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JEE Main 201219 MayOnline

Exam: JEE Main
Year: 2012
Date: 19 May
Mode: Online
Subject: Chemistry
Chapter: Surface Chemistry

JEE Main 2012 · 19 May · Online · Chemistry · Surface Chemistry

On addition of 1 ~mL of 10 \% NaCl solution to 10 mL gold sol in...

On addition of

1 \mathrm{~mL}

of

10 \% \mathrm{NaCl}

solution to 10

\mathrm{mL}

gold sol in the presence of

0.025 \mathrm{~g}

of starch, the coagulation is just prevented. Starch has gold number

Options

A $2.5$
B25
C $0.25$
D $0.025$

Correct answer

B. 25

Step-by-step solution

Gold Number is the minimum amount of lyophilic colloide in miligrams (starch in given case) which prevents the flocculation of

10 \mathrm{ml}

gold sol by the addition of

1 \mathrm{ml}

of

10 \% \mathrm{NaCl}

solution.

\therefore

Gold number = miligram of starch

=0.025 \times 10^3 \mathrm{mg}

=25

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