CHM116 week 4 Mon probs

# CHM116 week 4 Mon probs - and the final pH after adding...

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Use an ICE table to calculate the pH of a solution that is 0.195 M in CH 3 NH 2 (methyl amine) and 0.105 M CH 3 NH 3 Br (methylammonium bromide). You can solve this using the K a for CH 3 NH 3 + , which equals 2.3 x 10 - 11 . (It’s also possible to use the K b for CH 3 NH 2 , which equals 4.4 x 10 -4 . CHM116 Week 4 Mon 9/20 discussion problems Solve the problem above using the Henderson-Hasselbach equation. (You’ll need to calculate the p K a of methlyammonium ion) 1a. 1b. Can you predict the pH of a solution that is is 0.100 M in CH 3 NH 2 and 0.100 M CH 3 NH 3 Br without doing a calculation? (Otherwise, work it out using the Henderson-Hasselbach equation) 1c. The p K a of HF (hydrofluoric acid) is 3.5. Calculate the pH of 250 mL of a solution that contains 0.2 moles of HF and 0.3 moles of NaF using the H-H equation. 2. Calculate the ratio of CH 3 NH 2 to CH 3 NH 3 Br that would be required to yield a solution with a pH of 10.24 (you’ll need to use the p K a for CH 3 NH 3 + that you determined above) 3.

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For each of the following solutions, calculate the initial pH
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Unformatted text preview: and the final pH after adding 0.010 mol NaOH. 4. a) 250.0 mL of pure water b) 250.0 mL of a buffer solution that is 0.195 M in HCOOH (formic acid) and 0.275 M in KCOOH (potassium formate). The K a of HCOOH = 1.8 x 10-4 . Determine whether or not the mixing of each of the two solutions indicated below will result in a buffer. Explain why or why not. 5. a) 75.0 mL of 0.10 M HF; 55.0 mL of 0.15 M NaF b) 150.0 mL of 0.10 M HF; 135.0 mL of 0.175 M HCl c) 165.0 mL of 0.10 M HF; 135.0 mL of 0.050 M KOH d) 125.0 mL of 0.15 M CH 3 NH 2 ; 120.0 mL of 0.25 M CH 3 NH 3 Cl e) 105.0 mL of 0.15 M CH 3 NH 2 ; 95.0 mL of 0.10 M HCl The fluids within cells are buffered by H 2 PO 4-and HPO 4 2-. 6. a) Calculate the ratio of H 2 PO 4-and HPO 4 2- required to maintain a pH of 7.1 in a cell. (p K a of H 2 PO 4-is 7.2) b) Could a buffer system employing H 3 PO 4 as the weak acid and H 2 PO 4-as the weak base be used as a buffer system within cells? Explain...
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CHM116 week 4 Mon probs - and the final pH after adding...

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