Two scientists wanted to test the solubility of different substances. Solubility is a measure of how many moles of a given substance (known as the solute) can dissolve in a given volume of another substance (known as the solvent). The solvent can also be thought of as the substance present in greater amount, while the solute can be seen as the substance present in lesser amount. The scientists performed the following experiments to investigate this property.

Experiment 1

The scientists tested the number of moles of several substances that could be completely dissolved in  of water at various temperatures. They made their solutions by slowly adding amounts of each substance to beakers sitting on a hot plate containing water and a stirring rod until no more of the substance dissolved in the solution. The beakers were weighed before and after the additions and the difference in mass was calculated to be the added mass of the substance. The researchers then calculated the number of moles that dissolved for each trial using the molecular mass and the recorded mass for each trial. Results are recorded in Table 1.

Table 1

Experiment 2

In this experiment, the scientists wanted to test the solubility of  in a variety of liquids at several temperatures. Their procedure was similar to that of Experiment 1, but with a range of liquids and only one solid. The results are compiled in Table 2.

Table 2

In Experiment 2, which of the following combinations of temperature and solvent dissolved the greatest number of moles of ?

An experiment was carried out measuring the boiling point and freezing point of an unknown organic liquid (Sample X) with varying levels of salt dissolved within it. The experiment was conducted in the following manner:

First, the experimenter measured the boiling point and freezing point of Sample X. 

Next, a known quantity of salt was dissolved into the sample and then the boiling point and freezing points were measured again. 

The results of the experiment are outlined in the table below:

What can we say is the relationship between concentration of salt in Sample X and the boiling point of Sample X?

An experiment was carried out measuring the boiling point and freezing point of an unknown organic liquid (Sample X) with varying levels of salt dissolved within it. The experiment was conducted in the following manner:

First, the experimenter measured the boiling point and freezing point of Sample X. 

Next, a known quantity of salt was dissolved into the sample and then the boiling point and freezing points were measured again. 

The results of the experiment are outlined in the table below:

If the variable  represents concentration, the variable  represents change in melting point, and the variable  represents a constant, which of the following equations could be used to roughly model the melting point trend observed in the chart above?

An experiment was carried out measuring the boiling point and freezing point of an unknown organic liquid (Sample X) with varying levels of salt dissolved within it. The experiment was conducted in the following manner:

First, the experimenter measured the boiling point and freezing point of Sample X. 

Next, a known quantity of salt was dissolved into the sample and then the boiling point and freezing points were measured again. 

The results of the experiment are outlined in the table below:

If the variable  represents concentration, the variable  represents change in boiling point, and the variable  represents a constant, which of the following equations could be used to roughly model the boiling point trend observed in the chart above?

In studying the effects of adding heat to different substances on each substance's temperature, a researcher conducted the following experiment. The researcher added 1,000 Joules of energy by a controlled heat lamp to four different substances. The temperature change in each substance that was caused by the heat was then measured and recorded. The results of this experiment are shown below.

The researcher is aware of a concept called specific heat and knows that lead has a lower specific heat than wood, which has a lower specific heat than cardboard, which has a lower specific heat than styrofoam. Therefore, the researcher has ordered the objects in the table from lowest specific heat (lead) to highest (styrofoam).

The researcher wants to use the information collected to build a container to store some cell samples that must remain at a low temperature to survive. According tot he data, which substance would be ideal for this container?

In studying the effects of adding heat to different substances on each substance's temperature, a researcher conducted the following experiment. The researcher added 1,000 Joules of energy by a controlled heat lamp to four different substances. The temperature change in each substance that was caused by the heat was then measured and recorded. The results of this experiment are shown below.

The researcher is aware of a concept called specific heat and knows that lead has a lower specific heat than wood, which has a lower specific heat than cardboard, which has a lower specific heat than styrofoam. Therefore, the researcher has ordered the objects in the table from lowest specific heat (lead) to highest (styrofoam).

Which of the following equations would most likely allow us to model the temperature change  as a function of specific heat  and heat added ?

When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:

Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.

Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.

"Dipole moment" is a measure of IMFAs. A higher dipole moment corresponds with greater IMFAs. Water has a high dipole moment (1.85 debyes) but is a relatively small molecule (molecular weight = 18 amu). 

A gas (Compound X) is found to have a dipole moment of about 1.84 debyes and is much larger than water, weighing approximately 190 amu. Assuming Student 1's statements are correct, how would the volume of a quantity of Compound X gas compare with that of the same quantity of water vapor when we do not assume ideal behavior?

The above chemical equation describes the dissociation of carbonic acid  into bicarbonate  and hydrogen ion . A chemistry student wants to study the behavior of carbonic acid, as it is a part of one of the most important physiological control systems in the human body.

When carbon dioxide  enters the blood in your body, it takes on the form of carbonic acid. Carbonic acid is in what we call "equilibrium" with bicarbonate ion and hydrogen ion. This equilibrium functions in the following manner: if more carbonic acid is present, more will dissociate into bicarbonate and hydrogen ion. On the other hand, if there is more bicarbonate and/or hydrogen ion, we say that equilibrium as shown in the above equation will "shift left" and more carbonic acid will be produced from bicarbonate and hydrogen.

To study this effect, the student obtains a mixture of carbonic acid, bicarbonate, and hydrogen ion. Next, the student conducts trials in which she adds a certain amount of one of the chemicals one at a time and then measures how the concentrations of each chemical change after each addition.

pH is a measure of hydrogen ion concentration and is used to measure acidity. A pH of 7 is neutral, while a low pH corresponds to a high concentration of hydrogen ions, or an acid. What can we infer would happen to the pH of a person's blood if a large amount of carbon dioxide were to be produced in that person's body, such as during exercise?

The above chemical equation describes the dissociation of carbonic acid  into bicarbonate  and hydrogen ion . A chemistry student wants to study the behavior of carbonic acid, as it is a part of one of the most important physiological control systems in the human body.

When carbon dioxide  enters the blood in your body, it takes on the form of carbonic acid. Carbonic acid is in what we call "equilibrium" with bicarbonate ion and hydrogen ion. This equilibrium functions in the following manner: if more carbonic acid is present, more will dissociate into bicarbonate and hydrogen ion. On the other hand, if there is more bicarbonate and/or hydrogen ion, we say that equilibrium as shown in the above equation will "shift left" and more carbonic acid will be produced from bicarbonate and hydrogen.

To study this effect, the student obtains a mixture of carbonic acid, bicarbonate, and hydrogen ion. Next, the student conducts trials in which she adds a certain amount of one of the chemicals one at a time and then measures how the concentrations of each chemical change after each addition.

What can we infer would happen to one of the student's trials if the student added both bicarbonate ion and hydrogen ion to that trial?

Enzymes (large molecules) serve to catalyze, or speed up, chemical reactions in the human body. This process of catalysis begins with the binding of a substrate (the reactant) to the active site of an enzyme. This active site is simply the portion of the enzyme that interacts with the substrate. Following the binding event, products separate from the enzyme active site, at which point the enzyme is prepared to undergo another reaction cycle. Two scientists offer conflicting views on the nature of the enzyme-substrate interaction.

Scientist 1

The enzyme-substrate interaction can be modeled with a Lock and Key paradigm. In this model, the enzyme represents a lock and the substrate represents a key. Only the substrate of proper size and shape will fit into a particular enzyme's active site and catalyze the reaction. The enzyme-substrate complex, the intermediate of this reaction, is stabilized mostly by strong ionic and hydrogen bonds. Following the formation of this intermediate, the enzyme changes the substrate in some way, leading to formation of a product, which subsequently dissociates from the enzyme.

Scientist 2

The shapes of substrate and enzyme are not exactly complementary. When it binds to the enzyme, the substrate induces the active site to alter its shape in order to enhance the fit. Thus, at first the interaction between substrate and enzyme is weak, but subsequent changes in the active site lead to stronger binding. Only the correct substrate will be able to modify the active site in the proper manner. Experimental data seems consistent with this Induced Fit model and inconsistent with the Lock and Key model.

In the following sequences, hyphens denote bound complexes and plus signs indicate separate species. Which of the sequences is consistent with the viewpoint of Scientist 1?