Unit 5: Physical and Chemical Change

Unit 5: Physical and Chemical Change

By Latasha Chong

Multiple Choice

Student A mixes table salt into water. He says that the result is an example of a chemical change. Student B disagrees.

She says the result is an example of a physical change.

Which student is right and why?

• Student A is right because salt water has different properties than fresh water.

• Student B is right because the water can be evaporated and the salt can be recovered.

• Student B is right because a new substance has been formed that cannot change.

• Student A is right because the mixture now tastes Student A is right because the mixture

The correct answer is choice (B) Student B is right because the water can be evaporated and the salt can be recovered.

Choice (A) is incorrect because the properties of salt water, which are different from those of fresh water, happen because salt water is a mixture.

Choice (C) is incorrect because since salt and water can be separated by evaporation, a new substance has not been formed.

Choice (D) is incorrect because the change is physical and tasting salty while looking the same is not evidence of a chemical change.

Multiple Choice

Which statement BEST describes what happened to the papers during each change?

• The papers went through physical changes because the shape changed.

• The papers went through chemical changes because the shape changed.

• The papers went through physical changes because a new substance was produced.

• The papers went through chemical changes because a new substance was produced.

The correct answer is choice (A) The papers went through physical changes because the shape changed.

Choice (B) is incorrect because a shape change is not a chemical change.

Choice (C) is incorrect because a change in shape does not produce a new substance.

Choice (D) is incorrect because a new substance was not produced.

Multiple Choice

Use the drop-down menus to BEST complete the steps in the procedure to separate the parts of the mixture back into the original materials.

For step 2, "sand" is the correct response for the first dropdown menu and "pouring the mixture through a filter into another container" is the correct response for the second drop-down menu. These are the correct responses because a filter will trap the sand while the sugar and water mixture will pass through the filter, so the sand will be separated.

For step 3, "sugar" is the correct response for the third drop-down menu and "setting the jar in sunlight and letting the water evaporate" is the correct response for the fourth drop-down menu. These are the correct responses because the sugar will be left behind when the water evaporates.

The two steps must be done in the correct order, sand first and then sugar, because letting water evaporate from the mixture in step 2 will leave the sugar mixed with the sand, and separating the sugar from the sand would have to be done by mixing the sugar/sand mixture with water again and doing the steps in the correct order.

Multiple Choice

The student claims that changing the temperature of water causes a physical change that turns water into ice.

Use the drop-down menus to construct the argument that

BEST supports the student's claim about a physical change.

"Removed" is the correct response for the first drop-down menu because removing heat causes ice to form. "Slower" is the correct response for the second drop-down menu because when heat is removed from a substance, the small particles that make up the substance move more slowly.

"Changes the water from a liquid to a solid" is the correct response for the third drop-down menu because the change of state of water from liquid to solid is the important characteristic of the formation of water ice.

Multiple Choice

A student is investigating chemical changes by using different materials.

Which investigation would provide evidence of a chemical change and why?

• Melting a solid with fire would provide evidence of a chemical change because the solid changes shape.

• Cutting cardboard into many smaller pieces would

  provide evidence of a chemical change because the pieces cannot be put back together.

• Placing a solid into hot water and stirring while the solid dissolves would provide evidence of a chemical change because the dissolved material is lost.

• Combining two liquids that give off heat and gas would provide evidence of a chemical change because the particles react to make a new material with different properties.

The correct answer is choice (D) Combining two liquids that give off heat and gas would provide evidence of a chemical change because the particles react to make a new material with different properties.

Choice (A) is incorrect because the solid retains its properties despite melting, so this is only a physical change.

Choice (B) is incorrect because the cardboard retains its properties, so this is only a physical change.

Choice (C) is incorrect because the solid can be regained by evaporating the water, so this is only a physical change.

Multiple Choice

Which investigation would provide evidence of a chemical change?

• Spray perfume into the air, and when the air and perfume mix, observe the change in odor that

  happens as they mix.

• Put an antacid tablet in water, and when the antacid and water mix, observe the bubbles that form as a

  new substance is created.

• Heat water in a pan on a stove, and observe the steam that forms as the state of matter of the water

  changes.

• Blow air through a wand filled with soap solution, and observe the bubbles that form as the air becomes

  trapped.

The correct answer is choice (B) Put an antacid tablet in water, and when the antacid and water mix, observe the bubbles that form as a new substance is created.

Choice (A) is incorrect because no chemical reaction takes place, and a change in state of matter is a physical change.

Choice (C) is incorrect because no chemical reaction takes place.

Choice (D) is incorrect because no chemical reaction takes place.

Multiple Select

Students are investigating chemical changes that occur in different materials.

Which TWO investigations would provide evidence of a chemical change?

• Placing a liquid in a freezer until the liquid becomes a a solid would provide evidence of a chemical change because the state of matter changes.

• Using a saw to cut a solid into two different pieces b would provide evidence of a chemical change because the pieces cannot be put back together.

• Using a hot plate to heat a solid until it changes color and releases an odor would provide evidence of a chemical change because the particles cannot be changed back.

• Placing two different liquids together in a beaker and observing that a solid forms when they mix would provide evidence of a chemical change because a new material is formed.

• Placing a mixture containing a solid and a liquid on a windowsill and letting the liquid evaporate would provide evidence of a chemical change because the evaporated material is lost.

The correct answers are choice (C) Using a hot plate to heat a solid until it changes color and releases an odor would provide evidence of a chemical change because the particles cannot be changed back and choice (D) Placing two different liquids together in a beaker and observing that a solid forms when they mix would provide evidence of a chemical change because a new material is formed.

Choices (A) and (E) are incorrect because a change in the state of matter is a physical change. Choices (B) and (F) are incorrect because no chemical reaction takes place.