Scientific Method Activity Name ______Key______
An experiment was performed in which the respiration rate of gold fish was observed in response to changing water temperature. Fish were placed in a container of water and the water temperature was changed indirectly by placing the container in water baths of increasing temperature. Examine the data that follows and answer questions pertaining to the data.
1. Identify the dependent or responding variable. _____Respiration rate______
2. If you were going to perform this experiment, name two variables that you would want to remain constant throughout the course of this experiment?
Water source, volume of water, species of fish, amount of time at each temperature, etc.
3. What might you use as a control for the experiment?
Respiration rate at room temperature
4. How would you describe the data’s trend? Direct or Indirect (inverse)
5. Based on the data as it is presented, can you tell how well correlated the variables are? Explain.
The data is well correlated. The R2 value (correlation coefficient) is close to a value of one which indicates a perfect correlation. If you are not familiar with this statistic, looking at the data points of a linear relationship can help. If the data points are random such that it is difficult to draw a best fit line, then chances are your variables are not well correlated.
6. Without looking ahead, propose an explanation for this data.
There may be several plausible explanations based on the little information presented and one’s background knowledge.
The Effect of Water Temperature on the Dissolved Oxygen Content of Water
Examine the following graphs and answer the questions below.
1. Which of the variables is independent or manipulated? Dissolved oxygen content
2. Describe the similarities and differences between the two graphs.
Similarities – Same variable, same response (indirect relationship between water temperature and dissolved oxygen concentration, measurement scale.
Differences – Water source (creek vs. river), different years, and different intervals between measurements.
3. Write a statement that describes the trend of the data.
As the temperature of the water increases the amount of dissolved oxygen decreases (an indirect relationship between variables).
4. Based on the information contained in this graph and the one on the first page why do you think that the respiration rates of fish increase at higher water temperatures?
As the temperature of the water increases, there is less dissolved oxygen available to the fish. When the concentration of oxygen is low in the water, the fish need to move more water through their gills at a faster rate to achieve the same level of oxygen in their systems.
5. Of the five branches of chemistry that you learned about, which chemistry would be responsible for creating a graph such as this?
Analytical chemistry because they are responsible for determining the composition of matter.
Solubility and Temperature
Soon we will be studying the composition of mixtures. When oxygen is dissolved in water, a mixture or solution is created. Solubility refers to the amount of a substance, in this case oxygen, that dissolves in a given quantity of solvent, in this case water, under specific temperature and pressure conditions.
Examine the following graph and answer the questions below.
1. What affect does atmospheric pressure (air pressure exerted over the surface of the water in this case) have on the solubility of oxygen in water at any temperature?
When atmospheric pressure is high, the solubility of oxygen in water is high (a direct relationship)
2. By what process (think bioJ) do you think the oxygen gets into the water?
Oxygen in the atmosphere diffuses into the water.
3. Unlike most solids, the solubility of a gas generally decreases as temperature increases. This phenomenon has to do with the kinetic energy of the gas particles in solution. Kinetic energy is the energy a particle (i.e., oxygen) has related to its motion. If increasing the temperature of the solution causes the gas to leave the solution, what effect do you think temperature has on kinetic energy of the gas?
Temperature causes the gas particles to become more energetic. When energized particles overcome the pressure exerted by the atmosphere over the water, then they leave the solution.