# [MIn - ]/[HIn 2

```考古題 99-5
Relative error : ( Ksp’ – Ksp ) / Ksp x 100%
Ksp = (γCd2+ x [Cd2+])2 x ( γFe(CN6)4- x [Fe(CN)64-])

Relative error : ( Ka’ – Ka ) / Ka x 100%
Ka‘ = (γH3O+[H3O+] • γNO2-[NO2-]) / (γHNO2[HNO2])

b) For the electrolyte AmBn: γ± = mean activity coefficient
= (γAm γBn )1/(m+n)
2
c)
- log γ X 
0 . 51 Z X
1  3 . 3 X


Z=3
γM : activity coefficient of the species M3+
ZM : charge on the species M3+
μ : ionic strength of the solution
αM : effective diameter of the hydrated ion M3+ in nanometers

2
a)
- log γ X 
0 . 51 Z X

1  3 . 3 X

b) Shielding effect , explain it
μ = ½ (0.015 x 32 + 0.045 x 12) = 0.09
ZA : # of charge  A+
ZB : # of charge  B+
αA  effective diameter of the hydrated ion A
αB  effective diameter of the hydrated ion B
Example 17-1
Calculate the molar Y4- concentration in a 0.0200M
EDTA solution buffered to a pH of 10.00

Example 17-2
Calculate the equilibrium concentration of Ni2+ in a
solution with an analytical NiY2- concentration of
0.0150M at pH (a) 3.0 and (b) 8.0

Example 17-3
Calculate the concentration of Ni2+ in a solution that
was prepared by mixing 50.0mL of 0.0300M Ni2+ with
50.00mL of 0.05M EDTA. The mixture was buffered
to a pH of 3.0

Example 15-35
Construct a titration curve for 50.00 mL of 0.015
M Fe2+ with 0.0300M EDTA in a solution buffered
to pH 7.0. Calculate pFe values after the addition
of 0.00, 10.00, 24.00, 25.00, 26.00, and 30.00 mL
of titrant.

1)當量點前 

2)當量點時

3)當量點後

[MIn-]/[HIn2-] ≥ 10
~red, before end point (pM small)
[MIn-]/[HIn2-] ≤ 1/10 ~blue, after end point (pM large)

(當pH=9)

pH=9)
[MIn-]/[HIn2-] ≤ 1/10 ~blue, after end point (pM large)

Excess EDTA  blue
blue
pCa
red
Volume of EDTA (ml)

Kf : CaY2- > MgY2-
pCa
Volume of EDTA (ml)

A 0.3284-g sample of brass(containing lead, zinc, copper, and tin)
Pb2+ , Zn2+ , Cu2+ , Sn2+ (total : 0.3284g)
The sparingly soluble SnO2 ‧4H2O was removed by filtration, and the combined filtrate
and washings were then diluted to 500.0 mL.
Removed Sn2+
A 10.00-mL aliquot was then suitably buffered; titration of this aliquot required 37.56
mL of 0.002500 M EDTA.
Titrated  (Pb2+ , Zn2+ , Cu2+) 37.56mL x 0.0025M EDTA x (500/10) mL
The copper in a 25.00-mL aliquot was masked with thiosulfate; the solution was then
titrated with 27.67 mL of EDTA solution
Titrated  (Pb2+ , Zn2+) 27.67mL x 0.0025M EDTA x (500/25) mL
Cyanide ion was used to mask the copper and zinc in a 100-mL aliquot; 10.80 mL of the
EDTA solution were needed to titrate this aliquot
Titrated  (Pb2+) 10.80mL x 0.0025M EDTA x (500/100) mL
Titrated  (Pb2+ , Zn2+ , Cu2+) 37.56mL x 0.0025M EDTA x (500/10) mL = 4.695 mmol
Titrated  (Pb2+ , Zn2+) 27.67mL x 0.0025M EDTA x (500/25) mL = 1.384 mmol
Titrated  (Pb2+) 10.80mL x 0.0025M EDTA x (500/100) mL = 0.135 mmol
(Zn2+) 1.384 – 0.135 = 1.2485 mmol
(Cu2+) 4.695 – 1.384 = 3.3115 mmol
(Cu2+)%  3.3115 x 0.06355 / 0.3284 g x 100% = 64.08%
(Zn2+)%  1.2485 x 0.06539 / 0.3284 g x 100% = 24.86%
(Pb2+)%  0.1350 x 0.2072 / 0.3284 g x 100% = 8.518%
(Sn2+)%  100% - (Cu2+)%- (Zn2+)% - (Pb2+)% = 2.54%
Exercise
Chromel is an alloy composed of nickel, iron, and chromium. A 0.6472-g sample was
dissolved and diluted to 250.0 mL. When a 50.00 mL aliquot of 0.05182 M EDTA was
mixed with an equal volume of the diluted sample, all three ions were chelated and a 5.11
mL back titration with 0.06241 M copper(II) was required. The chromium in a second 50.0
mL aliquot was masked through the addition of hexamethylene-tramine; titration of the
Fe and Ni required 36.28 mL of 0.05182 M EDTA. Iron and chromium were masked with
pyrophosphate in a third 50.0 mL aliquot, and the nickel was titrated with 25.91 mL of the
EDTA solution. Calculate the percentages of nickel, chromium, and iron in the alloy.
1. Chromel is an alloy composed of nickel, iron, and chromium
2. A 0.6472-g sample was dissolved and diluted to 250.0 mL
3. When a 50.00 mL aliquot of 0.05182 M EDTA was mixed with an equal volume of the diluted
sample, all three ions were chelated and a 5.11 mL back titration with 0.06241 M copper(II) was
required
4. The chromium in a second 50.0 mL aliquot was masked through the addition of
hexamethylenetramine; titration of the Fe and Ni required 36.28 mL of 0.05182 M EDTA
5. Iron and chromium were masked with pyrophosphate in a third 50.0 mL aliquot, and the
nickel was titrated with 25.91 mL of the EDTA solution.
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