Using a Colorimeter
- Select a filter with the complementary colour to the solution being tested.
- Zero the colorimeter (calibrate it) using a cuvette of distilled water.
- Make up solutions of known concentrations both above and below that of the unknown sample.
- Measure the absorbance of each concentration and plot a calibration curve of the results. (absorbance against concentration)
- Measure the absorbance of the unknown soluton and read off the concentration from the calibration curve once results have been plotted.
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- Spot mixtures and reference samples on a pencil line 1cm from the bottom of the T.L.C. plate.
- Place T.L.C. plate in beaker containing solvent. Solvent level must be below 1cm base line. Cover beaker.
- Remove plate when solvent is near top and mark how far it reached.
- Allow plate to dry. Locate spots using a locating agent such as iodine or ninhydrin.
- Find Rf values for each spot and compare these to reference sample Rf values to decide what the unknown is.
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- Dissolve solid in a minumum volume of hot solvent.
- Filter and retain the filtrate.
- Allow filtrate to cool, which will form crystals.
- Collect the crystals using vaccum filtration and wash them in a minimum volume of cold solvent.
- Dry in an oven set below the melting point of the crystals.
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Potassium manganate (VII) Titration: Used to find the concentration of iron(II) ions or hydrogen peroxide
- Use a pipette to transfer a known volume of the test solution (iron(II) ions for example) into a conical flask.
- Acidify this solution with dilute sulfuric acid.
- Slowly add potassium manganate(VII) to the solution in the conical flask from a burette.
- Swirl gently until a pale pink colour persists.
- Repeat the titration until you have two titres within 0.1cm^3.
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Iodine-Thiosulfate Titrations: Used to find the concentrations of solutions of oxidising agents
- A known amount of the oxidising agent is reacted with an excess of acidified potassium iodide solution.
- The iodine produced is then titrated against a standard solution of sodium thiosulfate.
- Near the end point of the reaction, a few drops of starch solution are added giving an intense blue/black colour which disappears at the end point.
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