Chapter 15 notes

Chapter 15 notes - 15.1 Solutions of Acids or Bases...

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

View Full Document Right Arrow Icon
15.1 Solutions of Acids or Bases Containing a Common Ion common ion effect- a shift in equilibrium position due to the addition of an ion already involved in the equilibrium reaction Example HF and NaF H F (s) ! Na + (aq) + F - (aq) HF (aq) H + (aq) + F - (aq) " Equilibrium Shift " The additional F - decrease the pH by increasing the formation of molecular HF 15.2 Buffered Solutions Buffered Solutions- resist pH changes when additional OH - or H + are added . Buffered solutions contain weak acids or bases with their salts (ex. HF and NaF, or NH 3 and NH 4 Cl) SAMPLE EXERCISE 15.3 Calculate the pH change that occurs when 0.010 mol solid NaOH is added to 1.0 L of a buffered solution containing 0.50 M acetic acid and 0.50 M sodium acetate. OH - + HC 2 H 3 O 2 C 2 H 3 O 2 - + H 2 O Before 0.010 mol 0.50 mol 0.50 mol After 0.010-0.010 0.50-0.010 0.50+0.010 0 mol 0.49 mol 0.51 mol mol/L HC 2 H 3 O H + + C 2 H 3 O 2 - initial 0.49 0 0.51 x -x +x +x equilibrium 0.49 x 0.51 1.8 x 10 -5 = x(0.51) 0.49 1.7 x 10 -5 = x (5% rule satisfied) pH= -log[H+] = -log[1.7 x 10 -5 ] = 4.76 *pH without the addition of excess OH - is 4.74 (only an increase of +0.002 pH units) Hints in Solving Buffer Problems 1. Determine what the new concentrations of the species involved in equilibrium after the addition of H + or OH - ions. Assume the reaction between H and OH goes to completion. 2. Proceed with equilibrium calculations to determine pH Buffering: How does it work? - pH is governed by the ratio of [HA]/[A - ] [H+]= K a [HA] [A - ] - If the amounts of HA and A are large in comparison to the amount of H or OH added, then the change in the ratio is small.
Background image of page 1

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

View Full DocumentRight Arrow Icon
- If we can assume that the changes of concentration of H + and A - are insignificant (initial concentrations are equal to equilibrium concentrations), then we can use the Henderson-Hasselbalch equation to solve for pH. pH= pK a + log([base]/ [acid]) see SAMPLE EXERCISES 15.4, 15.5, 15.6 15.3 Buffer Capacity Buffer Capacity represents the amount of protons and hydroxide ions that can be absorbed without a significant change in pH - Buffer solutions containing large quantities of buffering components will have a high buffering capacity - Optimal buffering occurs when the ratio of [A - ] and [HA] is 1. ( the concentrations are equal). - The best buffer will be a weak acid with a pKa similar to the desired pH see SAMPLE EXERCISE 15.8 15.4 Titrations and pH Curves pH curve (titration curve) - a curve based on the plotting of the pH of solution being analyzed as a function of the amount of titrant (standard) added. Strong Acid-Strong Base Titrations
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.

Page1 / 7

Chapter 15 notes - 15.1 Solutions of Acids or Bases...

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

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