3) What is the % by mass of oxygen in H 2 SO 4 ? [ GFM=98]

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3) What is the % by mass of oxygen in H 2 SO 4 ? [ GFM=98]

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3) What is the % by mass of oxygen in H 2 SO 4 ? [ GFM=98]

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3) What is the % by mass of oxygen in H2SO4? [ GFM=98]

% COMP (MASS) = PART X 100

WHOLE

% Oxygen = 63.9976 X 100

98

= 65.3 % ~ 65 %

#5) A hydrate is a compound that includes water molecules within its crystal structure. During an experiment to determine the percent by mass of water in a hydrated crystal, a student found the mass of the hydrated crystal to be 4.10 grams. After heating to constant mass, the mass was 3.70 grams. What is the percent by mass of water in this crystal?

Mass water

x

% H2O =

100

=

Mass hydrate

4.10 g – 3.70 g

9.8 % water

x

% H2O =

100

=

4.10 g

This is a modified version of part/whole x 100 from the reference tables!

7) Given the reaction:

6 CO2 + 6 H2O 1C6H12O6 + 6 O2

a) What is the total number of moles of waterneeded to make 2.5 moles of C6H12O6?

H2O. =

C6H12O6..

6

x

X = 15 moles of water

1

2.5

Theoretical mole ratio

#13) A compound contains 0.5 moles of sodium, 0.5 moles of nitrogen, and 1.0 moles of hydrogen. The empirical formula of the compound is

Na0.5N0.5H1.0

Multiply subscripts by 2

Na0.5x2N0.5x2H1.0x2

Subscripts can not be decimals, to get rid of a 0.5 decimal multiply all subscripts by 2!

The new subscripts are:

Na1N1H2

or

NaNH2

#15) A compound contains 40% CALCIUM, 12% CARBON and 48% OXYGEN by mass. What is the empirical formula of this compound?

Ca1C1O3

CaCO3

Assume 100g of the sample, this will allow you to assume 40% is 40 grams. Total mass does NOT affect % composition.