solutions and solubility. what is a solution? homogeneous mixture (one phase) consists of a solvent...
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Solutions and Solubility
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What is a Solution?
• Homogeneous mixture (one phase)
• Consists of a solvent and one/or more solute– Solvent is the “bigger” part – it is the part that
does the dissolving– Solute is the “smaller” part – it is dissolved in
the solvent
• A solution can be acidic (turn litmus RED), basic (turn litmus BLUE) or neutral (no change in litmus colour)
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Aqueous (aq) Solutions• Water is the solvent “universal
solvent”• Can be a(n):
– Electrolyte: conducts electricity• Ionic compounds (NaCl, KBr, etc)
• Bases (NaOH, KOH, etc)
• Acids (HCl, acetic acid, etc)
– Non-electrolyte: does NOT conduct electricity
• Molecular compounds (methanol, sugar)
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Electrolytes: Dissociation
• When you dissolve a solid in a solvent (eg. water), the solid dissociates (breaks apart) into charged IONS.– Dissolve salt (NaCl) into water, separates into charged
Na+ and Cl- ions. These ions can move from one point in a solution to another.
– Solid ionic compounds (salt itself) cannot conduct electricity because it is not mobile.
• Non-electrolytes can dissolve in water, but do not dissociate = no charged particles = no electricity.
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States of Solutions• Solutions need not have liquid/liquid has solute and
solvent. Solutions can exist in all 3 states (g, l, s)
Solute Solvent Example
Gas Gas
Gas Liquid
Solid Gas
Solid Solid
Humidity
Scuba diver tank
Butane lighter
Metal alloys (eg. Sterling silver – Ag/Cu)
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Solubility• The ability of a solute to dissolve in a
solvent
• Formal definition: the quantity of a solute that will dissolve in a specific amount of solvent at a given temperature
**It is NOT “the rate” that a solute will dissolve in a solvent (how fast).**
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• Saturated solution - a stable solution in which the maximum amount of solute has been dissolved.
• Unsaturated solution - a solution that contains less solute than a saturated solution under existing condition
• Supersaturated solution - a solution that temporarily contains more than the saturation amount of solute than the solvent can hold (unstable)
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Factors that affect Solubility
1. Nature of solute and solvent• “Like dissolves like” = rule of thumb to
predict solubility• Polar/polar & non-polar/non-polar = SOLUTION
• Depends on:• Intermolecular forces (forces within
molecules)• Type of bonding (I, C, PC)• Polarity
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Solubility of Polar Covalent Substances in Water
• The partial charges in a polar substance are attracted to the opposite partial charge in water’s polar molecules.
• As a result water molecules surround the polar molecules, causing them to dissolve.
Methanol in water intermolecular forces are hydrogen bonds
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Solubility of Ionic Compounds in Water• When a soluble ionic compound
dissolves in water, the attraction between the two ions is broken and the two ions are surrounded by molecules of water.
• Solubility therefore is the result of ion-dipole attraction.
• Some ionic compounds are not soluble in water. This is the result of the very strong attractions of their ions (eg. AgCl)
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2. Pressure
• Little effect on solubility of liquids/solids in liquid solvents
• However, for a gas in a liquid solvent, the solubility ↑ when pressure ↑.
• Pressure acts to keep gases from escaping the solution
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3. Temperature
• The solubility of a gas in a liquid solvent ↑ when temperature ↓.
– What foams more? – Warm pop or cold pop?
• The solubility of a solid in a liquid solvent usually ↑ with an ↑ in temperature.
– What dissolves more?– Tea in cold water or hot water?– Note - If you have a saturated solution,
solubility can be ↑ if you raise the temperature.
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Explain the solubility of a cold can of pop that is opened and left at room temperature pressure and temperature!
• Pop has gaseous CO2 in liquid solvent the solubility ↑ when pressure ↑. So pressure is higher in the sealed can. When opened, the pressure ↓, and solubility ↓ too. So CO2 escapes over time due to this less fizz (and less taste).
• The solubility of a gas in a liquid solvent ↑ when temperature ↓.
• When kept cold, CO2 tends to stay in solution = more fizz (and more taste). As pop warms up, solubility ↓, so CO2 escapes over time less fizz (and less taste).
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Solubility and Formation of a Precipitate
• In single and double displacement reactions, you can predict the formation of a precipitate (a solid formed in a liquid) by finding out the solubility of the products.
• Low solubility = generally insoluble (precipitate forms)
• High solubility = generally soluble (no precipitate)
***Note: If BOTH products are soluble in water, then there is NO reaction!***
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Example 1Determine the products (if any) when a solution of sodium sulfate is mixed with a solution of lead(II) nitrate. If a reaction occurs, summarize the reaction as a balanced chemical equation.
Na2SO4 (aq) + Pb(NO3)2 (aq) NaNO3 + PbSO4 2 (aq) (s)
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Example 2Determine the products (if any) when a solution of sodium acetate is mixed with a solution of potassium chloride. If a reaction occurs, summarize the reaction as a balanced chemical equation.
NaCH3OO (aq) + KCl (aq) NaCl + KCH3COO (aq) (aq)
NO REACTION!
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Total Ionic and Net Ionic Equations
When you have a chemical reaction, you know the reactants and products. But the chemical equation does not tell you WHICH ions are actually involved in the reaction.
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Total Ionic and Net Ionic Equations
Total Ionic Eq’n – shows all the soluble compounds written in their dissolved form and all the insoluble compounds written normally as compounds.
Net Ionic Eq’n – shows ONLY the ions that are actually involved in the reaction. The ions that are NOT involved are known as spectator ions.
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Example 1
Write the total ionic equation and net ionic equation between sodium chloride and lead(II) nitrate.
NaCl (aq) + Pb(NO3)2 (aq) NaNO3 + PbCl2 22 (aq) (s)
TOTAL IONIC EQ’N:
2Na+ (aq) + 2Cl- (aq)+ Pb2+ (aq) + 2NO3- (aq) 2Na+ (aq) + 2NO3
- (aq) + PbCl2 (s)
NET IONIC EQ’N:
Pb2+ (aq) + 2Cl- (aq) PbCl2 (s)
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Example 2
Write the total ionic equation and net ionic equation between barium chloride and silver nitrate.
BaCl2 (aq) + AgNO3 (aq) Ba(NO3)2 + AgCl2 2(aq) (s)
TOTAL IONIC EQ’N:
Ba2+ (aq) + 2Cl- (aq) + 2Ag+ (aq)+ 2NO3- (aq) Ba2+ (aq) + 2NO3
- (aq) + 2AgCl (s)
NET IONIC EQ’N:
2Ag+ (aq) + 2Cl- (aq) 2AgCl (s)