Question

Use this description to answer the questions:
Solution 1 is 0.1M weak acid HF and the pH is found to be 2.8. Write the acid dissocation reaction for HF.

Solution 2 consists of the same 0.1 M weak acid HF but in 1.0M sodium nitrate. Write T if the statement is true, F if it is false.

1. The pH of solution 1 and solution 2 will be the same within statistical error.
2. The pH of solution 2 will be lower than the pH of solution 1.  
3. The pH of solution 2 will be higher than the pH of solution 1.
4. The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift right due to the common ion effect.
5. The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift left due to the common ion effect.
6. The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift right due to the shielding of hydrogen ion and F-, the anion of the weak acid.
7. The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift left due to the shielding of hydrogen ion and F-, the anion of the weak acid.
8. Solution 2 will have the same amount of weak acid HF dissociated at equilibrium as solution 1.
9. Solution 2 will have more weak acid HF dissociated at equilibrium than solution 1.
10. Solution 1 will have more weak acid HF dissociated at equilibrium than solution 2.

Answer 1

HF(aq) + H2O(l) → H3O+ +F-

When HF is dissolved in water, water molecules orient themselves around HF so that the water dipole interacts with highly polarised HF bond. Though the moiety is highly stabilized by extensive hydrogen bonding, feeble dissociation of hydronium ion makes it a bit acidic as hydrogen bonding weakens the HF covalent bond.

The pH of solution 1 and solution 2 will be the same within statistical error. false

The pH of solution 2 will be higher than the pH of solution 1. true

The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift right due to the common ion effect. false

The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift left due to the common ion effect. false

The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift right due to the shielding of hydrogen ion and F-, the anion of the weak acid. true

The presence of sodium nitrate in solution 2 will cause the weak acid dissociation reaction to shift left due to the shielding of hydrogen ion and F-, the anion of the weak acid. false

Solution 2 will have the same amount of weak acid HF dissociated at equilibrium as solution 1. false

Solution 2 will have more weak acid HF dissociated at equilibrium than solution 1. true

Solution 1 will have more weak acid HF dissociated at equilibrium than solution 2. false