chapter 17

# chapter 17 - Chapter 17 Additional Aspects of Aqueous...

This preview shows pages 1–21. Sign up to view the full content.

Chapter 17 Chapter 17 Additional Aspects of Aqueous Additional Aspects of Aqueous Equilibria Equilibria

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

View Full Document
The Common-Ion Effect Consider a solution of acetic acid: If acetate ion is added to the solution, Le Châtelier says the equilibrium will shift to the left. What happens to the pH?
The Common-Ion Effect “The extent of ionization of a weak electrolyte is decreased by adding to the solution a strong electrolyte that has an ion in common with the weak electrolyte.”

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

View Full Document
The Common-Ion Effect Calculate the fluoride ion concentration and pH of a solution that is 0.20 M in HF and 0.10 M in HCl. K a for HF is 6.8 × 10 −4 .
The Common-Ion Effect Because HCl, a strong acid, is also present, [HF], M [H 3 O + ], M [F ], M Initially 0.20 0.10 0 Change x + x + x At Equilibrium 0.20 − x 0.20 0.10 + x 0.10 x

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

View Full Document
The Common-Ion Effect = x 1.4 × 10 −3 = x (0.10) ( x ) (0.20)
The Common-Ion Effect Therefore, [F ] = x = 1.4 × 10 −3 [H 3 O + ] = 0.10 + x = 1.01 + 1.4 × 10 −3 = 0.10 M So, pH = −log (0.10) pH = 1.00

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

View Full Document
Buffers: Solutions of a weak conjugate acid-base pair. They are particularly resistant to pH changes, even when strong acid or base is added.
Which of the following will produce a buffer solution? 1. HCl/NaCl 2. HC 2 H 3 O 2 /NH 3 3. NaH 2 PO 4 /Na 2 HPO 4 4. HNO 3 /Ca(OH) 2 5. KNO 3 / NaOH

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

View Full Document
Composition and Action of Buffered Solutions A buffer consists of a mixture of a weak acid (HX) and its conjugate base (X - ): Buffered Solutions HX( aq ) H + ( aq ) + X - ( aq )
Buffers If a small amount of hydroxide is added to an equimolar solution of HF in NaF, for example, the HF reacts with the OH to make F and water.

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

View Full Document
Buffers If acid is added, the F reacts to form HF and water.
Buffer Calculations Consider the equilibrium constant expression for the dissociation of a generic acid, HA: HA + H O H O + A

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

View Full Document
Buffer Calculations Rearranging slightly, this becomes Taking the negative log of both sides, we get p K a pH acid base
Buffer Calculations So p K = pH − log [base] [acid] Rearranging, this becomes pH = p K + log [base] [acid] This is the Henderson–Hasselbalch equation .

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

View Full Document
Henderson–Hasselbalch Equation What is the pH of a buffer that is 0.12 M in lactic acid, HC 3 H 5 O 3 , and 0.10 M in sodium lactate? K a for lactic acid is 1.4 × 10 −4 .
Henderson–Hasselbalch Equation pH = p K + log [base] [acid] pH = −log (1.4 × 10 ) + log (0.10) (0.12) pH = 3.85 + (−0.08) pH = 3.77

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

View Full Document
pH Range The pH range is the range of pH values over which a buffer system works effectively. It is best to choose an acid with a p K a close to the desired pH.
When Strong Acids or Bases Are Added to a Buffer… …it is safe to assume that all of the strong acid or base is consumed in the reaction.

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

View Full Document
Base to a Buffer 1. Determine how the neutralization reaction affects the amounts of the weak acid and its conjugate base in solution. 2. Use the Henderson–Hasselbalch
This is the end of the preview. Sign up to access the rest of the document.

## chapter 17 - Chapter 17 Additional Aspects of Aqueous...

This preview shows document pages 1 - 21. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online