Preparing NaOH solution..

Reply Sat 23 Apr, 2005 06:01 am
Hi everyone, I need some help please.
I was wondering if anyone could be of assistance in helping me with this question:

Describe in detail how you would prepare 2.5 of mol/dm3 sodium
hydroxide solution.
Also, mol/dm3 is also known by moles of hydrogen ions (H+) per liter (1000 cm^3) on this board.

Any assistance would be appreciated.
Thanks in advance

Rose Very Happy
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Reply Sat 23 Apr, 2005 09:07 am
Ok lifted straight out of my a-level coursework... with a bit of an edit because i was making 0.1mol: (if anything doesn't make sense it's cos i forgot to edit it Embarrassed)

Method for making up a sodium hydroxide solution

Element Relative molar mass
Na (Sodium) 22.9897
O (Oxygen) 15.9994
H (Hydrogen) 1.0079

Relative molecular mass of sodium = 22.9897 + 15.9994 + 1.0079 = 39.997

This means that in order to make a 1mol/drm³ solution of Na(aq) one must dissolve 39.997g of sodium hydroxide flakes or pellets in 1dm³ of distilled water.

The solution that I require is 2.5mol/dm³ and so to form a solution of the correct concentration I need to dissolve 99.99g of sodium hydroxide in each decimetre³ of water.

1. Place a weighing boat on the pan of a balance, and equilibrate it to 0.
2. Use a metal spatula to carefully add sodium hydroxide flakes until the screen of the balance registers 20.000g
3. Tip the flakes into a 100cm³ beaker, and use the metal spatula to remove any left-over flakes from the surface of the weighing boat into the beaker.
4. Slowly add a minimal volume of distilled water until all of the sodium hydroxide flakes have dissolved.
5. Place the glass funnel into the neck of the 200cm³ volumetric flask and carefully pour the solution into it.
6. Use a wash bottle of distilled water to rinse out the beaker (also pour this in), then rinse through the funnel, and finally remove the funnel and rinse the neck of the bottle.
7. Replace the funnel in the neck of the bottle, and gradually add distilled water using the wash bottle until the meniscus of the solution is slightly below the line marked on the bottle neck to indicate 200cm³
8. Use a glass teat pipette to add a tiny volume at a time until the meniscus rests on the line.
9. Bung the volumetric flask, and add labels indicating the name and concentration of the solution, the date on which it was made up and the nature of the solution (i.e. irritant)
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