acids & bases

• | pH scale

  • lower pH = more acidic
  • rain, vinegar, lemon juice
  • higher pH = more alkaline
  • washing up liquid, bleach, soap powder
  • pH 7 (eg pure water) = neutral
• | measuring pH

  • an INDICATOR is a dye that changes colour based on whether its below or above a certain pH
  • some contain a mixture of dyes which are called WIDE RANGE INDICATORS & used to estimate pH of a solution
  • pH probe attached to a pH meter measures pH electronically
  • probe is placed in solution & pH is given as a numerical value meaning its more accurate than an indicator
• | acids & bases

  • acids and bases neutralise each other
  • ACID is a substance that forms AQUEOUS SOLUTIONS with a pH below 7
  • BASE is a substance with a pH over 7
  • ALKALI is base that dissolves in water to form substance over 7
  • form OH- ions in water
  • neutralisation
  • acid + base -> salt + water
  • H+ + OH- -> H2O
  • hydrogen + hydroxide makes water
• what does a low pH imply?

  that it is acidic
• what does a high pH imply

  that it is alkali
• what does a pH of 7 imply

  that it is neutral
• what is an example of a neutral substance

  pure water
• whats an indicator?

  a dye that changes colour based on whether it is above or below a certain pH
• what do you call an indicator with more than dye?

  a wide range indicator
• why’s might a probe be better than an indicator

  because pH is given as a value so it’s more accurate
• why are wide range indicators useful?

  estimating pH of a solution
• what’s an acid?

  substance that forms an aqueous solution with a pH less than 7
• whats an aqueous solution

  forms when a substance dissolves in water
• what ions do acids form when in water

  H+ ions
• what does acid produce in water?

  H+ ions
• what are H+ ions?

  hydrogen ions
• so what does acid form in water?

  hydrogen ions