Question

The following data were obtained when a Ca2+ ion selective electrode was immersed in a series of standard solutions.

Ca2+ (M)

3.38E-5
3.38E-3
3.38E-1


E(mV)

-74.8
-18.7
37.7

Calculate the concentration of a sample that gave a reading of -22.5 mV

Answer 1

I suggest you plot the data, then read concn from the graph at -22.5 mV.

Answer 2

Did that multiple times and the answer is still incorrect. The equation I computed was y=252.346x+(-47.318)

I've also tried plugging in -22.5 as y and solved for x and still got .098M which was incorrect

Answer 3

Just a glimmer of hope here but it might be worth trying. You data has three significant figures and your answer only two; these on-line data bases are notorious about s.f. Try adding another place to your answer.

Answer 4

the correct answer is 2.45E-3M but I have no clue how that's possible