Question

I have 4.0 L of a 3.0 M NaCl solution and I want to dilute it to 2.0 M. How much water do I need to add?

Answer 1

We need to add 2 liters of water !

Step-by-step explanation:

Here we have , I have 4.0 L of a 3.0 M NaCl solution and I want to dilute it to 2.0 M. We need to find How much water do I need to add. Let's find out:

4.0 L of a 3.0 M NaCl solution , i.e.

⇒ Molarity = ( Number of moles ) / ( Volume of solution in L )

⇒
`Molarity = (n)/(V)`

⇒
`3 = (n)/(4)`

⇒
`n=12`

Now , Molarity is changed to 2M i.e.

⇒
`2 = (12)/(V)`

⇒
`V=6`

So , change in volume is :
`6L-4L` =
`2L`

Therefore , We need to add 2 liters of water !