Answer to Question #21605 in Organic Chemistry for Sadaam Ahmed

Question

A sample of a substance known to contain chloride ions was dissolved in distilled water in a 1L volumetric flask. Then 25.00 mL of this solution was treated with excess silver nitrate, AgNO3 (aq). The precipitate of silver chloride, AgCl (s) was filtered and dried. The mass of the dry precipitate was 0.765 g.

a. Calculate the concentration of chloride ions.
b. If the original substance was sodium chloride, NaCl (s), what mass of it was dissolved in the volumetric flask?

Answer 1

AgNO₃(aq) + NaCl(s) = AgCl(s) + NaNO₃
n(AgCl) = 0.765 g / M(AgCl)
M(AgCl) = 108 + 35.5 = 143.5 g/mol
n(AgCl) = 0.765 g /143.5 g/mol = 0.00533 mol
n(AgCl) = chloride ions = 0.00533 mol
C(chloride ions) = n/V
C(chloride ions) = 0.00533 mol/1l = 0.00533 mol/ L (a)
m(NaCl)=n(NaCl)*M(NaCl)
n(NaCl) = 0.00533 mol
M(NaCl) = 23 + 35.5 = 58.5 g/mol
m(NaCl) = 0.00533 mol * 58.5 g/mol = 0.3115 g (b)

Answer:
a) 0.00533 mol/ L
b) 0.3115 g