CHEM 206 Problems, Spring 2008

Analytical Chemistry Sample questions 1. What concentration of NaNO2 is necessary to buffer 0.050M HNO2 at pH 3, (Ka = 4.0x10-4). 2. An indicator HIn (Ka = 1.0x10-6) where HIn is red and In- is blue is placed in a solution of strong acid. The solution is then titrated with an NaOH solution. At what pH the indicator color change occur? 3. What volume of 0.500M HNO2 (Ka = 4.0x10-4) and 0.500M NaNO2 must be mixed to prepare 1.0L of a solution buffered at pH = 3.55 4. How would you prepare 1.00L of a buffer with a pH of 9.60 from 0.300M Na2CO3 and 0.200M HCl 5. Calculate the pH of a 1.0M solution of Na2HPO4 (For H3PO4, Ka1 = 7.5x10-3, Ka2 = 6.2x10-8, Ka3 = 4.8x10-13). 6. Calculate the pH of a 1.0M solution of NaHCO3 (For H2CO3, Ka1 = 4.3x10-7, Ka2 = 5.6x10-11). 7. Calculate the pH of a solution containing 0.100M of NaHCO3 and 0.100M of Na2CO3 (For H2CO3, Ka1 = 4.3x10-7, Ka2 = 5.6x10-11). 8. Calculate the pH of a solution prepared by mixing 500ml of 0.100M of NaOH and 500ml of 0.200M of H3AsO4 (For H3AsO4, Ka1 = 5.0x10-3, Ka2 = 8.3x10-8, Ka3 = 6.0x10-10). 9. 500ml of a 1.00M of a diprotic acid; H2A (Ka1 = 1.0x10-6, Ka2 = 1.0x10-10) is being titrated with 2.00M of NaOH. How many ml of 2.00M NaOH must be added to reach a pH of 10.00. 10. Calculate the equilibrium concentration of NH3, Cu2+, and Cu(NH3)4+ in a solution prepared by mixing 500ml of 3.00M NH3 with 500.0ml of 2.00x10-3M Cu(NO3)2. (logK1=4.04, logK2=3.43, logK3 = 2.80, and logK4 = 1.48) 11. Calculate the change in the pH (pH) at the onset (V = 5ml) during the titration of 25.00ml of two weak monoprotic acids at a concentration of 0.1500M (Ka of the first acid is 10-3 and Ka of the second acid is 10- 6). 12. What value should the indicator have to mark the equivalent point of the titration of 100ml of 0.100M HCN (Ka = 6.2x10-10) with 0.100M NaOH. Why does one have to be more selective in choosing an indicator for the titration of a weak acid than for the titration of a strong acid? 13. The pH of blood is 7.40. What is the ratio of the phosphated species, in the blood, if phosphate is the only specie responsible for the basicity of the blood? (Ka1 = 1.1x10-2, Ka2 = 7.5x10-8, Ka3 = 4.8x10-13)