Question

4.0 gm of NaOH are contained in one decilitre of solution. Its molarity would be
A . 4 M
B . 2 M
C . 1 M
D . 1.5 M

Answer 1

Hint: In order to answer this question, we must determine the concentration of NaOH using the molarity principle. By dividing the weight of the chemical NaOH by its molecular weight, we must first determine the number of moles. Using this information, it is then possible to calculate the solution's molarity in terms of moles per litre of volume.

Complete answer:The number of moles of solute present in a specific number of litres of the solution, or moles per litre of a solution, is known as molar concentration or molarity. It is one of the most often used concentration units and is represented by the letter M.
 The formula for it is:
$Molarity=\dfrac{moles\text{ }of\text{ }solute}{volume\text{ }of\text{ }solution\text{ }in\text{ }litres}$
The SI unit for molarity is mol/L.
In the given question, the solute is NaOH.
Molar mass of NaOH = molar mass of Na + molar mass of O + molar mass of H = 23+16+1 = 40g/mol
\[Number\text{ }of\text{ }moles=\dfrac{Given\text{ }mass}{Molar\text{ }mass}\]
Given the mass of NaOH = 4g
Moles of NaOH = $\frac{4}{40}=0.1$
Volume of solution= 1 decilitre= 0.1L
Therefore, molarity of solution = \[\dfrac{0.1}{0.1}=1\]M

The correct answer is C.

Note: The terms molarity, molality, and normalcy could all be confused. In contrast to molarity, which is symbolized by the letter "M," molality is represented by the letter "m." The molality of any solution is defined as the moles of solute per kilogram of solvent. It can be expressed by:
$Molality=\dfrac{moles\text{ }per\text{ }solute\left( mol \right)}{weight\text{ }of\text{ }solvent\text{ }in\text{ }kg}$
It has the SI unit mol/kg.
The term "normality" refers to the quantity of solute in a solution measured in grams or moles per litre. It is commonly referred to as a solution's equivalent concentration and is denoted by the letter "N". N or equivalents/Litre serve as the units of normality.