Question

${10}^{-4}$ of gelatin is required to be added to $100c{m}^3$ of a standard gold solution to just prevent its precipitation by the addition of $1mL$ of $10\%ofNaCl$ solution to it. Hence the gold number of gelatin in is?

• A. $10$
• B. $1.0$
• C. $0.1$
• D. $0.01$
• E. $0.001$

Answer 1

Answer: (D)

$0.01$

Solution:- (D) $0.01$

As we know that, gold number is the number of milligrams of dry protective colloids required to just prevent the coagulation of $10mL$ of red gold sol when $1mL$ of $10\%NaCl$ added to it.

Therefore,

Amount of gelatin required to protect $10mL$ of gold solution $=\frac{{10}^{-4}\times 10}{100}={10}^{-5}g={10}^{-2}mg=0.01mg$