SOLUTION CONCENTRATION: MASS PERCENT, MOLALITY AND MOLE FRACTION14.2: 480 - 488
MAIN IDEA
Concentration can be expressed in terms of percent or in terms of moles
METHODS FOR SHOWING CONCENTRATION
1. Molarity2. Percent by mass3. Percent by Volume4. Molality5. Mole Fractions
PERCENT SOLUTION
Two percentage 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)
solvent kg 1
solute of moles )(molality m
EXAMPLESEXAMPLES
How many grams of sodium fluoride are How many grams of sodium fluoride are needed to prepare a 0.40needed to prepare a 0.40mm NaF solution that NaF solution that contains 750.0g of water?contains 750.0g of water?
solvent kg 1
solute of moles )(molality m
EXAMPLESEXAMPLES
Calculate the molality of a solution prepared Calculate the molality of a solution prepared by dissolving 10.0g of NaCl in 600.g of water.by dissolving 10.0g of NaCl in 600.g of water.
solvent kg 1
solute of moles )(molality m
m = 0.290 m
MOLE FRACTION
Solution concentration can also be expressed by using the mole fraction
BA
AA nn
nX
Mole Fraction
Mol solute
Total moles in solution
EXAMPLESEXAMPLES
What is the mole fraction of each component in a What is the mole fraction of each component in a solution made by mixing 1.25 mol ethylene glycol solution made by mixing 1.25 mol ethylene glycol and 4.00 mol water?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 = 6.51molMoles of water = 27.8molMole fraction of ethanol =
6.51/(27.8+6.51) =0.190Mole 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.