What will the volume be of a soltuion created using 120 ml of 4.5 M stock solution if the final molarity needs to be 2.00 M

We need 540 mmoles of stock solution and complete to 270 mL of volume.

Explanation:

In order to determine the volume or concentration at diluted solution we apply this formula:

Dil volume . Dil concentration = Conc volume . Conc concentration

Stock solution is always, the concentrated.

Let's replace with data given:

Dil. volume . 2 M = 120 mL . 4.5 M

Diluted volume = (120 mL . 4.5M)  / 2M

Diluted volume = 270 mL

This problem can be also solved by rule of three:

1 mL of stock solution contains 4.5 mmoles

120 mL of stock solution contain (120 mL . 4.5 mmoles) / 1mL = 540 mmoles

This mmoles of stock solution are also contained at the diluted

If 2 mmoles are contained in 1mL of diluted solution

540 mmoles must be contained in (540 mmol . 1 mL) / 2 mmol = 270 mL

We need 540 mmoles of stock solution and complete to 270 mL of volume.