1. (10) The concentration of cyanide ion, CN, in a copper plating bath can be de
ID: 1029860 • Letter: 1
Question
1. (10) The concentration of cyanide ion, CN, in a copper plating bath can be determined by complexometric titration with Ag'. A 5.00 mL sample from the bath is treated with 100 mL water, made basic with 5 mL of20% NaOH solution, and 5 mL of 1000 Kl indicator added. The sample is then titrated with 0.1012 M AgNOs solution, forming a soluble complex Ag(CN)2 Ag (aq) 2 CN(aq) Ag(CN)2 (aq). When all the cyanide is complexed to the Ag, the next drops of AgNO, cause a yellow precipitate of Agl to form at the endpoint. It requires 27.36 mL of AgNO; to reach the end point. Calculate the concentration of cyanide as molarity of sodium cyanide, NaCN. (The NaCN concentration in such baths typically lies in the range of 1 to 2 M.)Explanation / Answer
moles of AgNO3 used = molarity x volume
= 0.1012 M x 27.36 ml
= 2.77 mmol
moles CN- present = 2 x 2.77 mmol
= 5.54 mmol
molarity of CN- in solution = 5.54 mmol/5 ml
= 1.11 M
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