Why standardize naoh with khp

The volume of the 50 mL buret used in titration was recorded to the 0. All the glassware were scrupulously cleaned and dried before use and the buret was rinsed down with its reagent before the titration. It was vital to check the buret for any air bubbles present before performing the titrations. To prepare the sodium hydroxide solution a liter of distilled water was boiled for 10 minutes and cooled to remove the carbon dioxide.

That step is necessary because Sodium hydroxide and carbon dioxide react in a solution to form an unwanted carbonate ion. Note that to cool the boiled liter of water in shorter time an ice bath was used. Crushed ice and cold water mixture serves well for the purpose because crushed ice alone is not efficient for cooling due to the air in spaces which is a poor conductor of heat 2. In the standardization process, three samples of known potassium hydrogen phthalate underwent titrations by the prepared 0.

Each sample consisted of 0. The phenolphthalein is an indicator that reacts to the addition of hydrogen or hydroxide ions, turning colorless with an addition of hydrogen ions and turning pink when hydroxide ions are added. The mols of sodium hydroxide were divided by the volume of 0. Similar step was taken to find the concentrations of unknown potassium hydrogen phthalate.

The average molarity of sodium hydroxide calculated from step before was multiplied by the volume of the titrating solution added and converted into mols of potassium hydrogen phthalate in the sample.

Then using the molecular weight The indicator used, phenolphthalein is a weak acid that responds to additions or subtractions of the hydrogen ion so it was proper that the unknown potassium hydrogen phthalate was diluted with a neutral diluents. The titrations had to be done with much care and precision because of its sensitivity.

A stir bar was used during titration which could hamper with the endpoint noticed by a slight pink indication that lasts about thirty seconds so during the experiment the titration was put to an end if the pink lasted about 10 seconds. It is important to note that the pink color in three titrations were all slightly different, some being darker than others.

It was crucial to make use of the half drop technique as well because the endpoint was very sensitive to even 0. The average molarity of the sodium hydroxide solution was found to be 0.

But if the students took the mass of the NaOH in the beginning, can they not just use that information to determine the approximate molarity of the solution? As the title says, why bother to standardize? If our NaOH solution had some room for error in measurement and calculation, surely titrating against another solution of "known" concentration would only introduce more error, no?

Usually, if we're doing these for basic application or experimentation, standardization doesn't really matter. But when it comes to anything analytical where you start to involve calculations, standardization is a must. This is done with NaOH because it's hygroscopic and readily sucks up the moisture in the air.

So what is being weighed isn't totally NaOH, but also the moisture that it has absorbed. So almost always the concentration will be lesser than what is sought to be prepared because of this. Tedious as it may be because you also have to heat up the KHP for around an hour before titrating , standardization brings you closer to the true concentration, but not exactly on the mark. At least in the end, calculations using the standardized concentrations will be analytical.

This is why they never introduce standardization in general chemistry courses, I only got to grips with it when I took up Analytical Chemistry, and back then it was really tedious to do.

For example, I actually experienced this before where we had to prepare a 1M stock of NaOH, but after standardization it turned out to be around 0. There are a list of compounds which are used for preparation of various standard solutions and appropriate protocols.

The chemical structure for such compounds does not depends on external factors following the protocol and can be used to determine the concentration precisely. Additionally more sensitive methods can be used to determine the final concentration of standard solutions, e.

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