What volume of a 2.5 M stock solution of H3PO4 is needed to prepare 3.8 L of a 1.5 M H3PO4 solution?

Given:

Let M be the molarity of the solution

Let V be the volume of the solution

M_1 = 2.5 M

M_2 = 1.5 M

V_2 = 3.8 L

Required:

V_1 = ?

Solution:

M_1 x V_1 = M_2 x V_2

Substitute all known values

V_1 = (1.5 M x 3.8 L) / 2.5 M

∴ V_1 = 2.28 L

Interpretation:

To prepare 3.8 L of 1.5 M H3PO4 solution you need 2.28 L of 2.5 M stock solution of H3PO4.