Chemical EquilibriumHard
Question
The average person can see the red colour imparted by the complex [Fe(SCN)]2+ to an aqueous solution if the concentration of the complex is 6 × 10-6 M or greater. What minimum concentration of KSCN would be required to make it possible to detect 1 ppm (part per million) of Fe(III) in a natural water sample? The instability constant for Fe(SCN)2+ ⇋ Fe3+ + SCN- is 7.142 × 10-3.
Options
A.0.0036 M
B.0.0037 M
C.0.0035 M
D.None of these
Solution
Fe3+ + SCN- ⇋ [Fe(SCN)]2+ K = 
Initial conc.
b 0
Final conc.
- 6 × 10-6 b - 6 × 10-6 6 × 10-6
on solving b = 0.0036 M.
Initial conc.
b 0Final conc.
- 6 × 10-6 b - 6 × 10-6 6 × 10-6 on solving b = 0.0036 M.
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