Aqueous SolutionsAqueous Solutions

Water containing dissolved substances are aqueous solutions.

The dissolving medium is the solvent.The dissolved particles are the solute.Solutions are homogeneous mixtures.Solute particles will pass through filter

paper.

Dissolving of solid sodium chloride.Dissolving of solid sodium chloride.

solute solvent solution

Polar water molecules interacting with positive and negative ions of a saltPolar water molecules interacting with positive and negative ions of a salt ..

SolvationSolvationSolvent molecules attract

solute particles.Solute particles break away

from each other and the crystal structure breaks apart.

SolvationSolvationMiscible: two liquids can dissolve in

each other. Ex. water and ethanolPolar solvents will dissolve polar

solutes.Non-polar solvents dissolve non-

polar solutes.“Like dissolves like”

The ethanol molecule contains a polar O—H bond.The ethanol molecule contains a polar O—H bond.

The polar water molecule interacts strongly with the polar O—H The polar water molecule interacts strongly with the polar O—H bond in ethanol.bond in ethanol.

An oil layer floating on waterAn oil layer floating on water

ElectrolytesElectrolytesCompounds that conduct electric current in

aqueous solutions or molten state.All ionic compounds, including insoluble

ones, are electrolytes.Some molecular compounds can conduct

electricity. (HCl, NH3)

Strong and weak electrolytes.

non-electrolyte electrolyte

Rate of DissolutionRate of DissolutionAgitation: increases rate of

dissolution. (rate)Temperature: increase in

temperature increases dissolution. (rate and amount)

Particle size: decrease in particle size increases dissolution. (rate)

SolubilitySolubilityAmount of a substance that dissolves in a

given amount of solvent at a given temperature to produce a saturated solution. Ex. sodium sulphate @ 0 oC 4.76 g/100 mL

Saturated solution: max. amount of solute that can be dissolved in a given amount of solvent at a specific temperature.

(a) A solid solute is added to a fixed quantity of water. (b) After a few minutes, the solution is colored due to the dissolved solute, and there is less undissolved solute than in (a). (c) After a longer time, the solution color has deepened, and the quantity of undissolved solute is further diminished from that in (b). The solution in (b) must be unsaturated because more can dissolve. (d) Still later, the solution color and the quantity of undissolved solute appear to be the same as that in (c). Dynamic equilibrium must have been attained in (c) and persists in (d). In both (c) and (d), the solution is saturated.

Solubility Solubility Supersaturated solution: a solution

that contains more solute than it can theoretically hold at a given temperature.

If the solution is agitated or a seed crystal is placed in the solution crystallization will occur.

Supersaturated solutionSupersaturated solution

Solubility of LiquidsSolubility of Liquids Dynamic Equilibrium: number of particles dissolving is

equal to the number of particles forming.

N2O4 and NO2 molecules are shown involved in bond

breaking and bond forming

Concentration/Molarity/Molar ConcentrationConcentration/Molarity/Molar Concentration

A measure of the amount of solute that is dissolved in a measured amount of solvent.

Dilute: a solution that contains a small amount of solute .

Concentrated: a solution that contains a large amount of solute.

ConcentrationConcentration

concentration = # of mol of solute (mol) # of litres of solution (L)

C = n V

Units mol/L or M

ExamplesExamples

What is the concentration of a solution if 5.6 mol of NaCl are dissolved to create a 20.8 L solution?

WS 20/5 - 1

c = n

V

c = 5.6 mol

20.8 L

c = 0.27 M

Parts per millionParts per million

Very dilute concentrations can be recorded as parts per million. (ppm)

One ppm can be thought of as one drop in a bathtub of water.

1 ppm = 1 mg/L

ExamplesExamples

What mass of chlorine is present in 15.0 L of solution, if the solution is 6.00 ppm of chlorine?

1 ppm = 1 mg/L

6 ppm = 6 mg/L

6 mg15.0 L

= 1 L

x

x = (6 mg) (15.0 L)

1 L= 90.0 mg

ExamplesExamplesThe label on a bottle of sparkling water lists

the dissolved minerals as 440 ppm. What mass of minerals is present in a 200 ml glass of water?

1 ppm = 1 mg/L

440 ppm = 440 mg/L

440 mg0.200 L

= 1 L

x

x = (440 mg) (0.200 L)

1 L= 88.0 mg

Percent solutionsPercent solutions

Percent means parts per one hundred.

percent by volume = volume of solute

volume of solution X 100

percent by mass = mass of solute

volume of solution X 100

grams of solute dissolved in 100 mL solution

ExamplesExamples10.0 mL of acetic acid is diluted to a total

volume of 200 mL. What is the percent by volume of acetic acid?

=

= 5.00 % (v/v)

% (v/v) = volume of solute

volume of solution X 100

0.010 L

0.200 L X 100

Make a 1.0 M NaCl solutionMake a 1.0 M NaCl solution

Convert 1.0 mol NaCl into grams of NaClObtain required mass of NaClDissolve NaCl in 500 mL waterTransfer solution to volumetric flaskAdd water to calibration line stopper and

invert to mix

DilutionDilutionThe process of making a

concentrated solution into a less concentrated solution.

There are two types of dilution questions– simple dilution– addition dilution

Simple dilution: addition of water

n1 = n2

c1V1 = c2V2

c1V1 = c2V2

Dissociation EquationsDissociation Equations

Non-electrolytes in solution separate into individual neutral, molecules that move freely throughout the solution. An equation showing a non-electrolyte dissolving simply shows it changing from the pure to its dissolved state.

C12H22O11(s) → C12H22O11(aq)

Dissociation EquationsDissociation Equations

When electrolytes dissolve they separate into ions that move freely throughout the solution. This is called dissociation. The solution as a whole remains neutral, since, although the individual ions are charged, they balance each other out.

Equations that show electrolytes dissolving show the solute changing from its pure state to aqueous ions.

Dissociation EquationsDissociation Equations

These equations are called dissociation equations.

Dissociation equations must be balanced, show correct ionic charge and physical states.

KCl(s) ↔ K+(aq)

+ Cl-(aq)

Al2(SO4)3(s) ↔ 2 Al3+(aq)

+ 3 SO42-

(aq)

Cu(NO3)2(s) ↔ Cu2+(aq)

+ 2 NO3-(aq)

Calculating ionic ConcentrationsCalculating ionic Concentrations

In solution electrolytic compounds exist as free, separate ions.

NaCl(aq) really means Na+(aq) and Cl-

(aq)

In chemical reactions involving such a solution the ions react independantly.

It is more correct to state the concentration of the ions present.

Calculating ionic ConcentrationsCalculating ionic Concentrations

To calculate the ionic concentration of ions in solution:– Step 1: write a balanced dissociation

equation– Step2: use a mole ratio from the equation to

determine the ion concentration

Calculating ionic ConcentrationsCalculating ionic Concentrations

What is the concentration of each ion in 0.23 M Al2(SO4)3 solution?

Balanced dissociation eqaution:– Al2(SO4)3(s) → 2 Al3+

(aq) + 3 SO4

2-(aq)

Use mole ratio:

0.23 M Al2(SO4)3 1 mol Al2(SO4)3

2 mol Al3+

= 0.46 M

Types of ionic EquationsTypes of ionic Equations

Equations involving ionic compounds can be written three ways.– non-ionic equations– total ionic equations – net ionic equations

Non- ionicNon- ionic

The elements and compounds are written as molecules or formula units.

2 AgNO3(aq) + BaCl2(aq) → 2 AgCl(s) + Ba(NO3)2(aq)

Total ionicTotal ionic

Electrolytes are shown as separate dissociated ions while non-electrolytes, precipitates and gases are written as molecules or formula units.

2 Ag+(aq) + 2 NO-

3(aq) + Ba2+(aq) + 2 Cl-(aq) → 2 AgCl(s) + Ba2+

(aq) + 2 NO-3(aq)

Net ionicNet ionic

Only the molecules, formula units or ions that have changed are shown in a net ionic equation.

Molecules and ions that do not change (spectator species) are not shown.

2 Ag+(aq) + 2 NO-

3(aq) + Ba2+(aq) + 2 Cl-(aq) → 2AgCl(s) + Ba2+

(aq) + 2 NO-3(aq)

2 Ag+(aq) + 2 Cl-(aq) → 2 AgCl(s)

Ag+(aq) + Cl-(aq) → AgCl(s)

Analysis for Metallic ElementsAnalysis for Metallic Elements

Qualitative analysis is designed to detect the presence of metal ions.

Quantitative analysis is designed to determine how much metal ion is present.

Solution ColourSolution Colour

The colour of a solution can be used to identify ions that are present in a solution.

What metals do colors indicate?What metals do colors indicate?

Solution colour Ion present

colourless Groups 1,2,17

blue Cr2+

green Cr3+

pink Co2+

green Cu+

blue Cu2+

pale green Fe2+

green Ni2+

purple MnO4-

Flame testFlame test

The flame test is used to visually determine the identity of an unknown metal.

How is the test performed?How is the test performed?A clean platinum or nickel-chromium loop is

required. They may be cleaned by dipping in hydrochloric acid, followed by rinsing with distilled water.

Test the cleanliness of the loop by inserting it into a Bunsen burner flame. If a burst of color is produced, the loop was not sufficiently clean.

The clean loop is dipped in a solution of an ionic salt. The loop with sample is placed in the clear or blue part of the flame and the resulting color is observed.

What metals do colors indicate?What metals do colors indicate?

Flame colour Ion present

bright red Li+

yellow Na+

violet K+

yellow-red Ca2+

bright-red Sr2+

yellow-red Ba2+

blue Cu2+ (halide)

green Cu2+ (others)

whitish-green Zn2+

sodiumlithium potassium

Selective Precipitation of IonsSelective Precipitation of Ions

Ions can be separated from each other based on their salt solubilities

Example: if HCl is added to a solution containing Ag+ and Cu2+, the silver precipitates while the Cu2+ remains in solution.

Removal of one metal ion from a solution is called selective precipitation.

ExampleExample

A precipitate is formed when HCl is added to a solution. Which of the following ions may be present?– silver ion– nickel ion– lead ion– calcium ion

ExampleExample

HCl, H2S, (NH4)3PO4 are added to a clear and colorless solution. No precipitate forms.Which of the following ions may be present?– cesium ion– nickel ion– lead ion– calcium ion