chemistry practicals for a level-cape

7/29/2019 Chemistry Practicals for a Level-CAPE

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Practical 1

Finding the formula of Epsom salts

REQUIREMENTS

Each student will need:

Eye protection, Rack and one clean, dry, hard-glass test tube, Solid hydrated magnesiumsulphate (Epsom salts) (approx. 2-3 g) Spatula, Bunsen burner, Test tube holder, Access to

balanceTime required 45 minutesIntroduction

Epsom salts are hydrated magnesium sulphate. Their formula is sometimes written as

MgSO4.xH2O. In this experiment, you will be trying to find the value ofx (i.e. the number of

moles of water associated with one mole of MgSO4 in Epsom salts).

Principle

When Epsom salts are heated, their water of crystallisation is driven off, leaving anhydrous

magnesium sulphate, MgSO4.

MgSO4.xH2O(s)MgSO4(s) + xH2O(g)By weighing the hydrated and anhydrous magnesium sulphate before and after heating, it ispossible to find the mass of MgSO4 and the mass of H2O in a sample of Epsom salts. From

these masses, you can calculate the number of moles of water associated with one mole ofMgSO4. You can then write the precise formula for Epsom salts.ProcedureWeigh a clean, dry test tube.

Put about 1 cm depth of Epsom salts in the test tube and reweigh.

Record these weighings and those which follow in a clear table.

Now, heat the test tube gently for a minute and then strongly for 5 minutes. Allow the tube to

cool and then reweigh it.


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g

Skill: analysis/interpretation

Criteria for assessment Marks

1) Calculating mass of Epsom salt 1

2) The water lost = the difference in mass=Initial mass of Epsom salt final mass

1

3) moles of water =mass / RMM =mass/ 18 2

4) Final moles of Epsom salt = mass of MgSO4/molar mass. 2

5) Ratio=moles of water /moles of MgSO4 2

answers to Questions:

6) What do you understand by the terms:

a hydrated, b anhydrous, c water of crystallization?3

7) How could you show that water is given off when Epsom salts are heated?1

8) Why must the Epsom salts be heated to constant weight?1

9) Suitable conclusion 1

TOTAL 14


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Structure, bonding and propertiesREQUIREMENTS

Each student. or pair of students, will need:

Eye protection Polythene rod and fur for charging Burette 3 beakers (100 ml) Rack with 6 test tubes Pair of carbon

electrodes100mA ammeter 6 V battery or power pack leads and crocodile dips Iodine (harmful) Calcium chloride

(solid) (irritant) Powdered graphite isopropyl alcohol(highly flammable) benzene (toxic) Distilled water Silver

nitrate solution (about 0.1 mol dm-3)

Introduction

Most of the physical and chemical properties of a substance can be related to the type of bonding present in it. In

this practical you will study properties such as volatility and conductivity and try to explain these properties in

terms of the bonding in the substance involved .

Substances that are ionically bonded contain positive and negative ions. Substances that are covalently bonded

contain molecules. If these molecules contain different elements, they may be polar due to the unequal sharing of

electrons between the different atoms. The degree of polarity in a molecule, determined by the shape of the

molecule and the relative e1ectronegativities of the atoms in it, has a significant effect on the properties of the

substance.

experiment 2:

The effect of a charged rod on thin streams of liquid

Charge a polythene rod by rubbing it on a piece of fur. Hold the rod about 1 cm from a thin stream of water

running from a burette. Note what happens.1 What sort of particles does water contain?

2 Are these particles polar?

3 Explain the effect of the charged rod on the stream of water.

4 What do you think would happen with a rod of opposite charge?

Explain your answer.

Repeat the experiment using benzene, and then isopropyl alcohol, instead of water.

5 Relate the behaviour of streams of these liquids towards a charged rod to the nature of the particles they contain.

6 Look up the boiling points and relative molecular masses of water, isopropyl alcohol and benzene. Try to explain

the relative magnitudes of their boiling points in terms of polarity.Experiment 3:

Miscibility of liquids

Test the miscibility of a water and isopropyl alcohol, b water and benzene, c benzene and isopropyl alcohol.


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and shake. Judge the relative solubility of calcium chloride in the three solvents from the amount of silver chloride

precipitated.

Answer questions 8 to 10 with reference to calcium chloride instead of iodine.

Experiment 7:

The volatility of iodine, graphite and calcium chloride

CARE!

Iodine vaporis corrosive and toxic. Use only a very small crystal of iodine and

work in a fume cupboard.

Heat a crystal of each of the solids in turn in a hard-glass test tube and judge their relative volatilities.

12 Try to explain the relative volatility of these three solids in terms of the particles they contain and the forces

between them.

Experiment 8:Conductivity

Collect each of the solutions produced in experiments 3, 4 and 5. Test the conductivity of each solution by the

following procedure.

Connect a pair of carbon electrodes in series with a 6 V battery and a100 mA ammeter. Dip the electrodes in the

solution under test and note the meter reading in each case. Test the same depth of solution each time. (If the

solid showed no sign of dissolving, do not bother to perform the test in that particular case.) You should also test

the conductivity of each of the pure solvents. Note: keep the electrodes clean and make sure they are not

contaminated with liquid from a previous rest.

13 Try to explain the relative conductivities of the different solutions.


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Skill: observation/recording/reporting

Experiment

number

Title observation marks

2 The effect of a charged rod

on thin streams of liquid

Jets of Water and isopropyl alcohol deflected

Benzene no deflection 3

3 Miscibility of liquids Water and isopropyl alcohol are miscible

Water and benzene immiscible

isopropyl alcohol and benzene immiscible however a layer

of emulsion formed distinctive layer still seen

3

liquid

Water isopropyl alcohol benzene4 The solubility of iodine in

different liquids

Slightly soluble soluble soluble 3

5 The solubility of graphite in

liquids insoluble

insoluble insoluble 3

6 The solubility of calcium

chloride In liquids

soluble soluble insoluble 3

substance

iodine graphite calcium chloride

7 The volatility of iodine,

graphite and calcium

chloride

high low low 3

substance

iodine Calcium chloride8 Conductivity

solv

water Does not conduct conducts 2

benzene Does not conduct Does not conduct 2


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YEAR 12 PRACTICAL 1

Aim: To determine the molarity of a solution of sodium hydroxide by titration against hydrochloric acid

using methyl orange indicator

Procedure

1. Rinse a burette with 0.500 moldm-3

hydrochloric acid.

2. Using a funnel, fill the burette with the acid until it is just below the zero mark. Check there are no air

bubbles in the tip of the burette. If there are, open the tap until the air bubbles disappear and re-fill the

burette. Then remove the funnel.

3. Use a pipette to place 25.0 cm3

of the sodium hydroxide solution into a clean conical flask. When

emptying the pipette into the conical flask, allow it to empty under gravity, and then touch the surface ofthe liquid with the pipette for approximately one second.

4. Add two drops of methyl orange indicator into the conical flask.

5. Record the initial volume in the following table:

Titration 1(rough)

Titration 2 Titration 3 Titration 4 Titration 5

Final volume (cm3)

Initial volume (cm3)

Titre volume (cm3)

Concordant? -

6. Titrate the acid into the alkali, 1 cm3 at a time until the mixture changes from yellow to pink. Record the

final volume in the table and work out the volume delivered (the titre volume).

7. Repeat steps 3 6, but now add the acid rapidly until the volume added is close to the previous titration,and then dropwise until the mixture changes colour Record the final volume in the table


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TO DETERMINE THE MOLARITY OF A SOLUTION OF SODIUM HYDROXIDE

YEAR 12 PRACTICAL 1Typical titre readings:

Rough 1 2 3 4

Initial reading 1.15 1.20 1.00 1.10 2.35

Final reading 30.15 28.70 28.00 27.70 29.05

Titre (cm3) 29.00 27.50 27.00 26.60 26.70

Titres 3 and 4 are concordant.

1) Average titre = (26.60 + 26.70)/2 = 26.65

Overall equation.

NaOH + HCl NaCl + H2O

Information

Concentration of HCl = 1.0 mol dm-33


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Skill:_ Analysis and Interpretation


) U l d t tit 1


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1.Follows instructions

2.Use of burette

(a) Using a funnel to transfer the hydrochloric acid to burette without spillage.(b)Rinsing the inside of the burette with a small amount of the acid to minimize

concentration error.

(c) Makes sure that eyes are level with bottom of meniscus when reading the burette(d)Ensures that the burette is free of air bubbles3. Use of pipette

(a) Uses the forefinger to monitor the flow of liquid in pipette so that bottom ofmeniscus is at the graduation mark.

(b)

Allows liquid to flow freely from pipette under gravity.

4. Reaction vessel

(a) Swirls conical flask to ensure proper mixing of reagents.(b)Takes care in adding acid so as not to exceed the end point.(c) Repeats titration to get agreeable results

1

1

1

1

1

1

1

1

1

1

TOTAL 10


10/27

Experiment # 10: Analyzing iron tablets

Apparatus/materials: Iron tablets (5) sold by chemists as ferrous sulphate tablets, 1.0 mol dm-3

sulphuric acid (irritant)(200 cm3), 0.01 mol dm-3 potassium manganate(VII), (75 cm3), conical flasks (250 cm3), Standard flask (250 cm3), Buretteand stand, Pipette (25 cm3) and safety filler, Filter funnel, Filter paper, Wash bottle and distilled water .

Introduction: Iron is essential to the human body. Its principal role is as a constituent of haemoglobin, the oxygen-carrying agent inthe blood. Iron is also present in a number of enzymes and co-enzymes involved in redox processes in the body.

Some groups in the population need substantial amounts of iron in their diet in order to produce extra haemoglobin. Such people

include growing children, pregnant and menstruating women, and people who have for various reasons lost considerable amounts of

blood. A satisfactory intake of iron can normally be ensured by eating a suitable diet, because certain foods - liver, kidney, egg yolk

and spinach for example - are rich in iron. Nevertheless, it is sometimes necessary to supplement the iron taken in the natural diet

with 'iron tablets'.

Iron tablets bought at the chemist usually contain iron(II) sulphate (ferrous sulphate) a cheap, soluble form of iron. In this practical

you will attempt to find the actual percentage of iron(II) sulphate in the tablets and then compare this result with the quantity statedon the bottle.

Assuming all the iron in the tablets is in the form of Fe2+

, it is possible to estimate the iron content by titration against potassium

manganate(VII), KMnO4.

The equation for the reaction of Fe2+

with 4 in acid solution is:

5Fe2+

(aq) + 4 (aq) + 8H

+(aq) 5Fe

3+(aq) + Mn

2+(aq) + 4H20(1)

1. How many moles of Fe react with 1 mole of4 P- ?ProcedureMaking a solution of the tablets

Weigh accurately 5 of the iron tablets, then dissolve them in about 100 cm3

of 1.0 mol dm-3

sulphuric acid in a conical flask. This

will probably require heating, but do not heat more than necessary to dissolve the tablets.

2. Why should the tablets not be heated more than necessary?3. Why are the tablets dissolved in sulphuric acid instead of water?

The outer coating of the tablets will probably not dissolve, so the solution will need filtering.

4. What do you think the outer coating might be?Filter the mixture into a beaker, making sure you do not lose any of the solution, then wash out the conical flask with

t d th hi th h th filt Fi ll di till d t th id d ll t th hi


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Skill: Analysis and Interpretation


1. How many moles of Fe react with 1 mole of MnO4

P

- ? ans:12. Why should the tablets not be heated more than necessary? To prevent

oxidation of Fe2+3. Why are the tablets dissolved in sulphuric acid instead of water? To

prevent oxidation of Fe2+4. What do you think the outer coating might be?5. How many moles of MnO4

were needed to react with 25 cm3 of your Fe2+solution?

[# of moles of MnO4 used = volume of MnO4

used concentration]1000

6. How many moles of Fe2+ are there in 25 cm3 of the solution?[# of moles of Fe2+ used = 5 x # of moles of MnO4

-(aq ]

7. How many moles of Fe2+ are there in all the tablets?250

25 # of moles of Fe

2+

in 25 cm

3

8. How many moles of Fe2+ are there in one tablet?answertoquestion7

5

9. What mass of:a) Fe, mass = molesx molar massb) FeS0

4, mass = molesx molar mass

c) FeS04.7H20 mass = molesx molar mass

is there in one tablet?

1

1

1

0

3

1

2

1

1

1


12/27

YEAR 12 PRACTICAL 11

Aim: To find the molar enthalpy change for the neutralisation of hydrochloric acid by sodium

hydroxide

Method:

1. Place a clean, dry polystyrene cup inside a glass beaker.2. Pipette 25.0 cm3 of 1.0 moldm-3 hydrochloric acid into the cup.3. Start the stopclock and record the temperature, to 1 decimal place, of the solution every 30 seconds

for 3 minutes.

4. While you are waiting, pour some 1.0 moldm-3 sodium hydroxide solution into a beaker and recordits temperature using another thermometer.

5. Using another pipette, prepare 25.0 cm3 of the sodium hydroxide solution and after the timer hasbeen running for 3 minutes run the sodium hydroxide solution into the cup containing the acid.

6. Place a lid on the cup and continue to measure the temperature of the solution every 30 seconds untilthe stopclock has been running for a total of 10 minutes. Continue to stir gently using thethermometer.

Analysis:

1. Plot a graph of temperature against time.2. Extrapolate the part of the graph with a negative gradient to find out what the temperature would

have been after 3 minutes. Use this as your final temperature.

3. Take the mean of the temperature of the acid and the alkali just before they were mixed. This isyour initial temperature.

4. Calculate the temperature rise using your initial and final temperatures.5. Taking the density of the solution to be 1.0 gdm-3, the specific heat capacity to be 4.18 JK-1g-1

and assuming the total volume of liquid has not changed, calculate the heat change during thereaction.

6. Write an equation for the reaction and work out the number of moles of NaCl produced. 7. Work out the enthalpy change per mole of salt produced. Include a sign and units in your answer.


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YEAR 12 P11 worked answer

TimeTemperature(deg C)

0 23.1

0.5 23.11 23.1

1.5 23.1

2 23.1

2.5 23.1

3

3.5 29.2

4 29.1

4.5 29.15 28.9

5.5 28.8

6 28.7

6.5 28.6

7 28.6

7.5 28.5

8 28.4

8.5 28.39 28.3

9.5 28.2

10 28.2

variation of temperature with time during neutralisation

25

30

35

)


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Skill:_ Observation/recording/reporting


1. Overall organization of work(a) Appropriate subheadings(b)Subheadings in logical order(c) Subject matter under appropriate subheadings

2. Report of method adopted(a) Logical sequence in steps(b)Concise account(c) Grammar and spelling: correct

One or two errors

Many errors

3. Graph:(a) Correct quantities plotted on axes [temperature (y-axis) against time]

(b) Title of graph with axes labeled with quantity and unit(1 mark deducted for each omission)

(c) Suitable scale for each axis(d)Fine circled points or sharp crosses, thin line(e) Accurate plotting of all readings (all points correct (3), one point incorrect

(2), two points incorrect (1), three or more incorrect (0)

(f) Line of best fit [as shown worked example]

111

1

1

2(1)

(0)

1

2

2

13

1

TOTAL 17

Skill: Manipulation/Measurement


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Skill:_ Analysis and Interpretation


a) extrapolate 0 3 mins to 3.5 mins gives 23.1 oCinitial temp of NaOH = 23.3 oC

so mean temp = 23.2 oC

b) extrapolate 4 10 mins to 3.5 mins gives 29.3 oC

so temperature change = 6.1oC

c) q = (25 + 25) x 4.18 x 6.1 = 1275 J = 1.275 kJ evolvedd) moles of HCl (or NaOH) = 25/1000 x 1 = 0.025 moles

e) so H = 1.275/0.025 = -51 kJmol-1

f) error = 57.6 51 = 6.6

o % error = 6.6/57.6 = 11.5 %

o

apparatus error= 0.1/6.1 x 100 = 1.64 % (thermometer)= (0.05/25) x 100 = 0.20 %

0.20 % x2 = 0.40 % (2 pipettes)total 2.04 % error

o so error is greater than apparatus error

g) the main sources of error are- heat loss to the surroundings, particularly through the top of the cup- the heat absorbed by the polystyrene cup

2

2

2

1

1

2

2

1

2


16/27

A SIMPLE KINETICS PLAN

Hydrogen peroxide decomposes in the presence of metal oxide catalysts to form oxygen and water

according to the following equation.

2H2O2 2H2O + O2

in the presence of the catalyst manganese (IV) oxide. Plan and design an experiment to investigate

how the rate of decomposition of hydrogen peroxide is affected by temperature.

(a) Determine a suitable number of moles of hydrogen peroxide to be used in the experiment.

(5)

(b) Suggest a suitable volume and concentration of hydrogen peroxide for the experiment.

(3)

(c) Outline the procedure in full, giving details of any apparatus used.

(10)

(d) Indicate any hazards or safety precautions specific to the experiment.

(2)

(Total 20 marks)

KINETICS PLAN MS


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Experiment 13

Data Analysis Lab

Aim : To determine the order of a reaction and the rate constant in a single species

reaction

For the experimental data

Time (mins ) Concentration of reactant (M)

0 0.819

2 0.619

4 0.468

6 0.353

8 0.267

10 0.202

15 0.100

20 0.050

i) Plot a graph of the data 4 mks


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Data Analysis Lab

Skill: Analysis/ I nterpretation

Plot a graph of the data 4 mks

Determine the order of the reaction 2 mks

Calculate the rate constant , k 2 mks

Using k find the time for the concentration to drop to a quarter ( ) of the original concentration

2 mks

Total = 10 marks


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A practical study of the third periodREQUIREMENTS

Eye protection, Samples of elements from period 3. Because of the hazardous nature of sodium (highly flammable),phosphorus (toxic) and chlorine (toxic), it is best for the teacher to demonstrate these elements. It is important to avoidconfusion between phosphorus (stored under water) and sodium (stored under oil).Ideally, phosphorus and sodium should notbe in the laboratory at the same time. Simple apparatus to test electrical conductivity 1 rack + 4 test tubes Full-range indicator

paper Samples of the following oxides: Na2O (or NaOH) (corrosive), MgO, AI2O3, SiO2, P2O5 (corrosive) Access to SO2cylinder, Dilute hydrochloric acid (irritant) Dilute sodium hydroxide solution (corrosive) Samples of the following chlorides:NaCI, MgCI2, AICI3, PCI3, SCI2 (or S2CI2) AICI3, PCI3, SCI2 and S2CI2 are all corrosive Bunsen burner

IntroductionThe periodic table provides a very important unifying pattern to the study of chemistry. The intention of this practical is tostudy some of the trends in properties across the third period of the periodic table.

A Patterns in the properties of elements

The properties of the elements show a repeating pattern with increasing atomic number. The most obvious pattern is the

steady change from metals on the left to non-metals on the right of each period.

Procedure

Examine samples of the elements sodium to argon in period 3. Test the electrical conductivity of those elements for which the

results are not given in table 1.

1. Copy and complete table 1. You will have to consult a data book, or Section 4.7 in Chemistry in Context, Fifth Edition,

for boiling point values.

Na Mg Al Si P S Cl Ar

Atomic number

Physical state and appearance

Boiling point/C

Conductivity at room temperature good poor poor poor

Structure (giant metallic, giant molecular or

simple molecular)

Type of element


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Test the solubility of each oxide in water. Add a very small measure ofeach solid to about 3 cm3 of distilled water and shake thoroughly. (In the case

of sulphur dioxide, bubble the gas through 3 cm3

of water in a fume cupboard

for a few seconds.)

If Na2O is not available, use sodium hydroxide (NaOH) (CARE Corrosive. Wearprotective gloves.) Some oxides will dissolve easily. Others will not dissolve at all.Test the pH of the solution obtained from each oxide using full-range indicator paper.Record your results in table 2.

5. Which of the oxides of period 3 elements:a) form acidic solutions with water,b) form alkaline solutions with water

c) are insoluble in water?6. Write equations for the reactions of the soluble oxides with water.

If an oxide is insoluble in water, its reactions with acids and alkalis canbe used to decide its acid-base character. If an oxide dissolves in acid, it 'musthave reacted with it. The oxide can therefore be classified as basic. If theoxide dissolves in alkali, it can be described as acidic. If the insoluble oxidedissolves in both acids and alkalis, it is both basic and acidic. The adjective

'amphoteric' (from a Greek word meaning 'both') is used to describe theseoxides.

Test the solubility of the insoluble oxides in dilute hydrochloric acid and then in

dilute sodium hydroxide solution. Remember to use small measures of solid.

7.Write equations for any reactions of the insoluble oxides:a) with hydrochloric acid,b) with sodium hydroxide solution.

8.Complete the last two lines in table 2.9. Describe the following patterns in the properties of the oxides

across period 3:


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Skill:_ Observation/recording/reportingNa Mg Al Si P S Cl Ar

Atomic number 11 12 13 14 15 16 17 18

Physical state and appearance Silverysolid

Silvery

solid

Silvery

solid

grey solid Red orwhite solid

Yellowsolid

Yellowgreen gas

Colourlessgas

Boiling point/C 883 1090 2467 2680 280 445 -35 -186

Conductivity at room temperaturegood good good fair poor poor poor poor

Structure (giant metallic, giant

molecular or simple molecular)giant

metallicgiant

metallicgiant

metallicgiant

metallicsimple

molecularsimple

molecularsimple

molecularsimple

molecular

Type of element

(metal, non-metal or metalloid)metal metal metal metalloid non-metal non-

metal

non-metal non-

metal

Oxide formula Na2O MgO Al2O3 SiO2 P4O10 SO2 C12O

State at room temp.(s) (s) (s) (s) (s) (g) (g)

Appearance white white white Colourless

Colourless

gas

yellow-red gas

Volatility low low low low high high high

Conductivity of molten oxide good good good poor poor poor poor

Solubility in watersoluble insoluble insoluble insoluble soluble soluble dissolves readily

pH of solution in water 13 7 7 7


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Data Analysis lab To determine the relative molecular mass, Mr, of a volatile liquidSkills assessed Analysing (6 marks) and Interpretation (6 marks)Topic: Kinetic TheoryIntroductionCompound X is a volatile liquid. In order to determine the relative molecular mass, Mr, of X, a student

carried out six experiments. In each experiment a measured mass of X was injected into an empty100cm3 gas syringe maintained at a pressure of 100 kPa and a temperature of 373 K. In each of thesix experiments the volume of gas produced was measured. The students results are shown in thetable below.The apparatus used is shown in the diagram below.

Volume/cm3

Mass/g

19.0 0.0433.5 0.07

38.0 0.08

46.0 0.09


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Skill assessed Analysing (6)

Q3 volume for 0.10g is 47.0 - 48.0 cm3

1 markNotes Donotallow other answers

Q4 PV = nRT 1 markQ5 100 10

3 47.5 10

-6= 0.1 8.31 373

MrMr = 66.0 - 64.5 1 markNotes Consequential marking from answer to Q3 Donotaward this mark if candidate gets the correct answer by an incorrectmethod; don.t penalise again in awarding the nomenclature markQ6 errors balance 0.01/0.1 100 = 10% 3 scoring pointssyringe 1/ 47-48 100 = 2.1% any 2 = 1 marktotal error 12.1%Notes Ignore precision of answers Consequential marking for volume from Q3 and for overall error Penalise doubled errorsonce Lose markif answers wrong because (x 100) missing from calculations; dont penalise again in awardingthe nomenclature mark

Which error being calculated isnotstated; allowifthe calculations are in the same order as in the question(balance, syringe). And donotpenalise in nomenclature

(a) The appreciation of precision quotes volume as integer or to 1 dp 2 scoring points(b) quotes Mr to 1 dp both = 1 mark

Notes If no answer to part 4 can.t score this mark(b) the correct use of nomenclature and terminology 3 scoring points

second graph has sharp trace all 3 = 1 markexplains the calculation of the Mr clearly and logically

explains the calculation of the errors clearlyexplains the calculation of the Mr clearly and logicallyexplains the calculation of the errors clearly

Notes


24/27

more accurate thermometer collect more gas repeat experiment

Q4 volume lower than expected (as some liquid lost) 1 markcalculated Mr would be larger 1 mark

Notes Mark points independently Accept less gas producedTotal 6 marks


25/27

Observing the reactions of cations

Testing with sodium hydroxide solutionAdd a few drops of sodium hydroxide solution to 3 cm3 of a solution containing Al 3+(aq).

What happens? Write an equation for the reaction.Does the precipitate remain or dissolve when excessNaOH(aq)

is added?

Testing with aqueous ammoniaRepeat test1 using aqueous ammonia

Testing with sodium carbonate solution

Repeat test1 using aqueous sodium carbonate solution

Repeat the experiment with solutions containing the following cations in place of Al3+:

Ba2+, Ca2+, Cu2+, Fe2+, Fe3+, K+, Mg2+, Mn2+, Na+, NH4+, Pb2+, Zn2+.Record your results in a table similar to table 2.Cationtested

Few drops of NaOH(aq)added

NaOH(aq) added Few drops ofNH3(aq) added

ExcessNH3(aq)

added

Few dropsof

Na2CO3(aq)added

Al3+: White pptAl3+(aq) + 3OH-(aq)Al(OH)3(s)

White precipitatedissolves forminga clear solutionAl(OH)3(s) + OH

-

(aq) Al(OH)-4(aq)

white ppt forms

Al(OH)3(s) +OH-(aq)Al(OH)-4(aq)

In excess,

insolubleWhite ppt2Al3+(aq) +3CO3

2-(aq)

Al2(CO3)3(s)

Ba2+, White pptBa2+ (aq) + 2OH-(aq)

Ba(OH)2(s)

soluble no ppt - White pptBa2+ (aq) +CO3

2-(aq)


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Pb2+ white ppt formsPb2+ (aq) + 2OH-(aq)

Pb(OH)2(s)

In excess, dissolves

giving colourless

solution

white ppt forms In excess,

insolubleWhite pptPb2+ (aq) +CO3

2-(aq)

PbCO3(s)

Zn2+ White pptZn2+ (aq) + 2OH-(aq)

Zn(OH)2(s)

solubledissolves giving

colourless solution

white ppt formsZn2+ (aq) +2OH-(aq)Zn(OH)2(s)

In excess,dissolves giving

colourless

solution

Zn(OH)2(s) +4NH3[Zn(NH3)4](OH)2

White pptZn2+ (aq) +CO3

2-(aq)

ZnCO3(s)

1 point for each correct observation1 point for each correct equationTotal 78 pointsdivide no. of points obtained by 78 then multiply by 10


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Skill:_ Observation/recording/reporting Subtract 1 mark for each omission.

Anion Test observation marksCarbonatepH>10

CO32

universal

indicator

Add (dil)HCl(aq). Pass gas through lime

water,

gasevolved turning lime water milky

2H

+

(aq)

+ 3()

2

CO2 (g) + H2O(l)Ca(OH)2(s) + CO2(g) CaCO3 (s) + H2O(l)

2

HydrogencarbonateHCO3

pH 8-9

Add (dil)HCl(aq). Pass gas through limewater,

gasevolved turning lime water milky

H+

(aq)+

3()

CO2 (g) + H2O (l)

Ca(OH)2(s) + CO2(g) CaCO3 (s) + H2O(l)

2

ChlorideCl

Acidify with (dil)HNO3(aq). Add

AgNO3(aq). Add dil NH3 to pptWhite ppt AgCl forms. Ppt dissolves leaving colourless solution

Ag+

(aq) + Cl-(aq) AgCl(s)

AgCl (aq) + 2NH3(aq) [Ag(NH3)2]+

(aq) + Cl-(aq)

2

BromideBr

Acidify with (dil)HNO3(aq) Add

AgNO3(aq) Add (conc)NH3 to pptCream ppt AgBr forms Ppt dissolves leaving colourless solution

Ag+

(aq) + Br-(aq) AgBr(s)

AgBr(aq) + 2NH3(aq) [Ag(NH3)2]+

(aq) + Br-(aq)

2

Iodide

I

Acidify with (dil)HNO3(aq) Add

AgNO3(aq) Add (conc)NH3 to pptYellow ppt AgI forms Ppt insolubleAg

+(aq) + I

-(aq) AgI(s)

2

NitrateNO3

Add NaOH(aq) Add Devardas alloy(powdered Zn, Al) Heat & hold moist

red litmus at mouth of test tube

NH3 evolved, litmus paper red blue 2Even without

equation

SulphateSO42 Add Barium nitrateBa(NO3)2(aq)/chloride BaCl2(aq)

Add HCl(aq)

White ppt. InsolubleBa

2+(aq) + SO4

2-(aq) BaSO4(s)

2

SulphiteSO3

2Add Barium nitrate

Ba(NO3)2(aq)/chloride BaCl2(aq)

Add HCl(aq)

White ppt. Dissolves

Ba2+

(aq) + SO32-

(aq) BaSO3(s)

BaSO3(s) + 2H+

(aq) Ba2+

(aq) + H2SO3(aq)

2Even without

2nd

equation

Or add (dil)HCl(aq) Heat SO2 evolved turning potassium dichromate(VI) solution/paper fromorange green

2

TOTAL 18

chemistry practicals for a level-cape

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