Ch 9 Salts

• What is a salt?

  An ionic compound that consists of a cation and anion
• What salts are soluble?

  All Sodium Potassium Ammonium Nitrate salts

  all chlorides -> except Silver, Lead (II) chloride

  all sulfates - except Calcium, Lead (II), Barium sulfate

  Sodium carbonate

  Potassium carbonate

  Ammonium carbonate
• What salts are insoluble?

  Silver chloride, Lead (II) chloride

  Calcium sulfate, Lead (II) sulfate, Barium sulfate

  All carbonates -> except Sodium, Potassium, Ammonium carbonate
• What are the factors of preparing salts?

  Solubility of salt in water

  Solubility of starting materials in water
• What are the factors of Method 1: Reaction of acid with insoluble substance?

  salt to be prepared is soluble in water

  both starting materials insoluble in water
• What are the factors of Method 2: Titration?

  salt to be prepared is soluble in water

  both starting materials soluble in water
• What are the factors of Method 3: Precipitation?

  salt to be prepared is insoluble in water
• Describe method 1: reaction of acid with insoluble substance

  Involves: acid + excess metal -> salt + hydrogen gas

  acid + excess insoluble base -> salt + water

  acid + excess insoluble carbonate -> salt + water + carbon dioxide

  Base / carbonate must be in excess and insoluble in water

  All acid should be reacted

  Excess reactant can be removed by filtration
• Describe method 2: titration

  Involves: acid + alkali -> salt + water

  acid + soluble carbonate -> (soluble) salt + water + carbon dioxide

  Both reactants soluble

  Volume of both starting materials should be exact

  -> starting material cannot be removed from salt solution by filtration, salt produced is impure

  Involves only Sodium, Potassium, Ammonium salts
• Describe method 3: precipitation

  general equation to precipitate salt:

  (aq) solution AB + (aq) solution XY -> insoluble salt AY + (aq) solution XB

  AB contains A+ cations, XY contains Y- anion

  Method is used for insoluble salts as salts can be separated from starting materials by filtration
• Describe method 3: precipitation procedure

  1)Add excess reactant to acid

  2)Filter to collect residue

  3)Rinse residue with distilled water to remove impurities

  4) Dry residue between a few sheets of filter paper
• Describe method 2: titration procedure

  1)Titrate aqueous reactant with acid using an indicator, titrate until end point

  2) Record volume of aqueous reactant used

  3)Repeat the titration without the indicator using the recorded volume of aqueous reactant used

  4)Evaporate until solution is saturated

  5)Allow the solution to cool.

  6)Filter to obtain crystals

  7)Rinse the crystals with small amounts of cold distilled water
• Describe procedure of method 1: reaction of acid with insoluble substance

  1)Add excess reactant to acid

  2) Filter to remove excess reactant, collect filtrate

  3) Heat filtrate until saturated

  4) Allow saturated solution to cool so salt crystallises

  5) FIlter to collect crystals, rinse crystals with small volume of cold distilled water to remove impurities.

  Dry crystals between a sheets of filter paper.
• Method 1: Reaction of acid with insoluble substance is not suitable for:

  very reactive metals as they react violently, and is extremely dangerous

  unreactive metals as they do not react with dilute acids
• What are examples of too reactive metals?

  Sodium -> react explosively

  Potassium -> react explosively

  Calcium -> react violently
• Why can't you add excess acid in Method 1?

  Acid is difficult to remove from salt after reaction

  while excess insoluble reactant is easy to remove using filtration
• Why is it not ideal to use the Universal indicator as an indicator during titration?

  It gives a gradual colour change instead of single, sharp colour change for titration
• Colours and test of gases

  H2 -> colourless, odourless -> burning split at mouth of test tube extinguishes with a 'pop sound'

  O2 -> colourless, odourless -> glowing splint into test tube rekindles

  CO2 -> colourless, odourless -> bubbled gas through limewater forms white precipitate

  Cl2 -> yellow-green with pungent smell -> damp blue litmus paper turns red

  NH3 -> colourless with pungent smell -> damp red litmus paper turns blue
• iron solutions -> green-yellow

  copper solutions -> blue-green