Question

Given 750mL of a 2.5M NaOH solution, how many moles of sodium hydroxide are there?

Answer 1

Hint: In 2.5M the M represents the term molarity. The molarity is defined as the number of moles which are present in per litre of the solution. The molarity of the substance changes with the change in the physical properties of the system such as the pressure and the temperature.

Complete step by step solution:
So, the formula which is used for calculating the molarity is the number of moles of the solute in the solution present divided by the volume of the solution in which the solute is dissolved. We will express the formula in the following way:
Molarity =\[\dfrac{\text{moles of solute}}{\text{volume of solution(L)}}\]
Now we will write the values that are given in the question,
Molarity = 2.5M
Volume = 750mL = 0.75L
Now we will substitute the values in the formula. We get,
2.5M = \[\dfrac{\text{moles of solute}}{0.75L}\]
\[\Rightarrow 2.5\times 0.75\] = mass of solute
moles of solute = 1.875
so the moles of sodium hydroxide present in 750mL of a 2.5M NaOH solution is 1.875 moles.

Note: In molarity we use the whole volume of the solution whereas in molality only the mass of the solvent is used in calculation. The symbol used for expressing molarity is M and for expressing molality is m. the unit of molality is moles/kg whereas for molarity is moles/ litre. Whereas normality is defined as the number of the equivalent present in per litre of the solution. It is expressed as N. The unit of normality is equivalent weight per litre.