acids and bases

• the pH scale goes from...

  0-14
• the pH scale is a measure of how ... or ... a solution is

  acidic, alkaline
• the lower the pH of a solution...


  the more acidic it is
• the higher the pH of a solution...

  the more alkaline it is
• the pH of a neutral substance is...

  7
• pH scale


  measurement system used to indicate the concentration of hydrogen ions (H+) in solution; ranges from 0 to 14
• how can you measure the pH of a solution?

  with universal indicator or a pH probe
• universal indicator


  a mixture of indicators which show different colours in solutions of different pHs
• pH probe


  a monitoring device on an industrial fermenter that is used to measure the acidity of the solution - this controls the acid/base input to change the acidity to the optimum
• is universal indicator or a pH probe more accurate?

  pH probe

  - a pH probe gives a numerical value and can continuously measure the pH and help identify the equivalence point with greater accuracy

  - universal indicator may be affected by human error as the results are subjective and it is harder to measure smaller differences in pH
• acids and bases ... each other

  neutralise
• what is an acid?

  a substance that forms an aqueous solution with a pH of less than 7
• what do acids form in water?

  H+ ions
• what is a base?

  any substance that will react with an acid to form a salt
• what is an alkali?

  a base that dissolves in water to form a solution with a pH of greater than 7
• what do alkalis form in water?

  OH- ions
• neutralisation


  a reaction of an acid with a base, forming a salt and water
• neutralisation reaction


  acid + base → salt + water
• hydrogen ions react with hydroxide ions to produce...

  water
• neutralisation with acids and alkalis

  H+(aq) + OH-(aq) → H2O(l)
• what happens when an acid neutralises a base (or vice versa)?

  the products are neutral (i.e. they have a pH of 7)
• what happens when you mix an acid with an alkali?

  hydrogen ions from the acid react with hydroxide ions from the alkali to make water and the leftover bits of acid and alkali make a salt