buffers - CH302 Chapter 8a Ionic Equilibria: Buffers 1 The...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
1 CH302 Chapter 8a Ionic Equilibria: Buffers 2 The Common Ion Effect and Buffer Solutions The Common Ion Effect and Buffer Solutions ± If a solution is made in which the same ion is produced by two different compounds the common ion effect is exhibited . ± Buffer solutions are solutions that resist changes in pH when acids or bases are added to them. ² Buffering is due to the common ion effect. 3 The Common Ion Effect and Buffer Solutions There are two common kinds of buffer solutions: 1 Solutions made from a weak acid plus a soluble ionic salt of the weak acid. 2 Solutions made from a weak base plus a soluble ionic salt of the weak base The change in pH in buffers is inhibited by the common ion effect .
Background image of page 1

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

View Full DocumentRight Arrow Icon
4 The Common Ion Effect and Buffer Solutions 1. Solutions made of weak acids plus a soluble ionic salt of the weak acid ± One example of this type of buffer system is: ² The weak acid - acetic acid CH 3 COOH ² The soluble ionic salt - sodium acetate NaCH 3 COO ² There are two sources of acetate ions (CH 3 COO ), acetic acid (the weak acid) and sodium acetate (the salt of the weak acid). 2 2 3 3 3 5 33 100% 1.8 10 HO a NaCH COO Na add to CH COOH H O CH COO CH COO Kx + +−  →+ → ++ = ← 5 The Common Ion Effect and Buffer Solutions The pH of the buffer solution (weak acid + salt of weak acid) is less acidic than a solution just comprised of the weak acid alone. ² Why? ² Adding additional acetate ion to a solution that is in equilibrium will ³ cause the increase of CH 3 COO to react with the H 3 O + and shift the equilibrium to the left to reform CH 3 COOH. 3 3 3 3 () ( ) additional CH COO from salt of weak acid CH COOH H O weak acid conjugate base conjugate bas CH COO from weak a e cid + → 6 The Common Ion Effect and Buffer Solutions Buffer solutions with weak bases and the salt of weak bases: ± Consider a solution that is comprised of ammonia and ammonium chloride: ± There are two sources of ammonium ions (NH 4 + ); ² ammonia (the weak base) and ammonia (the salt of the weak base). 2 2 4 5 3 4 4 100% 1.8 10 b NH Cl Cl ad NH dto N H HK x N OH −− + +  =
Background image of page 2
7 The Common Ion Effect and Buffer Solutions ± The pH of the buffer solution (weak base + salt of weak base) ± is less basic than a solution just comprised of the weak base alone. ± Adding more ammonium ion to a solution that is in equilibrium will cause the increase of NH 4 + to react with the OH and shift the equilibrium to the left to reform NH 3 . 4 34 () ( ) additional NH from salt of weak ba NH OH NH weak base con fr ju om weak ba gate acid conjugate acid s se e + + → ++ ← 8 The Common Ion Effect and Buffer Solutions Calculations with buffered solutions: 1(a). What is the pH and [H 3 O + ] of a solution that is 0.20 M HF and 0.10 M NaF?
Background image of page 3

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

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 19

buffers - CH302 Chapter 8a Ionic Equilibria: Buffers 1 The...

This preview shows document pages 1 - 4. Sign up to view the full document.

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