Chemical Changes

If we have any substance, it can be concluded that a chemical change has happened if –

• there is a color change.

• the state of matter changes.

• there is a decrease in mass.

• the matter is stirred thoroughly.

Which of the following situations provides evidence that a chemical change has taken place?

• Water, when boiled, evaporates and turns into vapor.

• Two liquids are mixed, and a solid substance forms.

• Sugar, when added to ice tea, dissolves into the liquid.

• A piece of paper is cut into many small pieces.

Which of the following would indicate the formation of a new substance?

• A liquid turns to a solid.

• A sample of metal melts.

• Bubbles and fizzing occur.

• A solid is dissolves in a liquid.

A student notices that sugar, when heated over a flame, turns black. How does the student know that a new substance is being formed?

• The temperature of the sugar increases.

• The color of the sugar changes to black.

• Sugar began to melt within the test tube.

• Sugar started as white crystals.

The image shows what happens when cold medicine tablets are placed in room-temperature water.

What evidence would indicate that a new substance is produced?

• The tablets dissolve in water.

• The water becomes cloudy.

• The water level increases slightly.

• Bubbles are given off.

A student measures out 100 mL of two different clear liquids and then pours one into the other. The mixture, which has a volume of 200 mL, turns bright red, then begins to become quite cold. In this process, the first evidence that a new substance had formed was observed when the –

• student measured the liquids.

• volume was seen to be 200 mL.

• color changed to bright red.

• temperature of the mixture decreased.

Four mixtures are made by combining two clear liquids and observations are made.

Which results indicate that a new substance has formed?

• Mixture 1: The combined liquids have a greater mass than either of the starting liquids.

• Mixture 2: The liquids, when mixed, produce a white solid which settles to the bottom.

• Mixture 3: The mixture of the two liquids takes the shape of the container they are in.

• Mixture 4: The denser of the two liquids lies below the other less dense liquid.

Which of the following observations is the best indicator that a new substance has been formed?

• A solid has become a liquid.

• A substance has changed color.

• A solid has dissolved in a liquid.

• The volume of a substance increased.

Bubbles and fizzing can be seen instantly when baking soda is mixed with vinegar. The bubbles are evidence of which of the following?

• A gas is formed when baking soda and vinegar are mixed.

• Baking soda dissolves in vinegar when they are mixed.

• Vinegar turns into alcohol when it is mixed with baking soda.

• A precipitate is formed when baking soda and vinegar are mixed.

When two substances are mixed, they might form a new substance. Which of the following would indicate that a new substance has been formed?

• The temperature of the mixture decreases.

• The volume of the mixture increases.

• The mass of the mixture increases.

• One of the substances dissolves.