GA Unit 3 Science Practice

If you were investigating a chemical change, which investigation below would provide evidence of one and why?

• Melting an ice cube because the solid would change shape.

• Cutting a piece of paper into smaller pieces because the pieces cannot be put back together.

• Putting a cube of sugar in hot water and stirring because the sugar is now dissolved and it is irreversible.

• Mixing vinegar and baking soda to blow up a balloon because they react to form a gas.

Answer explanation

The formation of bubbles is an indicator of a chemical change, except boiling water.

Which of the following is evidence of a chemical change?

• Boiling water and observing steam.

• Your classmate passing gas in class and producing a change in odor.

• Putting Mentos in coke and observing a bubbly explosion.

• Blowing air through a straw in your chocolate milk and observing bubbles form.

Answer explanation

The formation of bubbles is an indicator of a chemical change, except boiling water.

Which TWO are examples of a chemical change and why?

• Putting water in an ice tray and placing it in the freezer because the state of matter changes.

• Chopping up wood for a fire because the logs can't be put back together as a tree.

• Heating ferrous sulphate, a green colored iron salt, until it changes color and produces an odor because the change is irreversible.

• Allowing the water from the soil in your plant to evaporate because the liquid material no longer exists.

• Mixing sodium hydroxide and hydrochloric acid, two liquids, and they form a solid because a new substance is created.

Answer explanation

The formation of a new substance and the production of bubbles (except boiling water) or a gas are indicators of a chemical change. Don't forget that chemical changes are irreversible.

Mr. Bill is making a bookshelf for his granddaughter. In which step of his project does a chemical change occur?

• Chopping up wood into pieces because there is a change in mass.

• Taking the bark off and sanding the pieces of wood to make sure they are free of splinters because there is a change in texture.

• Forming the pieces of wood as a bookshelf because there is a change in shape.

• Burning the unused pieces of wood because a new substance, ash, is formed.

Answer explanation

Burning wood is an example of a chemical change because it is irreversible and it forms a new substance.

When you boil water, steam forms because...

• Chilling the water causes the formation of a gas.

• Heating the water causes the formation of a solid.

• Chilling the water causes the formation of a liquid.

• Heating the water causes the formation of a gas.

Answer explanation

When you boil or heat water, it produces steam or water vapor. This is an example of a physical change, from a liquid to a gas.

The absorption of heat causes ice cubes to melt.

• True

• False

Answer explanation

Ice cubes absorb heat.

Ice cubes melt in your hand because they release heat.

• True

• False

Answer explanation

Ice cubes absorb heat from your body or its environment, causing it to melt.

When a substance changes from a solid to a liquid, the molecules start to move faster.

• True

• False

Answer explanation

The molecules in a solid are packed close and tightly together unlike liquids, whose molecules are fluid and move freely. Therefore, when you heat a solid, the molecules begin to move faster.

This is a model of the molecules of what state of matter?

• Solid

• Liquid

• Gas

Answer explanation

The molecules of a solid vibrate because they are close and packed tightly together.

This a model of the molecules of what state of matter?

• Solid

• Liquid

• Gas

Answer explanation

The molecules of a liquid are fluid and move freely. They are loosely packed.