SOLUTIONS A solution is a homogeneous mixture of a

solute dissolved in a solvent.

The solvent is generally in excess.

Example The solution NaCl(aq) is sodium chloride NaCl(s) dissolved in water H2O(l) The solute is NaCl(s) and the solvent is H2O(l)

Solute + solvent

Solutions: homogeneous mixtures

• Two components (at the least) – Solute – the substance being dissolved – Solvent – the dissolving medium • usually water – aqueous solution can have multi-solute solutions - seawater

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Solubility experiment

Different solutions

• It’s possible to prepare solutions in all phases of matter.

Different solutions

However,

• The solutions in which the

solvent is water

are called “

AQUEOUS SOLUTIONS

.” • Aqueous solutions are indicated as

(aq)

in reaction equations.

Ni(s) + HCl(aq) NiCl2(aq) + H2(g)

dry

NiCl2(s)

Aqueous solutions

Types of Solutions

•

Are solutions made from only one solvent and one solute?

– –

By definition, there can only be one solvent However, many solutes can be dissolved in a solvent to create a solution

•

Air is an example of a solution with one “ solvent ” (nitrogen) and many “ solutes ” (oxygen, helium, argon, carbon dioxide, etc.)

Unsaturated solution a solution that is able to dissolve more solute.

Saturated solution a solution that cannot dissolve any more solute at the given conditions.

Supersaturated solution a solution holding more dissolved solute than is specified by its solubility at a given temperature

Electrolyte and Non-electrolyte

• Electrolyte:

electricity when dissolved in water.

– Acids, bases

a substance that conducts

and soluble ionic solutions are electrolytes.

• Non-electrolyte:

not conduct electricity when dissolved in water.

– Molecular compounds and insoluble ionic

compounds

a substance that does

are non-electrolytes.

Electrolytes

• Some solutes can

dissociate

into ions.

• Electric charge can be carried.

Types of solutes

high conductivity Strong Electrolyte 100% dissociation, all ions in solution Na+ Cl-

Types of solutes

slight conductivity Weak Electrolyte solution partial dissociation, molecules and ions in CH3COOH CH3COO H+

Types of solutes

no conductivity Non-electrolyte No dissociation, all molecules in solution sugar

Strong Electrolytes

Strong acids: HNO 3 , H 2 SO 4 , HCl, HClO 4 Strong bases: MOH (M = Na, K, Cs, Rb etc) Salts: All salts dissolving in water are completely ionized.

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Concentration

• the amount of solute dissolved in a

solvent at a given temperature

described as a low concentration of solute

dilute

if it has described as concentrated if it has a high concentration of solute described as

supersaturated

contains more dissolved solute than normally possible if

Units of Concentrations

amount of solute per amount of solvent or solution Molarity (M) = moles of solute(n) volume in liters of solution (V) moles = M x V(L)

Examples:

Example 1: What is the concentration when 5.2 moles of hydrosulfuric acid are dissolved in 500 mL of water?

Step one: Convert volume to liters, mass to moles.

500 mL = 0.5 L Step two: Calculate concentration.

C = 5.2 mol/0.5 L = 10mol/L

•

Example 2: What is the volume when 9.0 moles are present in 5.6 mol/L hydrochloric acid?

•

Example 3: How many moles are present in 450 mL of 1.5 mol/L calcium hydroxide?

•

Example 4: What is the concentration of 5.6 g of magnesium hydroxide dissolved in 550 mL?

•

Example 5: What is the volume of a 0.100 mol/L solution that contains 5.0 g of sodium chloride?

Answers

2) 9.0/5.6=1.

6 071428= 1.6 L 3) 1.5x0.45= 0.6

7 5=0.68 mol 4) Mg(OH) 2 = 58.

3 16 g/mol 5.6/58.

3 16=0.09

6 0285342 mol 0.09

6 0285342/0.55 = 0.1

7 45973349 M 0.17 M 5) NaCl=58.5 g/mol 5.0/58.5= 0.08

5 4700855 mol 0.08

5 4700855 mol/0.100= 0.8

5 47008547L 0.85 L

•

HOW MUCH SOLUTE IS NEEDED FOR A SOLUTION OF A PARTICULAR MOLARITY AND VOLUME?

EXAMPLE

How much solute is required to make 300 mL of 0.8 M CaCl 2 ?

ANSWER

(111.0 g) (0.8 mole) (0.3 L) = 26.64 g mole L

CaCl 2 solution CaCl 2

EXAMPLE:

Prepare 1 L, 1M Na 2 SO 4 solution.

PREPARING DILUTE SOLUTIONS FROM CONCENTRATED ONES

• Concentrated solution = stock solution • Use this equation to decide how much stock solution you will need:

M 1 V 1 =M 2 V 2

M 1 = concentration of stock solution M 2 = concentration you want your dilute solution to be V 1 = how much stock solution you will need V 2 = how much of the dilute solution you want to make

EXAMPLE

•

How would you prepare 1000 mL of a 1 M solution of KCl from a 3 M stock of the solution of KCl ?

– The concentrated solution is 3 M, and is M 1 .

– The volume of stock needed is unknown, ?, and is V 1 .

– The final concentration required is 1 M, and is M 2 .

–

The final volume required is 1000 mL and is V 2 .

SUBSTITUTING INTO THE EQUATION:

M 1 .V

1 = M 2 .V

2 3 M (?) 1 M (1000 mL)

? = 333.33 mL

So, take 333.33 mL of the concentrated stock solution and BTV (Bring to Volume)1 L.

EXAMPLE

•

How would you prepare 500 mL of a 1.2 M solution of NaNO 3 solution of NaNO 3 from a 2 M stock of the ?

– The concentrated solution is 2 M, and is M 1 .

– The volume of stock needed is unknown, ?, and is V 1 .

– The final concentration required is 1.2 M, and is M 2 .

–

The final volume required is 500 mL and is V 2 .

SUBSTITUTING INTO THE EQUATION:

M 1 .V

1 = M 2 .V

2 2 M (?) = 1.2 M (500 mL)

? = 300 mL

So, take 300 mL of the concentrated stock solution and BTV (Bring to Volume)500 mL.