How to mix up NaOH?

[greeter]

Hello,

    Various recipes call for a NaOH solution.  Some say use a 5% NaOH solution, some 25%, etc.  How do you know how much NaOH to add to dH2O to get the proper %?

    Also, I checked out a can of drain opener crystals the other day and the ingredients were listed only as NaOH.  The contents however were bright green, and did not look like any sort of homogenous mixture.  There were beads and what looked like little metal shavings in there.  Should I go searching for another brand of drain cleaner?  I've seen RD Lye mentioned here.  What does the stuff look like when you open the bottle?

Thanks!

greeter

[halfapint]

weight of solute per volume of solvent, w/v: put 5 grams NaOH in 100 ml water for a 5% solution, 25 g into 100 ml for a 25% solution, etc.

You got the wrong drain opener. Yours has little beads and what looks like metal shavings in there. R** D**** lye is NaOH, without colorants, crystals nor metal shavings. It is white, very hygroscopic.
turning science fact into <<science fiction>>

[PoohBear4Ever]

Come on halfapint; like he's gonna know what "hygroscopic" means  

PB

BTW, I though w/w was most commonly used ratio for percent???

edit: water = 1g/ml, depending on temp/pressure ... duh    

[PrimoPyro]

Pooh: It is the same for water. H₂O D = 1g/mL, therefore 100mL = 100g

                                                   PrimoPyro
Vivent Longtemps la Ruche!

[Chromic]

Ok guys, this is sad!!! Get it right...

100g of 25% NaOH is 25g of NaOH and 75g (75mL) of water. So the solution, which weighs 100g is 25% NaOH.

There are other types of percent, ie w/v (ie 25% NaOH would be 25g NaOH in 100mL solution) and v/v (ie 25ml of EtOH in 100mL of solution), but w/w is by far the most common!

[PoohBear4Ever]

That's what I thought...

PB

[greeter]

Chromic said:  100g of 25% NaOH is 25g of NaOH and 75g (75mL) of water. So the solution, which weighs 100g is 25% NaOH.

Thanks very much all.  Very helpful.  Nope, I don't know what hygroscopic means, but then I'm learning and wouldn't dream of dreaming unless I knew that and a whole lot more.  So, on with the questions...

what specifically do w/w, w/v, and v/v mean?  Chromic, you say that w/w is the most common.  Is w/w (i.e. 5g NaOH + 95g dH2O = 100g 5% NaOH soln.) the mixing method to be used in most (all?) of the rxn's here?  How about specifically for the benzo-meoh-wacker?  Under what circumstances would someone choose one method over another (It's almost like you're taking an exam, eh?  Except of course you're the instructor )?

Thanks,

greeter

[Chromic]

weight/weight, weight/volume, volume/volume. w/w is always used unless it's specified that it's something else.

[Tits]

By adding that 25g of NaoH you will see the water level ballance out at 100ml. 1g - 1 ml 

If you put 25g of gold in there.. the same would not happen.. amazing aint it?
Would you like to touch it?