Question

I need help getting this started. I made it through organic and this one stumps me, go figure :)

How many grams fo NaCl are needed to make 100mL of a 0.10M solution?

Answer 1

M = mols/L
mols = g/molar mass.

eqn 1.
M = mols/L (The definition of molarity is all you need to remember for this.)
0.10 M x 0.100 L = 0.010 mols

eqn 2.
mols = g/molar mass
g = mols x molar mass
g = 0.010 mols x molar mass NaCl = ??

You can put eqn 1 and 2 together to give
mols = M x L
mols = g/molar mass
set mols = mols
M x L = g/molar mass and
M x L x molar mass = g.

Check my work. Check my arithmetic.