chemistry module form 4 (8)

mohd faisol mansor/chemistry form 4/chapter 8

148

CHAPTER 8 SALTS

A salt is an ionic

substance produced

when the hydrogen

ion of the acid is

replaced by metal

ion or an ammonium

ion.

The salt consists of two

parts, cation from base

and anion from acid.

NaCl

NaOH

(Base)

HCl

(Acid)


149

Table of Salts

Complete the table below.

Metal ion Sulphate salt

(SO42-)

Chloride salt

(Cl-)

Nitrate salt

(NO3-)

Carbonate salt

(CO32-)

K+ K2SO4 KCl KNO3 K2CO3

Na+

Ca2+

Mg2+

Al3+

Zn2+

Fe2+

Sn2+

Pb2+

Cu2+

Ag+

NH4+

Ba2+

Based on the table above, mark the insoluble salt.


150

SOLUBLE & INSOLUBLE SALTS

SALT SOLUBLE INSOLUBLE

K+ , Na+ , NH4+ All soluble none

Nitrate salts

(NO3- ) All nitrate salts none

Chloride salts

(Cl-) All chloride salts

Lead (II) chloride,

PbCl2

Silver chloride, AgCl

Mercury chloride,

HgCl

Sulphate salts

(SO42-) All sulphate salts

Lead (II) sulphate

Calcium sulphate

Barium sulphate

Carbonate

salts (CO32-)

Sodium carbonate,

Na2CO3

Potassium carbonate,

K2CO3

Ammonium carbonate,

(NH4)2CO3

All others carbonate

salts

Oxide salts

(O2-)

Sodium oxide, Na2O

Potassium oxide, K2O

Calcium oxide, CaO (slightly soluble)

All oxide salts

Hydroxide salts

(OH-)

Sodium hydroxide, NaOH

Potassium hydroxide, KOH

Calcium hydroxide,

Ca(OH)2 (slightly soluble)

All hydroxide salts


151

Preparation and Purification of Soluble Salts

Soluble salt can be prepared by the following ways:

1. Reaction between acid and alkali - preparation for

sodium, potassium and ammonium salts only.

Eg: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

Buret

HCl solution

NaOH solution

[write the step of preparation of the salts on the diagram]


152

Preparation and Purification of Soluble Salts

Soluble salt can be prepared by the following ways:

1. Reaction between acid and metal oxide

Eg: HNO3(aq) + MgO(s) Mg(NO3)2 (aq) + H2O(l)

2. Reaction between acid and metal

Eg: H2SO4(aq) + Zn (s) ZnSO4(aq) + H2 (g)

3. Reaction between acid and metal carbonate

Eg: HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l)

[write the step of preparation of the salts on the diagram]


153

Crystallization

is a process to crystallize

the soluble salts.

Recrystallization

process will carried out in

order to get pure and

more defined crystal

Physical characteristic of

crystals

Fixed geometrical shapes

such as a cuboids,

rhombic or prism

Flat surface, straight edges

and sharp angles.

Same shapes for same

substance but differ in

sizes

Fixes angle between two

neighbouring surfaces.


154

Preparation of insoluble salts

An insoluble salt is prepared through precipitation method.

Aqueous solution of two soluble salts are mixed to form

insoluble and soluble salt:

The reaction is called double decomposition.

Two solutions contain ions that make up the insoluble salts.

Eg: Preparation of lead(II) iodide salt by using lead(II)

nitrate solution and potassium iodide solution. [write the balance chemical equation]

Double Decomposition

[write the general equation of preparation insoluble salt]


155

Chemical and Ionic Equation

Chemical and ionic equation can be written for all reaction

That used to prepare salts.

Example: Formation of precipitate Barium Sulphate, BaSO4.

1. Chemical Equation:

BaCl2 (aq) + Na2SO4 (aq) BaSO4(s) + 2NaCl (aq)

2. Ionic Equation:

Ionic equation shows the ions take part in the reaction.

1. Change each of the following word equations to a balanced

chemical equation.

a) Sulphuric acid + zinc zinc sulphate + hydrogen gas.

b) Silver nitrate + potassium iodide silver iodide + potassium

nitrate

c) Nitric acid + chromium(III) hydroxide chromium(III) nitrate

+ water

Exercise


156

2. Complete the following equations.

a) HCl (aq) + NiO (s)

b) HNO3 (aq) + Ca(OH)2 (aq)

c) H2SO4 (aq) + MgCO3 (s)

3. Write an ionic equation for each reaction between the following

pairs of substances.

a) Sulphuric acid, H2SO4 and barium hydroxide, Ba(OH)2 solution

b) Ammonium chloride, NH4Cl solution and silver nitrate, AgNO3

solution.

c) Lead(II) nitrate, Pb(NO3)2 solution and copper(II) sulphate,

CuSO4 solution.

d) Iron(III) oxide, Fe2O3 and hydrochloric acid, HCl.


157

Constructing Ionic Equation using the Continuous Variation Method

Continuous variation method can be used to construct ionic

equation for the formation of insoluble salts.

Fixed volume of a reactant A is react with varying volumes

of a reactant B to determine the mole ratio of reactant A

that react completely with reactant B.

If x mol of reactant A with y mole of reactant B, than the

empirical formula for insoluble salt is A x B y.

Example:

2Fe3+ (aq) + 3CO32- (aq) Fe2(CO3)3 (s)

1 2 3 4 5 6 7 8


158


159

1. 6.0 cm3 of 0.2 mol dm-3 Xn+ solution reacts completely with 4.0

cm3 of 0.1 mol dm-3 Ym- solution to form a salt XmYn. Write the

ionic equation and hence determine the empirical formula of

the salt reaction.

2. 18.0 cm3 of 0.1 mol dm-3 solution of Px+ ions reacts completely

with 9.0 cm3 of 0.1 mol dm-3 solution of Qy- ions to form a salt

PxQy. Write the ionic equation and hence determine the

empirical formula of the salt in this reaction.

Example


160

Solving Problem Involving Calculation of Quantities of Reactants or

Product in Stoichiometric Reactions

Since the quantities of chemicals involved in a reaction are in term

of moles, the quantities of chemicals (volume, mass and number of

particles) must be converted to moles in calculation regarding

quantities of reactant and products.

1. Calculate the number of moles of aluminium sulphate

produced by the reaction of 0.2 mole of sulphuric acid with

excess aluminium oxide. [0.067 mole]

2. 2.0 g of sodium hydroxide reacts with excess sulphuric acid.

What is the mass of sodium sulphate produces

[RAM: H,1 ; O,16 ; Na,23 ; S,32] [ 3.55 g]

Exercise


161

3. What the volume of carbon dioxide gas evolved at s.t.p when

2.1 g of magnesium carbonate reacts with excess nitric acid.

[ RAM: C,12;O,16;Mg,24; s.t.p = 22.4 dm3] [ 560 cm3]

4. What is the mass of magnesium required to react with 20 cm3 of

2.0 mol dm3 hydrochloric acid to produce 120 cm3 of hydrogen

at temperature? [RAM: Mg,24 ; 1 mol = 24 dm3 at room temp.]

[ 0.12 g]


162

Qualitative Analysis of Salts

Colour & Solubility of the Salt

GREEN PALE GREEN

Iron(II) Sulphate, FeSO4

Iron(II) Nitrate, Fe(NO3)2

Iron(II) Chloride, FeCl2

BROWN YELLOW/BROWN [depend on concentration]

Iron(III) Sulphate, Fe2(SO4)3

Iron(III) Nitrate, Fe(NO3)3

Iron(III) Chloride, FeCl3

REDDISH-BROWN INSOLUBLE

Iron(III) Oxide, Fe2O3

GREEN INSOLUBLE

Copper(II) Carbonate, CuCO3

BLUE BLUE

Copper(II) Sulphate, CuSO4

Copper(II) Nitrate, Cu(NO3)2

Copper(II) Chloride, CuCl2

BLACK INSOLUBLE

Copper(II) Oxide, CuO


163

Colour & Solubility of the Salt

WHITE COLOURLESS

Potassium Oxide, K2O

Sodium Oxide, Na2O

Calcium Oxide, CaO

WHITE INSOLUBLE

Magnesium Oxide, MgO

Aluminium Oxide, Al2O3

INSOLUBLE

Zinc Oxide, ZnO

BROWN [hot]

INSOLUBLE

Lead(II) Oxide, PbO

WHITE [cold]

YELLOW [hot]

YELLOW [cold]


164

Gas test

HCl acid

Carbon dioxide Sulphur dioxide

HCl acid

Sodium Carbonate,

Na2CO3

Sodium Sulphite, Na2SO3

Oxygen gas hydrogen gas

Carbon dioxide gas sulphur dioxide gas

chlorine gas ammonia gas

White fumes

Glass rod dipped into

concentrated HCl acid

Ammonia gas, NH3 Chlorine gas, Cl2

Red litmus paper

Wooden splinter

Oxygen gas, O2 Hydrogen gas, H2


165

EFFECT OF HEAT ON SALTS

Sodium carbonate & potassium carbonate are very stable. They do

not decompose on heating.

Carbonate Salt Metal Oxide + Carbon dioxide

Salts Chemical Equation

1. Calcium carbonate

2. Magnesium carbonate

3. Aluminium carbonate


1. Zinc carbonate

Carbonate salts

Heating

Heating

Carbonate salts [ white ]

residue [ white ]

Heating


residue [ yellow hot ] [ white cold ]


166

Carbonate Salt Metal Oxide + Carbon dioxide


1. Iron(III) carbonate


1. Copper(II) carbonate


1. Lead(II) carbonate

Heating

Carbonate salts [ brown ]

residue [ brown ]

Heating

Carbonate salts [ green ]

residue [ black ]

Heating


residue [ brown hot ]

[ yellow cold ]

Heating


167

Carbonate Salt Metal + Carbon dioxide + Oxygen gas


1. Mercury(II) carbonate


1. Silver carbonate


1. Aurum(II) carbonate

Heating


residue [ grey ]

Heating


residue [ shiny grey ]


residue [ golden yellow ]

Heating

Heating


168

Nitrate Salt Metal Oxide + Oxygen gas + Nitrogen dioxide


1. Calcium nitrate

2. Magnesium nitrate

3. Aluminium nitrate


1. Zinc nitrate

nitrate salts

Heating

Heating

nitrate salts [ white ]

residue [ white ]

Heating


residue [ yellow hot ] [ white cold ]


169

Nitrate Salt Metal Oxide + Oxygen gas + Nitrogen dioxide


1. Iron(III) nitrate


1. Copper(II) nitrate


1. Lead(II) nitrate

Heating

nitrate salts [ brown ]

residue [ brown ]

Heating

nitrate salts [ blue ]

residue [ black ]


residue [ brown hot ]

[ yellow cold ]

Heating

Heating


170

Nitrate Salt Metal + Nitrogen dioxide + Oxygen gas


1. Mercury(II) nitrate


1. Silver nitrate

Nitrate Salt Metal nitrite + Oxygen gas


1. Potassium nitrate

2. Sodium nitrate

Heating


residue [ grey ]

Heating


residue [ shiny grey ]

Heating

Heating

Heating


residue [ white ]


171

TEST FOR ANIONS

Salt needed to be

dissolved into water

first to produce

aqueous salt

solution.

Unknown aqueous salt solution

[ state the procedure ]

OBSERVATION

[ state the procedure ] [ state the procedure ] [ state the procedure ]

OBSERVATION OBSERVATION OBSERVATION

CONCLUSION CONCLUSION CONCLUSION CONCLUSION

[ label the diagram ] [ label the diagram ] [ label the diagram ] [ label the diagram ]

[ state the anion ] [ state the anion ] [ state the anion ] [ state the anion ]


172

TEST FOR CATIONS

Salt needed to be


(soluble salts) or in

dilute acid then

filtered (insoluble

salts) first to produce

aqueous salt solution.


No precipitate White precipitate Coloured precipitate

Green

Brown

Blue

Add NaOH drop by drop

Add NaOH drop by drop until excess

Dissolve in excess NaOH Insoluble in excess NaOH

* All coloured ions insoluble in excess NaOH


173

TEST FOR CATIONS

Salt needed to be


(soluble salts) or in

dilute acid then

filtered (insoluble

salts) first to produce

aqueous salt solution.


No precipitate White precipitate Coloured precipitate

Green

Brown

Blue

Add NH3 drop by drop

Add NH3 drop by drop until excess

Dissolve in excess NH3 Insoluble in excess NH3

Dissolved in excess NH3

Dark blue solution

* Fe2+ & Fe3+ ions insoluble in excess NH3


174

Confirmatory Test for Cation

Cation Procedure Observation

Fe 2+

Fe 3+

Pb 2+

NH4 +

1. Identify the aqueous solutions based on the test and observation given.

Type Observation Answer

a. Potassium thiocyanate,

KSCN, solution is added. Blood red solution formed.

b. Potassium iodide, KI, solution

is added.

Yellow precipitate is

formed.

c. Ammonia solution, NH3, is

added until excess.

Blue precipitate dissolve to

form dark blue solution.

d. A little hydrochloric acid is

added.

Effervescene occur and

lime water turn into chalky.

e. A sulphuric acid, iron(II)

sulphate solution and

concentrated sulphuric acid

is added.

Brown ring formed.

f. Ammonia solution is added

until excess.

White precipitate

dissolved.

Exercise

ZnCl2 NaNO3 PbCl2 CuSO4 FeCl3 K2CO3

chemistry module form 4 (8)

Documents