Question

200ml of a solution contains 5.85g dissolved sodium chloride. The concentration of the solution will be (Na=23; Cl=35.5)
A . 1 molar
B . 2 molar
C . 0.5 molar
D . 0.25 molar

Answer 1

Hint: In this question we have to use the concept of molarity. Firstly, we have to calculate the number of moles by dividing the weight of the compound by its molecular weight. Then, use this to calculate the molarity of the solution in moles per liter volume.

Complete answer:Molarity is a concept used to express concentration in terms of moles per litre of a solution and is frequently represented by the letter "M".
As a result, our definition is as follows: "Molarity of any solution is the number of moles of solute per litre of solution." The formula for it is: volume of solution in litres
$Molarity=\dfrac{moles\text{ }of\text{ }solute}{volume\text{ }of\text{ }solution\text{ }in\text{ }litres}$
The SI unit for molarity is mol/L.
In the given question, the solute is NaCl.
Molar mass of NaCl = molar mass of Na + molar mass of Cl = 23+35.5 = 58.5g/mol
\[Number\text{ }of\text{ }moles=\dfrac{Given\text{ }mass}{Molar\text{ }mass}\]
Given the mass of NaCl = 5.85g
Moles of NaCl = $\dfrac{5.85}{58.5}=0.1$
Volume of solution=200mL=0.2L
Therefore, molarity of solution = $\dfrac{0.1}{0.2}=0.5$M

The correct answer is C.

Note:The proportion of solute that is present in a solution is referred to as its "Concentration."
There may be confusion between molarity, molality, and normality. Molality is denoted by the letter "m," whereas molarity is denoted by the letter "M." The number of moles of solute present per kilogram of solvent is known as the molality of any solution. It is exemplified by the following:
$Molality=\dfrac{moles\text{ }per\text{ }solute\left( mol \right)}{weight\text{ }of\text{ }solvent\text{ }in\text{ }kg}$
It has the SI unit mol/kg.
The number of gram or mole equivalents of solute present in one litre of a solution is called normality. It is frequently referred to as the equivalent concentration of a solution and is abbreviated as "N". The units of normality are N or equivalents/Litre.