Chapter 7 2022/2023

a) Benzoic acid, C6H5COOH, is a weak monoprotic acid with a dissociation constant of 3.5 × 10-8 . The equation for ionisation of C6H5COOH is as follows: 

C6H5COOH + H2O ⇌ H3O+ + C6H5COO- 

Calculate     

i. The concentration of all the species in 0.1 M C6H5COOH    

[5 Marks] 

ii. The pH of this solution.     

[2 Marks] 

b) Magnesium hydroxide, Mg(OH)2 is used in the treatment of occasional constipation in children and adults.      

i. Calculate the molar solubility of Mg(OH)2 in water if the solubility product is 5.61 ×10-12.     

[4 Marks] 

ii. Explain the effect of solubility of Mg(OH)2 after addition of Mg(NO3)2.      

[3 Marks]