Which of the following is NOT evidence of a chemical change?

• Bubbles or fizzing

• Expected color change

• Temperature change

• Formation of a precipitate

Answer explanation

The expected color change can occur without a chemical reaction, such as in physical changes or mixing. In contrast, bubbles, temperature changes, and precipitate formation are clear indicators of a chemical change.

Tags

NGSS.MS-PS1-2

When vinegar and milk are added together, a chunky solid forms. This is called a _____.

• solution

• solute

• precipitate

• solvent

Answer explanation

When vinegar and milk are mixed, the acid in vinegar causes proteins in milk to coagulate, forming a chunky solid known as a precipitate. This is not a solution, solute, or solvent, making 'precipitate' the correct term.

When a solid goes through a phase change and changes straight to a gas, that is called ____.

• sublimation

• precipitation

• evaporation

• deposition

Answer explanation

When a solid transitions directly to a gas without becoming a liquid, this process is called sublimation. Examples include dry ice turning into carbon dioxide gas.

Tags

NGSS.MS-PS1-4

Which of the following is a physical change?

• Iron rusting

• A cake baking in the oven

• Dry ice sublimating to a gas

• Lighting a match

Answer explanation

Dry ice sublimating to a gas is a physical change because it involves a change in state from solid to gas without altering the chemical composition. In contrast, rusting, baking, and lighting a match involve chemical changes.

Tags

NGSS.MS-PS1-2

Identify which of these mixtures is a solution.

• Water and salt

• Water and sand

• Salt and Sugar

• Salt and Sugar

Answer explanation

A solution is a homogeneous mixture where one substance dissolves in another. Water and salt form a solution as salt dissolves completely in water, while water and sand do not, as sand does not dissolve.

In a sugar water solution, what is the sugar?

• The solvent

• The homogeneous mixture

• The heterogeneous mixture

• The solute

Answer explanation

In a sugar water solution, sugar is the solute, which is the substance being dissolved. Water acts as the solvent, while the resulting mixture is homogeneous, meaning it has a uniform composition throughout.

Which of the following would we see sugar dissolve the fastest?

• 50 degree water with a sugar cube in it

• 50 degree water with powdered sugar in it

• 60 degree water with a sugar cube in it

• 80 degree water with powdered sugar in it

Answer explanation

Sugar dissolves faster in warmer water due to increased molecular movement. Powdered sugar has a larger surface area than a sugar cube, enhancing dissolution. Therefore, 80 degree water with powdered sugar dissolves the fastest.

Tags

NGSS.MS-PS1-4

Why does powdered sugar dissolve faster than a sugar cube.

• It has greater surface area for the water to act on.

• It has less surface area for the water to act on.

• The water moves slower around the powdered sugar particles.

• The water moves faster around the powdered sugar particles.

Answer explanation

Powdered sugar has a greater surface area compared to a sugar cube, allowing more water molecules to interact with it simultaneously. This increased interaction leads to faster dissolution.

Which of the following is NOT a way to increase the rate of dissolution?

• Agitate (Stir)

• Heat it up

• Decrease the surface area of the solute

• Increase the surface area of the solute.

Answer explanation

Decreasing the surface area of the solute reduces the contact between the solute and solvent, slowing down dissolution. In contrast, agitation, heating, and increasing surface area all enhance the rate of dissolution.

How can we make a salt solution MORE dilute?

• Take out some of the water

• Take out some of the salt

• Add water

• Add salt

Answer explanation

To make a salt solution more dilute, you need to decrease the concentration of salt in the solution. The best way to do this is by adding water, which increases the total volume and reduces the salt concentration.