Unit 5: Chemical Change

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.
• Sugar, when added to ice tea, dissolves into the liquid.
• Two liquids are mixed, and a solid substance forms.
• 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.

Four substances were mixed with a clear liquid. The observations are recorded in the following table. Based on the observations, for which mixture is there the best evidence that a new substance was formed?

• Substance 1
• Substance 2
• Substance 3
• Substance 4

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 –

• volume was seen to be 200 mL.
• student measured the liquids.
• 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.
• temperature of the mixture decreased.
• 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

The table records the observations that result from four different combinations. Which combination of substances shows evidence that a new substance was formed?

• Baking soda and vinegar
• Sodium chloride and water
• Oil and water
• Iron filings and sand