Chemical v. Physical Changes

Which of the following is a physical change?

• Dissolving salt into a cup of water

• Fireworks exploding

• Burning a piece of paper

• Baking a cake

A teacher places iron filings that are mixed with sand in a bowl. The teacher uses a magnet to separate the iron filings from the sand. Did the teacher cause a chemical change or physical change? How do you know?

• Physical change, because the materials stayed the same and were separated using a property

• Chemical change, because the magnet created a new substance

• Physical change, because magnets add heat to change matter

• Chemical change, because mixtures can only be separated by reactions

A student pours cereal and milk into a bowl. The student then wonders if it is possible to separate the cereal from the milk. Which of the following methods of separation would BEST be used by the student?

• Use evaporation to boil the cereal out of the milk

• Use a magnet to remove the pieces of cereal, since magnets can pick up any small object

• There is no way to separate the mixture

• Pour the mixture into a strainer so the liquid milk flows through and the cereal is left behind

A student is asked to plan a demonstration to show a physical change with a piece of paper. Which of the following investigations could the student use to accurately represent the type of change?

• Fold the paper in half to show how the paper changed its chemical properties

• Cut the paper into tiny pieces to show how the paper changed its physical properties

• Burn the paper to show how the paper can also resemble ash and smoke to show a change in state

• It is not possible to create a physical change with paper

A student notices a pile of ice on the sidewalk before school. At lunch time, the student returned and the pile of ice had completely melted into a puddle. What is the best argument for what happened to the ice?

• The ice lost heat as the sun became more direct, causing it to melt into a liquid

• The ice gained heat as the sun became more direct, causing it to melt into a liquid

• The ice gained heat as the sun became more direct, causing it to evaporate into water vapor

• The ice lost heat throughout the day as the sun became more direct, causing it to evaporate into water vapor

Below is a chart to show observations that students made on a cup of water. Which explanation BEST describes what they found?

• Both students added heat to the water, which caused the water to change its state

• Both students removed heat from the water, which caused the water to change its state

• Student 1 removed heat from the water, which caused the water to change from a liquid to a solid. Student 2 added heat to the water, which caused the water to change from a liquid to a gas

• Student 1 added heat to the water, which caused the water to change from a liquid to a solid. Student 2 removed heat from the water, which caused the water to change from a liquid to a gas

A teacher places a tray of water in the freezer. The next morning the teacher takes the tray from the freezer and creates the table below with her observations. Which argument BEST describes what happened to the ice?

• Heat was added to the water, which caused the particles to move faster. This changes the water from a solid to a liquid

• Heat was added to the water, which caused the particles to move slower. This changes the water from a solid to a liquid

• Heat was removed from the water, which caused the particles to move faster. This changes the water from a solid to a solid

• Heat was removed from the water, which caused the particles to move slower. This changes the water from a liquid to a solid

Students take a tray of ice cubes out of the freezer and hold the ice in their hands. They create the table below to show their observations. Which argument BEST describes what is happening to the ice?

• The ice cube is melting in the student’s hand since the hands are much warmer than the ice. Heat is being added to the ice, which causes the particles to move faster

• The ice cube is freezing in the student’s hand since the hands are much warmer than the ice. Heat is being removed from the ice, which causes the particles to move slower

• The ice cube is melting in the student’s hand since state is changing from a solid to a liquid. Heat is being removed from the ice, which causes the particles to move faster

• The ice cube is melting in the student’s hand since state is changing from a liquid to a solid. Heat is being added to the ice, which causes the particles to move slower

Which of the following describes a chemical change?

• Melting butter

• Milk spoiling

• Cutting paper

• Water evaporating

Three students carried out experiments to cause chemical changes to occur. Below is a table of their observations. Only ONE student successfully created a chemical change. Which student created a chemical change?

• Student A because the water changed to a new blue substance

• Student B because new gas bubbles were formed

• Student C because you cannot separate the water and salt