Q1) Discuss the following: (30 Mark)
The effect of hydrogen bond on solubility.
Semipolar compounds can act as intermediate solvents.
Solutes are often precipitated from solutions by the addition of an electrolyte.
The effect of critical temperature on the solubilities of partially miscible liquids.
The effect of pH on the solubility of weak electrolyte drugs.
The effect of dilution of strong electrolytes on specific and equivalent conductance.
Q2) Representing the free acid form of phenobarbital as HP and the soluble ionized form as P–, the equilibria in a saturated solution of this slightly soluble weak electrolyte is written as:
Derive an equation to compute the pH below which the salt of sodium Phenobarbital begins to precipitate from aqueous solution. (8 Mark)
Q3) Below what pH will free phenobarbital begin to separate from a solution having an initial concentration of 5% (w/v)? The molar solubility, of phenobarbital is 0.005 and the pKa is 7.41 at 25°C. The secondary dissociation of Phenobarbital can be disregarded. The molecular weight of sodium phenobarbital is 254. (8 Mark)
Q4) The equivalent conductance of a 5.9 × 10–3 M solution of acetic acid is 14.4 ohm cm2/Eq, and the degree of dissociation of acetic acid at this concentration is 0.037. Calculate the equivalent conductance of acetic acid at infinite dilution. (4 Mark)