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Massachusetts Comprehensive Assessment System

2012, High School Chemistry

  Question 11: Open-Response  
The diagrams below show a 0.1 M aqueous solution of HCl and a 0.1 M aqueous solution of HF.
The diagram shows two beakers. Each beaker is filled with the same amount of liquid. The beaker on the left is titled zero point one molar H C L and contains 10 small circles labeled H plus and 10 small circles labeled C L minus. The circles are distributed uniformly in the liquid. The beaker on the right is labeled zero point one molar H F and contains 8 small circles labeled H F, two small circles labeled H plus, and two small circles labeled F minus. The circles are distributed uniformly in the liquid.
  1. Identify HCl and HF as acids or bases. Explain your answer.
  2. The pH of the 0.1 M HCl solution is expected to be lower than the pH of the 0.1 M HF solution. Explain why, based on the diagrams of the solutions and the definition of pH.

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

ScoreDescription
4 The response demonstrates a thorough understanding of acids, bases, and pH. The response correctly identifies both HCl and HF as acids, explains why they are acids, and clearly explains why the HCl solution would have a lower pH value than the HF solution.
4
3 The response demonstrates a general understanding of acids, bases, and pH.
2 The response demonstrates a limited understanding of acids, bases, and pH.
1 The response demonstrates a minimal understanding of acids, bases, and pH.
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.

High School Chemistry

Question 11: Solutions, Equilibrium, and Acid-Base Theory
Question 23: Properties of Matter and Thermochemistry
Question 33: Bonding and Reactions
Question 44: Atomic Structure and Periodicity
Question 45: Bonding and Reactions

Return to the MCAS 2012 Student Work Directory



Last Updated: September 2, 2008
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