E T S Praxis Series

Middle School Science (0439)

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Sample Test Questions

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Sample Question 1

A 4-liter, thin-metal can with its screw-top lid removed contains 100 milliliters of water. It is heated until the water boils. The can is then removed from the heat and its lid firmly replaced. Describe what will happen to the can as it cools and why.

Sample Response That Received a Score of 3:

The sides of the can will start to collapse inward until the point of equilibrium is reached between the pressure inside the can, the pressure outside the can, and the strength of the can's walls.

This is caused by the liquid water being heated enough to turn to vapor. This vapor then displaces the air molecules inside. When the can is taken off of the heat source, the vapor then condenses back into liquid, and because the lid was airtight, this creates a lower pressure inside the can than outside, since there are less air molecules in the same space. Thus the can collapses until the pressure inside the can equals that outside.

Sample Response That Received a Score of 1:

When the water in the can starts to boil, air escapes and water evaporates. Not much, because you'll remove it immediately and cover with the lid. As the can starts to cool, the can will produce sweat drops on the outside of the can. Being a thin metal can and tightly covered with a lid, the can will slowly alter. The sides will recede and pull inward as the cooling continues.

Sample Question 2

A

Given five different hand-sized samples of unidentified minerals, discuss how you would determine their order of relative hardness.

B

Describe, in terms of their relative hardness, how the shapes of these minerals would be affected over time in a fast-moving stream or river.

Sample Response That Received a Score of 3:

Geologists determine the hardness of various minerals by using Mohs hardness scale. Using the scale, you compare the hardness of the minerals you are trying to identify to the ones in Mohs scale. Talc, for example, is classified as a "1." If the mineral you are looking at scratches the talc, it has a hardness that is greater than "1" and you would try the next hardest mineral, which is gypsum, and so on, until you found the correct hardness. (Neither mineral would scratch the other one.)

Minerals that have a hardness of 1, such as talc, would be worn down very quickly by a fast-moving stream or river. Softer minerals would therefore be broken down, while harder minerals would be rounded and smoothed. The hardest minerals, such as diamond would not be affected as much over periods of time. It would take a very long time for rough edges to be worn down.

Sample Response That Received a Score of 1:

You would observe the surface of these rocks and look for fractures and cracks, then you would chip off pieces with a hammer and determine the amount of force it takes to break each one. Softer rocks would break up easily on the bed of a stream, and it would take a relatively short amount of time. Harder rocks would not break but they would be worn smooth by rolling along the bottom between the current and the streambed.