chp 8 salts

8/3/2019 CHP 8 Salts

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Group member Chuah Rui Han

Christina Loh

Farah

Faliq Haziq

Faez

4

CEKAL



8.1 SALTS



Many different types of salts can be foundin nature.

There are various types of salts from the seasuch as sodium chloride, potassiumchloride, magnesium sulphate andpotassium chloride.

The earth·s crust is made up of mineralscontaining various types of salts such ascalcium fluoride, magnesium sulphate,

lead(II) sulphide and calcium carbonate.



Agriculture

Chemical fertilisers

Pesticides

Medical Field

Medicines

Plasters

Food Industry

Flavouring

Preservatives

Chemical IndustryPlastic

Detergents

Plasters

Glass

Paintsdyes



Salt is a compound formed when the

hydrogen ion in an acid is replaced by a

metal ion or an ammonium ion. A salt is formed in a neutralisation

reaction between an acid and a base.

Asalt is an ionic compound consisting ofa cation such as metal ion or an

ammonium ion from a base and ananion from an acid.



Salts are ionic compounds and they can dissolve in water.

However, through experiments done by chemists, not all saltsare soluble in water.

Type of salts Soluble Insoluble

Ammonium salts All ammonium salts. -

Sodium and potassium salts All sodium and potassium salts. -

Ethanoate salts All ethanoate salts. -

Nitrate salts All nitrate salts. -

Sulphate salts All sulphate salts. except PbSO4, CaSO4, BaSO4

and Ag2SO4.

Chloride salts All chloride salts. except AgCl, HgCl and PbCl2.

Carbonate salts All carbonate salts. except Na2CO3, K 2CO3 and

(NH4)2CO3

Lead(II) salts All lead(II) salts. except Pb(NO3)2 andPb(CH3COO)2



A soluble salt can be prepared from a

reaction between an acid and a metal,

a base or a carbonate.

Soluble salts

- Sodium salts

- Potassium salts

- Ammoniumsalts

Acid + alkali salt + water

Other salts

Acid + metal oxide salt + water

Acid + metal salt + hydrogen gas

Acid + metal carbonate salt +

water + carbon dioxide

Reactions involved in the

preparation of salts.



The salts formed

contains impurities.

Therefore,

recrystallisation is

carried out to obtain pure

crystals of the salts(purified) from the

solution.



The salt is prepared by titration method ofacid and alkali using an indicator.

Acid + Alkali Salt + Water

A titration is conducted to determine thevolume of acid needed to neutralise a fixed

volume of an alkali with the aid of anindicator.

The same volume of acid is then added tothe same volume of alkali without any

indicator to obtain pure and neutral saltsolution.

- The salt solution is gently heated toevaporate the solution to 1/3 its original

volume, producing a saturated solution.- Dip in a glass rod, if crystals are formed, the

solution is saturated.

- The solution is cooled at room temperature.

- The solution is filtered and dried the residueby pressing it between filter papers.

- The crystals are placed in a beaker.

- Distilled water is added to cover the crystals. The mixture is gently heated while stirring with aglass rod. More distilled water is added a little at a time until all crystals are dissolved.

- The solution is filtered to remove impurities.

- The solution is evaporated to 1/3 its original volume to obtain a saturated salt solution.


- The solution is filtered and dried the residue by pressing it between filter papers.

RECRYSTALLISATION

CRYSTALLISATION NEUTRALISATION REACTION

TITRATION METHOD



The salt is prepared by reacting acidwith insoluble metal/metal/metalhydroxide

Acid + metal salt + hydrogen



Acid + metal carbonate salt + water + carbon

dioxide

Add metal/metal oxide/metalcarbonate powder until excessinto a fixed volume of the heated

acidFilter the mixture to remove excess

solid (residue)

The salt solution is gently heated toevaporate the solution to 1/3 its

original volume, producing asaturated solution.

Dip in a glass rod, if crystals areformed, the solution is saturated.

The solution is cooled at roomtemperature.

The solution is filtered and dried theresidue by pressing it between filter

papers.

- The crystals are placed in a beaker.

- Distilled water is added to cover the crystals.The mixture is gently heated while stirring with

a glass rod. More distilled water is added alittle at a time until all crystals are dissolved.

- The solution is filtered to remove impurities.

- The solution is evaporated to 1/3 its originalvolume to obtain a saturated salt solution.


- The solution is filtered and dried the residue

by pressing it between filter papers.

RECRYSTALLISATION CRYSTALLISATION



Crystals has the following PHYSICAL CHARACTERISTICS:

(i) Fixed

geometricalshape (cuboid,

rhombic or

prism)

(ii) Fixed angle

between 2

adjacentsurfaces

(iii) Flat surfaces,

straight edgesand sharp

corners

EXPLANATION

Particles in a crystal are arranged in an orderly manner, closely-packed, incontact and at fixed positions.

The orderly arrangement is extended repeatedly throughout the three-

dimensional crystal lattice to give the overall shape of the crystal and also the

characteristics of (ii) and (iii).

The pattern of orderly arrangement of the particles is not the same in crystals of

different substances. This gives rise to different geometrical shapes of crystals.



An insoluble salt is prepared throughPRECIPITATION REACTION through aDOUBLE DECOMPOSITION REACTION.

In this reaction, 2 aqueous solutions of

two different soluble salts are mixedtogether to form the insoluble salt.

The insoluble salt is formed as a

precipitate and can be obtained byFILTRATION.

The first solution must have a soluble saltwhich contains the CATION of theinsoluble salt.

The second solution must have a solublesalt which contains the ANION of the

insoluble salt.



1. Mix 2 solutions containing cations and

anions of insoluble salts.

2. Stir with glass rod.3. Filter the mixture using filter funnel.

4. Rinse the residue with distilled water.

5. Dry the residue by pressing it betweenfilter papers.



Chemical and ionic equations can be writtenfor all reactions that are used to prepare salts.

Example:

Barium sulphate, BaSO

4BaCl2(aq) + Na2SO4(aq) BaSO4(s) +

2NaCl(aq)

Ba2+ + 2Cl- + 2Na+ + SO42- BaSO4 + 2Na+

+ 2Cl-

Therefore, an ionic equation of the reaction is

formed:

Ba2+ + SO42- BaSO4(s)



The ionic equation for the formation of an

insoluble salt can be constructed if we know

the number of moles of cation and anionreacted to form 1 mole of the insoluble salt.

For example, 1 mole of silver chromate(VI) isformed from 2 moles of Ag+ ions and 1 mole

of Cr O42- ions.

This can be determined form experiment by a

continuous variation method.

Pb2+(aq) + 2Br -(aq) PbBr 2(s)



Use the ratio to construct the ionic equation.

Determine the simplest mole ratio of reactant A to reactant B whichcombine to form one mole of the insoluble salt.

Use the results of the experiment to calculate the number of moles ofreactant A and number of moles of reactant B which reacted

completely with each other.

Determine the volume of reactant B required to react completely

with the fixed volume of reactant A

Carry out a reaction between a fixed volume of reactant A withvarying volumes of a second reactant B



A balanced chemical equation can be used to calculate the stoichiometricquantities of masses of reactants, volume & concentrations of reactants,masses of products and volumes of products.

The calculation steps involved are:

STEP

1

Write a balanced equation.

STEP 2

Write the information from the question above the equation.

STEP 3

Write the information from the chemical equation below the equation.(thenumber of moles of reactants/products).

STEP 4

Change the information in STEP 2 into moles by using method shown in thenext slide.

STEP 5

Use the relationship between number of moles of substance involved inSTEP 3 to find the answer.

STEP 6

Change the information to the unit required using the method shown in

the next slide.



*EXAMPLES*



In Chemistry, qualitative analysis is a

chemical technique used to determine what substances are

present in a mixture but not their quantities.

Therefore, in qualitative analysis of salts, we need to identifythe ions that are present in salts.

This can be done by analysing their physical and chemical

properties.

Observations on the

physical properties of salts

Action of heat on salts

Tests for cations and anions

Confirmatory tests for

cations and anions



Observation on the

physical properties of salt

is carried out in order to

help us to infer certaincations and anions that

are present in the salts.

The observation is donein order to narrow down

the choices of cations and

anions present in a salt.

PHYSICALPROPERTIES

OF SALT

Colour

Solubilityof salts in

water



Salt

Colour

Solid Aqueoussolution

Potassium salts

Sodium salts

Ammonium salts

Aluminium salts

Calcium salts

Lead(II) salts

Zinc salts

(with colourless anions)

White Colourless

Carbonate salts

Chloride salts

Nitrate salts

Sulphate salts

(with colourless cations)

White Colourless



Iron(II) salts

[EX: Iron(II) chloride ,

Iron(II) nitrate , Iron(II)sulphate]

Green Green

Iron(III) salts

[EX: Iron(III) chloride ,

Iron(III) nitrate ,

Iron(III) sulphate]

Brown Brown

Iron(III) salts

[EX: Copper(II)

chloride , Copper(II)

nitrate , Copper(II)

sulphate]

Blue Blue

Copper(II) carbonate Green (Insoluble)



COMPOUND SOLUBILITY IN WATER

Sodium,potassium and

ammonium salts

All are soluble

Nitrate salts All are soluble

Ethanoate salts All are soluble

Chloride salts All are soluble except AgCl, HgCl and PbCl2

Sulphate salts All are soluble except BaSO4, PbSO4 and CaSO4

Carbonate salts All are insoluble except Na2CO3, K2CO3 and

(NH4)2CO3

Metal oxides All are insoluble except Na2O, K2O and CaO(slightly soluble)

Metal hydroxides All are insoluble except NaOH, KOH, and Ba(OH)2



Heating a salt may cause it to decompose. The decomposition may

result in:

- a colour change - evolution of a gas - liberation of watervapour

Gases such as carbon dioxide, oxygen, ammonia and nitrogen

dioxide can be evolved. By identifying the gas/gases liberated, it is

possible to pinpoint the anion present in the salt.

Examination of the residue can provide information to identify the

cation in the salt.



Carbonate salt Colour of salt

before

heating

Colour of residue Action of Heat/Effect on

limewaterHot Cold

Copper(II)

carbonate

Green Black Black Decompose to produce metal oxide

& carbon dioxide.

Limewater turns milky.

Sodium carbonate White - - Does not decompose.

No change.

Potassiumcarbonate White - -

Does not decompose.

No change.

Calcium

carbonate

White White White Decompose to produce metal oxide

& carbon dioxide.


Magnesium

carbonate

White White White Decompose to produce metal oxide

& carbon dioxide.Limewater turns milky.

Zinc carbonate White Yellow White Decompose to produce metal oxide

& carbon dioxide.


Lead(II)

carbonate

White Brown Yellow Decompose to produce metal oxide

& carbon dioxide.


ACTION OF HEAT ON CARBONATE SALTS

Most METAL C ARBONATES

decompose on heating to produce

METAL OXIDES & C ARBONDIOXIDE gas.

Metal carbonate metal oxide +

carbon dioxide



Alkali metal carbonates such as sodiumcarbonate and potassium carbonate arestable to heat (does not decompose).

Most metal carbonates decompose on heatingto produce metal oxides and liberate carbondioxide gas.

The carbon dioxide gas forms a whiteprecipitate with limewater, making thelimewater milky.

CONCLUSION:Heating a metal carbonate will decompose it into a

metal oxide and liberate carbon dioxide. Group 1

metal carbonates are not decomposed by heat.



Nitrate salt Colour of salt

before

heating

Colour of residue Tests for gases evolved

Hot Cold Colour of

gas

Glowing

splinter

Blue

litmus paper

Copper(II) nitrate Blue Black Black Brown gas

&

colourless

gas

Rekindles Turns red

Sodium nitrate White White White Colourless Rekindles No change

Potassium nitrate White White White Colourless Rekindles No change

Calcium nitrate White White White Brown gas

&

colourlessgas

Rekindles Turns red

Magnesium

nitrate

White White White Brown gas

&

colourless

gas

Rekindles Turns red

ACTION OF HEAT ON NITRATE SALTS

Most METAL NITRATES decompose

on heating to produce METAL

OXIDES, NITROGEN DIOXIDE &OXYGEN gas.

Metal nitrate metal oxide +

nitrogen dioxide + oxygen



Zinc nitrate White Yellow White Brown gas &

colourless gas

R ekindles Turns red

Iron(II) nitrate Green Black Black Brown gas & colourless

gas

Rekindles Turns red

Iron(III) nitrate Brown Brown Brown Brown gas & colourless

gas

Rekindles Turns red

Lead(II) nitrate White Brown Yellow Brown gas & colourless

gas

Rekindles Turns red

When nitrate salts are heated, they decompose to

liberate nitrogen dioxide and oxygen.

Only sodium nitrate and potassium nitrate decomposeto liberate oxygen.

Nitrogen dioxide is a acidic, brown gas that turns

moist blue litmus paper red.

Oxygen is a colourless gas that relights a glowing

wooden splinter.



When a salt is dissolved in water, the free anion will be pesent in

the aqueous solution. Tests can then be carried out to identify

the anion.Anion Procedure Observation/Inference/

Ionic Equation

Carbonate

ion, CO32-

2cm3 of dilute hydrochloric acid/nitric acid/sulphuric

acid is added to 2cm3 of carbonate salt.

The gas given off is passed through lime water.

Effervescence occurs and the

lime water turns chalky.

The gas is carbon dioxide.

Ionic equation: CO32-(aq)+2H+(aq)

CO2(g)+H2O(l)

Chloride

ion, Cl-2cm3 of dilute nitric acid is added to 2cm3 solution of

chloride ions followed by 2cm3 of silver nitrate

solution.

A white precipitate is formed.

The precipitate is silver chloride.Ionic equation: Ag+(aq)+Cl-(aq)

AgCl(s)

Sulphate

ion, SO42-

2cm3 of dilute hydrochloric/nitric acid is added to

2cm3 of sulphate solution followed by 2cm3 of barium

chloride solution/barium nitrate solution.

A white precipitate is formed.

The precipitate is barium sulphate.

Ionic equation: Ba2+(aq)+SO42-(aq)

BaSO4(s)

Nitrate

ion, NO3-

2cm3 of dilute sulphuric acid is added to 2cm3 of

iron(II) sulphate solution.

The mixture is shaken.

The test tube is slanted and held with a test tube

holder.

A few drops of concentrated sulphuric acid is dropped along the wall of the test tube and is held

A brown ring is formed between two

layers.



Cations Sodium hydroxide solution Ammonia solution

Small amount excess Small amount excess

K+ No change No change No change No change

Na+ No change No change No change No change

Ca2+ White precipitate Insoluble in excess No change No change

Mg2+ White precipitate Insoluble in excess White precipitate Insoluble in excess

Zn2+ White precipitate Soluble in excess White precipitate Soluble in excess

Al3+ White precipitate Soluble in excess White precipitate Insoluble in excess

Pb2+ White precipitate Soluble in excess White precipitate Insoluble in excess

Fe2+ Green precipitate Insoluble in excess Green precipitate Insoluble in excess

Fe3+ Brown precipitate Insoluble in excess Brown precipitate Insoluble in excess

Cu2+ Blue precipitate Insoluble in excess Blue precipitate Soluble in excess

NH4+ No change No change No change No change

Confirmatory tests are carried out by adding a small amount of sodium hydroxide solution / ammonia solution followed by excess

sodium hydroxide solution / ammonia solution to the solutionscontain the cations.



Al3+ and Pb2+ are differentiated by double composition reaction.

An aqueous solution containing SO42-/Cl-/I- anion is used to detect

the presence of Al3+ and Pb2+.

Precipitate is formed when solution containing SO42-/Cl-/I- added

to Pb2+.

No precipitate is formed when solution containing SO42-

/Cl-

/I-

added to Al3+.

Condition Al3+ Pb2+

Add sodium

sulphate solution

No change White precipitate

Add sodium

chloride solution


Add potassium

iodide solution




THANK

YOU!

chp 8 salts

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