aspirin back titration
Hey, wonder if anyone could help me,
I am doing a back titration to determine the purity of a sample of aspirin. I have made up a standard solution of the aspirin in 50/50 water and ethanol, to dissolve it, and i have calculated the moles of this standard solution. I will then add 20cm^3 of this standard solution into a flask and then add 20cm^3 of NaOH. I have also calculated the moles of the NaOH required taking into consideration that excess will be required. But in order to hydrolyse the aspirin I need to work out what the concentration of the NaOH solution must be. What calculations would I have to do to work out the concentration of NaOH needed?