Question

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?

Answer 1

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.