Question

Red cabbage is an organic indicator for acids and bases. In the pictures above, which test tube(s) may have ammonia dissolved in it?
A) Ammonia is probably in the middle since it is naturally a gas and will evaporate off leaving a neutral solution with pH = 7.
B) Ammonia could be in a couple of the test tubes on the right since it is a acid.
C) Ammonia could be in the middle or the right test tubes since it is a weak to moderate base.
D) Ammonia may be in one of the test tubes on the left since the pH of ammonia is below 7.
The image is

Answer 1

The answer is C. Ammonia could be in the middle or the right test tubes since it is a weak to moderate base.
 

Answer 2

Answer: Option (C) is the correct answer.

Explanation:

Indicators are the substances which show change in the color when added to a certain substance. An indicator helps in knowing whether the substance to which it is being added is acidic or basic.

For example, when a blue litmus is dipped into hydrochloric acid then it turns into red. Therefore, blue litmus indicates that hydrochloric acid is an acid.

Similarly, when ammonia is added to the red cabbage then the color changes from red to green. As ammonia is a basic solution therefore, when added to red cabbage the change in pH of solution will be greater than 7.

Thus, we can conclude that ammonia could be in the middle or the right test tubes since it is a weak to moderate base.