Nearly all mercury(II) compounds exhibit covalent bonding. Mercury(II)
chloride is a covalent molecule that dissolves in warm water. The stability of
this compound is exploited in the determination of the levels of chloride ion
in blood serum. Typical human blood serum levels range from 90 to \(115
\mathrm{mmol} \mathrm{L}^{-1}\) The chloride concentration is determined by
titration with \(\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2} .\) The indicator
used in the titration is diphenylcarbazone, \(\mathrm{C}_{6} \mathrm{H}_{5}
\mathrm{N}=\mathrm{NCONHNHC}_{6} \mathrm{H}_{5}\)
which complexes with the mercury(II) ion after all the chloride has reacted
with the mercury(II). Free diphenylcarbazone is pink in solution, and when it
is complexed with mercury(II), it is blue. Thus, the diphenylcarbazone acts as
an indicator, changing from pink to blue when the first excess of mercury(II)
appears. In an experiment, \(\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}(\) aq)
solution is standardized by titrating \(2.00 \mathrm{mL}\) of \(0.0108 \mathrm{M}
\mathrm{NaCl}\) solution. It takes \(1.12 \mathrm{mL}\) of
\(\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})\) to reach the
diphenylcarbazone end point. A 0.500 mL serum sample is treated with 3.50 mL
water, 0.50 mL of 10\% sodium tungstate solution, and \(0.50 \mathrm{mL}\) of
\(0.33 \mathrm{M}\) \(\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})\) to precipitate
proteins. After the proteins are precipitated, the sample is filtered and a
\(2.00 \mathrm{mL}\) aliquot of the filtrate is titrated with
\(\mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}\) solution, requiring \(1.23
\mathrm{mL}\). Calculate the concentration of Cl^- Express your answer in mmol
L \(^{-1}\). Does this concentration fall in the normal range?
