# Mass Percent_ Molality and Mole Fraction

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4/21/2012
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```							SOLUTION CONCENTRATION:
MASS PERCENT, MOLALITY AND
MOLE FRACTION
14.2: 480 - 488
MAIN IDEA
   Concentration can be expressed in terms of
percent or in terms of moles
METHODS FOR SHOWING CONCENTRATION
1.   Molarity
2.   Percent by mass
3.   Percent by Volume
4.   Molality
5.   Mole Fractions
PERCENT SOLUTION
 Twopercentage methods to show how
concentrated a solution is:
 Percent by volume = volume of solute x 100%
volume of solution
 Percent by (m/v) = mass of solute x 100%
solution volume(mL)
PERCENT SOLUTION
   Examples:
 If 10. mL of pure acetone is diluted with water to a
total solution volume of 200. mL, what is the percent
by volume of the acetone solution?
Percent by volume = volume of solute x 100%
volume of solution
Percent by volume = 10        x 100% = 50.%
200
PERCENT SOLUTION
   Examples:
Calculate the grams of solute needed to make 250. mL
of a 0.10% MgSO4 solution.
Percent by (m/v) = mass of solute x 100%
volume of solution (mL)
= 0.10%= ___?__ x 100%
250mL
? = 0.25g MgSO4
MOLALITY
   Another way to express solution concentration is
Molality (m)

moles of solute
m (molality ) 
1 kg solvent
EXAMPLES
   How many grams of sodium fluoride are needed
to prepare a 0.40m NaF solution that contains
750.0g of water?

moles of solute
m (molality ) 
1 kg solvent
EXAMPLES
   Calculate the molality of a solution prepared by
dissolving 10.0g of NaCl in 600.g of water.

moles of solute
m (molality ) 
1 kg solvent

m = 0.290 m
MOLE FRACTION
   Solution concentration can also be expressed by
using the mole fraction

nA                      Mol solute
XA 
n A  nB
Mole Fraction
Total moles in
solution
EXAMPLES
   What is the mole fraction of each component in a
solution made by mixing 1.25 mol ethylene glycol and
4.00 mol water?
EXAMPLES
What is the mole fraction of each
component in a solution made by mixing
300.g of ethanol (C2H5OH) and 500.g
water?

Moles of ethanol = 6.51mol
Moles of water = 27.8mol
Mole fraction of ethanol = 6.51/(27.8+6.51)
=0.190
Mole fraction of water = 27.8/(27.8+6.51)
=0.810
HONORS: BEFORE YOU GO…
   Calculate the mass of calcium cyanide needed to
make a 0.25m calcium cyanide solution using
450g of water.

```
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