4. Before approving your procedure, your advisor also wants to know how sensitiv

Question

4. Before approving your procedure, your advisor also wants to know how sensitive the method is, or the lowest limit of phosphate concentration that can be measured this way. The lowest mass of precipitate you can measure was from a sodium phosphate solution prepared by the following steps: a. 12.5 mL of a 1 mM solution is added to enough water to make 250.0 mL of dilute solution b. 20.0 mL of the dilute solution is diluted further to a total volume of 100.0 mL Work out the phosphate concentration (in M) needed to measure a precipitate.

Explanation / Answer

a )

before dilution moles = 12.5 x 1

after dilution = 250 x C

moles are same before and after dilution

12.5 x 1 = 250 x C

C = 0.05 mM

b)

now another dilution

0.05 x 20 = 100 x C1

C1 = 0.01 mM = 1.0 x 10^-5 M

phosphate concentration = 1.0 x 10^-5 M

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