Question

40 grams of sodium hydroxide is dissolved in enough water to make 1 liter of solution. Determine the molarity of the solution?
(A) 0.25M
(B) 0.5M
(C) 1M
(D) 1.5M
(E) 4M

Answer 1

Hint The concentration of solution which describes the composition of the solution either qualitatively or quantitatively. To describe the concentration of solution quantitatively more methods are available. There are mass percentages, volume percentage, ppm, mole fraction, normality, molarity, and molality.

Complete step by step solution:
Molarity (M): It is defined as the number of moles of solute dissolved in one liter of solution. The value of molarity expressed in moles/liter which represents the concentration of a solution. The molarity of solution can be calculated by using the below formula,
Molarity (M) = $\dfrac{n}{V(ml)}\times 1000$
Where n = number of moles of solute
V = volume of solution in ml.
In the given problem, solute = NaOH
The gram molecular weight or molar mass of NaOH = 40 g/mol
Given mass of sodium hydroxide = 40 grams
Total volume of the solution = 1 L
Number of moles of sodium hydroxide, n = $\dfrac{mass\text{ }of\text{ }NaOH}{molar\text{ }mass\text{ }of\text{ }NaOH}$ = $\dfrac{40g}{40g/mol}$ = 1 mole of NaOH
Substitute the values of volume and number of moles of solution in the molarity formula,
Molarity (M) = $\dfrac{1mole}{1L}$ = 1M
Hence, Molarity of NaOH is 1M.

The correct answer is option C.

Note: The volume of the solution may change with increasing or decreasing the temperature of the solution when the moles of solute are constant. At lower concentration with temperature-independent then molarity and molality values will be equal.