Exploring Matter and Chemical Changes

Front

Which subatomic particle has a negative charge and is found outside the nucleus of an atom?

Back

Electron

Answer explanation

The electron is the subatomic particle that carries a negative charge and is located outside the nucleus of an atom, unlike protons and neutrons, which are found within the nucleus.

Tags

NC.SCI.PS.8.1

Front

What is the chemical formula for water?

Back

H₂O

Answer explanation

The chemical formula for water is H₂O, which indicates that each molecule consists of two hydrogen atoms and one oxygen atom. The other options represent different compounds: CO₂ is carbon dioxide, O₂ is oxygen, and NaCl is sodium chloride.

Tags

NGSS.MS-PS1-1

Front

Example of a physical change: Burning wood, Melting ice, Rusting iron, Baking a cake

Back

Melting ice

Answer explanation

Melting ice is a physical change because it involves a change in state from solid to liquid without altering the chemical composition. In contrast, burning wood, rusting iron, and baking a cake involve chemical changes.

Tags

NC.SCI.PS.8.1

Front

What happens to the motion of particles in a solid when it is heated?

Back

The particles move faster

Answer explanation

When a solid is heated, its particles gain energy and move faster. This increased motion can lead to changes in the solid's properties, such as expansion. Therefore, the correct answer is that the particles move faster.

Tags

NGSS.MS-PS1-4

Front

Which of the following best describes a compound?

Back

A substance made of two or more elements chemically combined

Answer explanation

A compound is defined as a substance made of two or more elements chemically combined. This distinguishes it from mixtures, which are physical blends, and single-element substances.

Tags

NC.SCI.PS.8.1

Front

Which model best represents the arrangement of atoms in a molecule of carbon dioxide (CO₂)? Options: O–C–O, C–O–O, O–O–C, C–C–O

Back

O–C–O

Answer explanation

The correct model for carbon dioxide (CO₂) is O–C–O, indicating that one carbon atom is bonded to two oxygen atoms in a linear arrangement. This reflects the actual molecular structure of CO₂.

Tags

NGSS.MS-PS1-1

Front

A student observes that when salt is dissolved in water, the salt seems to disappear. Which statement best explains what happens to the salt?

Back

The salt forms a mixture with water

Answer explanation

When salt dissolves in water, it forms a solution, meaning the salt particles mix with water molecules. This is why the salt seems to disappear, but it is not destroyed or transformed into a gas or new element.

Tags

NC.SCI.PS.8.1

Front

A beaker of water is placed in a freezer. After several hours, the water turns to ice. Which change in particle motion best explains this process?

Back

The particles slow down and arrange in a fixed pattern

Answer explanation

As the water freezes, the temperature drops, causing the particles to slow down and arrange themselves into a fixed pattern, forming solid ice. This explains the transition from liquid to solid state.

Tags

NGSS.MS-PS1-4

Front

Which of the following is a mixture? Table salt (NaCl), Oxygen gas (O₂), Air, Water (H₂O)

Back

Air

Answer explanation

Air is a mixture of different gases, primarily nitrogen and oxygen, while table salt, oxygen gas, and water are pure substances. Therefore, air is the correct choice as a mixture.

Tags

NC.SCI.PS.8.1

Front

What is the process called when solid iodine changes directly to a gas when heated in a closed container?

Back

Sublimation

Answer explanation

The process of solid iodine changing directly to gas is called sublimation. This occurs without passing through the liquid phase, distinguishing it from melting, which involves a solid turning into a liquid.

Tags

NGSS.MS-PS1-4