Question

Sodium thiosulfate (Na2S2O3), photographer’s
“hypo” reacts with unexposed silver bromide in the film emulsion to form sodium bromide and a compound of formula Na5[Ag(S2O3) 3]. How many moles of Na2S2O3 formula units are needed to make 0.10 mol of AgBr soluble?

Answer 1

3Na2S2O3 + AgBr ------>Na5[Ag(S2O3) 3] +NaBr

from equation 3 mol 1 mol

given x mol 0.10 mol

x= (3*0.10)/1=0.30 mol Na2S2O3

Answer: 0.30 mol Na2S2O3

Answer 2

Answer:

0.30 moles of sodium thiosulfate formula units are needed to make 0.10 moles of AgBr soluble.

Explanation:

$3Na_2S_2O_3+AgBr\rightarrow NaBr+Na_5[Ag(S_2O_3)_3]$

According to reaction , 1 mole of silver bromide dissolves in 3 moles of Sodium thiosulfate .

Then 0.10 moles of AgBr will dissolve with:

$\frac{3}{1}\times 0.10 mol=0.30 mol$

0.30 moles of sodium thiosulfate formula units are needed to make 0.10 moles of AgBr soluble.