Chemistry Notes - The Mole (Page 2 of 4) in pdf

Chemistry Notes - The Mole Page 2

III.

molar mass—the mass, in g, of 1 mole of a substance

1) some books use “GFM” for all mass calculations

2) molar mass is a general term for doing GAM, GMM, or GFM

MOLAR MASS: general term for GAM, GMM, and GFM,

which refer to the same concept, done the same way:

period table mass in g (usually to tenths) = 1 mole of that substance

IV.

Mole-Mass Conversions (dimensional analysis)

“How do you go from grams to moles? Use the periodic chart.”

mol B x

grams A x

1 mol A

= mol A

MOLAR MASS (g) B = grams B

1 mol B

MOLAR MASS (g) A

examples:

E8) How many grams are in 3.50 mol CO

3.50 mol CO

x [1(12.0) + 2(16.0)] g CO

= 3.50 mol x 44.0 g CO

= 154 g CO

1 mol CO

E9) How many moles are in 150 g of NaBr?

150 g NaBr x

1 mol NaBr

= 1.5 mol NaBr

(23.0 + 80.0) g NaBr

MOLAR VOLUME

A. STP = standard temperature and pressure:

1) standard temperature = 0 °C, 273 K

2) standard pressure = 101.3 kPa, 1 atm, 760 mm Hg, 14.7 psi

B. At STP, all gases occupy the same amount of space:

MOLAR VOLUME of any gas at STP: 22.4 L = 1 mol

C. examples

E10) What is the volume, in L, of 0.495 mol of NO

gas at STP?

0.495 mol NO

x 22.4 L NO

= 11.1 L NO

1 mol NO

E11) How many moles are found in 84 L of neon gas at STP?

84 L Ne x 1 mol Ne = 3.8 mol Ne

22.4 L Ne

VI.

Gas Density and Molar Mass

A. gas density usually measured in g/L

B. use 22.4 L = 1 mol to calculate molar masses (g/mol, the mass of 1 mole)

C. examples

E12) The density of a gas is 3.64 g/L in STP conditions. What is its molar mass?

3.64 g x 22.4 L = 81.5 g/mol

1 mol

E13) At STP, 6.00 L of a gas has a mass of 25.10 g.

Calculate the density of the gas and its molar mass.

D = M = 25.10 g = 4.18 g/L

MOLAR MASS = 25.10 g x 22.4 L = 93.7 g/mol

6.00 L

1 mol

Chemistry Notes - The Mole Page 2

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