Question

How much water do you add to 150 mL of a 6.0 molar solution of
magnesium sulfate to make it into a 4.0 molar solution?

75 ml
100 ml
50 ml
225 ml​

Answer 1

Given :

• Initial volume of magnesium sulfate solution ( V₁ ) = 150 mL
• Initial molarity of magnesium sulfate solution ( M₁ ) = 6M
• Water is added to solution
• Final molarity of solution (M₂) = 4 M

To find:

Volume of water added

Formula used :

M₁V₁ = M₂V₂

Here ,

• M₁ = Initial molarity of solution
• V₁ = initial volume of solution
• M₂ = Final molarity of solution
• V₂ = Final volume of solution

Solution :

First of all we need to find out final volume of solution.

$\sf \implies \: 6M \: \times \: 150mL \: = \: 4M \: \times \: V_2$

$\sf \implies \: 900(M )\: (mL) \: = \: 4M \: \times \: V_2$

$\sf \implies \:V_2 \: = \dfrac{900(M )\: (mL) \:}{4M} \:$

$\sf \implies \:V_2 \: = 225\: (mL)$

Now , we know that

➝ Final volume of solution = Initial Volume of solution + volume of water added

➩ 225mL = 150mL + Volume of water added

➩ Volume of water added = 225mL - 150mL

➩ Volume of water added = 75mL

________________________________

ANSWER : 75mL