Hi all, I stuffed up. I am out by factor of 10 in my answer key to the colloidal cold prac, for the mass of NaOH required. Those of you in the know will know, for the rest just keep marking! out by 10 on NaOH the calc is 0.571g 1/210 moles x 3 x 39.99 (g/moles)= 0.571g per 100ml stock solution. Cheesr, Leon