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Topic 6: Mole and stoichiometry - Mathematics of formulas and equations
7. Percent composition of hydrates. Calculating percent composition of water in hydrates
1. A student measured 8.24 g sample of a hydrated salt and heated it until it has a constant mass of
6.20 g. What is the percent by mass of water in the hydrated salt?
1) 14.1 % 2) 24.8 % 3) 32.9 % 4) 75.2 %
2. A hydrated salt is a solid that includes water molecules within its crystal structure. A student heated
a 9.10 gram sample of an unknown hydrated salt to a constant mass of 5.41 gram. This mass
represents the mass of the anhydrous compound. What percent by mass of water did the salt
contain?
1) 3.69 % 2) 16.8 % 3) 40.5 % 4) 59.5 %
3. During an experiment to determine the percent by mass of water in a hydrated crystal, a student
found the mass of a hydrated compound to be 4.10 grams. After heating to constant mass, the mass
was 3.70 g. What is the percent by mass of water in this crystal? 4) 0.40 %
Teacher Preview Copy
x 100
x 100
Teacher Preview Copy
x 100
3) 11%
2) 90 %
x 100
1) 9.8 %
4. A 10.0 gram sample of a hydrate was heated until all water of hydration was driven off. The mass of
the anhydrous product remaining was 8.00 grams. What is the percent of water in the hydrate?
1) 12.5 2) 20.0 3) 25.0 4) 80.0
5. The following data was obtained by a student during an experiment to determine the percent by
mass of water in a hydrate compound.
Mass of evaporated dish + hydrated compound 32.5 g
Mass of evaporated dish 25.3 g
Mass of evaporated dish + anhydrous compound 30.8 g
What is the percent composition of water in the hydrate?
1) 12 % 2) 76 % 3) 5 % 4) 24%
6. A hydrated salt was heated in a crucible until the anhydrous compound that remained has a constant
mass. The following data were recorded during this lab experiment.
DATA:
Mass of crucible 17.2 g
Mass of hydrate + crucible 22.0 g
Mass of anhydrous + crucible 20.4 g
What is the percent composition of water in the hydrated compound?
1) 33 % 2) 67 % 3) 7 % 4) 23 %
7. A student determining the percent by mass of water in a hydrated sample of salt obtained the
following data: 6.25 g
Mass of hydrate
Mass of sample after 1 heating 5.45 g
st
Mass of sample after 2 heating 5.10 g
nd
The correct expression for obtaining the percent by mass of water in the sample is
2) 5.10 x 100 x 100 x 100
x 100
1) 5.42 3) 0.8 4) 1.15
6.25
6.25
6.25
6.25
Copyright©2010 E3 Scholastic Publishing. All Rights Reserved. SurvivingChem.com 227
Topic 6: Mole and stoichiometry - Mathematics of formulas and equations
7. Percent composition of hydrates. Calculating percent composition of water in hydrates
1. A student measured 8.24 g sample of a hydrated salt and heated it until it has a constant mass of
6.20 g. What is the percent by mass of water in the hydrated salt?
1) 14.1 % 2) 24.8 % 3) 32.9 % 4) 75.2 %
2. A hydrated salt is a solid that includes water molecules within its crystal structure. A student heated
a 9.10 gram sample of an unknown hydrated salt to a constant mass of 5.41 gram. This mass
represents the mass of the anhydrous compound. What percent by mass of water did the salt
contain?
1) 3.69 % 2) 16.8 % 3) 40.5 % 4) 59.5 %
3. During an experiment to determine the percent by mass of water in a hydrated crystal, a student
found the mass of a hydrated compound to be 4.10 grams. After heating to constant mass, the mass
was 3.70 g. What is the percent by mass of water in this crystal? 4) 0.40 %
Teacher Preview Copy
x 100
x 100
Teacher Preview Copy
x 100
3) 11%
2) 90 %
x 100
1) 9.8 %
4. A 10.0 gram sample of a hydrate was heated until all water of hydration was driven off. The mass of
the anhydrous product remaining was 8.00 grams. What is the percent of water in the hydrate?
1) 12.5 2) 20.0 3) 25.0 4) 80.0
5. The following data was obtained by a student during an experiment to determine the percent by
mass of water in a hydrate compound.
Mass of evaporated dish + hydrated compound 32.5 g
Mass of evaporated dish 25.3 g
Mass of evaporated dish + anhydrous compound 30.8 g
What is the percent composition of water in the hydrate?
1) 12 % 2) 76 % 3) 5 % 4) 24%
6. A hydrated salt was heated in a crucible until the anhydrous compound that remained has a constant
mass. The following data were recorded during this lab experiment.
DATA:
Mass of crucible 17.2 g
Mass of hydrate + crucible 22.0 g
Mass of anhydrous + crucible 20.4 g
What is the percent composition of water in the hydrated compound?
1) 33 % 2) 67 % 3) 7 % 4) 23 %
7. A student determining the percent by mass of water in a hydrated sample of salt obtained the
following data: 6.25 g
Mass of hydrate
Mass of sample after 1 heating 5.45 g
st
Mass of sample after 2 heating 5.10 g
nd
The correct expression for obtaining the percent by mass of water in the sample is
2) 5.10 x 100 x 100 x 100
x 100
1) 5.42 3) 0.8 4) 1.15
6.25
6.25
6.25
6.25
Copyright©2010 E3 Scholastic Publishing. All Rights Reserved. SurvivingChem.com 227
