solution. Then titrate with the standard potassium iodate (KIO:) solution (M) until the solution changes from brown to i
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- Solution Then Titrate With The Standard Potassium Iodate Kio Solution M Until The Solution Changes From Brown To I 1 (45.76 KiB) Viewed 60 times
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solution. Then titrate with the standard potassium iodate (KIO:) solution (M) until the solution changes from brown to intense blue. Write down the standard potassium iodate (KIO:) solution volume. 2. Pipette 25 cm of unknown ascorbic acid sample, a kind of juice, into a 250 cm conical flask, then follow the same procedure of step 1 and write down the volume of the standard KIO, solution Repeat the steps 1 and 2 to check the precision of the experiment. Use the mean result of step 2 to determine the concentration (mol/em) of ascorbic acid in the selected sample Note: The end point is reached when the solution turns a permanent, dark blue colour, due to the complex formed between starch and iodine. During an iodometric titration an intermediate dark blue iodine-starch complex may form momentarily, before the iodine reacts with ascorbic acid. However, if the colour disappears upon mixing, the end point has not yet been reached. Thus, magnetic stirrers or glass rod are employed in the titration to ensure proper mixing and to facilitate the reaction of iodine with ascorbic acid, Report 1. Write up this experiment results in full (including the discussion) and hand in at the beginning of the next lab session. Marks awarded are shown in brackets. 2. Tabulate your results as follows: [2] Standardization 1" Titration pod Titration Final reading cm Initial reading/cm Titre/ cm Unknown sample 7" Titration za Titration
Experimento To determine ascorbic acid (vitamin C) concentration by a redox titration with potassium iodate Object: To determine vitamin C (C.H.O.) by potassium iodate titration and to master iodometric titrations Introduction A suitable method for the determination of vitamin C (CHO) quantities is a titration with potassium iodate (KTO). Potassium iodate is used as a titrant and it is added to an ascorbic acid solution that contains strong acid and potassium iodide (KI). Potassium iodate reacts with potassium iodide, liberating molecular iodine (te): KIO; + SKI + 6H - 36+6K* +3H20 (1) As long as the solution contains ascorbic acid, the iodine produced in (1) is used up in a rapid reaction with ascorbic acid, during which dehydroascorbic acid and iodide ion are formed CH4O6 + 1 - CHO% + 2 + 2HP Potassium iodide must be added in excess to keep iodine dissolved. Once all the ascorbic acid has been consumed, any excess iodine will remain in solution. Since aqueous iodine solutions are brown in colour, iodine can act as its own indicator However, it is quite difficult to detect endpoints using iodine coloration alone, and it is more usual to add starch, which forms an intensely blue coloured complex with iodine but not with the iodide ion According to the above reactions, each mole of potassium iodate added corresponds to 3 moles of ascorbic acid dehydrogenated in the sample Procedure 1. Pipette 25 cm of the provided ascorbic acid solution into a 250 em conical flask, add 24 cm' of 2M HCI, = 5 cm of potassium iodide (KD) solution and 3 cm starch 1
Result Standardization Unknown sample 1st Titration 2nd Titration 11 Titration 2nd Titration 42.9 Final reading/cm 42.5 41.8 42.4 20 20 39.8 40 Initial reading/cm Titre/ cm Mean titre / cm?