Chapter 7 2019/2020

a) Nitrous acid, HNO2 is used to distinguish between primary, secondary, and tertiary amines. At 25 °C, an aqueous solution of 0.215 M HNO2 is 4.0% dissociated.      

i. Write a balanced equation for the dissociation of HNO2 in water.   

[1 Mark] 

ii. Determine the acid dissociation constant, Ka for HNO2.   

[3 Marks] 

iii. Calculate the pH of the solution.    

[2 Marks] 

b) Calcium hydroxide, Ca(OH)2 is used to neutralize excess acidity in lakes and soils. Calculate the pH of 0.30 M Ca(OH)2 solution. 

[4 Marks]

c) In a weak acid-strong base titration, 25.00 mL of KOH solution is titrated with 21.45 mL of 0.10 M HCN to reach equivalent point.       

i. Write a balance chemical reaction equation for the titration.  

[1 Mark] 

ii. Calculate the concentration of KOH solution at the equivalence point.   

[1 Mark] 

iii. Explain why potassium cyanide, KCN is not a neutral salt using appropriate equations.     

[4 Marks] 

iv. Suggest a suitable indicator for the titration.    

[1 Mark]