examples: .ro?nhatcaqtpoecaqgmgcoh)zcs examples · • a saturated solution (ionic solution at...
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Chemistry 12 Unit III – Solubility Notes
III.1 – A Review of Solubility
• Recall that Solution = Solute + Solvent
• There are only three classes of compounds that form ionic solutions: ACIDS, BASES and SALTS. This unit will deal only with SALTS. Acids and bases will be thoroughly covered in the next unit.
• Acids… inorganic acids begin with H whereas organic acids end with COOH
• Bases… inorganic bases end with OH. Common bases contains GRP I or II metals.
• Salt… combination of metal and non-metal or contains polyatomic ion
Electrolyte: A substance that dissolves to give an electrically conducting solution containing ions. AKA ionic solution. Examples: (NH4)3PO4(s) ! 3 NH4+(aq) + PO4
3-(aq) HCl(s) ! H+(aq) +Cl-(aq)
Non-Electrolyte: A substance that dissolves to give a solution that does not conduct electricity and contains only molecules. AKA molecular solution. Examples: C12H21O11(s) ! C12H21O11(aq)
Br2(l) ! Br2(aq)
• Electrical conductivity requires the presence of ions in solution. The more ions present, the greater the electrical conductivity.
• In summary, we can have either a molecular solution, which contains only neutral molecules, or an ionic solution, which contains ions. How can we recognize ahead of time whether a molecule will form an ionic or molecular solution?
Ionic or Molecular Solution: General Rules
I. A compound made up of a metal and a non-metal is likely to be ionic in solution.
FeCl3(s) ! Fe3+(aq) + 3 Cl-
(aq)
II. A compound made up of a polyatomic ion(s) will be ionic in solution.
NH4NO3(s) ! NH4+
(aq) + NO3-(aq)
III. Covalent compounds (NON-METAL + NON-METAL), especially organic compounds, generally form molecular solutions.
CH3OH(l) ! CH3OH(aq)
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← bigger component of Solin
eg) usually H2O, acetone
eg) vinegar - Ctb COOHH COOH (carboxylic{ OH''
de},metalOHmetal non-metal polyatomic ion eg)N④
Salt crystallization(NH④P⑧cs) E*.ro?NHatcaqtPoEcaqgMgcoH)zcs) S MgYatg,T2OHIaq)base
table sugar→ C,zH21011 Cag)421421011 CS)
Brace) → Brzcaq)
ion= Stronger electrolyte .
metal non-metal⇐ stronger electrolyte
polyatomic compared to
NH4NO3
Non-metal t non-metal nbutthey are not acid nor base
eg ) Which is the strongest electrolyte ? (Data page 5)A. [email protected]
CH3 OH* Methanol
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• Salts are ionic compounds that differ in their ability to dissolve in water. All salts dissolve in water to produce electrolyte solutions. Some dissolve more than others = stronger electrolyte. How much a salt can dissolve in water is expressed as solubility.
The “old,” Chemistry 11 definition of solubility was:
Solubility: the maximum amount of substance that can dissolve in a given amount of solvent at a given temperature.
• A solution, which has dissolved the “maximum amount” of a substance, is said to be saturated. Once a solution has been saturated with a substance, the addition of more of the substance will simply cause this extra material to accumulate in undissolved form (usually on the bottom of the container).
Saturated Solution: A solution in which there exists a dissolved substance in equilibrium with the undissolved substance
• In contrast, an unsaturated solution contains less than the maximum amount of a substance, which can dissolve. So that there is no undissolved solid present and no equilibrium exists.
• The chemistry 12 definition of solubility is:
Solubility: the equilibrium concentration of the substance in solution at a given temperature. • The common method to determine solubility is to take an accurately measured volume of a saturated
solution and boil it dry. The mass of the dry solute is weighed and concentration can be calculated by moles / litres.
• The solubility is referred to as the MOLAR SOLIBILITY when the concentration of the salt is expressed in “moles/litre” or “M”. Solubility is also commonly expressed in “gram/litre” or “gram/100 ml”. Note that the solubility refers to the salt, not the ions.
• A saturated solution (ionic solution at equilibrium) must meet two conditions:
1. Some undissolved material must be present.
2. Equilibrium must exist between the dissolved and undissolved material.
• We can show that a solution is saturated by writing an equilibrium equation:
Mg(OH)2(s) ⇌ Mg2+(aq) + 2OH-
(aq)
This equation is interpreted as follows:
When solid Mg(OH)2 dissolves and enters the solution we have two opposing reactions:
Dissolving Reaction: Mg(OH)2(s) ! Mg2+(aq) + 2OH-
(aq)
Crystallization Reaction: Mg2+(aq) + 2OH-
(aq) ! Mg(OH)2(s)
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oldsaturated
Undissolved
saturated = at equilibrium
N④,
The* amount of solute needed to produce saturated Soth
(using a given amount of H2O at some T.anumber
molar solubilityMol/L M g l L
91100ML
① Some undissolved solute is visible
② There is an equilibrium
fytaateesareaoeonrstant[pro] t [Rea ]←Salt Cs) → catctaggt AnIag) No macro change
A particular keg isreached
Mg(OH)zcs, → MgZtt 20ft
- Microscopic changesCag) Cag) occur
Mg Tag, t 2OHIag, → Mg COHL Cs)
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Example:
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Solubility depends on
% :*:: : :O:::Temperature