{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Buffers H08 - rote(cmr2495 H08 Buers mccord(51620 This...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
rote (cmr2495) – H08: Bufers – mccord – (51620) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices be±ore answering. 001 10.0 points Which o± the Fve solutions below is most ba- sic? 1. 0.10 M aq NH 3 and 0.10 M NH 4 Cl cor- rect 2. 0.10 M CH 3 COOH and 0.20 M NaCH 3 COO 3. 0.10 M HClO and 0.10 M NaClO 4. 0.10 M CH 3 COOH and 0.10 M NaCH 3 COO 5. 0.10 M aq NH 3 and 0.20 M NH 4 Cl Explanation: All are bufer where pH = p K a + log p [base] [acid] P 002 10.0 points Explain why the salt o± a weak acid, as well as the acid itsel±, must be present to ±orm a bufer solution. 1. The anion ±rom the salt is needed to partially neutralize added base. 2. Actually, a weak acid by itsel± is a bufer; no salt is needed. 3. The anion ±rom the salt is needed to partially neutralize added acid. correct 4. The cation ±rom the salt is needed to partially neutralize added base. 5. The cation ±rom the salt is needed to partially neutralize added acid. Explanation: The salt o± the acid provides the anion which is the conjugate base o± the bufer sys- tem: HA + H 2 O A - + H 3 O + This anion A - reacts with any added acid (H 3 O + ) to prevent any appreciable change in pH. 003 10.0 points What is the pH o± an aqueous solution that is 0.018 M C 6 H 5 NH 2 ( K b = 4 . 3 × 10 - 10 ) and 0.12 M C 6 H 5 NH 3 Cl? 1. 8.54 2. 9.37 3. 5.46 4. 4.63 5. 10.19 6. 4.02 7. 2.87 8. 3.81 correct Explanation: 004 10.0 points A bufer solution is made by dissolving 0.45 moles o± a weak acid (HA) and 0 . 23 moles o± KOH into 700 mL o± solution. What is the pH o± this bufer? K a = 1 . 8 × 10 - 6 ±or HA. Correct answer: 5 . 76403 pH. Explanation: n HA = 0 . 45 mol n KOH = 0 . 23 mol K a = 1 . 8 × 10 - 6 ±or HA You must substract the 0 . 23 moles o± KOH ±rom the 0.45 moles o± HA because the strong base will neutralize the weak acid. You there- ±ore would make 0 . 23 moles o± A - and be left with 0 . 22 moles o± HA. You can now plug this ratio into the equilibrium equation or in the Henderson-Hasselbalch equation to get pH. 005 10.0 points
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
rote (cmr2495) – H08: Bufers – mccord – (51620) 2 Which one oF the Following combinations is NOT a bufer solution? 1. HBr and KBr correct 2. NH 3 and (NH 4 ) 2 SO 4 3. CH 3 COOH and NaCH 3 COO 4. NH 3 and NH 4 Br 5. HCN and NaCN Explanation: A bufer must contain a weak acid/base conjugate pair. HBr/Br - is a strong acid conjugate pair. CH 3 COOH / CH 3 COO - , HCN / CN - and NH + 4 / NH 3 are weak acid/base conjugate pairs.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 7

Buffers H08 - rote(cmr2495 H08 Buers mccord(51620 This...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon bookmark
Ask a homework question - tutors are online