A 0.552 g sample of ascorbic acid(Vitamin C) was dissolved in water to a total volume of 20.0 ml and titrated with 0.1103 M KOH. The equivalence point occurred at 28.42 ml. The pH of the solution at 10.0 ml of added base was 3.72. From this data, determine the molar mass and Ka for vitamin C.
All I got do far is..
Vitamin C+ H2O-->
I don't know what to do?!:0
28.42mL of O.1103mol/L KOH titrated / reacted with all the Vit C there was.
O.1103mol/L * 28.42mL *1L/1000mL = 3.13*10^-3mol KOH = 3.13*10^-3mol Vit C
O.552g/3.13*10^-3mol = ~176g/mol
To find Ka use pH=pka + log[base]/[acid]
pH is 3.72,
Initial [acid]=0.552g/176g/mol = 3.13*10^-3mol
Change is the amount of base added that will react with the initial amount of acid, = 3.13*10^-3mol - (0.1103M*.01L=1.103*10^-3mol) = 2.03*10^-3mol
pH=pka + log[base][acid]
3.72 = pka + log(1.103810^-3(/(2.03*10^-3)
pka = 3.72-(-0.2649...) = 3.984..
pka = -log[ka]
10^-pka = ka
10^-3.984... =ka = 1.04*10^-4
To solve this problem, we need to consider the reaction between ascorbic acid (Vitamin C) and KOH.
The balanced chemical equation for the reaction is as follows:
C6H8O6 + 3KOH → C6H5O6K3 + 3H2O
Based on the given data, we have the following information:
Mass of ascorbic acid (Vitamin C) = 0.552 g
Volume of ascorbic acid solution = 20.0 mL
Volume of KOH solution at equivalence point = 28.42 mL
pH of the solution at 10.0 mL of added base = 3.72
To determine the molar mass of Vitamin C:
1. Calculate the number of moles of KOH used at the equivalence point:
Moles of KOH = Molarity × Volume
Moles of KOH = 0.1103 M × 0.02842 L
2. Since the balanced equation shows that the stoichiometric ratio between ascorbic acid and KOH is 1:3, the number of moles of ascorbic acid can be calculated as follows:
Moles of ascorbic acid = (1/3) × Moles of KOH
3. Calculate the molar mass of Vitamin C using the equation:
Molar mass of Vitamin C = Mass / Moles
To determine the Ka for Vitamin C:
1. From the balanced equation, we see that 1 mole of ascorbic acid reacts with 3 moles of KOH. This means that at the equivalence point, all the ascorbic acid has reacted and been converted to ascorbate ion (C6H5O6K3).
2. We can calculate the concentration of ascorbic acid (C6H8O6) at the equivalence point:
Concentration of ascorbic acid = Moles of ascorbic acid / Volume of solution
3. Since ascorbic acid can donate one proton (H+), the concentration of H+ ions at the equivalence point is equal to the concentration of ascorbic acid.
4. Use the equation for pH to find the concentration of H+ ions:
pH = -log [H+]
5. Calculate the concentration of H+ ions at pH 3.72 using the equation:
[H+] = 10^(-pH)
6. Use the concentration of H+ ions to calculate the concentration of ascorbic acid at the equivalence point.
7. Finally, use the concentrations of ascorbic acid and ascorbate ion to calculate the Ka using the equation:
Ka = ([C6H5O6K3] × [H+]) / [C6H8O6]
You can now proceed with these steps to find the molar mass and Ka for Vitamin C.
To determine the molar mass and Ka for vitamin C (ascorbic acid), you can use the given data and the concept of titration. Here's how you can proceed:
Step 1: Write the balanced chemical equation for the reaction of ascorbic acid (C6H8O6) with KOH (potassium hydroxide):
C6H8O6 + KOH → H2O + K(C6H7O6)
Step 2: Use the equation to determine the number of moles of KOH used in the reaction:
Moles of KOH = Molarity of KOH × Volume of KOH used (in liters)
Moles of KOH = 0.1103 mol/L × 0.02842 L
Step 3: Determine the moles of ascorbic acid that reacted with KOH. Since the balanced equation has a 1:1 stoichiometric ratio between ascorbic acid and KOH, the moles of ascorbic acid are equal to the moles of KOH.
Step 4: Determine the mass of ascorbic acid used in the reaction:
Mass of ascorbic acid = Moles of ascorbic acid × Molar mass of ascorbic acid
Mass of ascorbic acid = Moles of ascorbic acid × (molar mass of C6H8O6)
Step 5: Calculate the molar mass of ascorbic acid:
Molar mass of ascorbic acid = Mass of ascorbic acid / Moles of ascorbic acid
Step 6: Determine the concentration of ascorbic acid in the solution:
Concentration of ascorbic acid = Mass of ascorbic acid / Volume of solution (in liters)
Concentration of ascorbic acid = (Mass of ascorbic acid / 0.552 g) / (20.0 mL / 1000 mL/L)
Step 7: Use the given pH information to determine the concentration of ascorbate ion [C6H7O6-] in the solution at 10.0 ml of added base. The pH of 3.72 corresponds to the concentration of the ascorbate ion using the equation:
pH = -log [C6H7O6-]
Step 8: Use the Henderson-Hasselbalch equation to calculate the ratio of [C6H7O6-] to [C6H8O6]. The Henderson-Hasselbalch equation is given as:
pH = pKa + log ([C6H7O6-] / [C6H8O6])
Step 9: Substitute the given pH and calculate the pKa value.
By following these steps, you should be able to determine the molar mass and Ka for vitamin C (ascorbic acid).