Question

If you recovered 4.65 g of Cu from a 42.0 mL sample of material, what would the molarity be?

4.65 g Cu/ 63.5 g/mol = 0.0732 mol

0.0732 mol/ 42 mL x 1000 mL/ 1 L =1.74 M ~ 2 M Cu??? Is this correct sig fig because you go off of the 1 sig in 1,000 mL??? So you get 2 with rounding 1.74 with following sig fig rules..

Answer 1

I would say M = mols/L
mols - 0.0732
L - 0.0420
M - 1.74M and use all three digits because, by definition, 1000 mL = 1 L.

Answer 2

oh, but with 1 L it is still only one sig fig? right?

Answer 3

Yes, 1 L has only 1 s.f.; however, 42.0 mL = 0.0420 L and there are 3 s.f. in 4.65g and in 0.0420. The "1 L" is never used since the definition is M = mols/L. The "L" in the formula happens to be 0.0420.

Answer 4

Okay that makes sense but if you had 40 mL which is just .04 then it would just be 1 sig fig.

Answer 5

.04 L to be exact

Answer 6

As I undersand it, yes. 0.04 has 1 s.f.