AP Chemistry : Laboratory Equipment and Procedure

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

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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? 

Possible Answers:

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

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 unsaturated solution. 

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

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 #1 : 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 #31 : Laboratory Techniques And Analysis

1

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

Possible Answers:

Precise but not accurate

Accurate but not precise

Neither precise nor accurate

Precise and 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 #1 : Drawing Conclusions From Observations

2

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

Possible Answers:

Accurate and precise

Neither accurate nor precise

Accurate but not precise

Precise but not accurate

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 #1 : Laboratory Equipment And Procedure

3

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

Possible Answers:

Accurate and precise

Accurate but not precise

Neither accurate nor precise

Precise but not accurate

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.

Example Question #3 : Laboratory Equipment And Procedure

You have a stock solution of 12M HCl, but want to dilute it to 1M HCl. What is the safest way you could go about doing this?

Possible Answers:

Add the correct amount of water and 12M HCl to a common beaker at the same time

Measure out the water first, then slowly add the correct amount of 12M HCl

Measure out the 12M HCl first, then slowly add the correct amount of water

Measure out the 12M HCl first, then rapidly add the correct amount of water

Measure out the water first, then rapidly add the correct amount of 12M HCl

Correct answer:

Measure out the water first, then slowly add the correct amount of 12M HCl

Explanation:

Always add acid to water. You should mix solutions slowly because you run the risk of solutions spilling, which may ruin your reaction entirely. Rapid mixing can also lead to inadvertently speeding up reactions and releasing energy or heat in a dangerous manner. During dilution of acids with, water heat is released; if a small amount of water is added to a concentrated acid it has the possibility of bubbling over the counter and onto you. 

Example Question #1 : Laboratory Equipment And Procedure

Which procedure separates two substances using their different boiling points?

Possible Answers:

Dehydration

Filtration

Hydration

Fermentation

Distillation

Correct answer:

Distillation

Explanation:

During the distillation process, the combined substances are heated until the first one boils. The substance that boils and becomes a gas is then separated from the still liquid or solid substance via condensation into a separate container. Filtration involves separating substances in solid and liquid phases through a filter paper, and is often facilitated by a vacuum. Dehydration and hydration are types of reactions where water is a product, and a reactant, respectively. Fermentation is a biochemical process that occurs under anaerobic conditions. Some organisms produce lactic acid as a byproduct of fermentation, (humans), others produce ethanol (yeast). 

Example Question #4 : Laboratory Equipment And Procedure

You are trying to create a new chemical structure. You need exactly 9mL of phenyllithium for your next reaction. Which measuring tool would be the most accurate to measure out that liquid?

Possible Answers:

10mL syringe

100mL beaker

9mL volumetric pipet

9mL watch glass

10mL graduated cylinder 

Correct answer:

9mL volumetric pipet

Explanation:

When measuring any liquid in the lab, a volumetric pipet or flask is always going to be the most accurate. This makes the 9mL volumetric pipet the best choice.

There is no such thing as a 9mL watch glass. Though a 10mL syringe and graduated cylinder would be quite accurate, the 9mL volumetric pipet is more accurate, and remember the question asked for the best out of the answer choices. A beaker is very inaccurate and should only be used to transfer solutions, not to measure them.  

Example Question #5 : Laboratory Equipment And Procedure

An experiment calls for you to titrate a  solution of  with a solution of  of unknown concentration. The solution of  is held in an Erlenmeyer flask. What piece of laboratory equipment should you use to administer the  solution?

Possible Answers:

Buret

Volumetric pipet

Watch glass and spatula

Graduated cylinder

Correct answer:

Buret

Explanation:

In a titration, you should use a buret to administer the  solution into the  solution. A buret gives you the most accuracy in running the titration as you can dispense the solution drops at a time. The buret will also allow you to accurately determine the volume of  needed to complete the titration. A watch glass and spatula would be inappropriate for this situation because you are dealing with liquids. Pouring from a graduate cylinder would not be accurate enough and the titration results would be subject to lots of error. A volumetric pipet will not allow you to keep track of the volume needed to complete the titration.

Example Question #2 : Laboratory Equipment And Procedure

An experiment calls for measuring  of a solution in a graduated cylinder. How should the graduated cylinder be read?

Possible Answers:

Hold the graduated cylinder so the meniscus is slightly below eye level, then make sure the bottom of the meniscus is at 

Crouch down until your head is on the same level as the table top, then look to make sure the bottom of the meniscus is at 

Hold the graduated cylinder so the meniscus is at eye level, then make sure the bottom of the meniscus is at 

Hold the graduated cylinder so the meniscus is slightly above eye level, then make sure the bottom of the meniscus is at 

Correct answer:

Hold the graduated cylinder so the meniscus is at eye level, then make sure the bottom of the meniscus is at 

Explanation:

In order for an accurate reading of a graduated cylinder, hold the graduated cylinder at eye level then make sure the bottom of the meniscus is at the desired volume. Having the graduated cylinder slightly below eye level will result in readings that are higher than they are supposed to be. Having the graduated cylinder slightly above eye level will result in readings that are lower than they are supposed to be. Never place your head on the same level as the table to read a graduated cylinder. If the graduated cylinder tips over for any reason, you will splash the solution held within on your face.

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