Acids, bases, and buffers

Question 1

Define Brønsted-Lowry acid

Answer 1

Any species that can donate a proton

Question 2

Define Brønsted-Lowry base

Answer 2

Any species that can accept a proton

Question 3

State the conjugate base of HNO3

Answer 3

NO3-

Question 4

State the conjugate base of HBr

Answer 4

Br-

Question 5

What is meant by a monoprotic acid?

Answer 5

An acid that releases one H+ ion per molecule

Question 6

What is meant by a diprotic acid?

Answer 6

An acid that releases 2 H+ ions per molecule

Question 7

Explain how Kw varies with temperature

Answer 7

-As temperature increases, the equilibrium moves right to oppose this increase
-Causes [H+] and [OH-] to increase
-Causes Kw to increase, so pH decreases
-Water is still neutral as [H+] = [OH-]

Question 8

How do you select the appropriate indicator for a titration?

Answer 8

The colour change pH range must coincide with the vertical section of the titration curve

Question 9

What indicator is normally suitable for a strong acid?

Answer 9

Methyl orange

Question 10

What indicator is normally suitable for a weak acid?

Answer 10

Phenolphthalein

Question 11

What is the role of a buffer solution?

Answer 11

To minimise the change in pH when small amounts of acid or base are added

Question 12

What are the 2 ways of making a buffer solution?

Answer 12

-Mixing a weak acid solution with its salt
-Partial neutralisation of a weak acid by mixing a weak acid with an alkali

Question 13

What happens when you add H+ ions to a buffer solution?

Answer 13

-H+ ions react with the conjugate base
-E.g. H+ + CH3COO- —> CH3COOH
-The position of equilibrium moves to the LHS

Question 14

What happens when you add OH- ions to a buffer solution?

Answer 14

-OH- ions react with H+ ions
-OH- + H+ —> H2O
-The acid has to dissociate to replace the H+ ions, so equilibrium moves to the RHS
-E.g. CH3COOH —> CH3COO- + H+

Question 15

How can you make a buffer solution?

Answer 15

By mixing ammonia (weak base) and ammonium chloride