A student wants to perform an experiment that tests the relationship between the pressure of a gas and the volume it occupies. To perform this experiment, the student places a specific type of gas in a sealed chamber that can change pressure and that can adapt its volume to the gas within it. The chamber also adjusts to the changing pressure such that the temperature (which also has an effect on gas volume) does not change. The following data was obtained:

Based on the data obtained by the experiment, what can be said about the relationship between pressure (atm) and volume (liters)?

A brilliant but underpaid high school chemistry teacher, together with his former student, manufactures a chemical compound, which they sell for a large mark-up. Their set of reactions are given below:

(1) A + B + C + acid --> D

(2) D --> intermediate

(3) Intermediate --> E

(4) E + acid --> X

His student notes the following observations:

Observation 1) If a greater amount of B and C are used in the reaction, this yields no increased amount of product D.

Observation 2) At any given point, D, the intermediate, and E may co-exist in equal proportions. However, at higher temperatures, higher proportions of product E are noted.

Observation 3) The addition of a strong base can reverse reaction 4.

If reagent A was the limiting reagent, how might the student determine this?

There are two types of forces that occur with all substances on Earth. Intramolecular forces occur between atoms in a molecule, while intermolecular forces occur between neighboring molecules. Intermolecular forces can be dipole-dipole forces, hydrogen bonding, or London dispersion forces.

Professor 1:

Water molecules represent an example of hydrogen bonding due to the attraction between the hydrogen atoms and the oxygen atoms in the molecule. This strong dipole-dipole occurs due to lone pairs present on such atoms as Fluorine, Nitrogen, and Oxygen, which are able to pair more closely to the hydrogen atom in another nearby molecule. Water can be present in a solid, liquid, or gaseous state on Earth depending on the competition between the strength of intermolecular bonds and the thermal energy of the system. In 1873, a Dutch scientist, Van der Waals derived an equation that included both the force of attraction between the particles of a gas and the volume of the particles at high pressures. This equation led to a better fit for experimental data than the Ideal Gas Law.

Professor 2: 

Water is the only substance on Earth that we routinely encounter as a solid, liquid, and gas. At low temperatures, the water molecules lock into a rigid structure, but as the temperature increases, the average kinetic energy of the water molecules increases and the molecules are able to move more creating its other natural states of matter. The higher the temperature, the more likely water is to be a gas. Water is proof of the kinetic theory, which assumes that there is no force of attraction between the particles of the gas state. The best fit for experimental data involving water in a gaseous form is found by using the Ideal Gas Law, since there is no interaction between the gaseous molecules. This law accounts for all of the forces that occur with gases on Earth.

Which of the following experiments could solve the debate between the two professors?

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

How did the procedures of the two experiments differ?

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

Why did the scientists weigh the beakers before adding any solutes to them?

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

Suppose the scientists conducted a third experiment in which they dissolved  in  of methanol at . Which of the following might have been the number of grams dissolved?

The rate of a reaction is defined as the rate at which the products of a reaction are produced. A researcher wants to investigate the rate of reaction of the combustion of theoretical compound . The researcher combusts different amounts of starting material (the theoretical compound and oxygen gas ) and measures how the rate of reaction is affected by changing the amounts of starting material. Because the researcher is concerned about how the conditions of his lab may change, the researcher repeats trial 1. The researcher finds that the results of repeating trial 1 were identical each time.

The results of the experiment are shown in the table below. The brackets ([]) indicate concentration measured in mol/L. 

Which of the following is the best explanation for the repetition of trial 1 during the experiment?

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 if the student were to add hydrochloric acid (a source of hydrogen ions) into a flask of a predetermined amount of carbonic acid, bicarbonate, and hydrogen ion?

Kevin wants to know if a particular kind of chemical fertilizer will help or hinder the growth of his tomato plants. He decides to conduct an experiment in which he grows three plants, one left untreated, one treated with the chemical fertilizer RapidGro and one treated with an organic compost. He records his findings in the charts below, measuring plant height and number of tomatoes over a period of time.

Height of plant (inches):

Number of tomatoes:

On the fourteenth day Kevin picks the biggest tomato from each plant and record its dimensions, as well as other information, which is found below.

Tomato 1 (no fertilizer):  in diameter, dull red, lumpy in shape, wormholes, flavorful.

Tomato 2 (RapidGro):  in diameter, shiny red, round, somewhat tasteless.

Tomato 3 (compost):  in diameter, deep red, lumpy shape, very flavorful.

Which plant is the control?

The Environmental Protection Agency compiled the following information about heavy metals in drinking water. Heavy metals are toxic, and thus must be monitored very closely. All amounts are given in parts per billion (ppb), a common measurement of concentration for trace contaminants. Figure 1 shows total heavy metal contamination in each city as a makeup of various percentages of specific contaminants. Figure 2 shows specific amounts of contaminants (with the same color coding) in ppb as well as total contamination level in ppb.

Figure 1

Figure 2

Which city has the most total cadmium in parts per billion?