pH

pH

1. Bronsted Lowry

   • Bronsted-Lowry acid is a proton donor.
   • Bronsted-Lowry base is a proton acceptor
   • Conjugate acid base pairs contain two species that can be interconverted by transfer of a proton.

2. pH

   • pH is a logarithmic scale
     • The lower the H+ concentration, the higher the pH.
     • The higher the H+ concentration, the lower the pH.
     • pH= -log[H+]
     • H+ = 10^-pH

3. Strong Acid

   • For a mono basic acid [HA] = H+
   • HA ---> H+ + A-
   • For a dibasic acid, multiply the HA concentration by 2 to get the H+ concentration.
   • For a tribasic acid, multiply HA concentration by 3 to get H+

4. Weak Acid

   • Ka = [H+][A-] / [HA]
     • Can be simplified to [H+]^2 / [HA]
   • Ka is the acid dissociation constant
   • Ka has large negative values so it is converted to pKa in order to help with comparison.
   • pKa = -logKa
   • Ka = 10^-pKa
   • Low pKa, high Ka = stronger acid
   • High pKa, low Ka = weaker acid
   • These acids partially dissociate
   • APPROXIMATION 1: [H+] = [A-]
   • APPROXIMATION 2: [HA]eqm = [HA]start

5. Kw

   • Ka = [H+][OH-] / [H2O]
     • Ka x H2O = [H+][OH]
   • Kw = Ka x [H2O]
   • H+ = OH-
   • Kw = [H+]^2
   • H= > OH- = acidic
   • H+ < OH- = alkaline
   • Kw = 1x10^-14 mol^2/dm^6
   • OH- = Kw/H+

6. Types of acids

   • Monobasic - 1 Hydrogen ion can be replaced per molecule in an acid-base reaction
   • Dibasic - 2 hydrogen ions can be replaced per molecule in an acid-base reaction.
   • Tribasic - 3 hydrogen ions can be replaced per molecule in an acid-base reaction.

7. Acid + metal ---> salt + hydrogen

8. Acid + carbonate ---> salt + water + hydrogen

9. Acid + base ---> salt + water

10. Acid + alkali ---> salt + water

    • Alkalis are soluble bases

11. Strong base

    • MOH ---> M+ + OH-

12. Arrhenius Model

    • Acids dissociate to release H+ into solution.
    • Alkalis dissociate to release OH- into solution
    • So H+ + OH- <=> H2O

13. Ka by experiment

    • 1. Prepare a standard solution of known concentration for the weak acid.
    • 2. Measure the pH using a pH probe / titre with NaOH to calculate H+ concentration.
    • 3. Calculate H+ by 10^-pH
    • 4. Calculate Ka.

14. Dilution

    • Original volume divided by new volume
    • Multiply this by the concentration to calculate the new concentration