• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month
Page
1. 1
1
2. 2
2
3. 3
3
4. 4
4
5. 5
5

# Determination of the Amount of Vitamin C in a Commercial Tablets

Extracts from this document...

Introduction

DETERMINATION OF THE AMOUNT OF VITAMIN C IN A COMMERCIAL TABLETS AIM To find out the concentration of a given Na2S2O3 solution by titrating against standard KIO3 solution in excess KI and H2SO4 solution. To find out the amount of vitamin C in a commercial tablets with adding excess but known amount of standard KIO3 and excess KI and H2SO4 solution. Finding the amount of I2 left and amount of vitamin C used by back titration against standard Na2S2O3 solution. RESULT Mass of KIO3 weighed by electric balance: 0.69g Mass of Vitamin C commercial tablet: 4.48g Titration result of standard KIO3 solution in excess KI and H2SO4 solution against given Na2S2O3 Trial 1 2 3 Final burette reading (cm3) 20.92 40.42 28.10 47.50 Initial burette reading (cm3) 1.08 20.92 8.64 28.10 Volume of Na2S2O3 added (cm3) 19.84 19.5 19.46 19.40 Mean volume of Na2S2O3 used = ( 19.5 + 19.46 + 19.4)/3 = 19.45 cm3 Titration result of excess I2 solution (after reacted with vitamin C) ...read more.

Middle

It is because starch could form a blue-black complex with iodine. As the colour change of iodine to iodide is insignificant and difficult to observe, so starch is used as the indicator. However, Starch solution is being added in the later stage of titration. It is because starch would combine with iodine irreversibly when iodine is at a very high concentration. At the endpoint, the blue-black colour would completely disappear. REASON OF STANDARDIZING SODIUM THIOSULPHATE SOLUTION We have to standardize the given sodium thiosulphate solution before use. It is because thiosulphate is unstable in acidic medium, it would decompose easily. Also, it would be unstable in the presence of microorganism, Cu2+ and sunlight. So the concentration of the sodium thiosulphate solution might be inaccurate. Therefore, we have to standardize it before use. REASON OF NOT USING IODINE SOLUTION DIRECTLY In this experiment, we dissolve known mass of KIO3 into excess KI and H2SO4 solution to form iodine instead of using iodine solution directly. IO3- + 5I- + 6H+ --> 3I2 + 3H2O This is because iodine is volatile, I2 would escape and cause inaccurate concentration of the solution. ...read more.

Conclusion

However, after adding distilled water, the colour of the solution becomes paler. We can hardly make comparison of solution colour with the previous one. We have to add less distilled water to wash the droplets back into the flask next time. ERROR IN CONCENTRATION OF SOLUTIONS After standardizing the sodium thiosulphate solution, it might decompose by air and sunlight. As a result, the concentration of the solution would be lower than we expected and the calculated amount of vitamin C would be smaller. OTHER CHEMICALS IN THE TABLET MIGHT REACT In this experiment, we have assumed that only vitamin C in the tablet would react with I2. However, we don't know whether other chemicals and ingredients inside the tablet would react with iodine solution. If some of the ingredients would react with iodine solution, the calculated amount of vitamin C in the tablet would be greater. CONCLUSION The mass of vitamin C inside the tablet is 0.9624 g, the tag on the vitamin C tablet claimed that it contain 1.0000 g vitamin C. The percentage error is 3.76%, which is insignificant. So the claim of the tablet maker is justified. ?? ?? ?? ?? Lam Hei Yan (24) 6A ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Physical Chemistry section.

## Found what you're looking for?

• Start learning 29% faster today
• 150,000+ documents available
• Just £6.99 a month

Not the one? Search for your essay title...
• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

# Related AS and A Level Physical Chemistry essays

1. ## Indigestion Tablet

Apparatus: * 50ml burette * 25ml measuring cylinder * 250ml conical flasks * Funnel * Stand and clamp * Teat Pipette * 2 different types of indigestion tablets * Methyl orange indicator * 50 ml of 2 mol/dm3 hydrochloric acid * 50 ml of 2 mol/dm3 sodium hydroxide Procedure: 1.

2. ## Analysis of commercial vitamin C tablets

Results Mass of NaIO3 : 0.63 g ? Molarity of 250cm3 standard NaIO3 solution : (0.63 �197.89 � 0.25)M = 0.012734 M By equation III, no. of moles of I2 formed = no. of moles of NaIO3 x 3 �10 = (0.63 �197.89 x 0.3)mol = 9.550761x10-4 mol By equation II, no.

1. ## Aim:To investigate the content of vitamin C (ascorbic acid) content in a commercial tablets ...

27.7 46.1 25.05 Initial burette reading (cm3) 8.8 5.85 8.64 Volume of Na2S2O3 added (cm3) 18.9 18.4 19.2 Mean volume of Na2S2O3 used = ( 18.4+19.2)/2=18.8cm3 Titration result of excess I2 solution (after reacted with vitamin C) against standard Na2S2O3 Trial 1 2 Final burette reading (cm3)

2. ## The Determination of rate equation

Volume of HCl / cm3 Volume of Na2S2O3 / cm3 Volume of H2O / cm3 Molarity of Na2S2O3 / mol Time /S Average/s 10.00 4.00 41.00 0.03 10.00 8.00 37.00 0.08 10.00 12.00 33.00 0.14 10.00 16.00 29.00 0.21 10.00 20.00 25.00 0.30 I have decided to use smaller concentration

1. ## Investigating the Rate of the Reaction between Bromide and Bromate Ions in Acid Solution

CONCLUSION 5: (Equation 3.6.5) 3.7 - Analysis of the Results of Using different Transition Metal Ions as Catalysts These results allow me to compare the catalytic affect of different transition metal ions on the reaction. Table 3.7.1 shows the values of the average time (t)

2. ## Aspirin tablets

This can increase the rate of reaction. 2. Why is it unwise to boil it vigorously?

1. ## Analysis of commercial vitamin C tablets

]/10 =(0.6808/214)/10 =0.0003181308411mol ?No. of mole of I2 produced=3x No. of mole of KIO3 titrated =0.0009543925234mol ?No. of mole of Na2S2O3(aq) titrated=2x No. of mole of I2 produced =2x0.0009543925234 =0.001908785047mol ?Molarity of Na2S2O3(aq) =No. of mole of Na2S2O3(aq) titrated/Average volume of Na2S2O3(aq) titrated =0.001908785047/(19.20/1000)

2. ## Investigating how concentration affects rate of reaction

Gradient = -1.75 0.00024 = -7291.7 Gradient = -Ea = -7291.7 R R (the gas constant) = 8.31 J K-1 mol-1 The gradient equation can be rearranged as: -Ea = gradient x R = -7291.7 x 8.31 = -60594 Ea = 60594Jmoles-1 This can be converted to kJmoles-1 by dividing

• Over 160,000 pieces
of student written work
• Annotated by
experienced teachers
• Ideas and feedback to