Download Moles and Formulas 1 Practice Problems ANSWERS

Chemistry 11
The Mole I – Practice Problems
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Show all your work in a clear, organized and complete manner.
Respect significant figures.
A. MOLES AND NUMBERS
1.
Calculate the number of moles in each of the following:
a)
1.2 x 10
30
atoms of gold
c)
6
2.4 x 10
20
2.
–4
molecules of sugar
n = 5.00 x 10 mol
worms
n = 4.0 x 10
28
4
n = 2.0 x 10 mol
b)
3.01 x 10
d)
mol
8.00 x 10
12
homework assignments
n = 1.33 x 10
–11
mol
Calculate the following:
a)
the number of atoms in
5.0 moles of copper
3.0 x 10
b)
24
d)
atoms
3.31 x 10
the number of molecules in
-15
3.0 x 10 mole of carbon dioxide
e)
9
1.8 x 10 molecules
c)
the number of bananas in
-8
8.88 x 10 mol of bananas
the number of hydrogen atoms in
0.00275 mole of water
16
H atoms
the number of oxygen atoms in
3
1.2 x 10 mol of Mg(NO3)2
4.3 x 10
5.35 x 10
21
27
oxygen atoms
bananas
B. MOLES AND MASS
3.
Calculate the molar mass of:
a)
KBr
e)
M = 119.01 g/mol
b)
O2
M = 120.37 g/mol
f)
M = 32.00 g/mol
c)
Ca(NO3)2
(NH4)3PO4
M = 149.12 g/mol
C6H12O6 (glucose)
M = 180.18 g/mol
g)
M = 164.10 g/mol
d)
MgSO4
NaC5H8NO4 (MSG)
M = 169.13 g/mol
h)
C10H14N2 (nicotine)
M = 162.26 g/mol
Chemistry 11
4.
Calculate the mass (in grams) of the following:
a)
-3
1.75 x 10 mol of oxygen gas
mass = 0.0560 g
b)
2
3.4 x 10 mol of KBr
4
mass = 4.0 x 10 g
c)
0.00670 mol of C6H12O6
mass = 1.21 g
d)
8.35 x 10
-12
mol of MSG
mass = 1.41 x 10
5.
–9
g
Calculate the number of moles in each of the following:
a)
43.2 g of Ca(NO3)2
n = 0.263 mol
b)
-3
8.27 x 10 g of MgSO4
n = 6.87 x 10
c)
–5
mol
7.2 mg of nicotine
-5
n = 4.4 x 10 mol
d)
2
2.82 x 10 kg of ammonium phosphate
3
n = 1.89 x 10 mol
6.
You have a sample of an “unknown metal chloride” with the formula XCl2. Experiments show that the
sample contains 0.20 mole of the compound, and its mass is 22.2 g. What is the identity of element X?
M = 22.2 g / 0.20 mol
= 111 g/mol
Mr = Ar (X) + 2 Ar (Cl)
111 = Ar (X) + 2 (35.45)
∴ Ar (X) = 111 – 70.90
= 40
∴ element X is most likely calcium (Ar = 40.08)
Chemistry 11
C. MASS, MOLES AND NUMBERS
7.
Calculate the number of atoms in:
a)
72.0 g of lead
# atoms = 72.0 g x (1 mol / 207.19 g) x (6.02 x 10
b)
23
atoms / 1 mol) = 2.09 x 10
2
2
27
atoms
23
molecules /1 mol) x ( 2 oxygen atoms /1 molecule)
Calculate the mass of
a)
b)
atoms of silver
21
atoms x (1 mol / 6.02 x 10
23
atoms) x (107.87 g / 1 mol) = 0.821 g
18
molecules of ammonia (NH3)
18
molecules x (1 mol / 6.02 x 10
2.9 x 10
mass = 2.9 x 10
c)
21
4.58 x 10
mass = 4.58 x 10
23
-5
molecules) x (17.04 g / 1 mol) = 8.2 x 10 g
26
molecules of glucose (C6H12O6)
26
molecules x (1 mol / 6.02 x 10
1.47 x 10
mass = 1.47 x 10
23
4
molecules) x (180.18 g / 1 mol) = 4.40 x 10 g
Calculate the number of hydrogen atoms in
a)
2.5 mg of water
# H atoms = 2.5 mg x (1 g / 1000 mg) x (1 mol / 18.02 g) x (6.02 x 10
20
= 1.7 x 10 H atoms
b)
23
molecules / 1 mol) x (2 H atoms/1 molecule)
3
8.0 x 10 kg of methane (CH4)
3
# H atoms=(8.0 x10 kg) x (1000g /1kg) x (1 mol /16.05 g) x (6.02 x 10
30
= 1.2 x 10 H atoms
10.
atoms /1 mol) = 1.1 x 10
-2
-2
9.
23
7.00 x 10 g of oxygen gas = O2
# atoms = 7.00 x 10 g x (1 mol / 32.00 g) x (6.02 x 10
21
= 2.63 x 10 atoms
8.
atoms
3.5 x 10 kg of gold
# atoms = 3.5 x 10 kg x (1000 g / 1 kg) x (1 mol / 196.97 g) x (6.02 x 10
c)
23
23
molecules /1mol) x (4 H atoms/1 molecule)
a)
What is Avogadro’s favourite board game? Moleopoly ….. HA HA ha ha haaa!
b)
What is Avogadro’s favourite chip dip?
Guacamole …. HA HA ha ha haaa ha ha!