Question

4L of 0.02M aqueous solution of NaCl was diluted by adding 1L of water. The molarity of the resultant solution is:
A.0.004
B.0.008
C.0.012
D.0.016

Answer 1

Molarity is a unit of concentration, measuring the number of moles of a solute per liter of a solution. The strategy for solving molarity problems is fairly simple. This outlines a straightforward method of calculating the molarity of a solution. The key to calculating molarity is to remember the units of molarity: moles per liter.

Complete step by step answer:
There are several different ways to quantitatively describe the concentration of a solution. Molarity is a useful way to describe solution concentrations for reactions that are carried out in solution. Mole fractions are used not only to describe gas concentrations but also to determine the vapor pressures of mixtures of similar liquids.
Here we use the formula of, ${M_1}{V_1} = {M_2}{V_2}$
Here ${M_1}$ and ${V_1}$ are defined as molarity and volume of the solution.
Given values are, ${M_1} = 0.02$
${V_1} = 4L$
${V_2} = 5L$
Here we put the values in the equation,

$$0.02 \times 4 = {M_2} \times 5 \\\ {M_2} = 0.016M \\\$$

Hence, option (D) is correct.

Note: Molarity is used to express the concentration of a solution. Also known as molar concentration, molarity is the number of moles of solute per liter of solution.
$concentration = \dfrac{{number\,of\,moles}}{{volume}}$
The units of molarity are moles per cubic decimeter, written simply M. The cubic decimeter is identical to the liter; in many older cases you will find concentrations are written in moles per liter. Be careful not to confuse molality and molarity. We must understand the difference between molarity and molality.