CHEMISTRY SPM FORM 4 Short Notes Chapter 8 SALTS

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STUDYSMART CHEMISTRY FORM 4 CHAPTER 8 : SALTS

8.1 Synthesising Salts 8.2 Synthesising qualitative analysis of salts 8.3 Practising to be systematic and meticulous when carrying

out activities 8.1 SYNTHESISING SALTS

A salt is a compound formed when the hydrogen ion, H+ from an acid is replaced by a metal ion or an ammonium ion, NH4

+

Examples HCl + NaOH NaCl + H2O 2HNO3 + Zn Zn(NO3)2 + H2 H2SO4 + MgCO3 MgSO4 + H2O + CO2

Complete the table below

Metal Ion

Sulphate salt (From H2SO4)

Chloride salt (From HCl)

Nitric Acid (From HNO3)

Carbonate salt (From H2CO3)

Na+

K+

Zn2+

Mg2+

Ca2+

Fe2+

Fe3+ Cu2+ NH4

+ Ba2+ Al3+ Pb2+ Ag2+

INSOLUBLE SALT

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Solubility of salt.

All K+ , Na+ and NH4+ salts are soluble

All nitrate salts are soluble

All carbonate are soluble except K2CO3, Na2CO3 and (NH4)2CO3

All Sulphate salts are soluble except BaSO4 , CaSO4, and PbSO4

All chloride salts are soluble except AgCl2 and PbCl2 The preparation of salt on its solubility of the salt and the nature of the reaction. METHOD 3

METHOD 1 METHOD 2

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Preparation of salt

Soluble Insoluble

K+ , Na+ NH4+

Acid + Alkali Salt + H2O

Titration of acid and alkali

- Add acid to the alkali until it is neutral with the aid of an indicator - Repeat the procedure without using an indicator

- Gently heat the filtrate to obtain a saturated solution (one-third of its original volume remains) - Cool the hot saturated solution to allow it to crystallize - Filter and dry the crystals by using filter paper

Other than K+ , Na+

NH4+ salts

Acid + basic oxide Salt + water Acid + metal Salt + Hydrogen gas Acid + Metal Carbonate Salt + Water + CO2

- Add basic oxide fillings/metals/metal carbonate to the acid and heat it until some of it no longer dissolves. (This mean all acid has reacted with the basic oxide/metal/metal carbonate) - Filter to move excess solid residue

- Mix two solution containing cations and anions of insoluble salts - Stir using glass rod - Filter using filter funnel - Rinse the residue with distilled water - Dry the residue with filter paper

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TRY THIS 1 Write all possible chemical equation to prepare soluble salts and chemical equation for insoluble salt

SALT SOLUBILITY CHEMICAL EQUATION

Zinc Chloride

Sodium Nitrate

Silver Chloride

Copper(II) Sulphate

Lead(II) Sulphate

Aluminium Nitrate

Lead(II) Chloride

Magnesium Nitrate

*******KEY******* S = SOLUBLE SALT

IS = INSOLUBLE SALT

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Potassium Chloride

Lead(II) Nitrate

Barium Sulphate

Ammonium Sulphate

Numerical problem involving stoichiometry reactions in the preparation of salts

A student prepare copper(II) nitrate, Cu(NO3)2 by reacting copper(II) oxide, CuO with 100 cm3 of 1.5 mol dm-3 nitric acid, HNO3. Calculate the mass of copper(II) oxide, CuO needed to react completely with the acid. [RAM : Cu,64 ; O,16]

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8.2 SYNTHESISING QUALITATIVE ANALYSIS OF SALTS

Colour of Salts

Confirmatory test for several gases

GAS COLOUR SMELL EFFECT ON DAMP

LITMUS PAPER

REAGENT USED

CONFIRMATORY TEST

Hydrogen Colourless Odourless No effect Lighted splinter

Bring a lighted splinter to the mouth of test tube. It gives “pop” sound

Oxygen Colourless Odourless No effect Glowing Splinter

Bring a glowing splinter to the mouth of test tube. The glowing splinter lights up

Carbon Dioxide

Colourless Odourless Blue red Lime water Bubble the gas produce into lime water. Lime water will turns chalky/milky/cloudy

Ammonia Colourless Pungent Smell

Red blue Concentrated HCl

Dip a glass rod into concentrated HCl. White fumes is released

Chlorine Greenish yellow

Pungent Smell

Blue red white

- -

Nitrogen Dioxide

Brown Pungent Smell

Blue red - -

Sulphur dioxide

Colourless Pungent Smell

Blue red Acidified potassium manganate(VII) solution

Turns acidified potassium manganate (VII) solution from purple to colourless

Hydrogen chloride

Colourless Pungent Smell

Blue red Concentrated ammonia, NH3 aqueous

Dip a glass rod into Concentrated ammonia, NH3, white fumes is released

SOLID AQUEOUS SOLID/METAL OXIDE

White salt Colourless

Green Insoluble

Light Green Light Green

Blue Blue

Brown Brown

Black Insoluble

Yellow when hot White when cold

Insoluble

Brown when hot Yellow when cold

Insoluble

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Action of heat on salts a) Most compound which decomposes leave behind oxides Salt metal oxide + gas (residue identification (gas identification refers to specific cations refers to anion) only) b) c) Test of carbon dioxide gas liberated when the carbonate salt is heated strongly

Types of gas

released

Can predict the

identify of anions

presence in salt

Colourless

residue

Can predict the

identify of cations

presence in salt

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d) Write down the chemical equation for the reactions that occur.

Ion Carbonate Salt Nitrate Salt

Is not decomposed by heat Decompose into O2 gas and metal nitrate

K+ Na+

Ca2+

Decompose into metallic oxide and CO2 Decompose into metal oxide, NO2 and O2

Mg2+ Al3+

Zn2+

Fe2+ Fe3+ Pb2+

Cu2+

Sulphate salts usually do not decompose

Chloride salts do not decompose except NH4Cl NH4Cl (s) NH3 (g) + HCl (g) [sublimation]

Confirmatory test for anions + H2SO4 dilute + dilute +HNO3 + HNO3 + FeSO4 acid + AgNO3 + Ba(NO3)2 + H2SO4 conc Confirmatory test for cations

a) The presence of cation can be detected by using two common bench alkalis namely i) _____________________________ solution ii) _____________________________ solution

b) Write the ionic equation for the reaction of cations and sodium hydroxide

Unknown Salt Solution

Gas turns limewater

__________

__________Precipitate

formed

__________precipitate

formed

________ __________

The function of the alkalis is to produce a precipitate that is Metal hydroxide METAL + HYDROXIDE ION METAL HYDROXIDE

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Ion Ionic equation for the reaction of cations and sodium hydroxide

Aluminium ion Al3+ + 3OH- Al(OH)3

Lead (II) Ion Zinc Ion Magnesium Ion Calcium Ion Copper (II) Ion Ferrum (II) Ion Ferrum (III) Ion

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NH4+ Ca2+ , Fe2+ ,,Fe3+ , Zn2+ , Al3+, Pb2+

Cu2+ , Mg2+ No Formation of Formation of white Precipitate precipitation & precipitate & then Non-soluble in soluble in excess excess

Fe2+ , Fe3+ K2Fe(II)(CN)6 Light Blue Blue precipitate precipitate K2Fe(III)(CN)6

Dark Blue Brown Precipitate Solution KSCN No Change Red solution +NaOH a little

and then in excess

+NH4OH a little and then in excess

NH4+, Ca2+ Fe2+ ,,Fe3+, Al3+ Zn2+ Cu2+

Pb2+, Mg2+ No Formation of precipitate is Precipitate precipitation & formed & dissolve Not dissolve in in excess excess

Examples

Anion Test Observation CO3

2- + HCl Gas form white precipitate with lime water SO4

2- + HCl White precipitate is + BaCl2/ Ba(NO3)2 formed Cl- + HNO3 White precipitate is + Ag(NO3)2 formed NO3

- + H2SO4 (Dil) Brown ring is formed + FeSO4 + H2SO4 (conc)

Anion to be test: CO3

2- SO42- Cl- NO3

-

CATIONS TEST

Pre-Test

Confirmatory test

ION TEST

Gas evolved from the reaction with salt

NH4+

+ Nessler reagent, brown precipitate is form

+ KI, yellow precipitate occurs and dissolved in hot water

Pb2+

,

+ HCl, white precipitate occurs and dissolved in hot water Fe2+ Fe3+

ANION TEST

Confirmatory test

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Test for cations

Cations Test with a small amount of NaOH solution until in excess

Test with a small amount of NH4OH until in excess

Al3+ White precipitate soluble in excess. NaOH solution

White precipitate, insoluble in excess NH4OH solution

Pb2+ White precipitate, soluble in excess NaOH solution


Zn2+ White precipitate, soluble in excess NaOH solution

White precipitate, soluble in excess NH4OH solution

Mg2+ White precipitate, insoluble in excess NaOH solution


Ca2+ White precipitate, insoluble in excess NaOH solution

No precipitate

Cu2+ Blue precipitate, insoluble in excess NaOH solution

Blue precipitate, soluble in excess NH4OH solution

Fe2+ Green precipitate, insoluble in excess NaOH solution

Green precipitate, insoluble in excess NH4OH solution

Fe3+ Brown precipitate, insoluble in excess NaOH solution

Brown precipitate, insoluble in excess NH4OH solution

NH4+ No precipitate No precipitate

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CHEMISTRY SPM FORM 4 Short Notes Chapter 8 SALTS