Study of quantity of casein present in different samples of milk.

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Solution

Reaction involved-
$C a l c i u m c a s e i n a t e + 2 C H_{3} C O O H ⟶ C a s e i n (s) + (C H_{3} C O O)_{2} C a (a q)$
The volume of milk taken in each case = $20 m l$
$% o f c a s e i n = \frac{W e i g h t o f c a s e i n}{v o l u m e o f m i l k t a k e n} \times 100$
PROCEDURE:
(1)Take a clean dry beaker, put into it $20 m L$ of sample milk and add $20 m l$ of saturated ammonium sulfate solution slowly and with stirring. Fat along with casein will precipitate out.
(2)Filter the solution and transfer the precipitates in another beaker.
(3)Add about $30 m l$ of water to the precipitate.
(4)Only casein dissolves in water forming milky solution leaving fat undissolved.
(5)Heat the milky solution to about $40^{o} C$ and add $1 %$ acetic acid solution dropwise, when casein gets precipitated.
(6)Filter the ppt., wash with water, and let the ppt. dry.
(7)Weigh the dry solid mass in a previously weighed watch glass.
(8)Repeat the experiment with other samples of milk.

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