I have test procedure to evaluate the clarity of a sodium hydroxide (NaOH) sample that goes like this:

Question

Dissolve 10g of NaOH in carbon dioxide free water and dilute to 100ml with the same solvent.
Please explain how to perform this test.
Do I boil 100ml of deionized water and pour the hot water into a beaker containing 10g of NaOH?
Thanks.

Answer 1

Definitely not, for two reasons.
1. the total volume after solution may exceed 100ml, in which case the required concentration is not attained.
2. DO NOT pour hot water onto solid NaOH, it is an extremely exothermic process and you can end up splashing very corrosive NaOH onto your face or even your eyes. Always put solid NaOH into cold water, giving enough time for the heat to dissipage.

Answer 2

Thanks, can you then explain the exact steps (including the apparatus to use) so that the procedure can be followed?
Thanks a lot:)

Answer 3

I assume you have some CO2 free water. Place 10 g solid NaOH in a 100 mL volumetric flask and add some CO2 free water (about 25 mL or so). When the solid has dissolved (it is quite exothermic as Mathmate has written), let it cool to room temperature, then dilute to the 100 mL mark with CO2 free water.
Note: I would note that if you are trying to prepare a NaOH solution that is free of carbonate ion, this isn't the way to do it. Why? Because solid NaOH picks up CO2 from the air and forms Na2CO3.

Answer 4

Thanks Dr Bob,the purpose of this experiment is to test for the clarity of my sodium hydroxide sample.
I intend to boil deionized water to get CO2 free water, cool the water and add it to a 100mL volumetric flask containing 10g of solid NaOH. Would that be alright?
Also, can you share with me how to prepare a NaOH solution that is free from carbonate ion?
Thanks a lot.

Answer 5

OK. Boil the water, add about 25 mL of the cooled water to the 100 mL volumetric flask containing the solid NaOH, let the NaOH dissolve, then let the whole thing cool. Finally, dilute to the 100 mL mark.

How to prepare carbonate free NaOH. Prepare a concd solution of NaOH by dissolving solid NaOH in deionized water (you want about 50% NaOH solution but I like to make it stronger than that). Na2CO3 is not very soluble in such a concd NaOH solution. Allow to stand (I usually suggest several days), then pipet a portion of the clear, colorless solution into a clean flask and dilute with water. This solution must then be standardized by an appropriate titration. Here is a site you can read about it. (Broken Link Removed)