For the next three problems, consider 1.0 L of a solution which is 0.5 M HF and 0.2 M NaF (Ka for HF = 7.2 x 10-4). Assume 2 significant figures in all of the given concentrations so that you should calculate all of the following pH values to two decimal places. 1. Calculate the pH of this solution. 2. Calculate the pH after 0.10 mol of HCl has been added to the original solution. Assume no volume change on addition of HCl. 3. Calculate the pH after 0.20 mol of NaOH has been added to the original buffer solution. Assume no volume change on addition of NaOH.