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SALTS……..continuation of

Acids and Alkalis

Overview of Today’s Lesson

What are Salts?

Uses of Salts

Methods of Preparing Salts

What is a Salt?Recap: Reactions of Acids

✽ Acids + Metal

✽ Acids + Carbonate

✽ Acids + Alkalis

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What is a Salt?Recap: Reactions of Acids

✽ Acids + Metal

✽ Acids + Carbonate

✽ Acids + Alkalis

Salt + H2 (g)

2HCl + Zn ZnCl2 + H2

2HCl + CaCO3 CaCl2 + CO2 + H2O

Salt + CO2 (g) + H2O (l)

Salt + H2O(l) HCl + NaOH NaCl + H2O

What is a Salt? A salt is a compound formed when the hydrogen of

an acid is replaced by a metal.

They are made when acids react with a metal, an alkali or a metal carbonate.

Mg + 2HCl → MgCl2 + H2

acid

metal

NaOH + HNO3 → NaNO3 + H2O

acid

metal

What is a Salt?

Different acids form different salts.

The salts of sulfuric acid are known as sulfates.

The salts of hydrochloric acid are known as chlorides.

The salts of nitric acid are known as nitrates.

Some Acids and their Salts

Hydrochloric acid HCl

Sodium chloride

Magnesium chloride

Copper(II) chloride

Aluminium chloride

NaCl

CuCl2

AlCl3

MgCl2

Some Acids and their Salts

Sulfuric acid H2SO4

Sodium sulfate

Copper(II) sulfate

Aluminium sulfate

Na2SO4

CuSO4

Al2(SO4 )3

Some Acids and their Salts

Nitric acid HNO3

Sodium nitrate

Potassium nitrate

Copper(II) nitrate

Aluminium nitrate

NaNO3

Cu(NO3)2

Al(NO3)3

KNO3

Importance of Salts Salts are important to our bodies. They help

us maintain the concentration of our body fluids.

We lose salt from our bodies through sweat and urine.

Salt must be replaced through food and drinks.

Uses of some salts1) Silver salts in photography eg. silver bromide (AgBr) A component on photographic film. A pale-yellow, insoluble, very sensitive to light. It turns black on exposure to light.

Uses of some salts

2) Food preservatives eg. sodium sulphite, sodium nitrite, sodium

citrate

Uses of some salts

3) Food flavourings eg. sodium chloride (salt),

monosodium glutamate (MSG)

4) Medical uses eg. calcium sulfate in plaster of Paris

Uses of some salts5) Fertilisers in agriculture eg. ammonium sulfate

6) Chemicals in industry eg. sodium chloride

Test your understanding1. Identify the acids needed to prepare the following

salts.

2. State the alkali that can react with the acid you mentioned in Question 1 to produce the three salts.

SALTS ACID NEEDED ALKALI

Potassium nitrate

Sodium sulfate

Aluminium ethanoate

Test your understanding1. Identify the acids needed to prepare the following

salts.

2. State the alkali that can react with the acid you mentioned in Question 1 to produce the three salts.

SALTS ACID NEEDED ALKALI

Potassium nitrate

Nitric acid

HNO3

Potassium hydroxide

KOH

Sodium sulfate

Sulfuric acid H2SO4

Sodium hydroxide

NaOH

Aluminium ethanoate

Ethanoic acid CH3COOH

Aluminium hydroxide

Al(OH)3

Methods of Preparing Salts

Depends on: Solubility of Salts in water;

Solubility of the chemicals used to prepare the salts.

• Acid + (Insoluble) Metal

Acid + Insoluble Carbonate

Preparation of soluble salts

Method 1

Method 2

Insoluble Metals

Insoluble metals that react with acid- magnesium, zinc, iron, aluminium

(Copper, silver and gold are insoluble metals that do not react with acid)

Solubility of Carbonates Soluble- carbonates of Group 1 elements e.g : sodium carbonate, potassium carbonate etc

Insoluble – All other carbonates e.g : calcium carbonate, copper carbonate zinc carbonate etc

PREPARATION OF SALT

Method 1

- Acid and Metal reaction

Acid + Metal → Salt + Hydrogen Salt: ZnSO4

Zn (s) + H2SO4 (aq) → ???

excess

Substances left

in the beaker?

Sulfuric

acid

Acid + Metal → Salt + Hydrogen

Salt: ZnSO4

Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2(g)

excess

Substances left in the beaker?

Zn (s) , ZnSO4 solution

all used up escapes

How to remove the zinc from the zinc sulfate solution?

●Excess zinc can be removed by filtration.

●The zinc sulfate solution will be collected as the filtrate

Zinc sulfate solution

How to obtain the zinc sulfate salt from its solution?

Carry out evaporation of the zinc sulfate solution until it is saturated.

(not to dryness as the salt might decompose )

Allow the saturated zinc sulfate solution to cool so that the crystals of zinc sulfate will appear.

Filter to obtain the zinc sulfate crystals and dry them between sheets of filter paper.

Crystallization- involves evaporation and cooling processes.

Solution of zinc sulfate

Evaporating dish

Crystals of zinc sulfate

Reviewing the whole process of preparing zinc sulfate salt

Mixing

Filtration Evaporation & Crystallisation

Drying crystals

zinc sulfate crystals filter paper

Hot Sulfuric acid

zinc sulfate solution

zinc sulfate solution from step 2

Crystals of zinc sulfate

Is this method suitable for preparing all salts?

Recall:

Under the topic on Acids, which metals cannot be used to react with acids?

• Metals that are too reactive, eg: Na, K and Ca

• Metals that are unreactive, eg: Cu, Ag and Au

Acid + Metal → Salt + Hydrogen

Method 2

Acid and insoluble carbonate reaction

Acid + Insoluble Carbonate

CuCO3(s) + 2HCl(aq) → CuCl2(aq) + H2O (l) + CO2(g)

Substances left in the beaker?

CuCO3 (s) , CuCl2 solution

• Salt : CuCl2

escapesexcess all used up

copper(II) carbonate powder

residue:CuCO3

filter paper

filtrate:CuCl2 solution

evaporating dish

copper(II) chloride crystals

filter paper

1

4

2

5

3

6

PREPARATION OF SALTS

Crystals of copper(II) chloride

dilute HClacid

dilute HClacid

IMPORTANCE OF THE VARIOUS STEPS

STEPS WHY?

1) Warm / Heat some acid in a beaker. More metal/carbonate can dissolve in the acid & to speed up reaction.

2) Add excess metal/carbonate to the acid.

Stir until no more solid can dissolve.

To ensure that all acid is used up.

3) Filter the mixture to remove the residue and collect filtrate of salt solution.

To remove excess metal/carbonate as residue.

4) Heat the filtrate until half or one-third of the original volume.

To obtain a saturated solution.

5) Allow the solution to cool. For crystallization to take place.

6) Filter to collect the crystals.

Dry the crystals between filter paper.

Filter to separate crystals from solution.

Dry to collect dry crystals.