Core Practicals and Techniques

Question 1

What are the safety hazards?

Answer 1

Irritant - dilute acids and alkalis - wear goggles
Corrosive - Stronger acids and alkalis - wear goggles
Flammable - Keep away from naked flames
Toxic - Wear gloves, fume cupboard
Oxidising - Keep away from flammable/oxidising agents

Question 2

Recrystallisation

Answer 2

1. Dissolve solid in minimum hot solvent
2. Filter the solution whilst hot
3. Cool filtrate
4. Filter with pump and wash with little cold solvent
5. Blot the crystals dry with filter paper

Question 3

Steam distillation

Answer 3

Used to extract volatile liquids from complex mixtures
Useful for obtaining products that can decompose when heated

Question 4

Gas collection

Answer 4

Don’t use too much carbonate as it will produce more gas than the syringe can take

Use diluted acid to slow the reaction down

Plunger may need a lubricant to let it move/prevent sticking

Gas can escape between addition of marble chips

Question 5

Preparing a standard solution

Answer 5

1. Weigh out acid salt and add into a clean beaker
2. Add 50cm^3 of distilled water and stir to dissolve
3. Transfer to a graduated volumetric flask and fill until 250cm^3
4. Stop the flask and mix by inverting and shaking

Question 6

Titration errors/key points

Answer 6

Make sure there’s no air bubbles in pipette or burette
Rinse burette and pipette with solutions that will be used
Read at eye level
Use concordant results

Question 7

Chlorination of a 3° alcohol

Answer 7

1. Add HCl and 3° alcohol into conical flask and swirl
2. Put rubber bung and swirl, releasing pressure from time to time
3. Add anhydrous CaCl2 and shake
4. Transfer into separating funnel and discard lower layer
5. Add NaHCO3 to remove unreacted HCl
6. Run off lower aqueous layer, then compile the organic layer into conical flask
7. Add anhydrous Sodium Sulfate to act as drying agent
8. Decant liquid and distill to purify product

Question 8

Finding Ka of a solution key points

Answer 8

Calibrate the pH meter
Subjective to end point of the reaction

Question 9

Iodoform Reaction - Titration and continuous monitoring

Answer 9

Catalyst: Sulfuric Acid
Add excess propanone and sulphuric acid so conc is effectively constant

1. Start the stop clock when you add the reactants
   2.Take samples of the reaction and quench with sodium hydrogencarbonate every 3 mins
2. Titrate samples with Sodium thiosulphate with starch indicator near the end
3. Repeat and find concentrations
4. Plot a graph of conc agains time (straight line)

Question 10

Iodine Clock Reaction

Answer 10

Total volume of solutions should be the same and volume of thiosulfate is the same
Plot a graph of concentration (volume) against rate
Vary volume of Iodine and persulfate
Stop the watch when starch indicator turns blue-black