Acids and Bases

Question 1

strong vs weak acids

Answer 1

Strong acids ionise completely in water to form a high concentration of H3O+ ions.
Weak acids ionise incompletely in water to form a low concentration of H3O+ ions.

Question 2

examples of strong acids

Answer 2

hydrochloric acid (HCl), sulphuric acid (H2SO4) and nitric acid (HNO3).

Question 3

Examples of weak acids

Answer 3

ethanoic acid (CH3COOH) and oxalic acid (C2H2O4).

Question 4

strong vs weak bases

Answer 4

Strong bases dissociate completely in water to form a high concentration of OH- ions.

Weak bases dissociate/ionise incompletely in water to form a low concentration of OH- ions.

Question 5

Examples of strong bases

Answer 5

Examples of strong bases are sodium hydroxide (NaOH) and potassium hydroxide (KOH).

Question 6

Examples of weak bases

Answer 6

ammonia (NH3),
calcium carbonate (NaCO3),
potassium carbonate (K2CO3),
sodium hydrogen carbonate (NaHCO3)

Question 7

Concentrated acids/bases vs diluted acids/bases

Answer 7

Concentrated acids/bases contain a large amount (number of moles) of acid/base in proportion to the volume of water.
Dilute acids/bases contain a small amount (number of moles) of acid/base in proportion to the volume of water.

Question 8

Which indicator to use when doing titrations

Answer 8

Strong acid & base: bromothymol blue (yellow when acidic, blue when basic)

Strong acid & weak base: methyl orange (orange when acidic, yellow when basic)

Weak acid & strong base: phenolphthalein (colourless when acidic, pink when basic)

Question 9

Putting a salt from a strong acid & strong base in water turns the solution . . . (and why)

Answer 9

stays neutral
- there is complete ionisation/dissociation of both acid and base to form a weak conjugate acid and base and neither react with water, so [H3O+]=1x10^-7

Question 10

Putting a salt from a strong acid & weak base base in water turns the solution . . . (and why)

Answer 10

acidic
- weak base forms strong conjugate acid. The strong acid reacts with water to increase [H3O+] so solution is acidic.

Question 11

Putting a salt from a weak acid & strong base in water turns the solution . . . (and why)

Answer 11

Basic
- weak acid forms strong conjugate base. The strong base then reacts with water to increase the [OH-] and the solution is basic.