AP Chemistry : Drawing Conclusions from Observations

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #1 : Drawing Conclusions From Observations

During lab you have a solution of 1M NaCl at room temperature. You accidentally add so much salt to the solution that you still see some at the bottom of the beaker no matter how vigorously you mix it. What conclusion can you arrive at based upon your knowledge of chemistry? 

Possible Answers:

The sodium chloride that sank to the bottom is a special isotope that can't be solubilized. 

The salt you spilled into the solution wasn't sodium chloride, but was magnesium chloride, which isn't soluble in water. 

The large spill caused hydrophobic clusters of sodium chloride to form, preventing them from being dissolved. 

The saturation limit of the water for sodium chloride has been surpassed. This is a unsaturated solution. 

The saturation limit of the water for sodium chloride has been surpassed. This is a saturated solution. 

Correct answer:

The saturation limit of the water for sodium chloride has been surpassed. This is a saturated solution. 

Explanation:

The addition of so much salt (NaCl) caused the water to reach its solubility limit for NaCl. This means that no matter how much more NaCl you add to that solution or how hard you stir, it will not dissolve, and will precipitate on the bottom of the beaker. This type of solution is saturated. If the solution were unsaturated, then more salt would still be able to dissolve.

There is no special isotope that makes NaCl insoluble in water. The vigorous mixing would have separated any clumps, and if the solution was unsaturated the salt would have eventually dissolved. Magnesium chloride, another salt, is very soluble in water and would not result in the scenario described.

Example Question #2 : Drawing Conclusions From Observations

There is a beaker full of a clear liquid on the counter. It was left unlabeled by your lab partner, and you are required to find out what it is. You perform a number of tests and observe the follwing results. 

1. The liquid is miscible with water.

2. You add the liquid to 1M phosphoric acid. The beaker gets extremely warm. 

3. You grab a piece of red litmus, and it turns blue upon exposure to the unknown liquid. 

Which of the following could be the identity of the unknown liquid?

Possible Answers:

Correct answer:

Explanation:

Each test gives us a different piece of information. The first test tells us that our compound is soluble in water. The second test tells us that heat is released when acid is added. The third test tells us that the solution turns red litmus paper blue, which means that the solution is basic. From these results, we can conclude that the compound is a water-soluble base. Now we can look at our answer options.

, and  are all acids.

, however, will generate cyanide ions in solution. Cyanide is basic; thus, this is our correct answer.

Example Question #33 : Laboratory Techniques And Analysis

1

Using the target shown, determine whether the shots were accurate and/or precise.

Possible Answers:

Precise and accurate

Neither precise nor accurate

Accurate but not precise

Precise but not accurate

Correct answer:

Precise but not accurate

Explanation:

The target is precise because the shots are closely grouped together. However, the shots are not accurate because they are not in the middle of the target.

Example Question #4 : Drawing Conclusions From Observations

2

Using the target, determine whether the shots are accurate and/or precise.

Possible Answers:

Accurate but not precise

Precise but not accurate

Accurate and precise

Neither accurate nor precise

Correct answer:

Accurate and precise

Explanation:

The target is accurate because the shots are all in the middle of the target. It is also precise because all the shots are grouped together.

Example Question #4 : Laboratory Equipment And Procedure

3

Using the target shown, determine whether the shots are accurate and/or precise.

Possible Answers:

Accurate but not precise

Accurate and precise

Precise but not accurate

Neither accurate nor precise

Correct answer:

Accurate but not precise

Explanation:

The shots are not precise because they are not grouped together. However, one of the shots is in the center of the target, and thus is accurate.

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