The Kb of hydroxylamine, NH2OH, is 1.10 x10-8. A buffer solution is prepared by mixing 120 mL of a 0.36 M hydroxylamine solution with 50 mL of a 0.28 M HCl solution.

Find the pH of the resulting solution.

pH = 5.9

Explanation:

NH₂OH + HCl => NH₂Cl + H₂O

=> 120ml(0.36M NH₂OH) + 50ml(0.28M HCl)

=> 0.12L(0.36M) NH₂OH + 0.05L(0.28M) HCl

=> 0.0432 mole NH₂OH + 0.014 mole HCl

=> (0.0432 - 0.014) mole NH₂OH + 0.0432 mole NH₂Cl

=> 0.0292 mole NH₂OH + 0.0432 mole NH₂Cl in 170 ml of solution

=> (0.0292mol/0.17L) NH₂OH + (0.0432mol/0.17L) NH₂Cl

=> (0.172M) NH₂OH + (0.254M) NH₂Cl

=> in water 0.172M HONH₃OH + 0.254M HONH₃Cl

        HONH₃OH              ⇄          HONH₃⁺           +         OH⁻

C(i)      0.172M                               0.254M                      0.0 M

ΔC          -x                                         +x                             +x

C(eq) 0.172-x = 0.172M         0.254+x = 0.254M                x  

Kb = [HONH₃⁺][OH⁻]/[HONH₃OH] = (0.254)[OH⁻]/(0.172) = 1.1 x 10⁻⁸

=> [OH⁻] = (1.1 x 10⁻⁸)(0.172)/(0.254)M = 7.5 x 10⁻⁹M

=> [H⁺} = Kw/[OH⁻] = (1 x 10⁻¹⁴/7.5 x 10⁻⁹)M = 1.33 x 10⁻⁶M

pH = -log[H⁺] = -log(1.33 x 10⁻⁶) = 5.9

Calculation check using base form of Henderson-Hasselbalch equation:

pOH = pKb + log([acid]/[base])

pKb = -log(Kb) = -log(1.1 x 10⁻⁸) = 7.9

pOH = 7.9 + log(0.254/0.172) = 7.9 + log(1.48) = 7.9 + 0.17 = 8.13

pH + pOH = 14 => pH = 14 - pOH = 14 - 8.13 = 5.87 ≅ 5.9 (check!)

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).