Atoms and G/FM
% Comp
Hydrates
Moles to Mass and Back Again
Grab Bag
100
What is the formula Mass of methane, CH4?
16.05 u
100
What is the percent composition by mass of hydrogen in NH4HCO3 (gram-formula mass = 79 grams/mole)?
6.3%
(5 divided by 79) x 100
100
Mass of hydrate 6.25 g
Mass of sample after heating 5.12 g
What is the numerical setup of % mass of water in the hydrate?
100
What is the total number of moles in 80.0 grams of C2H5Cl (gram-formula mass = 64.5 grams/mole)
1.24 moles
100
magnesium sulfate heptahydrate formula
MgSO4 * 7H2O
200
What is the total number of atoms in Al2(SO4)3?
17
200
What is the percent composition by mass of nitrogen in NH4NO3 (gram-formula mass = 80.0 grams/mole)?
35%
( [2x14.01)/ 80.0 ] x100
200
A 10.0 gram sample of a hydrate was heated and the mass of anhydrous product remaining was 8.00 grams. What is the percent of water in the hydrate?
20.0%
200
The molar mass of Ba(OH)2 is
171.35 g/mol
Ba +2(O) +2(H) = 137.33 + 2(16.00) + 2(1.01)= 171.35 g/mol
200
What is the total number of moles of hydrogen atoms in one mole of (NH4)3PO4?
12 moles of H atoms
300
What is the formula and gram formula mass of silver chloride?
AgCl 143.32 g
300
In which compound is the percent composition by mass of chlorine equal to 42%?
(1) HClO2 (gram-formula mass = 68 g/mol)
(2) HClO4 (gram-formula mass = 100. g/mol)
(3) HClO3 (gram-formula mass = 84 g/mol)
(3) HC1O3 (gram-formula mass = 84 g/mol)
[35.45 g /84 g] x100 = ~42%
300
The percent by mass of water in the hydrate Na2SO4•10H2O (GFM = 322.24g) is approximately
56%
( 180.2 g / 322.24 g ) x 100
300
How many moles of water are in one mole of magnesium sulfate heptahydrate?
7 moles of H2O.
300
Write the formula for copper (II) sulfate pentahydrate
CuSO4 * 5H2O
400
How many moles of H are in one mole of the following compound:
Al(CH3COO)3
9 moles of H
(THINK: how many H atoms in one molecule of Al(CH3COO)3. There is the same number of moles of H in one mole of the compound)
400
What is the percent by mass of hydrogen in NH3 (formula mass = 17.0)?
17.8%
(3.03u/17.0 u) x 100
400
Determine the gram-formula mass of the magnesium sulfate heptahydrate.
246.50 g
400
What is the mass in grams of 2.0 moles of NO2
molar mass = (14.01g) + 2x(16.00g) = 46.01 g/mol
2x molar mass= 92.02 g
400
How many H, S, and O atoms are in 0.50 moles of H2SO4
1.0 mol H
0.50 mol S
2.0 mol O
500
What is the formula mass of Ca3(PO4)2?
310.18 u
500
What is the approximate percent composition by mass of CaBr2 (formula mass = 200)
20% calcium and 80% bromine
500
A student heated a 9.10-gram sample of a hydrated salt to a constant mass of 5.41 grams. What percent by mass of water did the salt contain?
40.5%
500
How many moles are in 39 grams of LiF?
1.5 moles
molar mass LiF = 25.94 g/mol
39g x ( 1mole/25.94 g) = 1.5 moles
500
How many moles of Na2O contain 4 moles of Na?
2 moles of Na2O contain 4 moles of Na