Massachusetts Comprehensive Assessment System

2012, High School Chemistry

Question 11: Open-Response

Reporting Category: Solutions, Equilibrium, and Acid-Base Theory
Standard: 8.2 - Relate hydrogen ion concentrations to the pH scale and to acidic, basic, and neutral solutions. Compare and contrast the strengths of various common acids and bases (e.g., vinegar, baking soda, soap, citrus juice).

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.

Identify HCl and HF as acids or bases. Explain your answer.
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.

Score	Description
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 2012 MCAS Sample Student Work: High School Chemistry

Last Updated: May 5, 2020