Concentration of Solutions

•The concentration of a solution is “the amount of solute per quantity of solvent”

•There are many different ways of expressing concentration:▫mass/volume percent (m/v %)▫mass/mass percent (m/m %)▫volume/volume percent (v/v %)▫parts per million (ppm)▫parts per billion (ppb)▫molar concentration (mol/L)

m/v %

•To calculate m/v % we use the following equation:

•Mass of solute is in g•Volume of solution is in mL

Example •What mass of CuCl2(s) is required to make

1.0L of 5.2% (m/v) CuCl2(aq)?

m/m %

•To calculate m/m% we use the following equation:

•Mass of solute and mass of solution are in g

Example •Brass has a (m/m) % composition of 85%

Cu and 15% Zn. If a sample of brass contains 5.21g Cu, then what mass of Zn is present in the sample?

v/v %

•To calculate v/v% we use the following equation:

•Volume of solute and volume of solution are both in mL

Example •Beer usually contains 5.0% (v/v) ethanol.

How much pure ethanol is present in one 341mL bottle of beer?

Parts Per Million (ppm)

•As usual, both masses are in g

•Note that ppm does NOT refer to the number of particles, but the masses of the solute and solution

Parts Per Billion (ppb)

•Once again, both masses are in g

•Again, we are comparing masses, not number of particles

Example•A 155.3g sample of pond water is found to

contain 1.7x10-4g of phosphates. What is the concentration of phosphates in ppm? In ppb?

Learning Check•A 500.0 g bottle of water has a sodium ion

concentration of 5.50ppm. What mass of sodium is present in the bottle?

Molar Concentration•The molar concentration of a solution is

the number of moles of solute that are dissolved in 1L of solution

•Amount of solute is in mol•Volume of solution is in L•Molar Concentration is in mol/L

Example•A 450.0 mL solution contains 0.75 mol of

CuCl2(s). What is the molar concentration of this solution?

Learning Check•12.0g of sucrose (C12H22O11(s)) are

dissolved in a 0.250 L aqueous solution. What is the molar concentration of this solution?

Learning Check•How many moles of HCl(s) are present in

587mL of a 2.5 mol/L solution?

Diluting Solutions•Diluting means to take a stock solution (a

highly concentrated original solution) and add more solvent to it

•We using the following formula to calculate how to dilute a stock solution

•Ci = initial concentration

•Vi = initial volume

•Cf = final concentration

•Vf = final volume

Example•Calculate the volume of water necessary

to dilute 50 mL of a 0.50 mol/L sodium chloride solution to 0.30 mol/L.

Homework

•Pg 373 Q 1-4•Pg 375 Q 11, 14, 16•Pg 376 Q 21, 23, 28•Pg 378 Q 31, 34•Pg 386 Q51, 53