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# Massachusetts Comprehensive Assessment System

## 2013, High School Chemistry

 Question 23: Open-Response Reporting Category: Properties of Matter and ThermochemistryStandard: 1.2 - Explain the difference between pure substances (elements and compounds) and mixtures. Differentiate between heterogeneous and homogeneous mixtures. Particle models of four different types of matter are shown in the diagram below.Identify which of the four models best represents a pure compound. Explain your answer and give a specific example of a compound.Identify which of the four models best represents a homogeneous mixture. Explain your answer and give a specific example of a homogeneous mixture.Describe one method that could be used to separate a homogeneous mixture.

### 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 differences among pure substances, homogeneous mixtures, and heterogeneous mixtures. The response correctly identifies the particle models that correspond to a pure compound and to a homogeneous mixture, clearly explains the answers, and gives specific examples of each. The response also clearly describes one method that could be used to separate a homogeneous mixture.
4
3
The response demonstrates a general understanding of the differences among pure substances, homogeneous mixtures, and heterogeneous mixtures.
2
The response demonstrates a limited understanding of the differences among pure substances, homogeneous mixtures, and heterogeneous mixtures.
1
The response demonstrates a minimal understanding of the differences among pure substances, homogeneous mixtures, and heterogeneous mixtures.
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 11:
Question 23:
Question 33:
Question 44:
Question 45: