molar mass & percent composition. the mass of 1 mole of an element or compound – the mass in...
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Molar Mass & Percent Composition
MOLAR MASS
• The mass of 1 mole of an element or compound– The mass in grams from the Periodic Table
Unit = grams per mole (g/mol)
MOLAR MASS
• Step One – Identify the molecular formulaEx: calcium fluoride
• Step Two – Determine the number of atoms of each element
Ca = F =
• Step Three – Multiply the atomic mass by the number of atoms
Ca = x =F = x =78.08 g/mol
CaF2
1 2
40.08 1 40.0819.00 2 38.00 +
MOLAR MASS - Examples
1) PbCl2
Pb = x = Cl = x =
2) Aluminum sulfate Al = S = O =
g/mol+
207.2 1 207.2
35.45 2 70.90278.10
Al2(SO4)3
26.98 x 2 = 53.96
32.07 x 3 = 96.21
16.00 x 12 = 192.00 +342.17 g/mol
MOLAR MASS - Examples
3) Copper (II) chloride Cu = 63.55 x 1 = 63.55
Cl = 35.45 x 2 = 70.90
4) NH4Cl
N = 14.01 x 1 = 14.01
H = 1.01 x 4 = 4.04
Cl = 35.45 x 1 = 35.45
g/mol+
134.45
CuCl2
+53.50 g/mol
PERCENT COMPOSITION• Step One – Identify the molecular formula
Ex: iron (III) oxide • Step Two – Calculate the molar mass of the compound
Fe = 55.85 x 2 = 111.70 O = 16.00 x 3 = 48.00
• Step Three – Divide the mass of the individual elements by the total, then multiply by 100
Fe =
O =
Fe2O3
159.70 g/mol+
111.70159.70
x 100 = 69.9%
48.00159.70
x 100 = 30.1%
PERCENT COMPOSITION1) H2O2
H = 1.01 x 2 = 2.02
O = 16.00 x 2 = 32.00
2) Sn(OH)4
Sn = 118.71 x 1 = 118.71
O = 16.00 x 4 = 64.00
H = 1.01 x 4 = 4.04
34.02 g/mol
/ 34.02 x 100 = 5.9 %
/ 34.02 x 100 = 94.1 %
186.75 g/mol
/ 186.75 x 100 = 63.6 %
/ 186.75 x 100 = 34.3 %
/ 186.75 x 100 = 2.2 %
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