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 Cati ons Sodium hydroxide solution Ammonia solution Confirmat ory tests For ms no preci pitat e NH 4 + 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 Catio ns Sodium hydroxide solution Ammonia solution Confirm atory tests For ms no pre cipi tate Na + No change K + No change

Forms white ppt Ca +2 White precipitate No change Mg +2 White precipitate NO Cations Sodium hydrox (aq Ammonia solution Confirm atory tests

Form s white ppt Solubl e in excess Zn +2 soluble in excess White precipitate soluble in excess White ppt CationsSodium hydroxide solution Ammonia solutionConfirmatory tests

Video test on zinc ion- click to play

Form s white ppt Solubl e in excess Al +3 White ppt soluble Add …………… sulphate solution or add potassium sulphate solution- NO PPT White pptsodium Catio ns NaOH solution Ammonia solution Confirmato ry tests

NaOH (aq) Ammoni a (aq) Confirmatory test Forms white ppt Solubl e in excess Pb +2 White precipit ate soluble in excess White precipita te Add Na 2 SO 4 solution OR add K 2 SO 4 solution- WHITE PRECIPITATE OR KI solution turns ……………. PRECIPITATE yellow

Forms coloure d ppt Fe +2 ……… ……….. precipit ate Green precipitate Potassium hexa………… (III) turns dark blue Fe +3 Brown precipit ate ………… …….preci pitate ………………….. hexacyanoferrate (II) turns dark blue green cyanoferrate brown Potassium CationsSodium hydroxide solution Ammonia solutionConfirmatory tests

Forms coloured ppt Cu +2 Blue precipitate Blue precipitate soluble in excess to form dark blue solution NO CationsSodium hydroxide solution Ammonia solutionConfirmatory tests

Test for anions Anionsprocedureobservations nitratesAdd dilute sulphuric acid to nitrate solution Add iron (II) sulphate solution Add conc sulphuric acid Brown ring formed

Test for anions Anionsprocedureobservations carbon ates Add any dilute acid to carbonate solution Bubbles of gas produced that turn lime water cloudy

Test for anions Anionsprocedureobservations chlorideAdd dilute nitric acid to chloride solution Add silver nitrate solution White precipitate

Test for anions Anionsprocedureobservations Sulphat e Add dilute hydrochloric acid to sulphate solution Add barium chloride solution White precipitate

2) ( remember this table )Effect of heating on salts SaltsGas released Residue formed 1)Nitrate s All nitrates Nitrogen dioxide and ……………. Metal oxide Except sodium nitrate and potassium nitrate oxygenMetal 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 SALTSSOLUBLEINSOLUBLE CHLORIDE S ALL PAH=== Pb chloride, …….. chloride, Hg chlorides SULPHATE S allPCB == Pb sulphate, ………..sulphate, Ba sulphate silver calcium

Soluble and insoluble in water

NITRATES All solublenone CARBONA TES 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 metal s Grey in colour except i)Silver is shiny ………………………………. ii)Gold is shiny …………………………. iii)Copper is …………………………………. Other s Lead(II) iodide is …………………………………, lead(II) chromate is yellow, white yellow brown yellow

Experiment Salt /cation/anion 1Blue 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 3A 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 5A 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 7A 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 9A solution which gives bubbles of gas with sulphuric acid Cl – ion Chloride ion CO 3 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 11A solution which gives white precipitate with nitric acid and barium nitrate solution NO 3 – ion Nitrate ion SO 4 2 – ion sulphate ion

12 A solution which gives yellow precipitate with potassium iodide solution 13A 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

ProcedureObservationInference 1Heat salt Y strongly Lime water turns chalky Residue is brown when hot, yellow when cold Salt Y Gas CO 2 Salt Y is carbonate salt Residue is lead(II) oxide

ProcedureObservationInference 2Cool 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 cm 3 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 Zn 2+ / Al 3+ /Pb 2+

NH 3 aqueous Pour 2 cm 3 of solution X into a test tube. Add ammonia aqueous, little first and shake well, and then in excess and shake well White precipi tate X contains Al 3+ /Pb 2+

Potassiu m iodide solution Pour 2 cm 3 of solution X into a test tube. Add 1 cm3 of potassium iodide solution Yellow precipitat e is formed Therefore salt Y is ……….. X contains Pb 2+ ion Lead(II) carbonate

Procedu re ObservationInference 1Heat salt Y strongl y 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 NO 2 gas and O 2 gas Y contains nitrate Residue is zinc oxide

ProcedureObservationInference 2Cool 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, 1NaOH aqueous Add NaOH solution, little first, then in excess White precipitate, soluble in excess X contains Zn 2+ / Al 3+ /Pb 2+

To the solution X, 2NH 3 aqueous Add NH 3 aq, solution, little first, then in excess White precipitate, soluble in excess X contains Zn 2+

Reaction with ProcedureObservationInference 1NaOH aqueous Question 3 – Solution Q is magnesium chloride Add NaOH solution, little first, then in excess White precipitate X contains Mg 2+ / Ca 2+

2NH 3 aque ous Add NH 3 solution, little first, then in excess White precipitate X contains Mg 2+

3Hydroc hloric acid and barium chlorid e solutio n Add HCl followed by barium chloride solution No change No sulphate ion

4Nitric acid and silver nitrate solution Add nitric acid followed by AgNO3 solution White precipitate Chloride ion present

Reaction with ProcedureObservationInference 1NaOH aq Question 4 Solution Y is aluminium sulphate. Add NaOH solution, little first, then in excess White precipitate soluble in excess X contains Zn 2+ / Al 3+ /Pb 2+

2NH3 aqueou s Add NH 3 solution, little first, then in excess White precipitate X contains Al 3+ /Pb 2+

3Hydroc hloric acid and barium chloride solution Add hydroclo ric acid followed by barium chloride solution White precipitate Sulphate ion present

4Nitric acid and silver nitrate solutio n Add nitric acid followed by AgNO3 solution No change No Chloride ion present

5Dilute sulphuri c acid, iron (II) sulphate, concentr ated sulphuri c acid Add dil H 2 SO 4, followed by Fe(SO 4 ) 2 solution Carefully add con H 2 SO 4 drop by drop No brown ring formed No nitrate ion present

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