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Massachusetts Comprehensive Assessment System

2013, High School Chemistry

  Question 33: Open-Response  
Formaldehyde (CH2O) occurs in smoke from forest fires and in automobile exhaust.
  1. Calculate the total number of valence electrons in one molecule of formaldehyde. Show your calculations.
Carbon is the central atom in a CH2O molecule.
  1. Draw a Lewis dot structure for formaldehyde.
  2. Identify the shape of the formaldehyde molecule predicted by valence-shell electron-pair repulsion (VSEPR) theory. Explain your answer.

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 how to use valence-shell electron-pair repulsion (VSEPR) theory to predict the molecular geometry of molecules. The response correctly calculates the total number of valence electrons in formaldehyde, draws a Lewis dot structure for formaldehyde, identifies the shape of the formaldehyde molecule, and clearly explains why formaldehyde has this shape.
4
3
The response demonstrates a general understanding of how to use valence-shell electron-pair repulsion (VSEPR) theory to predict the molecular geometry of molecules.
2
The response demonstrates a limited understanding of how to use valence-shell electron-pair repulsion (VSEPR) theory to predict the molecular geometry of molecules.
1
The response demonstrates a minimal understanding of how to use valence-shell electron-pair repulsion (VSEPR) theory to predict the molecular geometry of molecules.
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.

High School Chemistry

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

Return to the MCAS 2013 Student Work Directory



Last Updated: September 30, 2003
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