Cu+ reacts with neocuproine to form the coloured complex (neocuproine)2Cu+, with
ID: 838969 • Letter: C
Question
Cu+ reacts with neocuproine to form the coloured complex (neocuproine)2Cu+, with an absorption maximum at 454 nm. Neocuproine is particularly useful because it reacts with few other metals. The copper complex is soluble in 3-methyl-1-butanol, an organic solvent that does not dissolve appreciably in water. If (neocuproine)2Cu+ is present, virtually of it goes into the organic phase. For the purpose of this problem, assume that all of the coloured complex transfers into the organic phase. Supposed that the following procedure is carried out:
Explanation / Answer
(a) Cu+ + 2 (neocuproine) => (neocuproine)2Cu+
Moles of Cu in 250.0 mL of solution A = Moles of Cu in rock = mass/molar mass of Cu
= 3.00 x 10^(3)/63.546 = 4.721 x 10^(-5) mol
Moles of Cu in organic phase = moles of Cu in 15.00 mL of solution A
= 15.00/250.0 x 4.721 x 10^(-5) = 2.833 x 10^(-6) mol
Concentration of Cu in organic phase = moles/volume of organic phase
= 2.833 x 10^(-6)/0.03000
= 9.442 x 10^(-5) mol/L = 9.44 x 10^(-5) mol/L
(b) Beer's law: A = ecl
where A is absorbance, c is concentration, e is molar absorptivity and l is path length
e = 7.90 x 10^3, c = 9.442 x 10^(-5) mol/L, l = 1.00 cm
Absorbance A = 7.90 x 10^3 x 9.441 x 10^(-5) x 1.00
= 0.7459 = 0.746
Observed absorbance = absorbance + blank absorbance
= 0.746 + 0.072
= 0.818
(c) Absorbance of other rock solution = observed absorbance - blank absorbance
= 0.753 - 0.072 = 0.681
Since absorbance is proportional to initial amount of Cu in rock:
Mass of Cu in other rock
= absorbance of other rock/absorbance of original rock x mass of Cu in original rock
= 0.681/0.746 x 3.00
= 2.74 mg
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.