WKS Moles 4
Particles ⟷ Mass of Compounds
Name
Period
Answer Key
Date
Mass of Compound ⟷ Mass of Element
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: Grams to moles and moles to grams (Show short calculation of MM first!)
1) How many moles of Ba(OH)2 are in 7.32 g of Ba(OH)2?
MM = (1 Ba ) (137.3 g/mol) + ( 2 O ) (16.00 g/mol) + ( 2 H ) (1.008 g/mol) = 171.3 g Ba(OH)2 mol Ba(OH)2
? mol Ba(OH)2 = 7.32 g Ba(OH)2 ×
1 mol Ba(OH)2
= 0.0427 mol Ba(OH)2
171.3 g Ba(OH)2
2) How many moles of Na2SO4are in 105.8 g of Na2SO4?
MM = ( 2 Na ) ( 22.99 g/mol) + (1 S) ( 32.06 g/mol) + ( 4 O ) (16.00 g/mol) = 142.04 g Na 2SO 4 1 mol Na 2SO 4
? mol Na 2SO 4 =
105.8 g Na 2SO 4
1 mol Na 2SO 4
142.04 g Na 2SO 4
= 0.7449 mol Na 2SO 4
3) What mass of Ba(C2H3O2)2, in g, is in 2.50 moles of Ba(C2H3O2)2?
MM = (1 Ba ) (137.3 g/mol) + ( 4 C ) (12.01 g/mol) + ( 6 H ) (1.008 g/mol) + ( 4 O ) (16.00 g/mol)
= 255.3 g Ba(C2 H 3O 2 )2 1 mol Ba(C2 H 3O 2 )2
? g Ba(C2 H 3O 2 )2 =
2.50 mol Ba(C2 H 3O 2 )2
255.3 g Ba(C2 H 3O 2 )2
1 mol Ba(C2 H 3O 2 )2
= 638 g Ba(C2 H 3O 2 )2
PART II: Grams to particles and particles to grams. (Show short calculation of MM first!) Remember th
→ moles ←⎯
→ particles
flowchart: mass ←⎯
4) How many molecules of methane (CH4) are in 36.7 grams of CH4?
MM = (1 C ) (12.01 g/mol) + ( 4 H ) (1.008 g/mol) = 16.04 g CH 4 1 mol CH 4
? molec. CH 4 =
36.7 g CH 4
1 mol CH 4
6.022 × 1023 molec. CH 4
16.04 g CH 4
1 mol CH 4
= 1.38 × 1024 molec. CH 4
5) What mass of methyl amine (CH3NH2), in g, is in 2.27×1024 molecules of CH3NH2?
MM = (1 C ) (12.01 g/mol) + (5 H ) (1.008 g H/mol) + (1 N ) (14.01 g N/mol) = 31.06 g CH 3NH 2 mol CH 3NH 2
2.27 × 1024 molec. CH 3NH 2
1 mol CH 3NH 2
31.06 g CH 3NH 2
6.022 × 1023 molec. CH 3NH 2
1 mol CH 3NH 2
= 117 g CH 3NH 2
PART III: Moles/Mass of Compound → Moles/Mass of element. (If needed, show short calculation of
MM first)
6) How many grams of Cl are there in 6.92 mol of PCl5? [mol PCl5 → mol Cl → mass Cl.]
5 mol Cl
35.45 g Cl
? g Cl = 6.92 mol PCl5 ×
×
= 1230 g Cl
1 mol PCl5 1 mol Cl
7) How many moles of O are there in 88.2 g of N2O4? [determine moles of N2O4 first!]
MM = ( 2 N ) (14.01 g N/mol) + ( 4 O ) (16.00 g O/mol) = 92.02 g N 2O 4 mol N 2O 4
? mol O =
88.2 g N 2O 4
1 mol N 2O 4
4 mol O
92.02 g N 2O 4
1 mol N 2O 4
= 3.83 mol O
8) How many moles of I are there in 2.39×1024 formula units of PbI2? [determine moles of PbI2 first!]
mol I = 2.39 × 1024 f. un. PbI 2 ×
1 mol PbI 2
6.022 × 10
23
f. un. PbI 2
×
2 mol I
1 mol PbI 2
= 7.94 mol I
9) *How many grams of Na are there in 151.3 g Na2SO3? [determine moles of Na2SO3 first, then moles of
Na!]
126.04 g Na 2SO3
MM = ( 2 Na ) ( 22.99 g Na/mol) + (1 S) ( 32.06 g S/mol) + ( 3 O ) (16.00 g O/mol) =
1 mol Na 2SO3
? g Na =
151.3 g Na 2SO3
1 mol Na 2SO3
2 mol Na
22.99 g Na
126.04 g Na 2SO3
1 mol Na 2SO3
1 mol Na
= 55.19 g Na