Question

A student prepares a standardized solution of sodium hydroxide by the procedure outlined. The student first prepares a saturated solution of sodium hydroxide using freshly distilled or deionized water. She measures about 5 mL of the saturated solution with a graduated cylinder and dilutes to 1 L in a plastic bottle with freshly distilled or deionized water to make a solution that is about 0.1 M. To determine the exact concentration, she puts the NaOH solution in a buret and titrates a carefully-weighed pre-dried solid acid of known molar mass. She records the volume of NaOH needed to neutralize it and repeats the process several times to determine the concentration of the NaOH solution. She calculates the concentration and uncertainty in the concentration of the NaOH from the titration data.

Answer 1

Titration is an analytical chemistry technique used to find the concentration of an unknown solution. The process involves neutralizing an unknown acid with a base of known concentration and utilizing stoichiometry to calculate the concentration of the unknown acid.

Step-by-step explanation:

The process described by the student is known as titration, a fundamental method in analytical chemistry used to determine the concentration of an unknown solution. In this case, the titration involves a strong acid, such as hydrochloric acid (HCl), and a strong base, sodium hydroxide (NaOH), each of known molarity. When the HCl is titrated with the NaOH, the point of neutralization is indicated by a change in color of the pH indicator or by the reading on a pH meter. To determine the number of moles of the unknown acid that were neutralized, one multiplies the molarity of the NaOH by the volume of NaOH used (converted to liters).

Using dimensional analysis, we can convert this to moles: 0.100 M NaOH multiplied by the volume used, for example, 0.0126 L. From the stoichiometry of the balanced chemical equation (HCl + NaOH → NaCl + H₂O), the moles of acid can be deduced. These moles can be further used to calculate the molarity of the unknown acid by dividing the moles of acid by the volume of the acid solution used in the titration.

Answer 2

NaOH has the property of deliquescent hence it cannot be weighed directly instead a saturated solution is diluted and desired concentration is obtained.

Step-by-step explanation:

Sodium hydroxide undergoes deliquescent.

Deliquescence is the process in which substance absorbs moisture and carbon dioxide from the atmosphere to the extent of getting dissolved and form a solution.

Deliquescence happens when vapour pressure of solution formed is less than the partial pressure of water vapour in the air.

This is the reason that student did not measure the sodium hydroxide directly as the weight will change and proper solution cannot be made. Because of the deliquescence standard solution of NaOH is not prepared.

The student made a solution without weighing the NaOH instead she prepared a solution till the NaOH got dissolved and then diluted the solution.