what is the molarity

Question

A commercial juice is known to have 140 % of the daily allowance of vitamin C per serving (220 mL). If the daily allowance of vitamin C is 75.0 mg, what is the molarity of vitamin C in this juice (in M)?

Answer 1

You are on the right track, but you neglected the fact that the juice has 140% of the daily allowance, and also you didn't use the molar mass of vitamin C. Dividing by 0.220 and not 0.210 is also an error but may be a typo. See below:

Daily allowance = 75.0 mg

140% of daily allowance = 1.40 x 75.0 mg = 105 mg of Vit C in 220 ml

molar mass vitamin C (ascorbic acid) = 176 g / mole

moles Vit C in 220 ml = 105 mg x 1 g / 1000 mg x 1 mol / 176 g = 5.97x10^-4 moles

Molarity = 5.97x10^-4 moles / 0.220 L = 2.71x10^-3 M