Science Unit 5 Review

David watches a burning candle to determine whether a chemical or physical change is taking place. While David watches the candle, he writes down observations in his notebook. Which of David’s observations provides evidence that a chemical change is taking place?

• A. The wick of the candle is giving off light as it burns.

• The wax is running down the side of the candle.

• The wax is changing from a solid to a liquid.

• The candle is getting shorter.

Which statement describes a chemical change?

• Sugar dissolving in tea.

• The sun warms the surface of a road.

• Scissors are used to cut paper into small pieces.

• Acid produced in your stomach breaks down food you eat.

Which choice BEST represents a change that can be turned back into its original form?

• 
• 
• 
• 

You and a friend put some ice in a cup at 1:00 pm. An hour later, you both observed how the ice had changed. What type of change did you and your friend observe?

• chemical because a liquid formed

• chemical because heat caused the change

• physical because it happened over time

• physical because no new substance was formed

This bicycle is made of metal. If left outdoors, over time some of the metal will become flaky and turn reddish-brown. Which statement BEST describes what happened to the metal on the bicycle?

• The metal was damaged by insects.

• The metal became covered with pollution.

• The metal was used over time and became worn-out.

• The metal combined with water and formed a new substance.

In a dish, Matt dissolved 10g of salt into 100ml of water and left it outside for a few days in the hot sun. What would Matt find in the dish after a few days?

• Only a colored solution would be found in the dish.

• Matt would find dry salt crystals in the dish.

• Matt would not find anything in the dish.

• Only water would be found in the dish.

Jamal added a little baking soda to a beaker that contained vinegar; bubbles started coming from the mixture as gas was released. Which statement BEST describes why gas was produced?

• A chemical reaction took place.

• The mixture was starting to boil.

• The air in the beaker contracted.

• The vinegar and baking soda expanded.