. A 25.0 ml sample of Ni2+ gave a weight height of 2.36 uA( corrected for a residual current) in a polarographic analysis. When 0.500 ml of solution containing 28.7 nmol of Ni2+ was added the wave height increased to 3.79 uA. Find the concentration of Ni2+ in the unknown?

To find the concentration of Ni2+ in the unknown, you need to determine the change in wave height caused by the addition of the known amount of Ni2+, and then use that information to calculate the concentration.

Here's how you can calculate the concentration of Ni2+ in the unknown solution:

1. Calculate the change in wave height caused by the addition of the known amount of Ni2+:
Change in wave height = Final wave height - Initial wave height
Change in wave height = 3.79 uA - 2.36 uA
Change in wave height = 1.43 uA

2. Convert the known amount of Ni2+ added to moles:
Number of moles of Ni2+ added = Volume of solution added * Concentration of Ni2+
Number of moles of Ni2+ added = 0.500 ml * (28.7 nmol / 1 ml)
Number of moles of Ni2+ added = 14.35 nmol

3. Calculate the concentration of Ni2+ in the unknown solution:
Concentration of Ni2+ in unknown = Change in moles of Ni2+ / Volume of unknown solution
Concentration of Ni2+ in unknown = (Number of moles of Ni2+ added) / (Volume of unknown solution)
Concentration of Ni2+ in unknown = 14.35 nmol / 25.0 ml
Concentration of Ni2+ in unknown = 0.574 nmol/ml (or 0.574 μM)

Therefore, the concentration of Ni2+ in the unknown solution is 0.574 nmol/ml (or 0.574 μM).