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# Massachusetts Comprehensive Assessment System

## 2012, High School Chemistry

Question 33: Open-Response
Five chemical reactions are listed in the table below.
 Reaction 1 CaCO3 → CaO + CO2 Reaction 2 Ca(OH)2 + 2HCl → CaCl2 + 2H2O Reaction 3 NH3 + HCl → NH4Cl Reaction 4 PbO2 → Pb + O2 Reaction 5 2Mg + O2 → 2MgO
1. Identify one chemical reaction from the list that is a synthesis (combination) reaction. Explain why you identified this reaction as synthesis.
2. Identify one chemical reaction from the list that is a decomposition reaction. Explain why you identified this reaction as decomposition.
3. Describe a combustion reaction.
4. Write a balanced chemical equation for a combustion reaction using some or all of the substances from the table below.
 C3H8 CO2 O2 H2 C H2O

### 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 to classify chemical reactions. The response correctly identifies one example of a synthesis (combination) reaction and one example of a decomposition reaction and clearly explains each answer. The response also correctly describes a combustion reaction and gives a balanced chemical equation for a combustion reaction.
4
3 The response demonstrates a general understanding of how to classify chemical reactions.
2 The response demonstrates a limited understanding of how to classify chemical reactions.
1 The response demonstrates a minimal understanding of how to classify chemical reactions.
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.

Question 11:
Question 23:
Question 33:
Question 44:
Question 45: