5.8 Strong And Weak Acids

Question 1

Strong acid def

Answer 1

Acids that completely ionise in aqueous solutions

Question 2

Weak acid def

Answer 2

Acids that do not ionise completely in aqueous solutions

Question 3

Examples of strong acids

Answer 3

• hydrochloric acid
• nitric acid
• sulphuric acid

Question 4

Examples of weak acids

Answer 4

• ethanoic acid (found in vinegar)
• citric acid (found in citrus fruits)
• carbonic acid (found in rainwater, fizzy drinks)

Question 5

Why do acids have to dissolve in water before showing acidic properties?

Answer 5

• in water all acids ionise (split up)
• their molecules split to form H+ ions and negative ions

Question 6

How does hydrochloric acid (HCl) ionise?

Answer 6

HCl (aq) —> H+(aq) + Cl-(aq)

Question 7

How do weak acids ionise in a solution?

Answer 7

• only a small proportion of acidic molecules ionise
• the reactions in reversible, the molecules will split up and the ions recombine to form original molecules again

Question 8

Does a weak acid have a higher or lower pH?

Answer 8

Higher

Question 9

How does the concentration of H+ ions affect the pH?

Answer 9

When the concentration of H+ ions is reduced by a factor of 10, the pH value goes up by one unit

Question 10

Describe the difference between a strong and weak acid

Answer 10

A strong acid is fully ionised but a weak acid is only partially ionised

Question 11

Describe the difference between a dilute acid and a concentrated acid

Answer 11

A dilute acid contains a low proportion of acid compared to the total volume of a solution

Question 12

Write an equation to show how ethanoic acid ionises in water

Answer 12

CH3COOH(aq) —> (reversible) CH3COO(aq)+ H+ (aq)