1) 1.50 mols / 0.50L = **3.0 M **(with sigfigs in mind)

2) First convert grams to mols. The molar mass of KI is 165.998 g/mol. Converting...

58.5 ~~g~~ * (1 mol) / (165.998 ~~g~~) = 0.352413 mols

the molarity is given by....

0.352413 mols / 10.L = **0.35 M** (with sigfigs in mind)

3) First convert 5 micro grams Pb to grams Pb....

5ug = 5 x10^-6 g

To find ppb divide mass of Pb by mass of solution and multiply by 10^9...

(5x10^-6) / (200g) * 10^9 = 25 (if sigfigs are important, our answer should have only one sigfig. So our answer should be **30 ppb** or IF YOU USE THE FIVE-EVEN RULE: **20 ppb**** **)

4) given ppm, we work backwards to find the ratio of arsenic in the sample. First divide by 10^6...

5 / 10^6 = 5x10^-6

We know the amount of arsenic, which we'll denote A, in 50.0 g of sample has the ratio 5x10^-6. So we can write...

5x10^-6 = A / 50.0g

solving for A....

A = (5x10^-6) (50.0g) = 2.5 x10-4 g or 0.25 mg (again, if sigfigs are important: **0.30 mg** or with the five-even rule in effect: **0.20 mg**)

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