Asked by Kiley

How many grams of KF do you need to weigh in order to prepare 500. mL of solution with a concentration of 0.250 M?
Answered by DrBob222
M = mols/L and rearrange to mols = MxL
and mols = grams/molar mass
Therefore, since mols = mols we can set those equal to each other to obtain
mols = M x L = mols = grams/molar mass and
L x M x molar mass = grams.
Plug in the numbers and solve for grams.
Answered by Kiley
I'm sorry, I don't even know where I should start plugging in. I got lost when you rearranged to mols = MxL.
Answered by ~christina~
M=mol/L

L*M = mols

just multiply both sides by L
Answered by DrBob222
Just use what I ended up with; i.e.,
M x L x molar mass = grams.
You have M, L, and molar mass. Solve for grams.
Answered by Kiley
Okay...

M x L x mm = grams

0.250 M x 0.5 L x 57.9g = 7.24 grams
Answered by ~christina~
math looks fine but as for significant figures I'm not so sure.
Answered by Kiley
Is that it for the problem, or is there another step I have to do?
Answered by ~christina~
That is the answer for the problem but as for significant figures it just means how many numbers you show for the answer.

for example if your answer is 8.93383494 right ? but the initial numbers given is 33.28 and 8.9 and because the 8.9 has the least significant figures (2) vs the 33.28's (4), then the answer would be 8.9.

Answered by Kiley
So 7.2 g would be correct then?
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