A researcher studies the olfactory (scent-related) senses of the giant forest ant, Camponotus gigas. The researcher places 120 ants in a three-chambered cell. The cell has an end section with a cotton ball soaked in a saline solution and another end with a cotton ball soaked in a glucose solution. The ants are placed in the middle and timed for 15 minutes. Their initial and final positions in the cell are recorded (see Table 1). The researcher's null hypothesis states that the distribution of ants across the three chambers will be equal to one another. In other words, the glucose solution will have no effect and there will be no significant difference in the distribution of the insects.

                                 Table 1

The researcher decides to perform a statistical test known as a Chi-squared test of independence to interpret the experiment's results. The test is performed by calculating a Chi-squared statistic by utilizing observed and expected values for distribution (see Table 2). If the sum of the Chi-squared test statistic is higher than the critical value, then the null hypothesis can be rejected. This indicates that the distribution of insects is not random and the variable in question has a pronounced effect on the subjects. A critical value is calculated by determining the degrees of freedom, which in this experiment is equal to the number of categories in the study minus one, and then locating the proper number on a table (see Table 3). There are three possible categories in this experiment: the glucose end, the control end (with the saline-solution soaked cotton ball), and middle portion of the chamber.

                                 Table 2

                                 Table 3

What is the target organism of this study?

During digestion, the energy in food is converted to energy the body can use. Scientists use calorimetry experiments to measure the calories, or energy, provided by food when it is digested or burned. 

The relationship used to find the heat transferred energy  is given by , where  is the mass of the material,  is the given specific heat capacity, and  is the change in temperature of the material. 

In this experiment, food was burned over a Bunsen burner under a can of 200 ml of water. The temperature change of the water and mass change of the food can be used to determine the calories in four different food items.

Table 1 shows the values of the change of mass of the food items, the change in temperature of the water and the energy. Table 2 shows the energy to mass ratio of three of those food items.

                                                    Table 1

                                  Roasted Peanut  Peanut    Cracker    Cheese Puff

Water Temp. Initial         23.9 °C           33.2 °C     40.3 °C      53.9 °C

Water Temp. Final           30.0 °C           40.9 °C     55.9 °C      62.8 °C

Food Mass Initial             0.69 g             0.61 g       3.21 g        1.22 g

Food Mass Final               0.38 g             0.21 g       0.91 g        0.48 g

Energy                            1.22 Cal          1.54 Cal     3.12 Cal     1.78 Cal

                           Table 2

Sample         Energy to Mass Ratio (Cal/g)

     1                                 1.36

     2                                 3.93

     3                                 2.40

What is a controlled variable in this experiment?

During digestion, the energy in food is converted to energy the body can use. Scientists use calorimetry experiments to measure the calories, or energy, provided by food when it is digested or burned. 

The relationship used to find the heat transferred energy  is given by , where  is the mass of the material,  is the given specific heat capacity, and  is the change in temperature of the material. 

In this experiment, food was burned over a Bunsen burner under a can of 200 ml of water. The temperature change of the water and mass change of the food can be used to determine the calories in four different food items.

Table 1 shows the values of the change of mass of the food items, the change in temperature of the water and the energy. Table 2 shows the energy to mass ratio of three of those food items.

                                                    Table 1

                                  Roasted Peanut  Peanut    Cracker    Cheese Puff

Water Temp. Initial         23.9 °C           33.2 °C     40.3 °C      53.9 °C

Water Temp. Final           30.0 °C           40.9 °C     55.9 °C      62.8 °C

Food Mass Initial             0.69 g             0.61 g       3.21 g        1.22 g

Food Mass Final               0.38 g             0.21 g       0.91 g        0.48 g

Energy                            1.22 Cal          1.54 Cal     3.12 Cal     1.78 Cal

                           Table 2

Sample         Energy to Mass Ratio (Cal/g)

     1                                 1.36

     2                                 3.93

     3                                 2.40

Based on the information in Table 1, what variables must be measured in order to calculate the energy of the food samples?

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 information in the passage, which variable(s) are or were held as constants?

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?