Question

3. The following polarographic diffusion currents were measured at -0.6 V for CuSO4 in 2 M NH4Cl/NH3. Prepare an excel calibration plot and use it to estimate the molarity of an unknown solution giving Id = 15.6 μA.

    an unknown solution giving Id = 15.6 μA.

Cu2+(mM)	0.0393	0.0780	0.1585	0.489	0.990	1.97	3.83	8.43
Id(uA)	0.256	0.520	10.58	3.06	6.37	13.00	25.0	55.8

Answer 1

[Cu2+]	Id
0.0393	0.256
0.078	0.52
0.1585	1.058
0.489	3.06
0.99	6.37
1.97	13
3.83	25
8.43	55.8

Using this the excel plot was drawn as shown below

y = 6.6157x -0.0858 PL 0 1 2 3 6 7 8 9 4 5 [Cu2+]

The given plot follows the equation y= 6.6157x-0.0858 where

y= Id

x= [Cu2+]

This equation can be used to determine the concentration of unknown solution with y=15.6 $\mu$ A

15.6 = 6.6157x - 0.0858

x = (15.6+0.0858) / 6.6157

x= 2.37mM

Thus the unknown solution have concentration of 2.37mM