Chemistry Forum

0.005 g of a protective colloid is required to prevent precipitation of 1 ml of gold sol on addition of 10 ml of 10% NaCl. The gold number is

(A) 0.5
(B) 5
(C) 50
(D) 500

My answer is 0.05 milligrams. Is that correct? My computed answer is not appearing four multiple choices. So i think this question is poorly stated.

I would say its solution B 5. For 1 ml Goldsol 5 mg Protection colloid is needed.
Its 5 mg/ 1ml

Amount of starch added = 0.005 x1000
= 0.5 mg
Prevent Coagulation by addition of 1ml of colloid = 5/100 x 10
= 0.5 mg
Hence the gold number is 0.5 mg
The gold number is the minimum weight of a protective colloid required to prevent the coagulation of 10 ml of a standard hydro gold solution when 1 ml of a 10% sodium chloride solution is added to it.

If this is the calculation, then

0.005 * 1000 = 5 not 0.5 isn't it.

The result would be 5, answer B

Yes, your answer is correct.