Chemistry Summative Unit Assessment: Chemical vs. Physical Changes

Which of the following is an example of a physical change?

• a glass in the kitchen breaks

• apples brown when they are left on the counter

• logs burn in the fireplace

• milk sours in the refrigerator

Which of the following is true about the situations?

Situation 1: A gray iron bar is heated until it glows red.

Situation 2: A nail is placed in water and a red-orange rust forms.

Situation 3: A few drops of red food coloring are used to turn water red.

• All of the situations are examples of physical changes because they are reversible.

• None of the situations are examples of physical changes because all involve a color change.

• Situation 2 is a physical change because rust forming is a natural process.

• Use a magnet to attract the iron fillings so that they can be separated from the sand.

Tags

NGSS.MS-PS1-2

Suppose 15 grams of table salt and 15 grams of sand are mixed together. Both dry materials are mixed with 100 mL of water in a glass beaker. Which of the four students explains effective methods to separate the mixtures and draws appropriate conclusions about whether physical or chemical changes have occurred?

• Student A: “I noticed that the table salt dissolved in the water. This shows evidence that a chemical change occurred between the salt and water because there is no way to reverse this action. The sand did not dissolve in water. This shows evidence of a physical change because I can separate the sand from the water by using my hands.”

• Student B: “The table salt dissolved in the water, and the sand did not. However, the table salt is still there. To prove this, I can use filter paper to separate the sand from the saltwater solution. Then, I can boil the water to evaporate it so that only salt is left in the bottom of the glass beaker. All are examples of physical changes because they can be reversed.”

• Student C: “When the salt and sand were added to the water, a color change occurred. The water became cloudy. A color change shows evidence that chemical changes occurred. Therefore, the changes cannot be reversed. The cloudy water shows a new substance was produced.”

• Student D: My observations show that the table salt dissolved in water. Once something dissolves, you can no longer see it, so this shows evidence for a chemical change. The sand can be separated from the water. I can pour the sand and water mixture into a flat pan and place it outside in the sun. The water will evaporate leaving only the sand. Because both can be separated from each other again, mixing sand with water is a physical change.”

Tags

NGSS.MS-PS1-2

Iron filings are mixed with sand in a bowl. Which of the following is the most effective way to separate the mixture to demonstrate that a physical change has occurred?

• Add water to the bowl. The sand will dissolve in water, and the iron filings will be left.

• Place the contents of the bowl into a funnel made of filter paper, and use water to separate the sand from the iron filings.

• Pour the contents of the bowl into a pot with boiling water. The sand will rise, leaving the iron filings at the bottom of the pot.

• Use a magnet to attract the iron filings so that they can be separated from the sand.

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 throughout the day as the sun became more direct, causing it to melt into a liquid.

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

• The ice gained heat throughout the day 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.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

NGSS.MS-PS3-5

Which of the following is NOT an appropriate argument for how temperature affects the particles in water?

• As heat is added to water, the particles become “excited” and move faster. This can cause a solid to melt into a liquid, or a liquid to evaporate into water vapor.

• As heat is removed from water, the particles slow down and become more compact. This can cause water vapor to condense into liquid water, or liquid water to freeze into ice.

• As heat is added to water, the particles move slower and sit closer together. This can cause water vapor to condense into liquid water, or liquid water to freeze into ice.

• As the temperature of water changes, the speed of the water particles also changes. Slower moving particles that are closer together would exist in ice. Faster moving particles that are free moving and further apart would exist in water or ice.

Tags

NGSS.MS-PS1-4

Which of the following situations does not show evidence of a chemical change?

• A gallon of milk goes sour in the refrigerator.

• A match lights when it is struck at a party.

• A silver necklace becomes tarnished over time.

• An aluminum can is crushed on the sidewalk.

Tags

NGSS.MS-PS1-2

Which of the following student observations shows evidence that a chemical change has occurred?

a.

b.

c. Student C observes that sugar dissolves in her tea.

d. Student D sees glass glow red hot as it is molded at a glassblowing shop.

• Student A notices that hydrogen peroxide bubbles when it is placed on a cut.

• Student B watches as water evaporates from a puddle on his street.

• Student C observes that sugar dissolves in her tea.

• Student D sees glass glow red hot as it is molded at a glassblowing shop.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Three students at Winterville Elementary were given an assignment by their science teacher to plan and carry out experiments where chemical changes would occur. Below, you can see each student’s plan and the results he or she recorded.

• Student A was the only one to create an experiment where a color change occurred. This shows evidence of a chemical change.

• Student A, Student B, and Student C all created experiments where chemical changes occurred. Student A observed a color change, Student B saw bubbles, and Student C was able to dissolve salt.

• Student B and Student C created experiments were chemical changes occurred. Student A just dyed her water. Student B and Student C both changed their substances to prove that they had chemical changes. Student B created a gas while Student C got rid of the salt.

• Student B was the only one to create an experiment with evidence of a chemical change. She created a new substance, a gas.

Tags

NGSS.MS-PS1-2

In four different investigations, 25 mL of a mystery colorless liquid was mixed with 25 mL of four liquid substances labeled A-D in test tubes. Observations are recorded below. Which student draws appropriate conclusions from the results.

• Student W: “A chemical change did not occur in investigations 2 and 3 because temperature changes did not occur.” Chemical changes occurred in investigation 1 because the temperature increased and in investigation 4 because the temperature decreased.

• Student X: “Only investigations 1 and 2 showed evidence of chemical changes. In investigation 1, a color change happened. In investigation 2, a gas was created.”

• Student Y: “Investigations 1, 2, and 3 showed evidence of chemical changes. A color change in investigation 1 showed that a chemical change occurred. Something new was produced in investigations 2 and 3 to show that a chemical change occurred. Investigation 4 did not show evidence of a chemical change because the mixed liquids stayed colorless.”

• Student Z: “Investigations 2 and 3 had new substances that were created, so they showed evidence of chemical changes. Investigation 1 showed evidence of a chemical change due to a color change and an increase in temperature. Investigation 4 also showed evidence of a chemical change because a reaction caused the temperature to decrease.”

Tags

NGSS.MS-PS1-2