Answers IA-Chemistry A Survey of Chemistry AUnit Test

Percent Composition and Molecular Formula Answers

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A sample of a compound contains 60.0 g C and 5.05 g H. Its molar mass is 78.12 g/mol. What is the compound’s molecular formula?

C2H2

C6H6

C6H

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Which represents the empirical formula for A3B9?

AB3

AB2

A3B9

A9B27

A sample of a compound contains 32.0 g C and 8.0 g H. Its molar mass is 30.0 g/mol. What is the compound’s molecular formula?

CH3

CH4

C2H4

C2H6

What is the empirical formula for C2H6?

CH3

C2H4

C6H18

Which statement best relates an empirical formula with a molecular formula?

They are always different for the same compound.

Subscripts of empirical formulas can be reduced.

Molecular formulas can be determined from empirical formulas.

They both show the actual ratio of elements for a compound.

Webb has calculated the percent composition of a compound. How can he check his result?

by making sure they are in the lowest ratio

by adding them to see if they total 100

by checking that they are whole-number multiples

by dividing them by the molar mass

Which information must be known about a compound to find the molecular formula from the empirical formula?

density

formula mass

percent composition

mole ratio

What is the percent by mass of chlorine in NaCl?Use .

35.45%

39.34%

60.66%

70.90%

Which step would help a student find the molecular formula of a compound from the empirical formula?

Multiply the subscripts of the empirical formula by the value of the ratio of the molar mass of the compound to the empirical molar mass of the compound.

Subtract the value of the ratio of the molar mass of the compound to the empirical molar mass of the compound from the subscripts of the empirical formula.

Divide the subscripts of the empirical formula by the value of the ratio of the molar mass of the compound to the empirical molar mass of the compound.

Add the value of the ratio of the molar mass of the compound to the empirical molar mass of the compound to the subscripts of the empirical formula.

The percent by mass of copper in CuBr2 isUse .

28.45%.

44.30%.

63.55%.

71.55%.

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Percent Composition and Molecular Formula Answers

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