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Lecture 1 - Acid-Base Equilibrium.pptx

Lecture 1 - Acid-Base Equilibrium.pptx - Lecture-1...

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Lecture-1 Acid-Base Equilibrium Assoc. Prof. Dr. A.K.M. Shafiqul Islam Department of Chemical Engineering Technology (Industrial Chemical Process) University Malaysia Perlis 06/04/2016
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ARRHENIUS THEORY-H + AND OHˉ An acid is any substance that ionizes (partially or completely) in water to give hydrogen ions Means associate with solvent to give hydronium ions HA + H 2 O ↔ H 3 O + + Aˉ
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A base ionizes in water to give hydroxyl ions. Weak (partially ionizes) bases ionizes as follows: B + H 2 O BH + + OHˉ For strong bases e.g.: (NaOH) M(OH) n M n+ + nOHˉ this theory is restricted to water as a solvent only ARRHENIUS THEORY-H + AND OHˉ
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Half reaction Acid = H + + base Acid and base of a half-reaction are called conjugate pairs. There must be a combination of two half reaction
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ACID-BASE EQUILIBRIA IN WATER When acid or base is dissolved in water, it will dissociate Amount of ionization depends on the strength of the acid Strong electrolyte completely dissociated Weak electrolyte dissociated partially
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Example: a) Hydrochloric acid (strong acid) b) Acetic acid (weak acid)  Equilibrium constant  is the thermodynamic activity constant Cl O H O H HCl 3 2 OAc O H O H HOAc 3 2 O H HOAc OAc O H a a a a a K 2 3 0 0 a K
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Pure water ionizes slightly (autoprotolysis) Equilibrium constant is thermodynamic autoptorolysis, self-ionization, constant OH O H O H 3 2 2 2 0 2 3 O H OH O H w a a a K 0 w K
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H + will be used instead of H 3 O + for simplification Molar concentration will be replaced by [] K a and K w are molar equilibrium constants [H + ]=1.0×10 -7 M = [OH - ]  HOAc OAc H K a  OH H K w
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pH Scale Negative log of hydrogen ion conc. pH of water ?
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Weak Acid A weak acid is an acid that does not completely donate all of its hydrogens when dissolved in water. These acids have higher pH compared to strong acids, which release all of their hydrogens when dissolved in water.
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Weak acids and bases weak acids (or bases) are only partially ionized. While mineral (inorganic) acids and bases such as HCl, HCl0 4 , HNO3. and NaOH are strong electrolytes that are totally ionized in water, most organic acids and bases, as found in clinical applications, are weak.
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Weak acids and bases Calculation for weak acids and bases Ionization cons. for some common acids have been calculated. Follow the rules for equi. cons. calculation. Example: Calculate the pH and pOH of a 1.0 x 10 -3 solution of acetic acid Solution : HOAc H + + OAc - 5 10 x 75 1 ] [ ] ][ [ - - a . HOAc OAc H K
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Weak Acid When acetic acid ionizes, it dissociates to equal portion of H + and OAc - by such an amount will always be equal 1.75 x 10 -5 If the original concentration of acetic acid is C and the concentration of ionized acetic acid species (H + and OAc - ) is x , then the final concentrationof each species at equilibrium is given by:
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Weak acids and bases Equation HOAc H + OAc - I nitial (M) C hange (M) E quilibrium (M) 1.0 x 10 -3 -x 1.0 x 10 -3 - x 0 +x x 0 +x x
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