《BUFFER SOLUTION》 1 What is a buffer solution

BUFFER SOLUTION DEPARTMENT OF MEDICAL CHEMISTRY Yongxiang Hu

BUFFER SOLUTION DEPARTMENT OF MEDICAL CHEMISTRY Yongxiang Hu

1. What is a buffer solution

1. What is a buffer solution

Example In I liter pure water add 0.01 mol of hydrochloric acid. Calculate this solution's pH change value. And in I liter contain 0.1 mol acetic acid and 0. 1 acetate ion mixture solution add 0.0lmol of hydrochloric acid. Calculate this solutions pH change value Notice: Square bracket will instead of equilibrium concentration in following time. Such as [H] instead hydrogen ion equilibrium concentration

Example: In 1 liter pure water add 0.01 mol of hydrochloric acid. Calculate this solution’s pH change value. And in 1 liter contain 0.1 mol acetic acid and 0.1 acetate ion mixture solution add 0.01mol of hydrochloric acid. Calculate this solution’s pH change value. Notice: Square bracket will instead of equilibrium concentration in following time. Such as [H+ ] instead hydrogen ion equilibrium concentration

Step 1. Calculate the pure water'S pH change value The pure waters hydrogen ion exponent (ph value (pure water)7.00 When add the hydrochloric acid TH=0.01mol/1 liter =0.01mol L-I pH=-og0.01=2.00 △pH=7.00-2.00=5.00( pH unit)

Step 1. Calculate the pure water’s pH change value The pure water’s hydrogen ion exponent (pH) value: pH(pure water) = 7.00 When add the hydrochloric acid: [H+ ] = 0.01mol/1 liter =0.01mol.L-1 pH = -log 0.01 = 2.00  pH = 7.00 – 2.00 = 5.00 (pH unit)

Step 2. Calculate contain acetic acid and its conjugate base solution's pH value In the solution acetic acid's concentration and acetate ions concentration HAc=0. 10 mol L- [Ac]=0.10 mol L-l Acetic acid equilibrium-constant Ka=1.70×105 In this solution has a acid-base equilibrium HAC Starting 0.10 0.10

Step 2. Calculate contain acetic acid and its conjugate base solution’s pH value In the solution acetic acid’s concentration and acetate ion’s concentration [HAc] = 0.10 mol.L-1 [Ac- ] = 0.10 mol.L-1 Acetic acid equilibrium-constant Ka = 1.7010-5 In this solution has a acid-base equilibrium HAc H+ + Ac￾Starting 0.10 0.10

Substitute the concentrations into the equilibrium constant equation Ka-HIACVHAc H]=Ka×[ HACAC] =1.70×10-5×0.10/0.10 =1.70×105(mol.L) pH=477

Substitute the concentrations into the equilibrium￾constant equation Ka = [H+ ][Ac- ]/[HAc] [H+ ] = Ka  [HAc]/[Ac- ] = 1.70  10-5  0.10/ 0.10 = 1.70  10-5 (mol.L-1 ) pH = 4.77

Step 3. Calculate solution's pH value when add hydrochloric acid HAC H++ AC Starting 0.10 0.10 Change +0.01 -0.01 Equilibrium 0.10+0.01 0.10-0.01 Step 4. Substitute the equilibrium concentration into the equilibrium-constant equation H+]=Ka×[ HACVAC] =1.70×10-5×0.11/0.09 =2.07×103 H=4.68 ApH=..68-0.09(pH unit)

Step 3. Calculate solution’s pH value when add hydrochloric acid HAc H+ + Ac￾Starting 0.10 0.10 Change +0.01 -0.01 Equilibrium 0.10+0.01 0.10-0.01 Step 4. Substitute the equilibrium concentration into the equilibrium-constant equation [H+ ] = Ka  [HAc]/[Ac- ] = 1.70  10-5  0.11/ 0.09 = 2.07  10-5 pH = 4.68  pH = 4.77–4.68= 0.09 (pH unit)

Definition of buffer solution A buffer solution is a solution characterized by the ability to resist changes in pH when limited amounts of strong acid or strong base are added to it

Definition of buffer solution : A buffer solution is a solution characterized by the ability to resist changes in pH when limited amounts of strong acid or strong base are added to it

2. Composition of Buffer Solution Buffer solution consist of weak acid and its conjugate base or weak base and its conjugate acid. The conjugate acid-base pair are called buffer system or buffer pair Important bufter pair such as HAC --AC NH4---- NH3 H2CO3-HCO3 HaPOA---- HPO H2PO4 --HPO4 HPO42-----POA3

2. Composition of Buffer Solution Buffer solution consist of weak acid and its conjugate base or weak base and its conjugate acid. The conjugate acid-base pair are called buffer system or buffer pair. Important buffer pair such as: HAc ---- Ac￾NH4 + ---- NH3 H2CO3 ---- HCO3 - H3PO4 ---- H2PO4 - H2PO4 - ---- HPO4 2- HPO4 2- ---- PO4 3-

3. Calculate the pH value of Buffer Solution Henderson-Hasselbalch Equation a buffer solution made up of a weak acid Ha and its conjugate base A. The acid-ionization equilib- rium Is HA(ag H(ag)t A(ag and the acid-ionization constant is Ka-HIATHAI

3. Calculate the pH value of Buffer Solution Henderson-Hasselbalch Equation: A buffer solution made up of a weak acid HA and its conjugate base A- . The acid-ionization equilib￾rium is HA(aq) H+ (aq) + A- (aq) and the acid-ionization constant is Ka = [H+ ][A- ]/[HA]