Strong and Weak Acids

Question 1

What do acids contain?

Answer 1

Hydrogen atoms

Question 2

What happens to acid molecules in water?

Answer 2

They ionise

Question 3

What happens to strong acids in water?

Answer 3

• They ionise completely
• Strong acid —> hydrogen ions + other ions, eg. HCl —> H^+ + Cl^-
• Lots of hydrogen ions so it seems very acidic
• High collision frequency so the acid and water react very quickly

Question 4

What happens to weak acids in water?

Answer 4

• Only partially ionise
• Reversible reaction is set up
• Weak acid hydrogen ions + other ions, eg. CH3COOH H^+ + CH3OO^-
• Forms equilibrium on the left because it contains lots of acid molecules but not many H^+ ions so they seem less acidic
• Lower collision frequency so the reaction is slower

Question 5

What does the pH number represent?

Answer 5

Concentration of H^+ ions, low number = high concentration

Question 6

Why do weak acids not conduct electricity as well as strong acids?

Answer 6

They don’t have as many hydrogen ions to move through the liquid during electrolysis.

Question 7

Why do weak acids produce the same amount of hydrogen gas that strong acids do as they undergo electrolysis?

Answer 7

As the hydrogen ions react and are used up at first, more acid molecules will become ionised producing more H^+ ions so if the volume was the same then it should produce the same volume of hydrogen gas as a strong acid.

Question 8

Why is ethanoic acid less conductive than hydrochloric acid?

Answer 8

There is a lower concentration of H^+ ions even in the same concentration of acid.