Question

Solid sodium bicarbonate was placed on a strip of $ pH $ paper. The color of the strip:
(A) Turned blue
(B) Did not change
(C) Turned green and suddenly yellow
(D) Turned light pink

Answer 1

Hint: The $ pH $ paper is used to find out if the given solution is acidic, basic or neutral in nature. This is done by dipping a part of the paper into the given solution and observing the change in color. There are two types of $ pH $ papers.

Complete answer:
Litmus paper is available in red and blue color. The red litmus paper turns blue if the $ pH $ of the solution is alkaline. The blue litmus paper turns red if the solution is acidic in nature. The litmus paper is mostly used to determine the $ pH $ of liquids. But it can also be used to test gases. This can be done by dampening the paper with distilled water before exposure to the gas. If solid sodium bicarbonate is placed on a strip of $ pH $ paper, then there will be no color change. As sodium bicarbonate is in solid form, there will be no dissociation of ions. Ions dissociate only in aqueous solutions.
Therefore, option B is the correct answer.

Note:
We use litmus paper or $ pH $ strips to measure the acidity or the alkalinity of a liquid. Remember that the $ pH $ strips are used to determine the $ pH $ value whereas the litmus paper only indicates whether the substance is acidic or basic. The reason for the blue litmus paper turning red under acidic conditions is because the pigment that is present in blue litmus reacts with hydrogen ions and changes chemically, so that the bonds are tuned to reflect a longer wavelength of light to appear red to the human eye.