1-What is the current (IUPAC, 2018) definition of mole? Why was the old definition abandoned? How many moles of hydrogen chloride are there in 0.5 L of 36.5% (w/w) hydrochloric acid solution (d=1.2 g/mL)? What is the molarity of this solution? (Cl: 35.5)

2- To prepare a pH=7.0 buffer, you can mix two solutions (each at 0.1 M concentration) from the following list at equal volumes. Which two solutions would you mix, and why?

H₃PO₄, NaH₂PO₄, Na₂HPO₄, Na₃PO₄, CH₃COOH, CH₃COONa, H₃BO₃, NaH₂BO₃

(For H₃PO₄, pK_a1 = 2, pK_a2 = 7, pK_a3 =12 ; for CH₃COOH pK_a= 5 ; for H₃BO₃ pK_a = 9)

3-The consecutive acidity constants of the physiologically important amino acid: methionine are pK_a1 = 2.3, pK_a2 = 9.2. What is the isoelectric pH (i.e.p.) of this amino acid? Why is it important to find the i.e.p.?