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```									                    Ohio Graduation Test for Science – Spring 2008
Annotated Item 1

Standard and Benchmark Assessed:

Standard:      Physical Sciences

Benchmark:     B. Explain how atoms react with each other to form other substances and how
molecules react with each other or other atoms to form even different
substances.

Multiple Choice Question:

1.     W reacts with X in the equation below.
W + X  Y+ Z
According to the law of conservation of mass, how many grams of W must react with
225 grams of X to result in 375 grams of product?

A.      150 grams
B.      225 grams
C.      375 grams
D.      600 grams

Commentary:

This multiple choice question asks students to determine the necessary mass of W to combine
with 225 grams of X and end up with 375 grams of the product of the reaction (Y+Z). Students
need to recall that the law of conservation of mass states that mass is neither gained nor lost.
This means that in order to get 375 grams of mass on the right hand side of the equation (Y+Z),
there must be 375 grams of mass on the left hand side of the equation (W+X). Since X is given
as having a mass of 225 grams, W must have 375-225=150 grams of mass. The correct answer
is answer choice A. Answer choice B is incorrect; it is the same as the mass of the reactant, X.
If W has a mass of 225 grams, the product would have a mass of 450 grams. Answer choice C
is incorrect; it is the same as the mass of the product. If W had a mass of 375 grams, the
product would have a mass of 600 grams. Answer choice D is incorrect; this is the sum of the
two masses, not the difference.

The cognitive demand of this question is Communicating Understanding / Analyzing Science
Information because the task requires the student to communicate their understanding of the
law of conservation of mass as it applies to chemical reactions so that the mass of reactant W
can be determined.

Performance Data:

The percent of public school students selecting answer choice A for question 1 on the March
Ohio Graduation Test for Science was 88%.

Keywords: reactant, product, mass

Source: Ohio Department of Education                                             July 08

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