4. What is the operating pH for following buffer solutions? (Refer to section 14-8 in [Pauling] for relevant acid constant) (a) A solution containing 0.2 M H2S and 0.15 M NaHS. (b) A solution containing 0.1 M NaHSO4 and 0.15 M K2SO4. 5. Enough water is added to 0.1 mole of acetic acid (CH3COOH) and 0.3 mole of sodium acetate (CH3COONa), in order to make one liter solution. What is the (approximate) molar concentration of (a) Na+, (b) H+ , (c) CH3COO and (d) CH3COOH in the solution? (Ka = 1:8 105). 7. An amino acid NH2 CHRCOOH dissociates in two steps with acid constant given below step 1: N+H3 CHRCOOH )* N+H3 CHRCOO + H+ Ka1 = 5:0 103 step 2: N+H3 CHRCOO )* NH2 CHRCOO + H+ Ka2 = 2:0 1010 (a) What is the isoelectric point pI of this amino acid? (b) In acid solution with pH = 1.0, what is the main form of this amino acid? In basic solution with pH = 12, what is its main form? (c) At pH = 2.0, what are the fractions of the three forms?

4. What is the operating pH for following buffer solutions? (Refer to section 148 in [Pauling] for relevant acid constant) (a) A solution containing 0.2MH2S and 0.15MNaHS. (b) A solution containing 0.1MNaHSO4 and 0.15MK2SO4. 5. Enough water is added to 0.1 mole of acetic acid (CH3COOH) and 0.3 mole of sodium acetate (CH3COONa), in order to make one liter solution. What is the (approximate) molar concentration of (a) Na+, (b) H+, (c) CH3COOand (d) CH3COOHCO in the solution? (Ka=1.8105) 7. An amino acid NH2CHRCOOH dissociates in two steps with acid constant given below step 1: N+H3CHRCOOHN+H3CHRCOO+H+Ka1=5.0103 step 2: N+H3CHRCOONH2CHRCOO+H+Ka2=2.01010 (a) What is the isoelectric point pl of this amino acid? (b) In acid solution with pH=1.0, what is the main form of this amino acid? In basic solution with pH=12, what is its main form? (c) AtpH=2.0, what are the fractions of the three forms