Acid-Base  Worksheet #5
More Buffers
1. Write ionic equations that illustrate how each pair of compounds can serve as a buffer pair. 

(a) H2CO3 and NaHCO3 (the "carbonate" buffer in blood) 

(b) NaH2PO4 and Na2HPO4 (the "phosphate" buffer inside body cells) 

(c) NH4Cl and NH3
2. Show that the equation  can be rewritten as 
3. Which buffer would be better able to hold a steady pH on the addition of strong acid, buffer 1 or buffer 2? Explain. 

Buffer 1: a solution containing 0.10 M NH4Cl and 1 M NH3. Buffer 2: a solution containing 1 M NH4Cl and 0.10 M NH3.

4.  How many grams of sodium acetate, NaC2H3O2, would have to be added to 1 L of 0.15 M acetic acid (pKa=4.74) to make the solution a buffer for pH 5.00? 
5. How many grams of sodium formate, NaCHO2, would have to be dissolved in 1.0 L of 0.12 formic acid (pKa) to make the solution a buffer for pH 3.80? 
6. What ratio of molar concentrations of NH4Cl and NH3 would buffer a solution at pH 9.25? 
7. To study the effect of a weakly acidic medium on the rate of corrosion of a metal, a chemist prepared a buffer solution by making it 0.11 M NaC2H5O2 and also 0.090 M HC2H3O2. What is the pH of this solution? 
8. How is the pH of a buffered solution related to the pKa of the weak acid in the buffer if 

(a) the ratio of [anion] to [acid] is 10 to 1? 

(b) The ratio of [anion] to ]acid] is 1 to 10? 
9. A solution of acetic acid is pink in the presence of the indicator methyl orange. When solid sodium acetate is added to the acid solution, the colour changes to yellow. Why?