administration student task rubric student work technical quality
Soapy Water
Examples of Student Work
Contributed by: Connecticut Academic Performance Test (CAPT)

There is one example for each score point ranging from 3 down to 0. Explanations of the scores were written by staff from the Division of Teaching and Learning at the Connecticut State Department of Education who conducted training and scoring of field tested events.

Students in a science class were conducting experiments to explore the use of various substances in removing soap from the water. One way to remove soap from water is to have it react with other substances. When the reactions occur, a solid called a precipitate is sometimes formed. A precipitate can be filtered out of the water.

Group A carried out the following experiment.

  1. We put soapy water into three separate plastic cups.
  2. A different substance was added to each of the cups.
  3. After waiting five minutes, the mixture in each cup was filtered.
  4. We examined the precipitate (which remained in the filter paper) and the filtrate (which was in the test tube) for each mixture.

The table below shows our results.

1 2 3
Substance added to Soapy Water Epsom Salt Table Salt Sugar
Precipitate White, milky White, milky None
Filtrate Clear Slightly cloudy Cloudy

Question 1 - Event Score = 3

Based on their results, Group A concluded that Epsom salt removed the soap from the water. Is this a valid conclusion? Explain your answer fully.

Question 1
The response correctly questions the validity of the conclusion.It explains that "you cannot assume that cloudy water means soapy" and that "the filtrate should have been shook and the suds measured carefully." The response also points out that it is not clear if variables have been controlled and that, "There is no control either."

Question 2 - Event Score = 3

Do you have enough information to replicate Group A's experiment? If you think so, explain what information you have. If you think not, explain what other information you would need.

Question 2
The response correctly states that there is not enough information to replicate the experiment. It explains that "how much soapy water" and "how much epsom salt, table salt, and sugar" should be included in the experiment. The response also explains that a control is missing.

Group B carried out the following experiment.

  1. We placed 50 mL of soapy water into three plastic cups.
  2. We added 10 grams of sugar to cup 1, 10 grams of table salt to cup 2, and 10 grams of Epsom salt to cup 3. We mixed each with a plastic spoon.
  3. We filtered all three mixtures.
  4. We then poured the filtrate (remaining liquid) into 3 separate test tubes, shook them and measured the height of the soap suds.

The table below shows our results.

Cup Substance Final Soap Suds Height
1 Sugar 9.1 cm
2 Table Salt 1.2 cm
3 Epsom Salt 0.2 cm

Question 3 - Event Score = 3

Group B did not include a control in their experiment. What would be an appropriate control? Explain your answer fully, including how the control might improve the experiment.

Question 3
The response is correct and well elaborated as to what would make an appropriate control for the experiment. It explains how the control would improve the experiment.

Question 4 - Event Score = 3

Compare Group A's and Group B's experiments. Which experiment, if either, is better designed? Explain your answer fully.

Question 4
The response discusses several factors pertaining to the quality of the experimental designs ("Group B included measurements", "both missing controls", "The most relevant factor that made the experiment better than Group A's is that they shook the tubes.")

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