The Properties of Mixtures:

ConcentrationLecture 19

Concentration

is the measure of how much of a given substance there is

mixed with another substance.

Concentration

applies to any sort of chemical mixture, but most frequently to homogeneous

solutions.

Concentration =

amount or mass or volume of solute=

--------------------------------------------------

amount or mass or volume of solution or solvent

Concentration =

amount or mass or volume of solute=

--------------------------------------------------

amount or mass or volume of solution or solvent

Molarity (M) =

amount (mol) of solute---------------------------

--------volume (L) of solution

Concentration =

amount or mass or volume of solute=

--------------------------------------------------

amount or mass or volume of solution or solvent

Molality (m) =

amount (mol) of solute---------------------------

----------mass (kg) of solvent

A sample problem

on calculating molality.

Another sample problemWhat is the molality of a solution prepared by dissolving 339.8 g of silver nitrate in 4000. g of water?Amount of AgNO3=339.8/169.91 = 2.000 molMass of water=4.000 kgMolality of solution= 2.000/4.000=0.500 m AgNO3

Another sample problemWhat mass of sodium phosphate is needed to prepare 0.750 m solution by dissolving it in 800. g of water?Mass of water=0.800 kgAmount of Na3PO4=0.750/0.800=0.938 mol

Mass of Na3PO4= 0.938x163.94=154 g

Another sample problemWhat mass of water is needed to prepare 0.250 m solution by dissolving 1 kg 382 g of potassium carbonate?Mass of K2CO3=1382 gAmount of K2CO3=1382/138.21=10.00 molMass of water=10.00/0.250=40.0 kg

Mass percent (%w/w) =

mass of solute= ---------------------------------------------- x 100% mass of solute + mass of solvent

A sample problemWhat is mass percent of magnesium sulfate in solution containing 43.5 g of solute in 0.348 kg of solution?Mass of solution=348 g%w/w MgSO4=(43.5/348) x 100%=12.5%

Another sample problemWhat is the mass of manganese (II) chloride in 640. lb of its 30.0% solution?Mass of MnCl2 =(640x30)/100=192 lb

Another sample problemWhat is the mass of 45% solution containing 9.00 kg of potassium iodide?Mass of solution=(9.00/45%)x100%=20.0kg

Volume percent (%v/v) =

volume of solute= -------------------------- x 100% volume of solution

Mole fraction (X) =

amount (mol) of solute---------------------------------

------------------------amount (mol) of solute + amount (mol)

of solvent

Mole percent (mol %) =

mole fraction x 100%

A sample problemWhat is the mole fraction and mole percent of 157.55g of nitric acid in mixture with 900.8 ml of water?Amount of HNO3=157.55/63.018 = 2.5000 molAmount of H2O=900.8/18.016=50.00 molTotal amount = 2.5000+50.00=52.50 molX HNO3=2.5000/52.50=0.04762

mol % HNO3= 0.04762 x 100%=4.762%

A sample problem

on expressing concentration in parts by mass, parts by volume, and

mole fraction.

A sample problem

on converting concentration units.

THE END