Units of Concentration

A solution is a homogeneous mixture of one substance (the solute) dissolved in another substance (the solvent).

Concentration is a ratio of the amount of solute to the amount of solvent.

Units of Concentration

Percent volume% volume = volume solute (ml) x 100

volume solution (ml)

Percent mass% mass = mass solute (g) x 100

mass solution (g)

Solution = solvent + solute

Units of Concentration

Example 1:What is the percent by volume concentration of asolution in which 75.0 ml of ethanol is diluted to avolume of 250.0 ml?

75.0 ml x 100 = 30.0% 250.0 ml

Units of Concentration

Example 2:What volume of acetic acid is present in a bottle

containing 350.0 ml of a solution which measures 5.00% concentration?

x = 0.05 350.0 ml

x = 17.5 ml

Units of Concentration

Example 3:Find the percent by mass in which 41.0 g of NaCl is dissolved in 331 grams of water.

41 g x 100 = 11.0% 372 g

Molarity (M) is the most common unit of concentration

Molarity is an expression of moles/Liter of the solute.

Units of Concentration

A mole is the SI unit of number of particles and can be used as an expression of the molecular weight of a substance.

Units of Concentration

The formula weight of an element is expressed as grams/mole

The molar mass of a compound can be calculated by adding the molar mass of the individual elements.

Units of Concentration

22.99 + 35.45 = 58.44 g/mol

You just calculated the molar mass of sodium chloride to be 58.44 g/mol.

To determine how to make a stock solution of sodium chloride, use the formula:

Making Solutions

g = M x L x molar mass

How many grams of NaCl would you need to prepare 200.0 mL of a 5 M solution?

Making Solutions

g = M x L x molar massg = (5mol/L) (0.2L) (58.44g/mol)g = 58.44 g

Diluting Solutions

Often once you have made a stock solution, you need to dilute it to a working concentration.

To determine how to dilute the stock solution, use the formula:

C1V1 = C2V2

C1 – concentration of stockC2 - concentration of diluted solutionV1 – volume needed of stockV2 – final volume of dilution

Example 5:How many milliliters of a 5 M stock solution of NaCl

areneeded to prepare 100 ml of a 0.4 M solution?

Diluting Solutions

C1 V1 = C2 V2

(5) V1 = (0.4)(100) V1= 8 ml

Diluting Solutions

Serial Dilutions are dilutions made in series (for example, if you needed to make solutions that were 2M, 1M, 0.5M, and 0.25 M)

The formula for serial dilutions is:Dilution Factor = (V1 + V2)

V1

V1 – volume of solution being dilutedV2 – volume of solvent

Units of Concentration

Example 6:Propose a method to prepare 100 ml of a 0.5 M

glucosesolution from a 5 M glucose solution.10 = (v1 + 100)

v1

10v1 = v1 + 100 -v1 -v1

9v1 = 100 9 9

v1 = 11.1 ml of 5 M glucose + 100 ml H2O

Dilutions tutorial

Diluting Solutions