Question

In a laboratory experiment, a fermenting aqueous solution of glucose and yeast produces carbon dioxide gas and ethanol. The solution was heated by burning natural gas in a Bunsen burner to distill the ethanol that formed in the flask. During the distillation, the ethanol evaporated and then condensed in the receiving flask. The flame of the burner was kept too close to the bottom of the flask and some of the glucose decomposed into a black carbon deposit on the inside of the flask. During this experiment the following changes occurred. Which of these changes involved a physical change and not a chemical change?

Answer 1

Answer:

The solution was heated.

to distill the ethanol that formed in the flask.

the ethanol evaporated and then condensed in the receiving flask.

Explanation:

In a physical change, the form of matter is altered but the substance stays the same (same chemical identity). The changes of state are examples of physical changes.

In a chemical change, a chemical reaction occurs and a substance transforms into another one.

From the text:

• In a laboratory experiment, a fermenting aqueous solution of glucose and yeast produces carbon dioxide gas and ethanol. Chemical change. The glucose reacts to form carbon dioxide and ethanol.
• The solution was heated. Physical change. The increase in the temperature does not imply a change in the chemical identity.
• by burning natural gas in a Bunsen burner. Chemical change. Burning means a combustion is taking place, in which a substance reacts with oxygen to produce carbon dioxide and water.
• to distill the ethanol that formed in the flask. Physical change. Ethanol is isolated but its nature does not change.
• the ethanol evaporated and then condensed in the receiving flask. Physical change. These are changes of state.
• some of the glucose decomposed into a black carbon deposit on the inside of the flask. Chemical change. Glucose is consumed and carbon is produced.