Question

What is the molarity of a $15mL,2M$ aqueous solution when $285mL$ of water is added to it?

• A. 0.400 M
• B. 0.100 M
• C. 0.111 M
• D. 0.105 M

Answer 1

The correct option is B 0.100 M

Given,
Initial concentration, $M_1=2M$
Initial total volume, $V_1=15mL$
Final total volume , $V_2=15+285=300mL$
Final concentraton, $M_2=?$
Before and after adding water number of moles of solute remain constant since it does not react with water.
Number of moles of solute = concentration x volume
Thus, $M_1\times V_1=M_2\times V_2$
On substituting, $M_2=(2\times 15)/300=0.1M$.