Post on 01-Jan-2016
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
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
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
Cations Sodium hydroxide solution
Ammonia solution Confirmatory tests
Forms coloured ppt
Cu +2 Blue precipitate
Blue precipitate soluble in excess to form dark blue solution
NO
Cations Sodium hydroxide solution
Ammonia solution Confirmatory tests
Test for anions Anions procedure observations
nitrates Add dilute sulphuric acid to nitrate solutionAdd iron (II) sulphate solutionAdd conc sulphuric acid
Brown ring formed
Test for anions Anions procedure observations
carbonates
Add any dilute acid to carbonate solution
Bubbles of gas produced that turn lime water cloudy
Test for anions Anions procedure observations
chloride Add dilute nitric acid to chloride solutionAdd silver nitrate solution
White precipitate
Test for anions Anions procedure observations
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
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
Procedure Observation Inference
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
Procedure Observation Inference
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
•X contains Zn2+ / Al3+ /Pb2+
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
Procedure Observation Inference
1 NaOH aqueous
Question 3 – Solution Q is magnesium chloride
•Add NaOH solution, little first, then in excess
•White precipitate
•X contains Mg2+ / Ca2+
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
•White precipitate
•Chloride ion present
Reaction with
Procedure Observation Inference
1 NaOH aq
Question 4Solution Y is aluminium sulphate .
•Add NaOH solution, little first, then in excess
•White precipitate soluble in excess
•X contains Zn2+ / Al3+ /Pb2+
2 NH3 aqueous
•Add NH3 solution, little first, then in excess
•White precipitate
•X contains Al3+ /Pb2+
3 Hydrochloric acid and barium chloride solution
•Add hydrocloric acid followed by barium chloride solution
•White precipitate
•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