When making a solution of sodium hydroxide and water, a student weighed out an certain amount of sodium hydroxide pellets and dissolved them in an certain amount of water. However, the sodium hydroxide concentration of the resulting solution was lower than the concentration that the student thought they made. What was the problem?

Hygroscopic nature of NaOH is the main reason for the lower concentration of the sodium hydroxide in the solution.

Explanation:

It is a well known fact that Sodium hydroxide pellets are hygroscopic in nature, which clearly means that the sodium hydroxide pellets absorbs moisture from the air, so that it becomes deliquescent. When the NaOH crystals are weighed, the crystals absorb moisture from the surroundings, and so the weight of the crystals may change, so the concentration of the solution was lower than the required one.So it is not possible to prepare NaOH solution under normal room temperature. So, while preparing the solution of NaOH we have to be more careful.