Laboratory Equipment and Procedure - AP Chemistry

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.

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.

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.

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.

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.

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.

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.

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.

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.

A volumetric pipette is made to dispense a specific amount of liquid very accurately. The Mohr pipette, beaker, and graduate cylinder will not measure a specific amount of liquid as accurately as the volumetric pipette.

Potassium hydrogen phthalate is a solid at room temperature, so we can use a balance and a weigh boat or weigh paper. When measuring precise amounts of chemicals, an analytical balance will be able to provide the most accurate reading of mass.

When you need to heat anything up to high temperatures, you must use a crucible. Glassware is not able to withstand as much heat as a crucible.

A spectrophotometer should be used because it is used to measure absorbance at specific wavelengths. An analytical balance is used for measuring mass. Chromatography paper is used to separate different pigments found in a chemical. Litmus paper is used to determine the pH of a substance.

A beaker is the best choice for mixing these two solutions. Graduated cylinders, burets, and pipets are all used to measure specific amounts of solution. Also, stirbars can be easily added to beakers to facilitate the reaction.

When you label chemical solutions, you should technically always use the full chemical name (though this is not always done). Using common abbreviations, like HCl for hydrochloric acid, is generally acceptable.

The reason why none of the other answers work is because they did not quantify how strong (concentrated) the HCl solution was. A 1 molar HCl solution is handled much differently than a 12 molar one. Even though the answer choice "1M of acid" did quantify the concentration, it did not say which acid was in solution, which would be very unsafe if someone else saw your beaker and needed to know how to dispose of the contents.

Labels should always provide information on the contents of the container, as well as its concentration strength.

Graduated cylinders are often used for measuring volumetric quantities. As these have several markings, they are considered accurate. Volumetric flasks are also used to accurately measure liquid volume quantities. Lastly, burettes are used to accurately measure volumes of liquid during titrations.

In contrast, beakers are not typically used to measure accurate quantities of liquid; though they have markings on them, these are approximate measurements. Graduated cylinders are often used to accurately measure out a liquid, and beakers to then hold the liquid.

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.

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.

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.