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# Massachusetts Comprehensive Assessment System

## 2012, Grade 8 Science and Technology/Engineering

 Question 12: Open-Response Reporting Category: Physical SciencesStandard: 9 - Recognize that a substance (element or compound) has a melting point and a boiling point, both of which are independent of the amount of the sample. A scientist has three unlabeled samples of pure metals. He wants to determine the identity of each metal.Identify which one of the following properties the scientist should use to determine the identity of the pure metal in each sample: color, melting point, mass, or volume.Explain why the property you identified in part (a) can be used to determine the identity of the pure metal in each sample.The scientist cuts each of the samples of pure metal into two smaller pieces. Is the property that is used to determine the identity of the metal affected when each sample is cut into two pieces? Explain your answer. The scientist can also use density to determine the identity of the pure metal in each sample. Describe how the scientist can determine the density of the pure metal in each sample.

### 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 how a substance has a melting point that is independent of the amount of the sample. The response correctly identifies which one of the properties the scientist should use to determine the identity of the metal in each sample, and clearly explains why the property can be used to determine the identity of the metal. The response clearly identifies whether the property used to determine the identity of the metal is affected when the sample is cut into two pieces, and explains why. The response also clearly describes how the scientist can determine the density of the pure metal in each sample.
4
3 The response demonstrates a general understanding of how a substance has a melting point that is independent of the amount of the sample.
2 The response demonstrates a limited understanding of how a substance has a melting point that is independent of the amount of the sample.
1 The response demonstrates a minimal understanding of how a substance has a melting point that is independent of the amount of the sample.
0 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.

Question 12:
Question 21: