[remeday86]

Ascorbic acid (vitamin C) is a diprotic acid having the formula H2C6H6O6. A sample of a vitamin supplement was analyzed by titrating a 0.5054 g sample dissolved in water with 0.0713 M NaOH. A volume of 10.80 mL of the base was required to completely neutralize the ascorbic acid. What was the percentage by mass of ascorbic acid in the sample? ____% asorbic acid

--My work

0.0713 M NaOH = mole NaOH/ 0.0108 L = 7.7004 E -4 mol NaOH

7.7004 E -4 mol NaOH x ( 1 mol asorbic acid / 1 mol NaOH ) = 7.7004 E -4 mol ascorbic acid

7.7004 E -4 mol ascorbic acid x 176.1248 g/mol ascorbic acid = 0.1356 g ascorbic acid

(0.1356 g ascorbic acid / 0.5054 g sample) x 100% = 26.8 % ascorbic acid

but...its wrong. I really tried... Where did I go wrong? Please explain. Thanks in advance!

[Astrokel]

Ascorbic acid (vitamin C) is a diprotic acid having the formula H2C6H6O6.

7.7004 E -4 mol NaOH x ( 1 mol asorbic acid / 1 mol NaOH ) = 7.7004 E -4 mol ascorbic acid

[aldoxime_amine]

This is only a suggestion, instead of working with moles and molarilty, it would be very helpful if you understood the concept of equivalents and normality.

[remeday86]

Ascorbic acid (vitamin C) is a diprotic acid having the formula H2C6H6O6.

7.7004 E -4 mol NaOH x ( 1 mol asorbic acid / 1 mol NaOH ) = 7.7004 E -4 mol ascorbic acid

Thanks!

7.7004 E -4 mol NaOH x ( 2 mol asorbic acid / 1 mol NaOH ) = 1.5401 E -3 mol ascorbic acid

1.5401 E -3 mol ascorbic acid x 176.1248 g/mol ascorbic acid = 0.2712 g ascorbic acid

(0.2712 g ascorbic acid / 0.5054 g sample) x 100% = 53.7% ascorbic acid

....but i still got it wrong.

[Astrokel]

2 mol asorbic acid / 1 mol NaOH

Think again, every 1 mole of acid has 2 moles of H⁺. So if you use 2 moles of acid, you have 4 moles of H⁺ but you use only 1 mole of base which has only 1 mole of OH^-. It can't neutralise.