Question

Jenna took an open bowl of leftover mashed potatoes from the refrigerator and noticed a difference in smell. She determined that chemical changes occurred since the potatoes were first placed there.

Which observations most likely led to Jenna’s conclusion?

a change of odor
a decrease in temperature
a change in moisture content
a decrease in mass


Henry mixed salt and water together in a cup until he observed a clear solution. He measured the mass of the solution. Then he placed the cup outside for several sunny days during the summer. After a week, he observed that only solid salt remained in the cup and the mass had decreased. Henry concluded that a physical and chemical change occurred in this investigation.

Which statements correctly defend or dispute his conclusion?

He is correct. Dissolving salt in water is a physical change, but evaporating the water is a chemical change. Formation of a solid is evidence that a chemical change occurred.
He is correct. Evaporation is a physical change, but dissolving salt in water is a chemical change. The change in mass is evidence that a chemical change occurred.
He is incorrect. Dissolving salt in water and evaporation of the water are both physical changes. The reappearance of salt is evidence that the change was reversible by a physical change, so it could not be a chemical change.
He is incorrect. Dissolving salt in water and evaporation of the water are both chemical changes. The reappearance of salt is evidence that the change was reversible by a chemical change, so it could not be a physical change.


Which laboratory activity involves a chemical change?

leaving a copper penny in vinegar until it turns green
boiling saltwater for several minutes until only solid salt remains
extracting iron filings from a sand mixture using a magnet
crushing a rock with a hammer to extract mineral deposits


In a science lab, Cash mixes two clear liquids together in a beaker. Bubbles are produced, and a white solid forms and settles to the bottom. He plans to heat the beaker over low heat and make more observations.

Which statement is most likely correct?

A physical change occurred, so if Cash heats it, the white solid will dissolve to form the original mixture of clear liquids.
A physical change occurred, so even if Cash heats it, the white solid will remain.
A chemical change occurred, so if Cash heats it, the white solid will dissolve to form the original mixture of clear liquids.
A chemical change occurred, so even if Cash heats it, the white solid will remain.


Which best explains why making a pancake from batter is an example of a chemical change?

The pancake that forms is a different state of matter.
The change from batter to pancake can be reversed.
A new substance forms when the batter is cooked.
The batter changes shape when it is cooked.


Which statement best describes chemical properties of matter?

Chemical properties, such as density, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure.
Chemical properties, such as reactivity, must be observed when a substance is in its natural state at room temperature and normal atmospheric pressure.
Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form.
Chemical properties, such as boiling point, are generally observed as the identity of a substance changes and one or more new substances form.


In a science demonstration, a teacher mixed zinc (Zn) with hydrogen chloride (HCl) in a flask and quickly attached a balloon over the mouth of the flask. Bubbles formed in the solution and the balloon inflated.

What most likely occurred during this demonstration?

The Zn and HCl both retained their identity.
Either Zn or HCl, but not both, retained its identity.
Evaporation of one of the substances occurred.
One or more new substances formed.


Which use of iron is due to its chemical properties?

producing colored sparks in fireworks
changing from liquid to gas at 2,862°C
conducting electricity and heat
changing from solid to liquid if heated to 1,538°C



Which statement best describes what happens during a chemical change?

Both the identity and the properties of a substance change.
Some properties of a substance change, but its identity remains the same.
The chemical properties of a substance change, but its physical properties remain the same.
The physical properties of a substance change, but its chemical properties remain the same.



Which statement describes all chemical changes, but not all physical changes?

Bubbles are produced.
A new substance forms.
Phase changes occur.
A color change occurs.

Answer 1

1) Jenna — which observation most likely led to conclusion chemical changes occurred?
- change of odor.
Reason: A new smell indicates new chemicals (volatile compounds) formed — a chemical change.

2) Henry — which statement(s) correctly defend or dispute his conclusion?
- He is incorrect. Dissolving salt in water and evaporation of the water are both physical changes. The reappearance of salt is evidence that the change was reversible by a physical change, so it could not be a chemical change.
Reason: Dissolving and evaporating are physical (no new substance formed); the salt simply recrystallized when water evaporated.

3) Which laboratory activity involves a chemical change?
- leaving a copper penny in vinegar until it turns green.
Reason: The penny reacts (forms new copper compounds/oxides), producing a different substance.

4) Cash mixing two clear liquids — bubbles and a white solid form; he will heat it. Which is most likely correct?
- A chemical change occurred, so even if Cash heats it, the white solid will remain.
Reason: Gas production and a precipitate indicate a chemical reaction; heating won’t revert products back to the original reactants.

5) Why is making a pancake from batter a chemical change?
- A new substance forms when the batter is cooked.
Reason: Cooking causes chemical reactions (e.g., protein denaturing, Maillard reactions) that create new compounds and flavors.

6) Which statement best describes chemical properties of matter?
- Chemical properties, such as combustibility, are generally observed as the identity of a substance changes and one or more new substances form.
Reason: Chemical properties are revealed during chemical reactions that produce new substances.

7) Zn + HCl with an inflating balloon — what most likely occurred?
- One or more new substances formed.
Reason: Zn reacts with HCl to form zinc chloride and hydrogen gas; new substances (and gas) were produced.

8) Which use of iron is due to its chemical properties?
- producing colored sparks in fireworks.
Reason: The color/sparks come from iron undergoing oxidation/combustion (chemical reaction), not a physical property like melting point or conductivity.

9) Which statement best describes what happens during a chemical change?
- Both the identity and the properties of a substance change.
Reason: Chemical changes create new substances with different properties.

10) Which statement describes all chemical changes, but not all physical changes?
- A new substance forms.
Reason: Formation of new substances is the defining feature of chemical changes; physical changes do not necessarily create new substances.