Why an accurate solution of sodium hydroxide Cannot be made up by accurate weighing?

Sodium hydroxide is deliquescent (absorbs moisture from the atmosphere) solid. It cannot be weighed accurately. Therefore, it is not possible to prepare a standard solution of sodium hydroxide of accurately known concentration by weighing NaOH.

Why is it difficult to weight NaOH?

However, it is very difficult to prepare a solution of NaOH of an exact concentration for two reasons: Solid NaOH is very hygroscopic, that is it absorbs water from the air, so it is very hard to weigh exactly. This decreases the concentration of the OH- ions in the solution.

Why can we not calculate the actual molarity of the NaOH solution by weighing NaOH pellets?

If you overestimate molarity of NaOH titrant, then the calculated \% KHP will be higher than the actual value. NaOH pellets absorb water in the air, so their actual weight cannot be determined.

Why is NaOH s to be taken out and weighed only when you are ready to make measurements?

Deionized water may contain NaOH , so the total amount of NaOH in the solution needs to be measured. NaOH is hygroscopic, so it is not possible to weigh it accurately. KHP is hygroscopic, so it is not possible to weigh it accurately. NaOH is hygroscopic, so it is not possible to weigh it accurately.

Why NaOH Cannot be used as a primary standard?

NaOH has no criteria given above. It is not suitable for the primary standards because they absorb the moisture from the atmosphere. It also absorbs carbon dioxide from the atmosphere. Hence, NaOH is not a primary standard because it has no quality of primary standard.

Why standard solutions of NaOH and h2so4 Cannot be accurately prepared in a laboratory?

(a) sodium hydroxide is deliquescent. It absorbs moisture and dissolves to form a solution. Hence, the concentration of this alkaline solution is not accurate.

Why do you weigh the solid NaOH by difference instead of directly weighing it on a weight boat?

So, even with two measurements rather than one, using the weighing boat method results in much less total uncertainty in the measured mass of your material as compared to weighing a small quantity of material directly into a large beaker.

Why can’t NaOH be used as a primary standard?

Why is it necessary to weigh by difference?

Weighing by difference is a way to weigh materials accurately. The weight of the material is the difference between the two weights of the vial before and after you transfer the material from the vial.

Why can’t we weigh NaOH crystals to prepare standard solution?

Thus it’s not possible to take NaOH crystals and weigh them in normal room conditions to prepare a standard solution, as it’s weight will change by absorption of water while we are weighing them, which can result in improper concentration of the standard solution being made.

Why are pellets of sodium hydroxide not pure NaOH?

Therefore, pellets of sodium hydroxide aren’t pure NaOH and a standard solution can’t be prepared by dissolving a known mass of NaOH in a known volume of water. Solutions must be titrated with a standard solution of acid. Well, such solutions would not have a very long shelf-life.

How do you make a standard solution of NaOH?

Standard NaOH solutions are usually prepared by diluting a 50 wt\% aqueous solution of NaOH to approximately the desired concentration. This solution is then standardized by titration of an acidic primary standard. In 50 wt\% solutions of sodium hydroxide, dissolved carbon dioxide precipitates as a carbonate.

Why does NaOH absorb water from the atmosphere while weighing?

NaOH is a deliquescent substance. hence it absorbs water from the atmosphere while weighing which leads to an increase in the weight due to which the original amount of NaOH is not taken and the solution has lower normality than a standard solution. NaOH is a deliquescent substance. It absorbs water when exposed to atmosphere.