You are titrating an apple juice soft drink for malic acid. You combine 5 mL dri

Question

You are titrating an apple juice soft drink for malic acid. You combine 5 mL drink, 25 mL distilled, deionized water,and 3 drops phenolphthalein in a 125 mL Erlenmeyer flask and titrate with standardized NaOH (0.09862 N). Whiletitrating, you get distracted an overshoot the endpoint by an unknown amount (the solution is very dark pink). All islost! But wait…your lab mate gets a brilliant idea! You record the volume of NaOH used (16.23 mL), rinse out theburette, and refill it with 0.1 N HCl. You titrate the overshot sample with the HCl until the pink color completelydisappears, which occurs after 4.77 mL HCl has been dispensed.

Assume that all of the acid in the drink is malicacid.Based on the information provided:

1. What is the concentration of malic acid in the drink (N)? (10 points)

2. What is the concentration of malic acid in the drink (M)? (2 points)

3. What is the concentration of malic acid in the drink (% w/v)? (2 points)

Explanation / Answer

since malic acid is a dicrboxylic acid it is taken as strong aicd here ion theis problem, otherwise the problem has to be solved by henderson equation applicable to buffer solutions of strong base and weak acid.

1)the excess base rub = 4.77 ml equal to HCl (strong acid) volume.

so overshot volume of base - volume of HCl = 16.23- 4.77 = 11.46 ml.

so milliequivalents of base = 11.46 x 0.9862 = 1.146 N

so milliequivalents of malic acid = 1.146 x 2 = 2.292 ( it is a dibasic acid)

     so concentration in Normality = 2.292/1000 = 0.002292 N

2)Concentraion in Molarity= 0.002292 / 2 = 0.001146 M (since malic macid is is a di basic acid.

3) molar mass of malic acid = 134.

weight of/ malic acid present in 100 ml of sample = 0.001146 x 134/10 = 0.01535 %

molarity is number of moles present i n 1000ml

moles converted to mass in grams.

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