Ascorbic Acid Amount Calculation (stoichiometry/)

• devon
In summary: I think we're on the right track. In summary, the conversation discusses the analysis of ascorbic acid content in vitamin tablets and kiwifruit juice. The calculations involve dilutions and titrations using standardised iodine solution, and the final results show the mass and concentration of ascorbic acid in the samples. Both attempts at calculating the mass and concentration are correct based on the given data.
devon
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!

devon said:
772mg

devon said:
64mg/100ml.

Both look OK to me.

devon
So I didn't need to do any additional dilution calculations for 2? Sweet! Thank you so much, I'v been stuck on this question for ages. I'm way to indecisive.

devon said:
So I didn't need to do any additional dilution calculations for 2?

You don't have information for that. You did all that could be done.

I got the same thing as you as well Devon

Last edited:
devon

1. How is the amount of ascorbic acid calculated using stoichiometry?

The amount of ascorbic acid can be calculated using stoichiometry by using the balanced chemical equation for the reaction in which it is involved. The coefficients in the equation represent the mole ratios of the reactants and products. By knowing the amount of one reactant or product, the amount of ascorbic acid can be calculated using these ratios.

2. What is the molar mass of ascorbic acid?

The molar mass of ascorbic acid, also known as vitamin C, is 176.12 g/mol. This value is important in stoichiometry calculations as it is used to convert between mass and moles of the substance.

3. How does the concentration of ascorbic acid affect its amount in a reaction?

The concentration of ascorbic acid, along with the volume of the solution, is used to determine the amount of ascorbic acid present in a reaction. A higher concentration of ascorbic acid will result in a larger amount of the substance being present in the reaction.

4. Can the amount of ascorbic acid be calculated for any reaction?

Yes, the amount of ascorbic acid can be calculated for any reaction in which it is involved. This can be done by following the principles of stoichiometry and using the appropriate coefficients and molar masses.

5. Why is it important to accurately calculate the amount of ascorbic acid in a reaction?

Ascorbic acid is a vital nutrient for humans and plays an important role in many biological processes. Accurate calculations of its amount in a reaction can ensure that the proper dosage is being administered for medical purposes or that enough of the nutrient is present in a food or beverage product. This can also help in determining the efficiency of a chemical reaction or process involving ascorbic acid.

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