A roll of 35-mm black and white photographic film contains about 0.27 g of unexposed AgBr before

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A roll of 35-mm black and white photographic film contains...

A roll of $35-\mathrm{mm}$ black and white photographic film contains about 0.27 $\mathrm{g}$ of unexposed AgBr before developing. What mass of $\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3} \cdot 5 \mathrm{H}_{2} \mathrm{O}(\text { sodium thiosulfate pentahydrate or hypo) in } 1.0 \mathrm{L} \text { of developer is }$ required to dissolve the $\mathrm{AgBr}$ as $\mathrm{Ag}\left(\mathrm{S}_{2} \mathrm{O}_{3}\right)_{2}^{3-}\left(K_{\mathrm{f}}=4.7 \times 10^{13}\right) ?$

Key Concepts

Molar Mass and Solution Concentration Calculations

Molar mass calculation is essential to convert between the mass of a substance and the number of moles. Combined with the concept of solution concentration (molarity), these calculations allow one to determine how much of a chemical is present per unit volume of solution, a necessary step in preparing solutions such as the developer used in photographic processing.

Chemical Equilibrium and Formation Constant

A reaction’s equilibrium is described by its formation constant (Kf), which quantifies the extent to which a complex ion is formed. A very high formation constant indicates that the reaction effectively goes to completion, simplifying the calculation by assuming nearly complete conversion of the silver halide to the silver-thiosulfate complex.

Photographic Fixing Process

The photographic fixing process involves the transformation of an otherwise insoluble silver halide into a soluble complex so that unexposed and undeveloped silver salts can be removed from the film. This step is essential in developing photographs, ensuring that the image remains stable and no further exposure occurs.

Complex Ion Formation

This concept deals with the process in which a metal ion binds to one or more ligands to form a complex ion. In the context of photographic chemistry, silver ions from silver halides react with thiosulfate ions to form a soluble complex ion, which is critical for the dissolution of the silver halide during the fixing process.

Stoichiometric Calculations

Stoichiometry in chemical reactions involves calculating the amounts of reactants and products based on balanced chemical equations. In this context, stoichiometric relationships are used to determine the necessary amount of sodium thiosulfate pentahydrate needed to react completely with the silver halide present in the film.

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