Dec 25, 2015
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.
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 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.
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.
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.
Solubility of LiquidsSolubility of Liquids Dynamic Equilibrium: number of particles dissolving is
equal to the number of particles 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
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-
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+
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