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ACID-BASE-pH-BUFFERS-2007-WEB

ACID-BASE-pH-BUFFERS-2007-WEB - Acids Bases pH and...

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Acids, Bases, pH, and Buffers (Dr. Toews) Use objectives (next slide) as guideto what’s important Study your .ppt slides Helpful to read the textbook (suggested readings) Work “homework” problems embedded in slides Lab ( 2 nd lecture , problems, more on buffers next week) Get help if you need Acid-base properties of biomolecules are some of the most fundamental properties in determining their shape and thus their function H + and OH - derived from water arefundamental to most of the biochemical Rx we will encounter (what is keeping us alive) We need to understand acid/base chemistry at basic level first - then see how they fit into biochemical context (chemistry of life) Why??
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Objectives: By the end of these two lectures and the associated two lab sessions, you should: 1. Understand the concept of acids, bases, and their dissociation in aqueous solutions, including K a (dissociation constant) 2. Be familiar with theself-ionization of water, and understand the terms hydroniumion, hydroxide ion, and hydrogen ion (proton) 3. Be familiar with some common acids and bases, and understand the concept of strong vs weak acids, strong vs weak bases, and salts 4. Understand the concept of pH and be able to relate it to [H + ] and acidity in both practical and quantitative (mathematical) terms 5. Understand the Henderson-Hasselbalch equation and its importance 6. Understand the relationship between pH, [H + ], and pKa 1. Understand the concept of buffers, how they work to resist changes in pH, and why they areimportant to living organisms. 2. Be ableto do basic calculations involving [H + ], pH, and buffers Suggested supplemental readings in textbook: DTC Chapter 8, pp. 239-262, 271-271 (ignore text problems – some “homework” problems included in slides) lots of calculations/problems/examples in lab exercises too
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Acids, Bases, pH, and Buffers Some definitions: ionization – a neutral molecule splits into (+) and (-) charged ions acids increase the hydrogen ion concentration, [H + ], in aqueous solutions bases decrease the hydrogen ion concentration, [H + ], in aqueous solutions H + - hydrogen ion (a proton = a hydrogen atom missing its electron) OH - - hydroxide ion – water that has lost a proton H 3 O + - hydronium ion – water that has gained a proton Hydrogen atom = H = 1 proton + 1 electron p+ e- Hydrogen ion = H + = proton [H + ] = hydrogen ion concentration = acidity
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- acids , when dissolved in H 2 O, dissociate to form H + - bases , when dissolved in H 2 O, dissociate to form OH - Arrhenius theory of acids and bases Useful, but not perfect – doesn’t cover all acids and bases H Cl (aq) H + (aq) + Cl - (aq) ) Svante August Arrhenius (1859-1927) The Nobel Prize in Chemistry, 1903 “in recognition of theextraordinary services hehas rendered to theadvancement of chemistry by his electrolytic theory of dissociation” Na OH (aq) Na + (aq) + OH - (aq)
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Brønsted-Lowry theory of acids and bases 1923 – Johannes Brønsted (Denmark) & Thomas Lowry (Britain) Acids are proton donors Bases are proton acceptors H Cl (aq) H + (aq) + Cl - (aq) ) H A H + + A - Dissociation Rx for acids are reversible - although to widely variable degrees HOH is a big player – life is aqueous – everything happens in H0H acid base conjugate acid-base pair This is better!
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