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SCH 3U1 1. Solubility of Ionic Compounds 2 All solutes will have some solubility in water. “Insoluble” substances simply have extremely low solubility.

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Presentation on theme: "SCH 3U1 1. Solubility of Ionic Compounds 2 All solutes will have some solubility in water. “Insoluble” substances simply have extremely low solubility."— Presentation transcript:

1 SCH 3U1 1

2 Solubility of Ionic Compounds 2 All solutes will have some solubility in water. “Insoluble” substances simply have extremely low solubility. low partial high solubility solubility solubility ( 1 g/100mL) “insoluble” “soluble”

3 Dissociation in Water Ionic compounds dissociate (break up) into ions when they form a solution:dissociate MgCl 2 (s) Mg 2+ (aq) + Cl - (aq) Positive ions are called cations. Negative ions are called anions. Dissociation equations show the number of each cation and anion produced by a compound when it dissolves in an aqueous solution. They must be balanced! 3 2

4 Examples: Na 3 PO 4 (s) Mg(NO 3 ) 2 (s) (NH 4 ) 2 SO 4 (s) 4 3 Na + (aq) + PO 4 3- (aq) Mg 2+ (aq) + 2NO 3 - (aq) 2NH 4 + (aq) + SO 4 2- (aq) Note that water (H 2 O) does not appear in dissociation equations!

5 Factors Affecting Solubility of Ionic Compounds in Water 1) The Charge on an Ion as ionic charge increases, the attraction between ions increases therefore as charge increases, solubility ________________ e.g. salts containing fluoride (F - ) ions are __________ soluble than salts containing oxide (O 2- ) ions 5 decreases more Solubility at 25 0 C: MgO : g/ 100 mL water MgF 2 : g / 100 mL water

6 Factors Affecting Solubility of Ionic Compounds in Water 2) Ion Size smaller ions form shorter ionic bonds these bonds are _____________ than bonds between larger ions with the same charge therefore as ion size increases, solubility ___________ e.g. fluoride salts are ________ soluble than chloride salts 6 increases stronger less Solubility at 25 0 C: MgF 2 : g/ 100 mL water MgCl 2 : 54 g / 100 mL water MgBr 2 : 101 g / 100 ml water

7 Predicting Solubility Predict which compound will be more soluble: Correct Answer? a) NaF vs. CaF 2 b) Ca(NO 3 ) 2 vs. CaSO 3 c) NaBr vs. NaCl 7 NaF Ionic charge: Na + vs. Ca 2+ Ca(NO 3 ) 2 NaBr Ionic charge: NO 3 - vs. SO 3 2- Ion size: Br - > Cl -

8 The Solubility Rules The following rules are useful for predicting if a salt is soluble or insoluble: Soluble: Compounds containing ammonium (NH 4 + ) or alkali metal ions (Li +, Na +, K +, Rb +, Cs + ) are soluble. Compounds containing the nitrate ion (NO 3 - ) are always soluble. Compounds containing Cl -, Br - or I - ions are soluble… except with Ag +, Pb 2+, Hg 2+ Compounds containing the sulfate ion (SO 4 2- ) are soluble…except with Ca 2+, Sr 2+, Ba 2+, Ra 2+, Pb 2+. 8

9 The Solubility Rules Insoluble: Compounds containing carbonate, phosphate or hydroxide ions (CO 3 2-, PO 4 3-, OH - ) are insoluble…. except with NH 4 +, Li +, Na +, K +, Rb +, Cs + 9

10 The Solubility Rules on the Periodic Table InsolubleSoluble CO 3 2-, PO 4 3-, OH - except with NH 4 +, Li +, Na +, K +, Rb +, Cs + NO 3 - NH 4 +, Li +, Na +, K +, Rb +, Cs + Cl -, Br -, I - except with Ag +, Pb 2+, Hg +. SO 4 2- except with Ca 2+, Sr 2+, Ba 2+, Ra 2+, Pb

11 Making Predictions Use the solubility rules to predict if the following compounds are soluble or insoluble. a) Mg(NO 3 ) 2 c) (NH 4 )CO 3 b) NaCld) Ca 3 (PO 4 ) 2 11 soluble insoluble

12 Mixing Solutions What will happen if two solutions are mixed? e.g. sodium chloride (aq) + potassium nitrate (aq) NaCl (aq) Na + (aq) + Cl - (aq) KNO 3 (aq) K + (aq) + NO 3 - (aq) Answer: NOTHING!!!!! All possible salts soluble! 12

13 Mixing Solutions What will happen if two solutions are mixed? e.g. iron (III) nitrate (aq) + potassium hydroxide(aq) Fe(NO 3 ) 3 (aq) Fe 3+ (aq) + 3 NO 3 - (aq) KOH (aq) K + (aq) + OH - (aq) Answer: A PRECIPITATION OCCURS 13

14 Precipitation Reactions These are double displacement reactions that occur when 2 solutions are mixed and a solid (insoluble) product is formed. Using the solubility rules, we can predict if a precipitation reaction will occur and the product(s) formed. e.g.1 sodium carbonate (aq) + barium chloride (aq) e.g.2 potassium nitrate (aq) + copper (II) chloride (aq) 14


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