Examples: .ro?NHatcaqtPoEcaqgMgcoH)zcs Examples ¢â‚¬¢ A saturated solution...

Examples: .ro?NHatcaqtPoEcaqgMgcoH)zcs Examples ¢â‚¬¢ A saturated solution (ionic solution at equilibrium)
Examples: .ro?NHatcaqtPoEcaqgMgcoH)zcs Examples ¢â‚¬¢ A saturated solution (ionic solution at equilibrium)
Examples: .ro?NHatcaqtPoEcaqgMgcoH)zcs Examples ¢â‚¬¢ A saturated solution (ionic solution at equilibrium)
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Transcript of Examples: .ro?NHatcaqtPoEcaqgMgcoH)zcs Examples ¢â‚¬¢ A saturated solution...

  • 1

    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) + PO43-(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)

    77

    ← bigger component of Solin

    eg) usually H2O, acetone

    eg) vinegar - Ctb COOHH COOH (carboxylic{ OH ''de},metalOH metal 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 n butthey are not acid nor base

    eg ) Which is the strongest electrolyte ? (Data page 5) A. coppe44IiFfpnospGateB.nPau@c.ammlomntiumssuifateo

    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) ! Mg 2+

    (aq) + 2OH-(aq) Crystallization Reaction: Mg2+(aq) + 2OH-(aq) ! Mg(OH)2(s)

    78

    old saturated

    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 solubility Mol/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 is

    reached

    Mg(OH)zcs, → Mg Zt t 20ft

    - Microscopic changes Cag) Cag) occur

    Mg Tag, t 2OHIag, → Mg COHL Cs)

  • 3

    Example:

    79

    Solubility depends on

    % :*:: : :O::: Temperature