Practicals Flashcards
Titrating iodine with sodium thiosulfate solution using starch and hence estimate oxidising agents by their reaction with excess acidified potassium iodide
- Rinse pipette with sodium iodate(V) solution, using pipette filler, pipette 25cm^3 of standard potassium iodate(V) solution into conical flask
- Add approximately 1.5g of potassium iodide (excess) and excess sulfuric acid
- Rinse burette with standard sodium thiosulfate, fill burette w it
- Add standard sodium thiosulfate from burette until solution is straw coloured, add 3 drops of starch indicator
- Titration until blue-black to colourless
- Repeat until results are concordant
Titrating acidified potassium manganate(VII) solution with reducing agents
- Rinse pipette with solution of reducing agent and use pipette to transfer 25cm^3 to conical flask
- Rinse burette w standard solution of potassium manganate(VII) and then fill burette
- Add excess sulfuric acid using measuring cylinder to conical flask
- Add potassium manganate(VII) solution from burette into conical flask and swirl until colourless to pink
- Repeat until results are concordant
Determine purity of a group II metal oxide or carbonate by back titration
- Weigh out mass of the solid
- Add excess HCl
- Add to 250 volumetric flask - make up w deionised water until meniscus on mark
- Rinse pipette with solution from volumetric flask and pipette 25cm^3 to conical flask
- 3 drops phenolphthalein
- Rinse burette with alkali and fill
- Add alkali until indicator changes colour
- Repeat until concordant
Carrying out paper and thin-layer chromatography and measure the Rf values of the components and interpret the chromatogram
- Base line in pencil close to bottom
- Spot samples on line using capillary tube - dry - repeat till spot concentrated
- Place paper in tank with shallow amount of solvent - cover with lid - allow solvent to run up over spots until solvent almost reaches top - mark solvent front - allow to dry
- If substances are colourless then spray with locating agent eg ninhydrin
- Measure dist travelled by the solvent front and each spot - calculate the Rf
Two-way chromatography
Chromatography method then
- Rotate through 90°
- Run in second solvent
- Locating agent if colourless
- Rf
Carrying out the reduction of acidified ammonium vanadate(V) with zinc and observing the sequence of colours
- Dissolve some ammonium vanadate(V) in HCl in conical flask
- Add two spatulas of zinc as reducing agent
- Stopper with cotton wool, allow H to escape and slow entry of air
- Observe sequence of colours
Determining the electrode potentials of a series of cells and predicting their values using standard electrode potentials
- Set up a half cell - a metal dipping in 1M solution of its ions in a beaker
- Attach via wires, and a voltmeter to a second half-cell using a different metal and a 1M solution of its ions
- Use salt bridge to connect two beakers
- Record the voltage
Preparing aspirin using salicylic acid and ethanoic anhydride
- Place 1g of 2-hydroxybenzoic acid in a dry pear shaped flask and add 2cm^3 of ethanoic anhydride
- Safely add 8 drops of concentrated phosphoric(V) acid
- Heat under reflux for 30 mins
- Add water to hydrolyse any unreacted ethanoic anhydride to ethanoic acid
- Pour the mixture onto 400g of crushed ice in a beaker
- Remove product by suction filtration
- Recrystallise from water
- Dry in low temp oven
- Determine melting point
Using chromatography to compare the purity of laboratory-made aspirin with commercial tablets
- Base line with pencil close to bottom and draw two pencil crosses on it
- Place some laboratory-made aspirin solid on watch glass and dissolve in a few drops of solvent such as ethanol - spot solvent on pencil cross using capillary tube, dry and repeat until conc - repeat for commercial solid
- Place in solvent, cover with lid, run up until near top - mark solvent front and allow to dry
- Spots visible by placing in beaker containing iodine crystals
- Rf
