Hannah does an experiment. She has two colorless chemicals that she mixes together in a beaker. Which of the following indicates that a chemical change occurs when she mixes the two chemicals together?

Question

I. The chemicals change color from colorless to purple.
II. A yellow gas forms.
III. A brown solid forms in the bottom of the beaker.
IV. The temperature of the chemicals rises 15°C.
A.
II and III only
B.
I, II, III, and IV
C.
I and III only
D.
I, II, and III only

Answer 1

To determine which statements indicate a chemical change, we need to evaluate each one:

I. The chemicals change color from colorless to purple.

• This indicates a chemical change, as a color change often signifies that new substances are formed.

II. A yellow gas forms.

• The formation of a gas is another indicator of a chemical change.

III. A brown solid forms in the bottom of the beaker.

• The formation of a precipitate (solid) also indicates a chemical change has occurred.

IV. The temperature of the chemicals rises 15°C.

• A temperature change can indicate a chemical change, but it can also occur in physical changes. However, in the context of mixing two chemicals, it is usually associated with a chemical reaction.

Now, looking at the options provided:

A. II and III only - This neglects the significance of I. B. I, II, III, and IV - This includes all indications of a chemical change. C. I and III only - This neglects the significance of II. D. I, II, and III only - This does not take into account the temperature rise.

Given that all of I, II, III, and IV suggest that a chemical change has occurred, the best answer is:

B. I, II, III, and IV