[Single-digit Integer] Molecular formula of starch can be represented as (C6H10O5)n. If the gold number of one such starch is 6.48 and 0.01 millimoles of this starch is required to be added in 10 ml o

Question

[Single-digit Integer] Molecular formula of starch can be represented as (C6H10O5)n. If the gold number of one such starch is 6.48 and 0.01 millimoles of this starch is required to be added in 10 ml of red gold sol to just prevent coagulation by adding 1 ml of 10% sodium chloride solution, then the value of 'n' is

Prashant Kotian · Accepted Answer

Correct answer: 4. Gold number is the mass in mg of protective colloid. Here, gold number = 6.48 mg. Moles of starch used = 0.01 mmol = 10^-5 mol. Molar mass of starch = (6.48 * 10^-3 g) / 10^-5 mol = 648 g/mol. Formula weight of repeating unit C6H10O5 = 162 g/mol. Thus, n = 648 / 162 = 4.

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