Physical v Chemical (Difficult)

A student mixes two clear liquids. A white solid forms and sinks. What type of change likely occurred?

• Physical, because a solid appeared

• Chemical, because a new substance formed

• Physical, because no temperature change occurred

• Chemical, because the mixture turned cloudy

Answer explanation

The formation of a white solid indicates a chemical change, as a new substance has formed from the reaction of the two liquids. This is not just a physical change, which would not involve the creation of a new substance.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Ice melts into water and refreezes. What does this example show?

• Physical changes are usually reversible

• Water forms a new compound

• Ice chemically reacts with air

• New substances form with each state

Answer explanation

This example shows that ice melting into water and refreezing is a physical change, which is typically reversible. The substance remains water in different states, rather than forming new compounds or substances.

Tags

NGSS.MS-PS1-4

A metal changes color and becomes flaky after being left outside. Which is the best explanation?

• Physical weathering occurred

• The metal was polished

• A chemical change happened due to oxidation

• A physical change occurred due to pressure

Answer explanation

The metal changing color and becoming flaky indicates a chemical change, specifically oxidation, which occurs when metals react with oxygen in the environment, leading to corrosion.

Tags

NGSS.MS-PS1-2

A sugar cube dissolves in water and the mixture is sweet. What best explains this change?

• A chemical change occurred with heat

• Sugar chemically combined with water

• Sugar physically changed by spreading out

• Sugar formed new atoms

Answer explanation

The sugar cube dissolves in water through a physical change, where the sugar molecules spread out in the water, creating a sweet mixture. No new substances are formed, and no chemical bonds are broken.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

What most likely occurred when baking soda and vinegar created bubbles in a sealed bag?

• A. A physical change

• B. A change in shape

• C. A chemical reaction with gas formation

• D. The vinegar evaporated

Answer explanation

When baking soda and vinegar mix, they undergo a chemical reaction that produces carbon dioxide gas, creating bubbles. This is a clear indication of a chemical reaction, making option C the correct choice.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

When butter melts and then burns, which changes occur?

• Physical only

• Chemical only

• Physical then chemical

• Chemical then physical

Answer explanation

When butter melts, it undergoes a physical change as it transitions from solid to liquid. When it burns, it undergoes a chemical change, producing new substances. Thus, the correct answer is 'Physical then chemical'.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

A piece of paper is cut and then burned. What kinds of changes happened?

• One physical, one chemical

• Both chemical

• Both physical

• No change

Answer explanation

Cutting the paper is a physical change as it alters its shape but not its chemical composition. Burning the paper is a chemical change because it transforms the paper into ash and gases, changing its chemical structure.

Tags

NGSS.MS-PS1-2

A student boils saltwater and collects the salt. What does this show?

• A chemical reaction occurred

• A compound formed

• A physical change separated the mixture

• Energy changed mass

Answer explanation

The process of boiling saltwater and collecting the salt demonstrates a physical change, as the salt is separated from the water without altering its chemical composition. This shows that the mixture can be physically separated.

Tags

NGSS.MS-PS1-4

Which of the following is strong evidence a chemical change occurred?

• A change in size

• A new gas forms with no heat added

• A change in shape

• A liquid cools

Answer explanation

A new gas forms with no heat added is strong evidence of a chemical change, as it indicates a reaction has occurred, producing new substances. In contrast, changes in size, shape, or temperature do not confirm a chemical change.

Tags

NGSS.MS-PS1-2

A student heats a substance and sees a color change and smoke. What is the most likely explanation?

• A. A physical change occurred due to melting

• B. The shape and color changed slightly

• C. The substance turned into a gas

• D. A chemical reaction formed a new substance

Answer explanation

The color change and smoke indicate a chemical reaction, suggesting that the substance transformed into a new substance, making option D the correct choice.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5