practical skills

Question 1

CP-01- Finding the molar volume of gas
determine the molar volume of a gas

Answer 1

1.Add dilute HCl to a conical flask.

2. Set up the delivery tube to an inverted measuring cylinder filled with water.
3. Add magnesium ribbon to the flask, quickly seal with a bung.
4. Measure the volume of gas collected.
5. Use moles = mass/Mr and volume = mol × 24 to find molar volume.

Question 2

cp-01 key points

Answer 2

Ensure airtight setup to avoid gas loss.

Collect gas over water, not air.

Use ideal gas equation if working at room temperature and pressure.

Question 3

CP02 – Preparation of a standard solution and titration

Answer 3

Accurately weigh a known mass of solute.
Dissolve in distilled water in a beaker.
Transfer to a volumetric flask and fill to the mark.
Rinse burette and pipette, then fill burette with acid.
Pipette base into a conical flask, add indicator.
Titrate until end point, repeat for concordant results.

Question 4

CP03 – Titration (Redox or acid-base)

Answer 4

Follow CP02 procedure, using appropriate redox indicators

Question 5

CP04 – Rate of hydrolysis of halogenoalkanes

Answer 5

Prepare water bath at constant temperature.

Add equal volumes of ethanol and halogenoalkane to test tubes.

Add silver nitrate solution and start timing.

Observe time taken for precipitate to form.

Compare rates for different halogens.

Question 6

CP05 – Oxidation of ethanol

Answer 6

Mix ethanol with acidified potassium dichromate.

Heat under reflux for full oxidation to ethanoic acid.

Distill for partial oxidation to ethanal.

Collect and test the product.

Question 7

CP06 – Chlorination

Answer 7

Add alkane and chlorine water to a test tube.

Expose to UV light.

Observe colour change and product formation

Question 8

CP07 & CP15 – Analysis of unknown compounds

Answer 8

Perform functional group tests:
2,4-DNP for carbonyl
Tollens’ for aldehyde
Bromine water for alkene
NaHCO₃ for carboxylic acid

Purify and recrystallise if solid.

Measure melting point and compare to known values.

Question 9

CP08 – Enthalpy change using Hess’s law

Answer 9

Measure temperature change in neutralisation or dissolution.

Record masses and temperatures.

Calculate q = mcΔT.

Use Hess’s law cycle to find unknown enthalpy.

Question 10

CP09 – Finding Ka

Answer 10

Measure pH of known concentration of weak acid.

Use pH = –log[H⁺] to calculate [H⁺].

Use Ka = [H⁺]² / [HA].

Question 11

CP10 – Electrochemical cells

Answer 11

Set up two half-cells: metal dipped in its ion solution.

Connect via a salt bridge.

Use a voltmeter to measure EMF.

Question 12

CP11 – Redox titration

Answer 12

Pipette reducing agent (e.g. Fe²⁺) into flask.

Titrate with oxidising agent (e.g. KMnO₄) from burette.

Stop when permanent pink colour persists.

Repeat for concordant results.

Question 13

CP12 – Transition metal complex preparation

Answer 13

Mix solutions of metal salt and ligand (e.g. NH₃).

Filter to collect precipitate (if solid).

Dry product and store.

Question 14

CP13 – Iodine reactions

Answer 14

Add iodine solution to flask with starch.

Titrate with thiosulfate until blue-black disappears.

Repeat for consistent titres.

Use data to calculate concentration of iodine.

Question 15

CP14 – Activation energy

Answer 15

Perform same reaction at different temperatures.

Measure time for reaction to occur (e.g. cross disappearance).

Calculate rate = 1/time.

Plot ln(rate) vs 1/T and find gradient = –Ea/R.

Question 16

CP16 – Synthesis of aspirin

Answer 16

Mix salicylic acid with ethanoic anhydride and acid catalyst.

Heat gently then cool.

Filter crystals and wash.

Recrystallise using ethanol or water.

Dry and measure melting point.