U3 T1

Question 1

What happens to the concentrations of products and reactants during equilibrium?

Answer 1

The concentrations remain the same as time passes, although they DO NOT need to be the same.

Question 2

What happens to the rate of forward/reverse reactions in equilibrium?

Answer 2

The rate of both forward and reverse are the same.

Question 3

What happens to the rate of change of products and reactants?

Answer 3

Not the same, but must remain constant.

Question 4

What is the relationship between changing concentration/pressure to collision theory to forward/reverse reactions.

Answer 4

Increase in conc, increase in molecules, increase in collisions between reactants, increase in rate of reaction.

Question 5

What happens to equilibrium when diluting the system?

Answer 5

The concentrations of all aqueous molecules decrease. Then according to le chat, it favours the reaction that produces more moles.

Question 6

Explain what adding acid/base does to an acidic buffer?

Answer 6

If acid is added, it dissociates into hydronium. It then reacts with the conjugate base in the reverse reaction.

If base is added, it dissociates into hydroxide ions. More acid is reacted to form increased hydronium. The increased hydronium neutralises the excess hydroxide ions.

Question 7

Explain what adding acid/base does to a basic buffer?

Answer 7

If base is added, it dissociates into hydroxide ions. It then reacts with the conjugate acid in the reverse reaction.

If acid is added, it dissociates into hydronium ions. More base reacts to from increased hydroxide ions wich neutralises the excess hydroxide ions.

Question 8

Explain Ka and Kb in terms of strength of acids/bases at equilibrium and dissociation.

Answer 8

Strong acids and bases dissociate mostly to completion. This results in the Ka / Kb calculated being very large.

Weak acids and bases only dissociate a little, so the Ka /Kb is very small.

Question 9

How does Ka and pKa work in terms of strength? Also for Kb pKb

Answer 9

The lower the Ka, the weaker the acid. (Same of Kb)
The lower the pKa, the stronger the acid. (Same for pKb)

Question 10

Difference between endpoint and equivalence point in titration?

Answer 10

Equivalence point: Just enough titrant added to neutralise the analyte, moles of base = moles of acid
Endpoint: Just the physical change to represent that the equivalence point has occurred. E.g When the colour changes of the solution.

Question 11

Relationship between pH and pKa for choosing indicator?

Answer 11

pH = pKa when choosing indicator, however the useful range is +- 1 like in data booklet.