Solution Chemistry(Chp. 7/8)

Chemistry 2202

Topics Molar Concentration (mol/L) Dilutions % Concentration (pp. 255 – 263) Solution Process Solution Preparation Solution Stoichiometry Dissociation/Ionization/Molecular

Solvation

What is a Solution?

A solution is a homogeneous (one phase) mixture. A solution forms when two substances are mixed together so evenly that they appear to be a single phase.

The components of a solution are the solute - the substance that dissolves, and the solvent - the substance in which the solute is dissolved.

Any solid, liquid, or gas which is evenly distributed throughout another solid, liquid or gas is said to be in solution.

There are nine possible combinations of these states of matter.

solid in liquid(eg.) brass

solid in liquid(eg.) sugar water

solid in gas(eg.) mothball in air

liquid in solid(eg.) dental amalgam

liquid in liquid(eg.) ethanol in water

liquid in gas(eg.) water in air

gas in solid(eg.) hydrogen in palladium

gas in liquid(eg.) O2 in water

gas in gas(eg.) oxygen in nitrogen

Summary : Possible Types of Solutions.

Solubility and Miscibility : Solubility refers to the maximum amount of a

solute that can be dissolved in an amount of solvent under specific temperature and pressure conditions.

A substance that cannot be dissolved in another (or does so to a very limited extent) is said to be insoluble.

Miscibility refers to the ability of a liquid to dissolve in another in all proportions. Alcohols like methanol and ethanol are miscible with water. There is no limit to the amount of these alcohols that can be dissolved in water

When the amount of one liquid exceeds the other, their roles reverse.

Solubility and Miscibility :

For example if you add alcohol to water, alcohol is said to be dissolved in water; however, if you add alcohol to the point where its volume is greater than the volume of water, then water becomes the solute and alcohol the solvent.

When a liquid does not dissolve in another to any extent, the liquids are said to be immiscible. Oil and water do not mix and are immiscible.

Formation of an Aqueous Solution Aqueous solutions are those in which the solvent is water;

such as sugar (solute) dissolving in water (solvent) or salt (solute) dissolving in water (solvent).

They form in at least three ways depending on the nature of the solute: 1) by molecular solvation 2) by dissociation 3) by ionization.

Classifying Solutions : Solutions can be classified as electrolytes and

nonelectrolytes. Electrolytic solutions will conduct electricity. Nonelectrolytic solutions do not conduct electricity. An electric current involves the movement of charged particles. Solutions

containing ions will conduct electricity. (Ionic Compounds) diagnostic test of using a conductivity tester can be used to tell if

the solution conducts electricity when a light on the tester glows or the needle on the meter moves

 Acidic, Basic, or Neutral Solutions. Diagnostic Test: Litmus Paper test

Type of solute Effect on litmus paper

Acidic turns blue litmus paper redBasic turns red litmus paper blueNeutral no change in colour

Classifying Solutions : Four Possible Solutions :

Neutral Molecular, Non-electrolyte : CH3OH(aq) Acidic, Electrolyte : HBr(aq) Neutral Ionic, Electrolyte : (NH4)2SO4(aq)

Basic, Electrolyte : LiOH(aq)

Summary of Two Important Diagnostic Tests: Litmus test

- blue to red - acid ; therefore H+ present. - red to blue - base ; therefore OH- present.

 Conductivity test - conducts (acid or ionic compound) ( ie.) Electrolytes. - doesn’t conduct (neutral molecular) (ie.) Non-electrolytes.

Behaviour of substances in solution Non-electrolytes will disperse electrically neutral particles

in solution; (they do not conduct). They include neutral molecular substances.eg. C12H22O11(s) C12H22O11(aq

Individual neutral sucrose molecules separate from each other and are surrounded by water molecules.( They do not break apart into individual atoms or ions). This process is called molecular solvation.

Behaviour of substances in solution Electrolytes will disperse electrically charged particles in

solution; (they conduct). They include acids and ionic compounds (neutral ionic and bases).

IONIC COMPOUNDS : When table salt dissolves in water the NaCl molecule

separates into Na+ and Cl- ions. This process of separating ions in an ionic compound is called dissociation.

Examples :1) NaCl(s) Na+

(aq) + Cl-(aq)

(Individual ions, Na+ and Cl- , are surrounded by water molecules).2) Ba(OH)2(s) Ba2+

(aq) + 2 OH-

(aq)

Behaviour of substances in solution

ACIDS: Acids are molecular compounds and therefore have neutral

molecules. How do they become charged? When acids are placed in water, the acid separates into individual molecules. The individual molecules become ionized by the water and form positive H+ and negative ions.

Ionization is the reaction of neutral atoms or molecules of molecular compounds to form ions.

Example : HCl(g) H+(aq) + Cl-(aq)

(Hydrogen chloride gas dissolving in water to form hydrochloric acid)

“Like Dissolves Like”

ionic solutes and polar covalent solutes both dissolve in polar solvents

non-polar solutes dissolve in non-polar solvents.

Examples of the ways of forming solutions

1. NaF(s) Na+ + F-(aq)

(Dissociation)

2. (NH4)2SO4(s) 2 NH4+

(aq) + SO42-

(aq) (Dissociation)

3. HBr(g) H+(aq) + Br -

(Ionization)

4. C12 H22O11(s) C12H22O11(aq) (Molecular Solvation)

Solubility of Substances in Water:Solubility Table1. If high solubility, then it is aqueous (aq). 2. If also ionic, then the compound dissociates into separate ions.

NaBr(s) + water Na+(aq) + Br -

(aq) + H2O(l)

3. If molecular, then the compound disperses into separate molecules.

CH3OH(l) + water CH3OH(aq) + H2O(l)

4. If a strong acid, then the substance ionizes. 5. If a weak acid, then the molecules disperses. Some ionizes6. If low solubility: elements such as Zn(s) or O2(g) will remain the same in H2O(l). Some ionic compounds (check solubility table) will remain as solids in water.

Ca3(PO4)2(s) + water Ca3(PO4)2(s) + H2O(l)

7. Remember that high solubility will form an aqueous solution; while low Solubility will form a precipitate.

Identifying Ions :

The solubility table can be used in another way. Let's say you wanted to see if a solution contains hydroxide ions and sulfate ions.

What tests can you perform to identify these ions? According to the solubility table, at least two ions will form a

precipitate with sulfate but not with hydroxide. Once sulfate has been precipitated out of the solution, you can separate the precipitate and the solution by filtration and try some tests to identify the hydroxide ion.

Types of solutions :

Solubility refers to the concentration of solute in a saturated solution, at a given temperature.

A saturated solution is a solution in which no more solute will dissolve at a given temperature. If the temperature and pressure conditions change, so

does the solubility of the solute. For example, 100.0 mL of water at 25°C dissolves 36.2 g

of sodium chloride. Another example would be the solubility of Na2SO4 in water is 4.67 g/100 mL at 0 oC.

NOTE : Solubility is temperature and pressure dependent. A solution that contains less than the maximum amount of

solute at specific temperature and pressure conditions is said to be unsaturated.

Types of solutions :

A solution that contains more than the maximum amount of solute at specific temperature and pressure conditions is a supersaturated solution. Supersaturated solutions are produced by heating a saturated solution

to dissolve more solute and then cooling the solution down to a lower temperature. These solutions are not stable and crystals eventually form in them.

Crystallization is the removal of the solvent from a solution to yield the solute. When water evaporates from a saturated solution, solids crystallize out of the solution.

Solubility Rules (Generalizations)1. Temperature: A) Solids (in general): The higher the temperature, the greater the solubility of solids in water.B) Gases (in general): The higher the temperature, the lower the solubility in water.

2. Pressure:A) Solids and liquids - pressure has no effect on the solubility of solids and liquids.B) Gases - the greater the pressure, the higher the solubility of gases in water ( and vice versa)

Miscibility:

A) Liquids such as methanol and ethanol which dissolve in water, in any proportion, are miscible with water.

B) Liquids ,such as oil, which do not dissolve in water are immiscible with water.

Dynamic Equilibrium :

Equilibrium is a condition where opposing processes occur at the same rate.

A solubility equilibrium can occur in a saturated solution that contains excess solute. Particles constantly leave the solid solute to enter the solution

(dissolving) while dissolved particles return to the crystal (recrystallization).

For every particle that dissolves, one recrystallizes. The rates of change are equal so the appearance of the system is static (unchanging).

Equilibrium does not necessarily mean that the numbers of things in one condition or another are the same.

For example, in a solution containing excess solute, the amount of dissolved solute may be greater, less than, or rarely equal to the amount of undissolved solute.

The only things that have to be equal in an equilibrium are rates of change of the opposing processes.

Dynamic Equilibrium :

When a solute is first added to a solvent, the rate of dissolving is much greater than the rate of recrystallization.

However as the solution approaches saturation levels, the rate of dissolving slows down and the rate of recrystallization increases.

The point at which the rate of particles leaving the crystal equals the rate of particles returning to the crystal is called an equilibrium.

It is a dynamic equilibrium because the opposing changes continue to occur, but since they occur at the same rate the system displays no visible changes.

It requires a closed system where no substance can enter or leave the system. The rates of dissolving and crystallizing are equal, but the total amount of solute and solvent are not necessarily equal.

Concentration of a Solution :

Concentration is the ratio of the quantity of solute to the quantity of solution.

Generally, concentrated means a high amount of solute relative to the amount of solvent and dilute means a low amount of solute relative to the amount of solvent.

A solution that is described as dilute when compared to one solution may be described as concentrated when compared to another.

Molar Concentration

Review:

- Find the molar mass of Ca(OH)2

- How many moles in 45.67 g of Ca(OH)2?

- Find the mass of 0.987 mol of Ca(OH)2.

Molar Concentration

The terms concentrated and dilute are qualitative descriptions of solubility.

A quantitative measure of solubility uses numbers to describe the concentration of a solution.

Molar Concentration

The MOLAR CONCENTRATION of a solution is the number of moles of solute (n) per litre of solution (v).

The unit for molar concentration is mol/L or (e.g. 1.0 mol/L). The symbol M is sometimes used to represent this unit (e.g. 1.0 M).

Molar Concentration

FORMULA:

Molar Concentration = number of moles

volume in litres

C = n

V

eg. Calculate the molar concentration of: 4.65 mol of NaOH is dissolved to

prepare 2.83 L of solution.

15.50 g of NaOH is dissolved to prepare 475 mL of solution.

Eg. Calculate the following:

a) the number of moles in 4.68 L of 0.100 mol/L KCl solution.

b) the mass of KCl in 268 mL of 2.50 mol/L KCl solution.

c) the volume of 6.00 mol/L HCl(aq) that can be made using 0.500 mol of HCl.

d) the volume of 1.60 mol/L HCl(aq) that can be made using 20.0 g of HCl.

Dilution (p. 272) Acids and sodium hydroxide are common examples

of substances that are sold as concentrated solutions.

They tend to be called stock solutions. There may be times when you have to dilute a stock solution to a lower molar concentration.

When a solution is diluted: The concentration decreases The volume increases The number of moles remains the same

ni = nf

Dilution (p. 272) ni = nf

Ci Vi = Cf Vf

eg. Calculate the molar concentration of a vinegar solution prepared by diluting 10.0 mL of a 17.4 mol/L solution to a final volume of 3.50 L.

Solution Preparation & Dilution standard solution – a solution of known

concentration volumetric flask – a flat-bottomed glass vessel

that is used to prepare a standard solution delivery pipet – pipets that accurately measure

one volume graduated pipet – pipets that have a series of

lines that can be use to measure many different volumes

To prepare a standard solution:

1. calculate the mass of solute needed

2. weigh out the desired mass

3. dissolve the solute in a beaker using less than the desired volume

4. transfer the solution to a volumetric flask (rinse the beaker into the flask)

5. add water until the bottom of the meniscus is at the etched line

To dilute a standard solution: 1. Rinse the pipet several times with

deionized water. 2. Rinse the pipet twice with the

standard solution. 3. Use the pipet to transfer the required

volume. 4. Add enough water to bring the

solution to its final volume.

Percent Concentration Concentration may also be given as a %. The amount of solute is a percentage of

the total volume/mass of solution. liquids in liquids - % v/v solids in liquids - % m/v solids in solids - % m/m

Percent Concentration

100x(mL) solutionofvolume

(g) soluteofmass(m/v)Percent

100x(g) solutionofmass

(g) soluteofmass(m/m)Percent

100x(mL) solutionofvolume

(mL) soluteofvolume(v/v)Percent

Concentration in ppm and ppbParts per million (ppm) and parts per

billion (ppb) are used for extremely small concentrations

eg. 5.00 mg of NaF is dissolved in 100.0 kg of solution. Calculate the concentration in:

a) ppm

b) ppb

ppm = 0.005 g x 106

100,000 g

= 0.05 ppm

ppb = 0.005 g x 109

100,000 g

= 50.0 ppb

Solution Stoichiometry

1. Write a balanced equation

2. Calculate moles given

n=m/M OR n=CV3. Mole ratios

4. Calculate required quantity

nMmORV

nCOR

C

nV

Solution Stoichiometry

eg. 45.0 mL of a HCl(aq) solution is used to neutralize 30.0 mL of a 2.48 mol/L NaOH solution.

Calculate the molar concentration of the HCl(aq) solution.

Sample Problems1. What mass of copper metal is needed

to react with 250.0 mL of 0.100 mol/L silver nitrate solution?

2. Calculate the volume of 2.00 M HCl(aq) needed to neutralize 1.20 g of dissolved NaOH.

3. What volume of 3.00 mol/L HNO3(aq) is needed to neutralize 450.0 mL of 0.100 mol/L Sr(OH)2(aq)?

Sample Problem Solutions

Cu(s) + 2 AgNO3(aq) → 2 Ag(s) + Cu(NO3)2(aq)

Sample Problem Solutions

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

Sample Problem Solutions

2 HNO3(aq) + Sr(OH)2(aq) →

2 H2O(l) + Sr(NO3)2(aq)

The Solution Process (p. 299)

Dissociation occurs when an ionic compound breaks into ions as it dissolves in water.

A dissociation equation shows what happens to an ionic compound in water.

eg. NaCl(s) → Na+(aq) + Cl-(aq)

K2SO4(s) → 2 K+(aq) + SO4

2-(aq)

The Solution Process (p. 299)

Acids form ions when dissolved in water.

eg. H2SO4(aq) → 2 H+(aq) + SO4

2-(aq)

HCl(s) → H+(aq) + Cl-(aq)

The molar concentration of any dissolved ion is calculated using the ratio from the dissociation equation.

eq. What is the molar concentration of each ion in a 5.00 mol/L MgCl2(aq) solution:

5.00 mol/L 5.00 mol/L 10.00 mol/L

Concentration of Ions in Solution

Examples:

1.In a 0.23 mol/L of Al2(SO4)3 solution, what is the molar concentration of each ion?

Examples:

2. A solution contains 9.61 g of (NH4)2CO3 ,(ammonium carbonate), dissolved in water to form 400. mL of solution. What is the concentration of each ion in the solution?

Examples:

3. In an ammonium dichromate solution where the concentration of the ammonium ion is 0.0466mol/L, what is the concentration of the solute?

Examples:

4. What mass of calcium chloride is required to prepare 2.00 L of 0.120 mol/L Cl-(aq) solution?