Chapter 7 2023/2024

a) A buffer solution is used to maintain pH for enzyme activity in organisms. To prepare a buffer, 150 mL of 0.20 M nitrous acid (HNO2) is mixed with 350 mL of 0.10 M sodium nitrite (NaNO2). Calculate the pH of the resulting solution. [Given the acid dissociation constant, Ka for HNO2 is 4.95 ×10-4]       

i. Write the chemical equations when a small amount of acid is added to the above buffer solution.    

[1 Mark] 

ii. Calculate the pH of the prepared buffer solution.     

[5 Marks] 

b) The equation for the titration of 0.10 M acetic acid, CH3COOH, with 10.0 mL 1.50 M sodium hydroxide, NaOH, is shown below: 

    CH3COOH (aq) + NaOH (aq) à CH3COONa (aq) + H2O (l)    

i. Calculate the pH of CH3COOH before the titration, given the Ka of CH3COOH is 1.8 ×10-5.      

[5 Marks] 

ii. Sketch the titration curve and label it completely. Show the pH at equivalent point and buffer region on the curve.       

[3 Marks]