How to calculate the pH of solution

Cards (16)

  • pH stands for power of hydrogen
  • how to calculate power of hydrogen
    pH=-log(H+)
  • to calculate the number of H+ ions 

    do inverse log
  • value of Kw
    always has the same value for water or an aqueous solution at a given temperature
    e.g. at 298k it is 1 times 10 to the power of -14
  • equation for Kw
    number of H+ ions times number of OH-
  • pure water always has a 1:1 ratio of H+ and OH- therefore:
    Kw= (H+)^2
  • steps on how to workout pH using Kw
    what is the concentration of OH- ions
    what is my value of Kw
    what is my expression
    rearrange to find concentration of H+
    workout pH
  • PKw
    is the understanding of OH- and H+ ions
    PKw=-log(Kw)
    PKw=-log(1 times 10 to the power of -14)=14 (always)
  • PKa
    measures the acidity of a solution
    Ka=10 to the power of -PKa
    the smaller the PKa the more acidic the solution
  • How to calculate the pH while only using PKa 


    convert PKa to Ka
    use the Ka expression to workout the concentration of H+ ions
    calculate the pH
  • pH meter used to measure pH of solution
  • how to work out Ka using mass and pH for ethanoic acid
    workout the number of moles of ethanoic acid
    calculate the concentration of ethanoic acid solution
    use the pH to work out the H+ at equilibrium
    for weak acid: Ka equals to H+ squared divided by HA
  • buffers
    minimises change minimises change in pH when small amount of acid and base added
    does not stop pH from changing just limits it
  • acid buffers
    created by mixing a weak acid and its conjugating base pair salt in equilibrium
  • examples of acid buffers
    sodium ethonate and ethanoic acid
    enthanoic acid and sodium hydroxide
  • what does a titration curve show
    how the pH of a solution changes as an increasing volume of acid or base is added