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QUESTION

# What is the mass of NaCl required to prepare 0.5 liters of a 2.5 molar solution of NaCl?

73 g

The molecular weight of NaCl is 58.44 g/mol

So, one mole of NaCl weighs 58.44 g.

A 2.5 M solution is 2.5 moles per liter (Molarity is just the number of moles per liter).

Therefore, 0.5 L would contain 1.25 mol. Hence, you would need 1.25 × 58.44 g = 73 g.

As equations:

M = "moles"/"vol"

M = "Molarity"

"vol" = "volume (in liters)"

"moles" = "grams"/(MW)

g = "weight of compound"

MW = "molecular weight"

So,

M = "moles"/"vol"

Substitute for moles

M = (g//MW)/"vol"

We need g, so rearrange

M × "vol" = g/(MW)

g = M × "vol" × MW

Put in the numbers:

g = "2.5 mol/L × 0.5 L × 58.44 g/mol"

g = "73 g"

Personally, I prefer the first approach!

You can find out more about moles and molarity here.