you lazy son/daughter of a bitch! UTFSE!
get a friggen highschool/college chemistry textbook!
this has been discussed _ad_nauseum_
% always means per mass:
25g NaOH + 475g H2O(=475ml H2O)
(this gives 500g of 5%NaOH, which is not exactly 500ml, but
close enough - if you really want exactly 500ml, then scale up
and measure 500ml of the obtained solution. and of course in
this case you could simply take 25g NaOH, dilute to 500ml and
be done, because nobody gives a fuck whether its 4%, 5% or maybe
6% (the 5% was taken directly out of the performing chemist's ass,
because it's a nice number - if he was calculating in hexadecimal,
it would probably have been 8%))
