NA Science (Chemistry) Chp 13b: Preparation of Salts (Notes)

Preparation of Salts Chapter 13b

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What are Salts?

Salts consist of two parts: the acid part and the base part.

Salts are formed when:

i. acid + alkalis salt + water

ii. acid + metal carbonate salt + carbon dioxide + water

iii. acid + metal salt + hydrogen

acids base or alkali salt product

name formula name formula name formula

hydrochloric acid HCl sodium hydroxide NaOH sodium chloride NaCl

hydrochloric acid HCl magnesium oxide MgO magnesium chloride MgCl2

sulphuric acid H2SO4 potassium hydroxide KOH potassium sulphate K2SO4

sulphuric acid H2SO4 zinc oxide ZnO zinc sulphate ZnSO4

nitric acid HNO3 iron (II) oxide FeO iron (II) nitrate Fe(NO3)2

nitric acid HNO3 copper (II) oxide CuO copper (II) nitrate Cu(NO3)2

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NA Science (Chemistry) Chp 13b: Preparation of Salts (Notes)

Solubility of Salts

Different salts have different solubility.

soluble salts insoluble salts

carbonates sodium potassium ammonium

all others

chlorides all except lead, silver

nitrates all nitrates none

sulphateall except

lead, barium, calcium

From the table above, deduce the solubility of the following salts.

name of saltsolubility in water

(yes or no)

sodium sulphate Yes

copper (ii) nitrate Yes

zinc carbonate No

aluminium chloride Yes

barium sulphate No

silver chloride No

magnesium nitrate Yes

lead(II) sulphate No

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NA Science (Chemistry) Chp 13b: Preparation of Salts (Notes)

Preparation of Salts (Overview)

1. Preparation of insoluble salt

The above diagram shows the preparation of an insoluble salt, barium sulphate.

i. Starting from barium chloride, name the other reagent needed to produce barium sulphate.

sulphuric acid

ii. Suggest what is the solid at A. barium chloride

iii. What is the separation method used in B? filtration

iv. Why is distilled water used in C? to wash away excess acid from the barium sulphate sample

v. How do you obtain dry samples of barium sulphate after step C?

Press residue between sheets of filter paper

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AB C

barium chloride

sulphuric acid

NA Science (Chemistry) Chp 13b: Preparation of Salts (Notes)

2. Preparation of soluble salt

The steps below show the preparation of zinc sulphate using zinc and dilute sulphuric acid.

i. Zinc is added until excess zinc is seen. Why is excess zinc added?

to ensure that all the sulphuric has reacted

ii. What is this separation technique?

filtration

It is used to remove insoluble solid from a suspension.

The residue is zinc and the filtrate is zinc sulphate.

step iii step iv step v step vi

Suggest what is the method shown in steps iii to vi and why.

steps method reason

iii evaporation obtain a saturated zinc sulphate solution

iv crystallization form zinc sulphate crystals from the saturated solution

v filtration obtain zinc sulphate crystals from zinc sulphate solution

vi drying obtain dry zinc sulphate crystals

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