Question

A roll of 35-mm black and white photographic film contains about 0.27 g of unexposed AgBr before developing. What mass of Na₂S₂O₃·5H₂O (sodium thiosulfate pentahydrate or hypo) in 1.0 L of developer is required to dissolve the AgBr as Ag(S₂O₃)₂³⁻ (Kf = 4.7 × 10¹³)?

a) 5.7 g

b) 11.4 g

c) 22.8 g

d) 45.6 g

Answer 1

To dissolve 1.00 g of AgBr in 1.0 L of developer, you would need 0.087 g of Na2S2O3·5H2O.

Step-by-step explanation:

To dissolve 1.00 g of AgBr in 1.0 L of developer, we need to calculate the mass of Na2S2O3·5H2O required. We can use the equation:

AgBr(s) + 2S2O3- (aq) → [Ag(S2O3)2]3- (aq) + Br- (aq)

From the equation, we can see that 1 mole of AgBr reacts with 2 moles of S2O3-, so we need to calculate the amount of S2O3- needed to react with 1 mole of AgBr. The molar mass of Na2S2O3 is 158.1 g/mol, so:

2 moles S2O3- → 0.0011 moles S2O3-

1 mole S2O3- → 0.00055 moles S2O3-

0.00055 moles S2O3- × 158.1 g/mol = 0.087 g S2O3-

Therefore, the mass of Na2S2O3·5H2O required to dissolve 1.00 g of AgBr in 1.0 L of developer is 0.087 g.