pH of Strong Bases - Equilibria Pt B - (5.2)

Question 1

What affects the size of Ka?

Answer 1

• anions, if they are more stable, equilibrium will go to the right hand side
• making the value for Ka larger

Question 2

Why do we use pka instead of Ka?

Answer 2

• Ka’s values tend to be very small + difficult to handle

Question 3

What is an anion stabilised by?

Answer 3

• electronegative atoms/groups, drawing the negative charge away from the COO- group
• benzene ring, as the negative charge can be delocalised into the ring

Question 4

What is the anion destabilised by?

Answer 4

• alkyl groups, pushing electrons towards the COO- group

Question 5

Why is pka preferrably used instead of Ka?

Answer 5

• Ka’s values tend to be very small + difficult to handle

Question 6

What is the equation for pka?

Answer 6

pka = -log10Ka

Question 7

What is the equation for Ka?

Answer 7

Ka = 10^-pka

Question 8

What does pka measure?

Answer 8

• the strength of an acid or base

Question 9

What is the ionic constant of water?

Answer 9

Kw = 1.00 x 10^-14 mol^2 dm^-6

at 298K

Question 10

Note on Le Chantelier’s Principle:

Answer 10

• it will try and use extra reactants to get back to its original equation

Question 11

When you are trying to find the pH of a molecule using its concentration, you have to note:

Answer 11

• pay attention to how many H moles there are if there are 4, e.g H4, multiply the concentration by 4.
• to get the correct concentration before finding the pH