Preparation for Practical chemistry

Preparation for Practical chemistry

Exercise on Chemistry Paper 4= 2014= form 5

Paper 4- practical chemistry • 2 sections ( 1 ½ hour)• Part A) carrying out experiment Example, taking volume, temperature, mass, time Then do calculations Part B) salt analysis – given unknown salt, you are asked

to determine what the salt is

Salt analysis

• To identify cations ( ions that go to the cathode , that is positive ions)

• To identify anions ( ions that go to the anode , that is negative ions )

SALT ANALYSIS - cations

Cations

Sodium hydroxide solution

Ammonia solution

Confirmatory tests

Forms no precipitate

NH4 +

No change, but when heated gas released which turns damp red litmus to

.

Add Nessler’s reagent - turns brown blue

No change

Test for ammonium ion – click to play

SALT ANALYSIS - cations

Cations

Sodium hydroxide solution

Ammonia solution

Confirmatory tests

Forms no precipitate

Na + No change No change

K + No change No change

Forms white ppt

Ca +2 White precipitate

No change

Mg +2 White precipitate

White precipitate

NO

NO

Cations Sodium hydrox (aq

Ammonia solution

Confirmatory tests

Forms white ppt

Soluble in excess

Zn +2

soluble in excess

White precipitate soluble in excess

White ppt

Cations Sodium hydroxide solution

Ammonia solution Confirmatory tests

Video test on zinc ion- click to play

Forms white ppt

Soluble in excess

Al +3 White ppt soluble

Add …………… sulphate solution or add potassium sulphate solution- NO PPT

White ppt sodium

Cations

NaOH solution

Ammonia solution

Confirmatory tests

NaOH (aq)

Ammonia (aq)

Confirmatory test

Forms white ppt

Soluble in excess

Pb +2 White precipitate soluble in excess

White precipitate

Add

Na2SO4solution

OR add K2SO4

solution- WHITE PRECIPITATE

OR KI solution turns

……………. PRECIPITATE

yellow

Forms coloured ppt

Fe +2 ……………….. precipitate

Green precipitate

Potassium hexa…………

(III) turns dark blue

Fe +3 Brown precipitate

……………….precipitate

…………………..hexacyanoferrate (II) turns dark blue

green

cyanoferrate

brown Potassium



Forms coloured ppt

Cu +2 Blue precipitate

Blue precipitate soluble in excess to form dark blue solution

NO



Test for anions Anions procedure observations

nitrates Add dilute sulphuric acid to nitrate solutionAdd iron (II) sulphate solutionAdd conc sulphuric acid

Brown ring formed


carbonates

Add any dilute acid to carbonate solution

Bubbles of gas produced that turn lime water cloudy


chloride Add dilute nitric acid to chloride solutionAdd silver nitrate solution

White precipitate


Sulphate

Add dilute hydrochloric acid to sulphate solutionAdd barium chloride solution

White precipitate

2) ( remember this table )Effect of heating on salts

Salts Gas released Residue formed

1)Nitrates

All nitrates Nitrogen dioxide and …………….

Metal oxide

Except sodium nitrate and potassium nitrate

oxygen Metal nitrite

oxygen

1)Carbonate All carbonates

Carbon dioxide

……………… oxide

Except sodium carbonate and potassium carbonate

Do not ……………………………. on heating

metal

decompose

3) Solubility of salts

SALTS SOLUBLE INSOLUBLECHLORIDE

SALL PAH=== Pb chloride,

…….. chloride, Hg chlorides

SULPHATES

all PCB == Pb sulphate, ………..sulphate, Ba

sulphate

silver

calcium

Soluble and insoluble in water

NITRATES All soluble none

CARBONATES

Soluble are KAN = K carbonates ,

…………….. carbonates,

Na carbonates

The rest not soluble

Ammonium

4) Colour of substances

All salts

WHITE in colour except

i)All copper salts are BLUE except copper(II) ……………which is GREEN

ii)All iron(II) salts are ………………………………

iii)All iron (III) salts are …………………………………

carbonate

Green

Brown

ALL oxides

WHITE except

i)Zinc oxide – white when cold, ………………………… when hot

ii)Lead(II) oxide – yellow when cold, …………………………when hot

iii)Copper(II) oxide – …………………………..

Yellow

Orange

Black

ALL metals

Grey in colour except

i)Silver is shiny ……………………………….

ii)Gold is shiny ………………………….

iii)Copper is ………………………………….

Others

Lead(II) iodide is …………………………………, lead(II) chromate is yellow,

whiteyellow

brown

yellow

Experiment Salt /cation/anion

1 Blue solid which when heated release brown gas and forms black solid as residue

EXAMPLE:

Salt:Copper(II) nitrate

5) Identify salts OR cation OR anion below

2 White solid when heated release carbon dioxide and residue which is white when cold and yellow when hot

3 A solution which gives white precipitate with sodium hydroxide , and white precipitate with ammonia solution

Zinc carbonate

Mg 2+ ion/ magnesium ion

4 A solution which gives white precipitate soluble in excess with sodium hydroxide , and white precipitate with ammonia solution

5 A solution which gives white precipitate soluble in excess with sodium hydroxide , and white precipitate soluble in excess ammonia solution

Al 3+ OR Pb 2+ ion

Zn 2+ ion

6 A solution which gives white precipitate with sodium hydroxide , and no change in ammonia solution

7 A solution which gives brown precipitate with sodium hydroxide

Ca 2+ ion

Fe 3+ ion

8 A solution which gives white precipitate with nitric acid and silver nitrate solution

9 A solution which gives bubbles of gas with sulphuric acid

Cl – ion

Chloride ion

CO3 2- ion

Carbonate ion

10 A solution which gives brown ring with sulphuric acid and iron(II) sulphate solution and with careful addition of concentrated sulphuric acid

11 A solution which gives white precipitate with nitric acid and barium nitrate solution

NO3 – ionNitrate ion

SO4 2 – ion sulphate ion

12 A solution which gives yellow precipitate with potassium iodide solution

13 A solution which gives white precipitate soluble in excess with sodium hydroxide , and white precipitate with ammonia solution . There was no change with the solution, when sodium sulphate solution is added to it

Pb 2 + ion/ lead(II) ion

Al 3+ ion / aluminium ion

Procedure Observation Inference

1 Heat salt Y strongly

Lime water turns chalky

Residue is brown when hot, yellow when cold

Salt Y

•Gas CO2

•Salt Y is carbonate salt •Residue is lead(II) oxide


2 Cool the residue, then add nitric acid and stir to form a solution

Residue dissolves in acid to form a colourless solution , X

Salt Y

•Residue is a carbonate salt

To the solution X, 1 NaOH

aqueous Pour 2 cm3 of solution X into a test tube.

Add sodium hydroxide solution , little first and shake well , and then in excess and shake well

White precipitate soluble in excess NaOH solution

•X contains Zn2+ / Al3+ /Pb2+

NH3

aqueous

Pour 2 cm3 of solution X into a test tube.

Add ammonia aqueous , little first and shake well , and then in excess and shake well

White precipitate •X

contains Al3+ /Pb2+

Potassium iodide solution

Pour 2 cm3 of solution X into a test tube.

Add 1 cm3 of potassium iodide solution

Yellow precipitate is formed

Therefore salt Y is ………..

•X contains Pb2+ ion

•Lead(II) carbonate

Procedure

Observation Inference

1 Heat salt Y strongly

Salt W is zinc nitrate . Fill in the table below for expected results

•Brown gas and •gas that rekindle glowing wooden splinter formed•Residue is yellow when hot and white when cold

•NO2 gas and O2 gas

•Y contains nitrate•Residue is zinc oxide


2 Cool the residue, then add hydrochloric acid and stir to form a solution

Salt W is zinc nitrate . Fill in the table below for expected results

•Residue is a base

•Residue dissolves in acid

To the solution X,

1 NaOH aqueous

•Add NaOH solution, little first, then in excess

•White precipitate, soluble in excess


To the solution X,

2 NH3

aqueous •Add NH3 aq, solution, little first, then in excess

•White precipitate, soluble in excess

•X contains Zn2+

Reaction with


1 NaOH aqueous

Question 3 – Solution Q is magnesium chloride


•White precipitate

•X contains Mg2+ / Ca2+

2 NH3

aqueous

•Add NH3 solution, little first, then in excess


•X contains Mg2+

3 Hydrochloric acid and barium chloride solution

•Add HCl followed by barium chloride solution

•No change

•No sulphate ion

4 Nitric acid and silver nitrate solution

•Add nitric acid followed by AgNO3 solution


•Chloride ion present

Reaction with


1 NaOH aq

Question 4Solution Y is aluminium sulphate .


•White precipitate soluble in excess


2 NH3 aqueous

•Add NH3 solution, little first, then in excess


•X contains Al3+ /Pb2+

3 Hydrochloric acid and barium chloride solution

•Add hydrocloric acid followed by barium chloride solution


•Sulphate ion present

4 Nitric acid and silver nitrate solution

•Add nitric acid followed by AgNO3 solution

•No change

•No Chloride ion present

5 Dilute sulphuric acid, iron (II) sulphate, concentrated sulphuric acid

•Add dil H2SO4, followed by Fe(SO4)2 solution•Carefully add con H2SO4 drop by drop

•No brown ring formed

•No nitrate ion present

End

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Preparation for Practical chemistry