Name_________________________________
Chemistry – Scientific thinking and reasoning practice
1. What is the difference between the research method and the technical method?
2. What is the difference between qualitative data and quantitative data?
Part 1:
A group of students wanted to find out if changing the composition of the atmosphere could affect the growth
rate of plants. After researching the problem, they decide they want to see if an increase in oxygen or an
increase in carbon dioxide will affect the growth of plants.
Using tanks of pure oxygen, carbon dioxide, and nitrogen, the students created artificial atmospheres with
varying percentages of the three gases. They adjusted the percentage of nitrogen to compensate for changes
in the other two gases. In the first experiment, the students varied the percentage of oxygen and kept the
carbon dioxide level at 0.03 percent, the value in normal air. In the second experiment, the students varied the
percentage of carbon dioxide and kept the oxygen level at 21 percent, the value in normal air.
The students grew pea plants in airtight chambers, replacing the air in the chambers with the artificial
atmospheres. The students assessed the growth rate of the plants by measuring the plants’ heights each day
for 10 days.
The table below shows the results of the students’ two experiments.
Experiment 1
Percent
Oxygen
Percent
Carbon
Dioxide
1
0.03
98.97
10
0.03
20
Experiment 2
Growth
Percent
Rate
Nitrogen (mm/day)
Percent
Oxygen
Percent
Carbon
Dioxide
Growth
Percent
Rate
Nitrogen (mm/day)
10
21
1
78
15
89.97
11
21
10
69
25
0.03
79.97
10
21
20
59
35
30
0.03
69.97
12
21
30
49
43
40
0.03
59.97
11
21
40
39
44
50
0.03
49.97
10
21
50
29
44
3. Identify the independent variable in Experiment 1. _____________________________________
4. Identify the independent variable in Experiment 2. _____________________________________
5. Identify the dependent variable in Experiment 1. ______________________________________
6. Identify the dependent variable in Experiment 2. ______________________________________
7. The students could have done just one experiment in which they varied both the oxygen and carbon dioxide
percentages at the same time. Why do you think they chose instead to vary the oxygen and carbon dioxide
percentages in separate experiments?
8. Based on the data gathered, the students created the following graphs to represent their data. What is missing
from the graphs below?
9. Develop a descriptive title for the graph on the left:
10. Develop a descriptive title for the graph on the right:
11. Based on the data gathered, what should the students’ conclusion be?
Part 2:
Two students are presented with a problem in science class. They need to identify specific compounds in an
unknown mixture. This “mystery” mixture could include one or more of the following compounds: cornstarch,
baking powder, and powdered sugar. All of these compounds are white and are difficult to distinguish using
sight alone.
To analyze the mixture, the students must first find ways to identify the individual compounds. Their teacher
gives them five test tubes; distilled water; two bowls for the water samples; samples of cornstarch, baking
powder, and powdered sugar; dropper bottles; iodine solution; white vinegar; three shallow pans; and a candle
with matches.
The students place small amounts of cornstarch, baking powder, and powdered sugar in separate piles in the
shallow pan. Then they place some distilled water in a small bowl. They add a drop of vinegar to each sample
and record what happens in a data table. Only the baking soda shows any change. The soda begins to fizz
due to a gas being given off.
Next they place small amounts of each compound into the other shallow pan and distilled water in another
small bowl. This time, they add a drop of iodine to each sample and record their results. Only the sample of
cornstarch turns blue.
They finally place a small amount of each compound in three separate test tubes and distilled water in a fourth
test tube. They use a lit candle to gently heat the bottom of each test tube. Only the sugar shows any signs of
melting. The other compounds are unaffected.
After finding unique ways of testing for each compound, students then repeat all three tests on the mystery
mixture. The following data table is a record of their results.
12.
Material tested
Addition of
Vinegar
Addition of
Iodine
Heated with
Candle
Distilled water
No change
No change
Boiled
Cornstarch
No change
Turns blue
No change
Sugar
No change
No change
Compound melted
Baking soda
Fizzing takes place
No change
No change
Mystery mixture
Fizzing takes place
Turns blue
No change
a.)Which method did the group of students follow, the research method or the technical method?
b.) How do you know?
13.
a.) Was this a qualitative or quantitative lab?
b.) How do you know?
14. a.) What was the control in the experiment?
b.) What is the purpose of a control?
15.
Which compounds are present in the mystery mixture? How do you know?
16. In a solubility experiment, students add various solutes (salt, sugar, etc.) to beakers containing the same
amount of water. The students observe that equal amounts of water dissolve different amounts of solute.
a.) What is the independent variable in this experiment?
b.) What is the dependent variable in this experiment?