Question

Given,$10$ml of $2M$ $NaOH$solution is added to $200$ml of $0.5M$ $NaOH$ solution. What is the final concentration?
A. $0.3M$
B. $0.6M$
C. $0.5M$
D. $0.4M$

Answer 1

Molarity is also known as molar concentration. It is defined as the number of moles of solute dissolved in volume of solution in liters. The mixing of two different or same solutions with differ in molarity and volume will lead to the formation of solutions of different molarity other than the reacted species molarity.

Complete answer:
Molar concentration can be calculated from the number of moles of solute and volume of solution in liters. The number of moles of solute can be determined from the weight of solute and molar mass of solute. The volume of solution must be in liters, if it is in milliliters it should convert into liters.
Given that $10$ml of $2M$ $NaOH$solution is added to $200$ml of $0.5M$ of $NaOH$ solution.
The number of moles in $10$ ml of $2M$ $NaOH$ solution will be $2 \times \dfrac{{10}}{{1000}} = 0.02mol$
The number of moles in $200$ml of $0.5M$ $NaOH$ solution will be $0.5 \times \dfrac{{200}}{{1000}} = 0.1mol$
Thus, the total number of moles of solution will be $0.02 + 0.1 = 0.12mol$
The total volume of the solution will be $200 + 10 = 210ml$
By converting this volume to litres, we will get $\dfrac{{210}}{{1000}} = 0.210L$
Thus, the molar concentration will be obtained by taking the above number of moles and total volume
$\dfrac{{0.12}}{{0.21}} = 0.58M$
Thus, the obtained concentration is nearer to $0.6M$
So, the correct answer is “Option B”.

Note:
Molarity can be used to express the concentration of chemical substances. It was represented by M. The molarity and other units used to express the concentrations are related to each other. The normality, molality and mole fraction are the other units used to express the concentration.