Early tables of atomic weights (masses) were generated by measuring the mass of a substance that reacts with 1.00 g of oxygen. Given the following data and taking the atomic mass of hydrogen as 1.00, generate a table of relative atomic masses for oxygen, sodium, and magnesium. Mass That Combines with Element 1.00 g Oxygen Assumed Formula Hydrogen 0.126 g HO Sodium 2.875 g NaO Magnesium 1.500 g MgO How do your values compare with those in the periodic table? How do you account for any differences?
Acid/Base Titrations • progress of an acid/base titration can be shown on a titration curve • titration - solution of known concentration is used to determine concentration of unknown solution • a reaction with an acid and a base produces water and a salt • Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]) —use when system is a buffer that undergoes no change • ex. You have a solution that is 0.20 M HC2H3O2 and 0.50 M C2H3O2- with Ka = 1.8 x 10^-5. Calculate the pH of the solution. pKa = -log(Ka) = -log(1.8 x 10^-5) = 4.745 pH = 4.745 + log(0.50/0.20) = 5.14 • common ion effect - suppresses ionization of a weak acid by adding more of an ion that is a product of that equilibrium • ex. when NaCl and KCl are
