Solution Concentration

Solute

Solvent

Concentration

Molarity

Molality

pH

Lets Review …

• Mixture: A mixture is a chemical substance which is a homogeneous or heterogeneousassociation without chemical bonding of elements and/or compounds in varying proportions and that retain their own individual properties and makeup.

• Remember that you “can see the parts”

http://en.wikipedia.org/wiki/Homogeneous_mixture

Lets Review …

• Solution: A solution is a homogenousmixture of two or more substances in a single physical state.

• Remember that you “cannot see the parts”

Zado, B. (2005). “Solutions”

How do we put it all together?

mixtures

heterogeneoushomogeneous

solutions

Aqueous solutionselectrolytes

How would you describe this picture?

Concentrated vs. Dilute

• In the tea example, the dark colored tea, is referred to strong tea, in chemistry we would say it is a concentrated solution of tea

• The lighter colored tea, would be referred to as weak tea, in chemistry we would say it is a dilute solution

What are Solutions?

• One compound is dissolved in another

• Solute – substance being dissolved (tea)

• Solvent – substance doing the dissolving (water)

In the tea example…

• A concentrated solution – a relatively large amount of solute (tea) is dissolved in the solvent (water)

Concentration of solvent is High

• A dilute solution – relatively little tea is dissolved in water

Concentration of solvent low

DefinitionsSolutions can be classified as saturated or

unsaturated.A saturated solution contains the maximum

quantity of solute that dissolves at that temperature.

An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature

What makes up a solution?

• Solute: the substance being dissolved

• Solvent: the substance doing the dissolving

Name the solute and solvent:

water

water

salt

Sugar, carbon dioxide

solution solute(s) solvent

Ocean water

Coca-cola

Humid air Water vapor air

Supersaturated

Unsaturated

Saturated

The Dead Sea

• The Dead Sea receives water from several streams but has no outflow

• The water is evaporated which concentrates the salt

• Uninhabitable for fishes but nearly impossible for swimmers to sink!

Human Blood

• The blood in our bodies has a certain concentration of salt

• This salt solution must be carefully matched

Molarity

Concentration of Solute

The amount of solute in a solution is given

by its concentration.

Molarity (M) = moles soluteliters of solution

PROBLEM: Dissolve 5.00 g of NiCl2•6 H2O in enough water to make 250 mL of solution. Calculate the Molarity.Step 1: Calculate the # of moles of NiCl2•6H2O

5.00 g • 1 mol

237.7 g = 0.0210 mol

0.0210 mol

0.250 L = 0.0841 M

Step 2: Calculate Molarity

[NiCl2•6 H2O ] = 0.0841 M

Find the Molarity

• If you have 1.0L of sodium chloride solution and 8.8g of sodium chloride

• What is the Molarity?

8.8gNaCl 1mol NaCl = 0.15mol/L NaCl or 0.15M

1 58.5gNaCl 1.0 L solution

Find mass from Molarity

• What mass of sucrose,C12H22O11 must be dissolved to make 460mL of 1.10M solution?

• Find: Mass C12H22O11 • Given: 460mL of 1.10M solution

Find mass from Molarity

• Molar mass of sucrose = 342.30g/mol

460mL soln 1L 1.10mol C12H22O11 342.30g C12H22O11 =

1 1000mL 1L solution 1mol C12H22O11

170g C12H22O11

Use Molarity to make Solutions

• We can use Molarity to prepare solutions

Making Solutions

• How would you prepare 2.50L of a 0.800M solution of Potassium Nitrate?

• Find: mass of KNO3• Given: 2.50L of 0.800M KNO3

KNO3…

• Molar mass: 101.10g/mol

2.50L soln. 0.800mol KNO3 101.10g KNO3 =

1 1L soln. 1mol KNO3

202g KNO3

To make this solution, dissolve 202g KNO3 in 2.50L of solution.

Dilution

• To dilute a solution means to add more solvent without the addition of more solute

• If the amount of solute is unchanged then:

Moles before dilution = Moles after dilution

Dilution continued

• Molarity = moles of solute equals the molarity times volume

M = mol/L or mol = MV

Moles before dilution = Moles after dilution

Then:

M1V1 = M2V21 = before dilution 2 = after dilution

Dilution Example

• 53.4mL of a 1.50M solution of NaCl is on hand, but you need some 0.800M solution. How many mL of 0.800M can you make?

• Find: V2 or mL of 0.800M solution

• Given: M1 = 1.50M, M2 = 0.800M

V1 = 53.4mL

Dilution Example

M1V1 = M2V2• Rearrange our equation to get “find” by itself

V2 = M1V1M2

V2 = (1.50mol/L)(53.4ml) = 100mL

(0.800mol/L)

Another Example

• How many mL must be added to 500.mL of 6.00M NaOH to make a solution that is 2.75M?

Find: Final Volume

Given: M1 = 6.00M M2 = 2.75M

V1 = 500mL

Dilutions

V2 = M1 V1M2

V2 = (6.00M) (500.ml) = 1090 mL

(2.75M)

mL added = V2 – V1mL added = 590. mL

Molality

Two Other Concentration Units

grams solutegrams solution

MOLALITY, m

% by mass =

% by mass

m of solution =mol solute

kilograms solvent

Calculating Concentrations

Calculate molality

Dissolve 62.1 g (1.00 mol) of ethylene glycol in

250. g of H2O. Calculate m & % of ethylene glycol

(by mass).

conc (molality) = 1.00 mol glycol

0.250 kg H2O 4.00 molal

%glycol = 62.1 g

62.1 g + 250. g x 100% = 19.9%

Calculate weight %

Try this molality problem• 25.0 g of NaCl is dissolved in 5000. mL of water.

Find the molality (m) of the resulting solution.

m = mol solute / kg solvent

25 g NaCl 1 mol NaCl

58.5 g NaCl

= 0.427 mol NaCl

Since the density of water is 1 g/mL, 5000 mL = 5000 g, which is 5 kg

0.427 mol NaCl

5 kg water

= 0.0854 m salt water

Review & Recap:

Qualitative Descriptors

• Concentrated

• Dilute

• Saturated

• Unsaturated

• Supersaturated

Quantitative Descriptors

• Molarity

mols solute

Liters solution

• Molality

mols solute

kg solvent

• Mole Fraction

mols part

total moles

Molarity, Molality, and Mole FractionEx. 1) How many grams of potassium chloride

(KCl) are needed to prepare 0.750 L of a 1.50 M solution of potassium chloride in water?

Molarity, Molality, and Mole FractionEx. 2) What is the molality of a solid solution

containing 0.125g of chromium and 81.3 g of iron?

Molarity, Molality, and Mole FractionEx. 3) A gas mixture contains 45.6 g of carbon

monoxide and 899 g of carbon dioxide. What is the mole fraction of carbon monoxide?

Molarity, Molality, and Mole FractionEx. 4) A gas mixture contains the following

gases with the mole fractions indicated: NH3(0.214), Cl2 (0.452), NH2Cl (0.118), and N2(0.175). The mixture also contains HCl gas. What is the mole fraction of HCl gas?

pH

pH Equations

• pH = -log[H+]

• pOH = -log[OH-]

• pH + pOH = 14

• [H+] = 10-pH

• [OH-] = 10-pOH

• Acidic 7

• 7 = Neutral