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devon

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**1. Ascorbic acid in vitamin tablet**

Vitamin tablets with advertised contents including 750 mg ascorbic acid were analysed.

A student took a whole tablet, crushed and dissolved all of it in water. He then diluted the tablet solution to a final volume of 250.0 mL. The student analysed 20.0 mL aliquots of the solution for ascorbic acid by titration using a standardised iodine solution. Data

Final volume containing whole tablet: 250.0 mL

Volume of tablet solution analysed: 20.0 mL

Standard Iodine solution concentration: 0.0198 mol L-1

Average titration volume 17.71 mL

Calculate the mass of ascorbic acid in the tablet. Enter your answer as a whole number of mg.

**Attempt:**So for this question I calculated the amount of mols of ascorbic acid per 20ml (it is in a 1:1 ratio with iodine) - 0.0198mol/L x 0.01771L = 0.00350658mol. Then I multiplied it by 250ml/20ml (12.5) to find the amount of mols in the entire 250ml solution - 12.5x 0.00350658mol = 0.004383225mol. I then multiplied this by the molar mass of ascorbic acid (176.14g/mol) to get grams of ascorbic acid - 176.14g/mol x 0.004383225mol = 0.7718859225g. I then multiplied this by 1000mg/1g to convert grams to milligrams - 0.7718859225g x 1000mg/1g = 771.8859225mg =

**772mg**(answer as whole number).

Is this right or did I forget something? I can do all of the math it's just that my problem solving skills aren't that great.

**2. Ascorbic Acid in Juice**

A selection of commercial fruit juices and fruit extracts were analysed for ascorbic acid content.

A student took kiwifruit juice to analyse. This juice is reputed to have ascorbic acid concentrations about 3 times greater than that of orange juice. The student diluted the juice by taking a 25.00 mL sample to a final volume of 100.0 mL. The student analysed 25.00 mL aliquots of the diluted juice solution for ascorbic acid by titration using a standardised iodine solution. Data

Volume juice for dilution: 25.00 mL

Final diluted volume: 100.0 mL

Volume of diluted juice analysed: 25.00 mL

Standard Iodine solution concentration: 0.00496 mol L-1

Average titration volume 18.44 mL

Calculate the concentration of ascorbic acid in the original juice in units of mg / 100 mL. Enter your answer as a whole number of mg

**Attempt:**I think I know how to do this one but the dilutions at the beginning are throwing me off, I'm not sure if I need to use C1V1=C2V2 to change anything before I start. Regardless this is how I did it:

I calculated the amount of mols of ascorbic acid per 20ml (it is in a 1:1 ratio with iodine) - 0.00496mol/L x 0.01844L = 0.0000914624mol. I then multiplied this by 4 to find the amount of mols in the 100mL solution = 0.0003658496mol/100ml. I then multiplied this by the molar mass of ascorbic acid 176.14g/mol = 0.06444074854g/100ml. I then multiplied this by 1000mg/1g to convert it to milligrams = 64.44074854mg/100ml.

**64mg/100ml.**I don't know if this is right or not as we did a lab with orange juice and got 72.3mg/100ml. It says the juice is reputed to have though so it could be false.

Sorry for the wall of text, thanks for the help!