SALTS

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SALTS

• METHODS OF PREPARATION

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Recap of Previous Session

• About salts
• What type of compound are salts?
• ANS IONIC compound
• What are some of the salts you have learnt?
• ANS Chlorides, Nitrates, Sulphates, carbonates,
  etc.
• Solubility of salts in water
• What are some of the soluble salts?
• ANS All sodium, potassium, and ammonium salts
• What are some of the insoluble salts?
• ANS Most carbonates, some chlorides, etc.

X-word Puzzle
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Objectives Of Todays Lesson

• To understand the factors determining the method
  of preparation.
• To learn the techniques use in the preparation
  of
• insoluble salt
• soluble salt (Part 1)
• To use the laboratory techniques learned before
• separation technique (for a solid-liquid mixture)
• purification technique (for a solute in solvent)

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METHODS OF PREPARATION

• The method of preparation of any salt depends on
  2 main factors
• the solubility of the salt in water
• Why is this important?
• Determine the reactants to be used
• one of the products must be water
• Determine the purification method
• the solubility in water of the reactants used.
• Why is this important?
• Determine if any one of them need to be in excess
• Determine the separation and purification method

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DECISION-MAKING
Is the salt soluble?
Is the cation Na, K, or NH4?
To be discussed today
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EXAMPLE (1)

• You are required to prepare Lead (II) Sulphate.
• Is Lead (II) Sulphate a salt?
• YES
• Is it a soluble salt?
• NO
• What preparation method can be used?
• IONIC PRECIPITATION
• What is the cation required, and hence possible
  reactant?
• Pb2
• Pb(NO3)2 (a soluble salt)
• What is the anion required, and hence possible
  reactant?
• SO42-
• Na2SO4 (a soluble salt)

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INSOLUBLE SALT

• Prepared by ionic precipitation.
• METHOD
• Aqueous salt solution containing the cation
• Aqueous salt solution containing the anion
• or an acid with the anion as its conjugate base.
• Filter to remove the precipitate (ppt).
• Wash the ppt with small amount of distilled
  water.
• Purpose to remove impurities
• Dry the precipitate on the filter paper.

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LEAD (II) SULPHATE (STEP 1)

• STEP (1) Precipitation
• Put lead (II) nitrate solution into a small
  beaker.
• Add sodium sulphate solution (in excess) until no
  more ppt forms.

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LEAD (II) SULPHATE (STEP 2)

• Step (2) Filtering
• Filter to remover the ppt.

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LEAD (II) SULPHATE (STEP 3)

• Step (3) Washing
• Wash the ppt with a small amount of distilled
  water to remove the impurities.

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LEAD (II) SULPHATE (STEP 4)

• Step (4) Drying
• Allow the ppt to dry.

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EXAMPLE (2)

• You are required to prepare Zinc Nitrate salt.
• Is Zinc Nitrate a soluble salt?
• YES
• Is the cation Group I element (Na or K) or
  NH4?
• NO
• What method of preparation will you use?
• Acid Metal Zinc
• What acid will you use to get the anion NO3-?
• Nitric acid (HNO3)
• Which reactant will you use in excess?
• Zinc metal
• Why?
• Excess can be removed by filtration
• If HNO3 (aq) is in excess, cannot be removed,
  hence impurity.

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SOLUBLE SALTS

• Possible Method of Preparation (1)
• Acid Metal
• METHOD
• React the acid with excess metal powder.
• Filter to remove the excess metal powder.
• Concentrate the filtrate to saturation point by
  evaporation.
• Test for saturation using a glass rod.
• Stand aside for crystallisation to take place.
• Filter to remove the excess solution.
• Dry the crystal on the filter paper.

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ZINC NITRATE (STEP 1)

• Step (1) Reaction
• Put some dilute HNO3 in a beaker.
• Add zinc powder, stirring constantly until no
  more zinc will dissolve in the acid.

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ZINC NITRATE (STEP 2)

• Step (2) Filtration
• Filter to remove excess zinc powder.

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ZINC NITRATE (STEP 3)

• Step (3) Evaporation / Concentration
• Evaporate the water to make a saturated solution.

heat
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ZINC NITRATE (STEP 4)

• Step (4) Testing for saturation
• Dip a glass rod into the solution to test if it
  is saturated.
• If yes, crystal can be seen forming on the glass
  rod.

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ZINC NITRATE (STEP 5)

• Step (5) Crystallisation
• Let the saturation solution stand for
  crystallisation to take place.

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ZINC NITRATE (STEP 6)

• Step (6) Filtration
• Filter off the excess zinc nitrate solution.

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ZINC NITRATE (STEP 7)

• Step (7) Drying
• Dry the crystal on a filter paper.

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EXAMPLE (3)

• You are required to prepare Copper Sulphate.
• Is Copper Sulphate a soluble salt?
• YES
• Is the cation Group I element (Na or K) or
  NH4?
• NO
• What method of preparation will you use?
• Acid Metal Oxide
• Why?
• Copper cannot displace H in the acid.
• What acid will you use to get the anion SO42-?
• Sulphuric acid (H2SO4)
• Which reactant will you use in excess?
• Copper Oxide powder
• Excess can be removed by filtration

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SOLUBLE SALTS

• Possible Method of Preparation (2)
• Acid Metal Oxide
• METHOD
• React the acid with excess metal oxide powder.
• Filter to remove the excess metal oxide powder.
• Concentrate the filtrate to saturation point by
  evaporation.
• Test for saturation using a glass rod.
• Stand aside for crystallisation to take place.
• Filter to remove the excess solution.
• Dry the crystal on the filter paper.

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COPPER SULPHATE (STEP 1)

• Step (1) Reaction
• Put some dilute H2SO4 in a beaker over heat.
• Add copper oxide powder, stirring constantly
  until no more copper oxide powder will dissolve
  in the acid.

heat
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ZINC SULPHATE (STEP 2)

• Step (2) Filtration
• Remove excess copper oxide powder.

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ZINC SULPHATE (STEP 3)

• Step (3) Evaporation / Concentration
• Evaporate the water to make a saturated solution.

heat
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ZINC SULPHATE (STEP 4)

• Step (4) Crystallisation
• Let the saturation solution stand for
  crystallisation to take place.
• Note that the other steps are similar, so they
  are not repeated in this example.

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Practice

• Complete Question 1 to 4 of pg 204 of your
  textbook

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Conclusion

• You have learned the following today
• know the factors to consider when preparing a
  salt.
• how to decide what method of preparation to use.
• how to prepare an insoluble salt.
• how to prepare a soluble salt by 2 methods.
• observe the application of the separation and
  purification techniques you have learned in
  earlier chapter.