Acids bases and pH

• What is a bronsted lowry acid?


  A proton donor
• What is a bronsted lowry base?


  A proton acceptor
• What is a conjugate acid-base pair?


  It is a pair which contain species which can be interconverted by the transfer of a proton
• What is an example of a conjugate acid base pair?


  Hcl releases a proton to form its conjugate cl-

  Cl- accepts a proton to form its conjugate acid (HCl)
• What is the hydronium ion?


  H3O+, in aqueous solution, disassociation requires a proton to be transferred from an acid to base, when this happens between HCl and water te H2O has to accept the proton from the acid as it is a proton donor and therefore this results in a H3O+ ion
• What is a monobasic, dibasic and tribasic acid?


  It refers to the total number of hydrogen ions in the acid that can be replaced per molecule

  mono- 1H+ ion

  di- 2H+ ion

  tri- 3H+ ion
• What is the ionic equation for Hcl + Mg?


  2H+(aq) + Mg(s) -> Mg2+ + H2
• What are spectator ions?


  They are simply ions which don't change during the reaction, spectator ions can simply be cancelled out.
• What is the equation for the reaction of acids and metals?


  Acid + Metal -> Salt + Hydrogen
• What is the equation for the reaction of acids and carbonates?

  Acid + Carbonate -> Salt + water + Carbon dioxide
• What is the equation for neutrilisation of acids with metal oxides?


  Acid + Alkali -> Salt + water
• What is the ionic equation for neutrilisation?


  H+(aq) + OH-(aq) -> H2O(l)
• What is the pH scale?


  It is a scale for measuring hydrogen ion concentrations
• What type of scale is pH?


  A logarithmic scale
• What is the mathematical relationship between pH and H+?


  pH=-log[H+(aq)]
• How do you calculate [H+] concentration from pH?


  H+= 10^-pH
• How do you calculate pH of strong acids?

  As in aqueous solutions pHs completely dissociate

  [H+(aq)]= [HA(aq)]

  It can be calculated directly from the concentration of the acid
• What happens to weak acids?

  They only partially dissociate in an aqueous solution
• What is the acid dissociation constant?

  Ka, it is a special version of Kc which is the equilibrium constant
• How can the dissociation of any weak acid be shown in general form?

  HA (aq) ⇌ H+(aq) + A- (aq)
• How can the Ka be written for weak acids?


  Ka= [H+][A-]/[HA] all in aqueous form
• What temperature is Ka happening at usually?


  25 degrees c
• What is pKa?


  It is a negative logarithmic scale to convert Ka
• What is the conversion between pKa and Ka?

  pKa= -logKa

  Ka= 10^-pKa
• What is the link between the pKa and the strength of the acids?

  The stronger the acid the larger the Ka value

  The weaker the acid the smaller the Ka value
• What happens with dissociation in acid?


  A weak acid only partially dissociates in water
• What is the Ka equation simplified?


  Ka= [H+]^2/[HA]
• What approximations to you need to simplify the Ka expression?

  HA will dissociate into equal parts H+ and A-, there will also be a dissociation from water but this is so small that it can be regarded as being neglible

  The equilibrium concentration of HA is smaller than the undissociated conc.

  HA(eqm)=HA(start)
• How can the Ka of a weak acid be determined?


  Preparing a standard solution of the weak acid of a known concentration, measuring the pH of a standard solution using a pH meter
• When do the assumptions break down for weak acid calculations?

  1. When the acid is very weak, as the dissociation will be significant
  2. Stronger weak acids and very dilute solutions, this is due to there being a greater difference between [Ha]eqm and [Ha]start - [H+]eqm
• What is Kw?


  It is the ionic product of water and is represented as

  Kw=[H+(aq)][OH-(aq)]
• What conditions is Kw valid at?


  298K

  it has a value of 1x10^-14 mol2dm-6
• What is the OH- concentration and H+ concentration at pH 3?


  H+ 10^-3

  OH- 10^-11
• How can the pH of a strong base be calculated from?


  concentration of the base and the ionic product of water kW