WKS – Moles 1
Moles ⟷ Particles; Moles ⟷ Mass of Elements
Name
Period
Answer Key
1) Explain what is meant by molar mass.
Molar mass is the mass in grams of exactly one mole of any pure substance. For elements, it is the Average
Atomic Mass on the periodic table, expressed in units of grams.
2) What conversion factor should be used to convert from mass to moles? Moles to mass?
1 mol
molar mass
Mass to moles:
; moles to mass:
molar mass
1 mol
Conversions: Use the dimensional analysis method to solve the following conversions. Every number must
have units. You must show all your work and write answers with correct number of sig figs.
PART I: Moles ⟷ Particles
3) How many atoms of O are in 2.25 moles of O?
23
6.022 × 10 atoms O
24
? atoms O = 2.25 mol O ×
= 1.35 × 10 atoms O
1 mol O
4) How many moles of H2O are in 4.00×1023 molecules of H2O?
1 mol H 2O
? mol H 2O = 4.00 × 1023 molec H 2O ×
= 0.664 mol H 2O
6.022 × 1023 molec H 2O
5) How many moles of Mg2+ are in 4.87×1024 ions Mg2+?
1 mol Mg 2+
? mol Mg 2+ = 4.87 × 1024 ions Mg 2+ ×
= 8.09 mol Mg 2+
23
2+
6.022 × 10 ions Mg
6) How many formula units of SnCl4 are in 0.562 moles of SnCl4?
6.022 × 1023 f. un. SnCl4
f. un. SnCl4 = 0.562 mol SnCl4 ×
= 3.38 × 1023 f. un. SnCl4
1 mol SnCl4
PART II: Grams ⟷ moles of elements
7) How many moles of C are in 3.03 g of C?
1 mol C
? mol C = 3.03 g C ×
= 0.252 mol C
12.01 g C
8) How many moles of Na are in 45.0 g of Na?
1 mol Na
? mol Na = 45.0 g Na ×
= 1.96 mol Na
22.99 g Na
9) How many grams of Au are in 8.18 moles of Au?
197.0 g Au
? g Au = 8.18 mol Au ×
= 1610 g Au or 1.61× 103 g Au
1 mol Au
10) How many grams of Mg are in 0.765 moles of Mg?
24.31 g Mg
? g Mg = 0.765 mol Mg ×
= 18.6 g Mg
1 mol Mg