how do you create a 0.2N solution of sodium hydroxide using powdered sodium hydroxide

[salvage11]

Hi,

Thank you for you help- we are looking to create a 0.2N solution of sodium hydroxide to use in our food processing business using powdered sodium hydroxide.  We currently purchase the solution pre-made for us, however to save cost we would like to start making this solution ourselves. Preliminary research came up with 4g of powder per liter to create a 0.2N solution. Not sure if this is correct or not.

Appreciate the help!

[scooke]

Dear Nicholas,

Normality is often used for titration purposes instead of molarity.  However, in the case of sodium hydroxide they are the same because one "equivalent" of NaOH is the same as one "mole".  Both are based on the molecular weight of NaOH - 40g/mol.  Four (4) grams is 0.1 mole NaOH, so dissolving it in one (1) liter of water will result in a 0.1M, or 0.1N solution of NaOH.  A 0.2N solution would require 8.0 grams of NaOH per liter of water.

NaOH adsorbs water quickly (with heat generation), so to ensure the most accurate preparation, make sure that your powder is dry and minimize its exposure to the air during use, and especially during storage.  Add the powder slowly, with active mixing to avoid "hot spots" in the solution.

Best regards,

Steven

[mbdowell]

Steven's explanation is just right, but a typo has gotten in-- 4 grams really is 0.1 mole, so 0.2 moles would be 8 grams NaOH rather than 0.8 grams.

Best regards,

Mike

[scooke]

Thanks for the catch, Mike!  I went back and edited it in the original to avoid confusion.

[hellerb]

Just to be difficult, you may want to check the purity of the NaOH.  Lots of times you can buy 97% or the NaOH has absorbed humidity.  That would reduce the strength of the solution.  You may not have a safe way of checking the NaOH powder strength, and a 3% difference in strength may not be an issue.

[NickatHU]

Also, NaOH usually comes in pellet form.  Powder would tend to pick up large amounts of moisture.   Handling it dry would be much more of a hazard too.  It is a strong base and as a powder it would be more likely that it could be inhaled.  Otherwise above comments are correct.

[salvage11]

Thank you all for your help, it has been a great help.

[salvage11]

Thank you.

[salvage11]

How could/should I account for using a powdered sodium hydroxide which is most likely not 100%?

Thank you all for your help with this.

[choroba]

NaOH will also absorb carbon dioxide from the air so again changing the strength. Use fresh pellets I'd say and titrate your solution against a standard acid to ascertain the exact concentration. Or make up a small batch first, determine the concentration and then make up the bigger batch and adjust the mass of NaOH accordingly if it needs to be more exact.