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Larry's Letters: FOSS Team—Check Your Data

Larry Malone, Co-Director of FOSS, Lawrence Hall of Science
September 03, 2002 | Observations by Larry

Top image: Fifth-grade students at Newport Heights Elementary School display their data.

On April 29, 2002, I got a thick envelope in the mail from Bellevue, Washington. Inside was a letter from Craig Parsley, 5th-grade teacher at Newport Heights Elementary School, and a stack of letters from his students. It seems they ran into a problem when they got to Part 3 of Investigation 2 in the Mixtures and Solutions Module. In the letters each student told me in his or her own words what they had discovered as a result of their experimentation and why they thought the answer in the teacher guide was wrong.

The activity involves testing a granular mystery material to find out how much of it is needed to saturate 50 ml of water. Students add the material to a small bottle containing 50 ml of water and shake the container. If the material dissolves, they add more solid and shake again, continuing until no more solid material will dissolve. By determining the mass of the saturated solution and subtracting 50 grams for the 50 ml of water, students can determine the mass of the solute in the saturated solution.

Mr. Parsley's students found that it took about 50 grams of the mystery material to saturate the 50 ml of water. Using the table of properties of six chemicals on student sheet 10, they determined that their mystery chemical was potassium thiosulfate. But the teacher guide said that the mystery chemical provided in the kit was Epsom salts. The students then repeated the experiment and confirmed their original finding.

The students carefully described their procedures and diplomatically suggested that I needed to look into the problem because the answer in the teacher guide was wrong. I love to see that kind of self-confidence in students. It indicates that they have achieved the level of critical thinking and understanding of concepts that we strive for in the FOSS program. I trotted off to my Mixtures and Solutions kit, got out the materials, conducted the investigation and found...they were right.

Thank you, Mr. Parsley's 5th-grade students. Now, when you look at student sheet 10, there are only five chemicals in the chart, and it says that it takes 48 grams of Epsom salts to saturate 50 ml of water.