Question

1. a sealed jar contains liquid water. the jar is placed in a freezer until all the water turns to ice.

what happens to the total mass inside the jar? (choose 2)
a. it increases because ice is heavier.
b. it decreases because water froze.
c. it stays the same because freezing is a physical change.
d. it stays the same because the jar is sealed.

1. a student stirs 15 g of salt into 200 g of water.

which statements are true? (select all that apply.)
a. the salt disappears and its mass is lost.
b. the total mass of the mixture is 215 g.
c. the salt is still present even though it cant be seen.
d. this is an example of the conservation of matter.
e. the mixture now has less mass because dissolving destroys matter.

1. the table shows the mass of a container during a phase change.

step	mass (g)
container + water	550 g
after freezing to ice	550 g

what does the data show?
a. some matter disappeared when water froze.
b. the ice has more mass than the liquid water.
c. the mass was conserved when water changed to ice.
d. freezing made the container lighter.

1. the diagram shows a sealed container with vinegar and a tablet reacting, forming bubbles.

what can be concluded about the systems mass? (select all that apply.)
a. the gas produced is matter.
b. the mass of the container stays the same because it is sealed.
c. the system lost mass when the gas formed.
d. the balloon fills because a gas was produced.
e. the system gains weight when the balloon expands.

Explanation:

1. In a sealed - system, mass is conserved during a physical change like freezing of water. Ice is just a different state of water and the number of water molecules remains the same.
2. When salt is dissolved in water, it is a physical change and the total mass of the mixture is the sum of the mass of salt and water. The salt particles are still present in the solution and this is an example of conservation of matter.
3. The data shows that the mass before and after freezing water in a container is the same, indicating mass conservation during the phase - change.
4. In a sealed container, the gas produced in a reaction is still part of the system, so the mass of the system remains the same. The balloon fills due to the gas production, but the overall mass of the system does not change.

Answer:

1. C. It stays the same because freezing is a physical change; D. It stays the same because the jar is sealed.
2. B. The total mass of the mixture is 215 g; C. The salt is still present even though it can't be seen; D. This is an example of the conservation of matter.
3. C. The mass was conserved when water changed to ice.
4. A. The gas produced is matter; B. The mass of the container stays the same because it is sealed; D. The balloon fills because a gas was produced.