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lukranit [14]
3 years ago
14

You want to determine the protein content in milk with the Kjeldahl method. You take 100 g whole milk and use 100 mL of 0.5 M hy

drochloric acid to collect ammonia. You needed 34.50 mL of 0.3512 M NaOH for the back-titration. Calculate the percentage of protein in the sample?
Chemistry
1 answer:
SCORPION-xisa [38]3 years ago
8 0

Answer:

82.53 % protein in the milk.

Explanation:

<em>Titration formula:</em>

Conc (acid) × Vol (acid) = Conc (base) × Vol (base)

<u>Beginning from back-titration:</u>

0.5 M HCl × Vol  (HCl) = 0.3512 (conc of NaOH) × 34.50 mL (vol of NaOH)

=  \frac{12.1164}{0.5} = 24.2328 mL

⇒ <em>Vol of HCl used in initial titration is 24.2328 mL</em>

So from Initial Titration:

Using same titration formula,

0.5 × 24.2328 = Conc. (base) × 100 ml

Conc (base) = 12.1164 ÷ 100

= 0.121164 M.

But concentration = mass ÷ molar mass

0.121164 = \frac{100 g}{ molar  mass}

= 825.3277 g/mol of protein

⇒ \frac{825.32765}{1000} × 100

= <u>82.53 % protein in the milk.</u>

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