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Study Quiz 1
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1
When calculating percent composition you are assuming
A)that the average atomic mass of each element does not change.
B)that every molecule contains the same elements.
C)that every molecule contains the same number of each element.
D)all of the above are true.
2
What is the percentage composition of a pure element?
A)It depends on the source of the element.
B)It depends on the isotopic abundance of the element.
C)It is 100%.
D)There is not enough information to answer the question.
3
A chocolate cream cookie consists of a creamy vanilla layer with a mass of 4.83 g between two chocolate layers each with a mass of 3.72 g. What is the percentage of chocolate in the cookie in terms of the number of layers?
A)33.3%
B)50.0%
C)66.7%
D)100%
4
What is the mass percent of the chocolate in the cookie?
A)30.3%
B)60.6%
C)66.7%
D)87.0%
5
Ethanol (C2H5OH) is a clear, colourless liquid. What is its percentage composition of hydrogen in terms of the number of atoms?
A)33.3%
B)50.0%
C)55.6%
D)66.7%
6
What is the mass percent of hydrogen in ethanol (C2H5OH)?
A)13.4%
B)13.2%
C)11.2%
D)11.4%
7
A 20.0 g sample of an oxide of iron is 77.8% iron by mass. What is the mass of iron in this sample?
A)15.6 g
B)11.2 g
C)7.78 g
D)4.40 g
8
A 8.23 g sample of an unknown substance contains 3.45 g of magnesium and 4.68 g of sulfur. Which of the following is true about the unknown?
A)It is 43.1% sulfur by mass.
B)It is 56.9 % sulfur by mass.
C)It is 0.431 % magnesium by mass.
D)It is 0.569 % sulfur by mass
9
A compound containing calcium, carbon and oxygen has the following percent composition: Ca - 40.0%, C - 12.0%. What mass of oxygen is found in 75.0 g of this compound?
A)There is not enough information to answer the question.
B)48.0 g
C)36.0 g
D)18.0 g





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