Practical experiments

Question 1

Give experimental details of how to titrate acidified potassium manganate with reducing agents

Answer 1

1. Rinse pipette with solution of reducing agent and use pipette and filler to pipette 25.0 cm3 into a conical flask
2. Rinse the burette with a standard solution of potassium manganate and fill the burette
3. Add excess sulfuric acid using measuring cylinder
4. Add potassium manganate solution until solution changes from colourless to pink
5. Repeat until you have concordant results

Question 2

How do you determine the purity of a group 2 metal oxide or carbonate with a back titration?

Answer 2

1. Weigh out a mass of solid with top pan balance
2. Add excess hydrochloric acid
3. Add solution to 250cm3 volumetric flask and make up to mark with deionised water. Meniscus on mark
4. Rinse pipette with solution from volumetric flask and pipette 25.0 cm3 into a conical flask
5. Add 3 drops of phenolphthalein
6. Rinse burette with NaOH, fill burette
7. Titrate until colour changes
8. Get concordant results

Question 3

How do you carry out two way chromatography

Answer 3

1. Carry out method for normal chromatography
2. Rotate paper / thin layer plate 90º
3. Run in a second solvent …
4. Use spotting agent
5. Calculate Rf for second solvent

Question 4

How do you use ethylene diamine, phenylamine and aqueous ammonia to demonstrate ligand replacement

Answer 4

1. Place 2cm3 of a metal ion solution in a boiling tube
2. Add 1cm3 of phenylamine, shake and record observations
3. Add 1cm3 of aqueous ammonia, shake and record observations
4. Add 1cm3 of ethylene diamine, shake and record observations

Question 5

How do you demonstrate the relative strength of ligands using hexaaquacopper (II) ions in solution and in hydrochloric acid

Answer 5

1. Add 2cm3 of hexaaquacopper (II) ions into a test tube

2. Add 2cm3 of concentrated hydrochloric acid and record observations

Question 6

How do you carry out detection tests for the formation of transition metal hydroxides with sodium hydroxide and aqueous ammonia

Answer 6

1. Add 2cm3 of a solution of a transition metal ion to the test tube
2. Add a few drops of aqueous ammonia and record observations
3. Add excess aqueous ammonia and record obervations
4. Repeat with sodium hydroxide instead of aqueous ammonia

Question 7

How do you carry out the reduction of acidified ammonium vanadate with zinc §

Answer 7

1. Dissolve some ammonium vanadate in hydrochloric acid in a conical flask
2. Add two spatulas of zinc as a reducing agent
3. Stopper the flask with cotton wool, allow H2 gas to escape and slow down entry of air
4. Observe the sequence of colours

Question 8

Preparing aspirin using salicylic acid and ethanoic anhydride

Answer 8

1. Place 1g of 2-hydroxybenzoic acid in a dry pear shaped flask and add 2cm3 of ethanoic anhydride
2. Safely add 8 drops of concentrated phosphoric acid
3. Heat under reflux for 30 mins
4. Add water to hydrolyse any unreacted ethanoic anhydride to ethanoic acid
5. Pour the mixture onto crushed ice
6. Remove the product by suction filtration
7. Recrystallise from water
8. Dry in a dessicator
9. Determine the melting point