Question

How many moles of solute are needed to make a 0.5 L solution of 2.5 M `HCl`?

Answer 1

1.25 moles of solute

Explanation:

Molarity is defined as the number of moles of solute per liter of solution.
Molarity = moles of solute / liter of solution

We are given the molarity and volume, both of which have the correct units. All we have to do is rearrange the equation to find the number of moles. You can do this by multiplying both sides of the equation by the volume to cancel it out on the right hand side. Afterwards, you should end up having the volume multiplied by the molarity equaling the number of moles of solute like so:

Moles of solute = Molarity * Volume

2.5M HCl * 0.5 L = 1.25 moles of HCl

I hope this made sense.