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# Massachusetts Comprehensive Assessment System

## 2011, High School Chemistry

 Question 33: Open-Response Reporting Category: Atomic Structure and PeriodicityStandard: 2.3 - Interpret and apply the laws of conservation of mass, constant composition (definite proportions), and multiple proportions. A student determines that a sample of an unidentified compound contains 0.8 mol sulfur and 2.4 mol oxygen. The student concludes that the chemical formula for the unidentified compound is S0.8O2.4. The student’s teacher explains that this chemical formula is not possible.Explain why the chemical formula S0.8O2.4 is not possible.Identify the most likely chemical formula for the unidentified compound, assuming that the molar ratio is correct. Show or explain your reasoning.A second student determines that another sample contains 0.5 mol sulfur and 1.0 mol oxygen.Determine whether the two students’ samples are the same compound. Explain your answer.

### Scoring Guide and Sample Student WorkSelect a score point in the table below to view the sample student response.

ScoreDescription
4 The response demonstrates a thorough understanding of the law of constant composition. The response explains why the chemical formula S
0.8
O
2.4
is not possible, identifies the most likely chemical formula for the compound, and shows or explains the reasoning. The response also explains whether the two students’ samples are the same compound and explains the reasoning.
4
3
The response demonstrates a general understanding of the law of constant composition.
2
The response demonstrates a limited understanding of the law of constant composition.
1
The response demonstrates a minimal understanding of the law of constant composition.
0
The response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured.

Note: There are 2 sample student responses for Score Point 4.

In 2011, the Department did not release any questions from the high school Chemistry and Technology/Engineering tests.
This was done in order to support the future development of tests in these subjects.