The molecular weight of NaOH is 40. the molecular weight of a widely used buffer, HEPES, is 255. HEPES has a pK of 7.5 and is available in the acid form. how many grams og HEPES and NaOH are needed to produce one liter of a 0.5 molar solution of pH 7.5? of pH 7.0? of pH 8.5?