Topic 8: Acids & Bases

Question 1

A Brønsted-lowry acid

Answer 1

A Brønsted-lowry acid is a proton donor

It must contain hydrogen

Question 2

Brønsted-lowry base

Answer 2

A Brønsted-lowry base is a proton acceptor

It must have a lone pair of electrons to accept a proton

Question 3

Conjugate acid-base pairs

Answer 3

Two species that differ by a proton are called conjugate acid-base pairs

Every Brønsted-lowry reaction has 2 conjugate acid-base pairs

e.g acid 1 and base 1

or

acid 2 and base 2

Question 4

Amphiprotic species

Answer 4

An amphiprotic species is a species that can act as both an Brønsted-lowry acid and a Brønsted-lowry base

e.g Water (able to donate or accept a proton)

Question 5

Types of reactions that acids undergo

Answer 5

• Neutralisation reactions with bases such as metal hydroxides, metal oxides, and ammonia
• Reactions with metal carbonates and metal hydrogen carbonates
• Reactions with active metals such as magnesium or zinc

Question 6

Acid + metal —> ?

Answer 6

Salt + water

Question 7

Acid + metal oxide —> ?

Answer 7

Salt + water

Question 8

Acid + ammonia —>

e.g HCl + NH3

Answer 8

NH4Cl

Question 9

Acid + metal carbonate —>

Answer 9

Salt + water + carbon dioxide.

Question 10

Acid + metal hydrogen carbonate —> ?

Answer 10

Salt + water + carbon dioxide

Question 11

Acid + metal —> ?

Answer 11

Salt + hydrogen

Question 12

Thermometric titration

Answer 12

A thermometric titration can be carried out to determine the concentration of a solution

An acid of unknown concentration is added to a base of known volume and concentration

The temperature of the mixture is recorded as the acid is added to the base and the results are plotted on a graph

The maximum temperature reached signifies the end-point of the titration

Question 13

The pH scale

What is the formula for pH?

What is the formula for [H+]?

Answer 13

The pH scale is used to measure how acidic or basic a substance is

pH = -log [H+]

[H+] = 10^-pH

Question 14

What happens to pH when there is x10 increase in H+ ions?

Answer 14

pH decreases by 1.

If H+ ions increase by x100, pH decreases by 2.

Question 15

Difference between strong acids and weak acids

Answer 15

Strong acids fully dissociate into their ions

Weak acids only partially dissociate into their ions

Question 16

The autoionisation of water

Answer 16

When water dissociates to form hydronium and hydroxide ions.

Question 17

Concentration of H+ ions vs concentration of OH- ions

Answer 17

When the concentrations are equal = the solution is neutral (pH is 7)

When there is a higher concentration of H+ than OH- = the solution is acid (pH is less than 7)

When there is a higher concentration of OH- ions than H+ ions =. the solution is basic (pH is more than 7)

Question 18

Calculating concentrations of ions from Kw:

How to calculate concentration of H+?

How to calculate concentration of OH-?

Answer 18

[H+] = Kw / [OH-]

[OH-] + Kw / [H+]

Question 19

Formula for Kw

Answer 19

Kw = [H+][OH-]

Question 20

Where does the position of equilibrium lie for a strong acid?

Where does the position of equilibrium lie for a weak acid?

Answer 20

For a strong acid, the position of equilibrium lies to the right.

For a weak acid, the position of equilibrium lies to the left.