Acid and bases

• Brønsted Lowry acid 


  A proton donor
• Brønsted Lowry base


  A proton acceptor
• Strong acid


  An acid that completely dissociates in water
• Weak acid


  An acid that only partially dissociates in water
• Strong acid equations

  pH = -log[H+]

  $\left[H+\right]\ =$$\ 10^{-pH}$
• Weak acids


  pKa = -log Ka

  Ka = $10^{-Ka}$

  $Ka\ =$$\ \frac{\left[H+\right]\left[OH-\right]}{\left[HA\right]}\approx\frac{\left[H+\right]^2}{\left[HA\right]}$
• Base equations

  Kw = [H+][OH-]
• EXAMPLE

  calculate the pH of the solution formed when 25cm$^3$of 0.250moldm$^{-3}$ $H_2SO_4$ is added to 100cm$^3$of 0.200moldm$^{-3}$ NaOH

  
• EXAMPLE - adding a strong acid

  Calculate the new pH of the buffer if 0.2cm3 of 0.5moldm-3 sulphuric acid is added to the sample from part A

  (0.015mol CH3COOH and 0.01mol CH3COO-)

  
• EXAMPLE - adding a strong base

  Calculate the new pH of a buffer if 1.0cm3 of 0.100moldm-3 sodium hydroxide is added to the sample from part A

  (0.015mol CH3COOH and 0.01mol CH3COO-)

  
• • When adding a strong acid to the buffer, you add the acid moles to the acid and subtract it from the salt
  • When adding a strong base to the buffer, you subtract the base moles from the acid and add it to the salt
• pH curves

  
• Equivalence point

  Vol of acid = vol of base

  Vertical part of pH curve
• Indicators


  Methyl orange: turns from red to yellow once neutralised

  Phenolphthalein: turns from colourless to pink once neutralised
• Buffer solution


  A solution that resists change in pH when small amounts of acid/alkali is added to it.
• Acidic buffer solution


  Mixture of a weak acid and one of its salts
• basic buffer solution


  Mixture of a weak base and one of its salts