Mole Unit Test Review Answers
A. What is the molar mass of carbon tetrachloride (CF4) ?
Carbon = 12 amu & Fluorine = 19 amu so 12 + 4(19) = 88 g/mol
B. How many molecules are there in 0.75 mol of sucrose (C12H22O11)?
0.75 mol C12H22O11
6.02 x 1023 #molecules C12H22O11
1 mol C12H22O11
=
4.52 x 1023 #molecules
C12H22O11
C. How many moles of carbon dioxide (CO2) contain 6.89 × 1023 molecules carbon dioxide?
6.89 x 1023 #molecules CO2
1 mol CO2
=
6.02 x 1023 #molecules CO2
1.15 mol CO2
D. What is the mass in grams of 3.55 × 1021 atoms of lithium (Li)?
Molar Mass of Li = 7 g/mol
3.55 × 1021 #atoms Li
1 mol Li
6.02 × 1023 #atoms Li
7 g Li
1 mol Li
=
0.413 g Li
E. Find the correct empirical formula for the compound whose percent composition is 38.62% (K, potassium);
13.87% (N, nitrogen); 47.50% (O, oxygen)?
MMK = 39; MMN=14; MMO=16
38.62 g K
1 mol K = 0.990 g K
𝐾
0.990
𝑁
0.991
𝑂
2.969
39 g K
13.87 g N
1 mol N = 0.991 g N
14 g N
47.50 g O
1 mol O = 2.969 g O
16 g O
=1
0.990
=1
KNO3
0.990
=3
0.990
F. Which is the percent composition of phosphorus in Cu3(PO4)2?
Cu = 3(64) = 192 amu
P = 2(31) = 62 amu
total all numbers = 382 g/mol
O = 8(16) = 128 amu
192
𝐶𝑢 382 𝑥100 = 50.26%
62
P382 𝑥100 = 16.23%
128
𝑂 382 𝑥100 = 33.71%
G. Copper is one of a group of metals called the coinage metals. How many atoms of copper (Cu) are in a
pure copper coin weighing 34.0 g? MMCu = 64 g/mol
34.0g Cu
1 mol Cu
64 g Cu
6.02 × 1023 #atoms Cu
1 mol Cu
= 3.20 × 1023 #atoms Cu
H. What is the mass of 6 moles of sodium chloride (NaCl)?
MMNaCl = 58 g/mol
6 mol NaCl
58 g NaCl = 348 g NaCl
1 mol NaCl
I. A volume of N2 is 11.762 L at STP. How many moles of N2 are present?
11.762 L N2
1 mol N2
22.4 L N2
= 0.525 mol N2
J. Ascorbic acid is used to improve the nutrient content of crops. It is composed of 40.92% carbon, 4.58%
hydrogen, and 54.50% oxygen. The molar mass of ascorbic acid is 176.0 g/mol. The empirical formula of
ascorbic acid is C3H4O3. Determine the molecular formula for ascorbic acid.
176
1) Molar Mass of C3H4O3 is 3(12) + 4(1) +3(16) = 88 g/mol
2)
88
=2
3). 2 (C3H4O3) = C6H8O6
K. What is the volume of a sample of methane gas (CH4) if it contains 16.3 moles?
16.3 mol CH4 22.4 L CH4
1 mol CH4
L.
= 365.12 L CH4
How many moles are present in 274 g of manganese (Mn)? MMMn = 55 g/mol
274 g Mn
1 mol Mn
55 g Mn
= 4.98 mol Mn