The concentration of Ca2+ in a water sample is determined using the method of external standards. The ionic strength of the samples and the standards was maintained at a nearly constant level by making each solution 0.5M in KNO3. The measured cell potentials for the external standards are shown in the following table. (Use decimal number in your final answer and do not include the unit)
Cu2+ (M) Absorbance
1.00 x 10-5 -0.125
5.00 x 10-5 -0.103
1.00 x 10-4 -0.093
5.00 x 10-4 -0.072
1.00 x 10-3 -0.065
5.00 x 10-3 -0.043
1.00 x 10-2 -0.033
What is the concentration of Ca2+ in a water sample if its cell potential is found to be –0.084 V?