How to calculate the pH of solution

• 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