BCHE 395-3 2013 pH Buffers Titrations

# Segway into buers a buer is a soluyon of a weak acid

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: & Bases •  Common range of pKa values for biochemical acids, weak electrolytes –  from 2 to about 13 or 14 –  The smaller the value of pKa, the stronger the acid (think of the pH scale and a low pH) –  Opposite of Ka where a large value indicates a strong acid •  Extent of dissociaYon is determined by the acid dissociaYon constant Ka Conjugate Weak Acid- Base Pairs •  pKa = –log Ka (strong acid → large Ka → small pKa) Weak Acids & Bases Ka = [H+][A- [HA] •  To calculate pH, solve for [H+] [H+] = Ka [HA] [A- •  Take the log + log [H ] = log Ka + [HA] log [A–] www.purplemath.com/modules/logrules.htm The Henderson- Hasselbalch EquaYon MulYply by (- 1): + –log [H ] = Use deﬁniYon of pH and pKa: –log Ka – [HA] log[A–] Soren Sorenson strikes again! pH = pK – log pH = pK + log ‘Have to know equaYon’ [HA] – [A ] [A-] Conj base [HA] Conj acid Henderson- Hasselbalch EquaYon [A-] pH = pK + log [HA] •  pKas are constants •  Allows you to calculate the concentraGon of each species of molecules in a dissociaGon equaGon at any given pH or concentraGons of some species •  Really good for test quesYons •  But for what? (segway into…) Buﬀers •  A buﬀer is a soluYon of a weak acid and its conjugate base that resists changes in pH upon addiGon of a strong acid or base –  Resistance is in both direcYons - either up or down •  Two important values deﬁne any buﬀer: •  1.) The pKa(s) of the weak acid •  2.) The total concentraYon...
View Full Document

## This note was uploaded on 03/02/2014 for the course BIOCHEMIST 395 taught by Professor Potenza during the Spring '14 term at NMSU.

Ask a homework question - tutors are online