The chloride content of blood scrum, cerebrospinal fluid or urine can be measure

Question

The chloride content of blood scrum, cerebrospinal fluid or urine can be measured by titration of the chloride with mercuric ion: Hg^2+ + 2Ci^- rightarrow HgCl_2(aq) When the reaction is complete, excess Hg^2+ reacts with the indicator, diphenyl carbazone, which forms a violet-blue color. Mercuric nitrate was standardized by titrating a solution containing 147.6 mg of NaCl. which required 28.06 mL of Hg(NO_3)_2 solution. Find the molarity of the Hg(NO_3)_2 When this same Hg(NO_3)_2 solution was used to titrate 2.000 mL of urine, 22.83 mL was required. Find the concentration of Cl^- (mg/mL) in the urine.

Explanation / Answer

(a)

Mass of NaCl = 147.6 x 10^ -3 g

Moles of NaCl = 147.6 x 10^ -3 /58.5 = 2.523 x 10^ -3

Moles of Hg required = 1/2 x 2.52 x 10^ -3 = 1.262 x 10^ -3

Volume = 0.02806 L

Moles of Hg = M x V = M x (0.02806)

Molarity = 1.262 x 10^ -3/(0.02806)

             = 4.49 x 10^-2 M

Molarity of Hg(NO3)2 = 0.04496 M

(b) Molarity = 0.04496

Volume = 22.83 ml = 0.02283 L

Volume of Urine = 2 ml = 0.002 L

Molarity of Urine = (0.04496 ) x (0.02283) /(0.002)

                          = 0.5132 M

So concentration Of Cl- = 0.5132 mol/ L

                                      = 0.5132 x 35.5

  concentration Of Cl- = 18.22 mg/ml

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