinegar, is applied to the skin, and it neutralises the base and soothes the pain.
(f) Baking soda, with pH 8.5, can be used to treat bee stings. As a bee sting is acidic (pH < 7), a base, such as baking soda, is applied to the skin, and it neutralises the acid and soothes the pain.