AP Chemistry : Drawing Conclusions from Observations
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Example Questions
Example Question #1 : Laboratory Equipment And Procedure
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?
The sodium chloride that sank to the bottom is a special isotope that can't be solubilized.
The saturation limit of the water for sodium chloride has been surpassed. This is a saturated solution.
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.
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 : Laboratory Equipment And Procedure
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?
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.
Example Question #1 : Drawing Conclusions From Observations
Using the target shown, determine whether the shots were accurate and/or precise.
Precise and accurate
Precise but not accurate
Accurate but not precise
Neither precise nor accurate
Precise but not accurate
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 #3 : Drawing Conclusions From Observations
Using the target, determine whether the shots are accurate and/or precise.
Precise but not accurate
Neither accurate nor precise
Accurate but not precise
Accurate and precise
Accurate and precise
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 : Drawing Conclusions From Observations
Using the target shown, determine whether the shots are accurate and/or precise.
Accurate and precise
Accurate but not precise
Neither accurate nor precise
Precise but not accurate
Accurate but not precise
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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