Acids and p h

1,291 views
799 views

Published on

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,291
On SlideShare
0
From Embeds
0
Number of Embeds
11
Actions
Shares
0
Downloads
5
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Acids and p h

  1. 1. Acids and pH
  2. 2. • Acids form H+ ions when they dissolve in water.• An H+ ion is a hydrogen atom that has lost it’s electron.• In other words, it is a 1 PROTON.• Therefore, acids are 1 H PROTON DONORS
  3. 3. ionisation• When an acid is dissolved in water the H+ ions dissociate from the acid.• This dissociation is referred to as ionisation• The strength of the acid is related to the level of ionisation
  4. 4. Strong and weak acidsThe pH scale is used to rank the strength of acids andbases.Strong acids and bases completely dissociate (separateinto ions) in water. HCl + H2O  H+(aq) + Cl−(aq)Weak acids and bases only partially dissociate in water. H2CO3 + H2O ⇄ H3O+(aq) + HCO3−(aq)
  5. 5. A closer look at strong and weak acids• In weak solutions, only some of the hydrogen ions dissociate
  6. 6. Don’t confuse strong and weak acidswith concentrated and dilute solutionsConcentrated solutions Dilute solutions• Have a greater number of • Have fewer particles particles• Strong acids have more ions • Weak acids have less ions dissociated dissociated Images from: http://tg103.wikispaces.com/Taylor+S
  7. 7. • pH = potential of Hydrogen• All acids and bases have a pH that shows the concentration of hydrogen ions [H+]• Because the pH is a ratio of H+ ions to OH- ions, we can calculate the pH of acids and bases• For aqueous solutions, the product of H+ and OH- must equal 1x10-14• [H+][OH-] = 1 x 10-14• Neutral [H+] = [OH-]• Acid [H+] > [OH-]• Base [H+] < [OH-]
  8. 8. pH Scale
  9. 9. To calculate pH• [H+] is the molarity of the acid in the solution• pH = -log[H+]• Youll need to be given (or calculate) the concentration of acid.
  10. 10. Example• To calculate the pH of a solution in which [H3O+] = 0.042mol/L using a calculator: – Key in 0.042 – Press the log key and note that -1.377 is displayed – Mentally change the sign (because of the –log) – The solution has a pH of 1.38
  11. 11. Example 2What is the pH of a solution that has a hydrogen ionconcentration equal to 0.003 M?pH = −log *H+] pH = −log (0.003) pH = 2.52
  12. 12. Example 3For strong acids, the concentration of hydrogen ions(H+) is approximately equal to the concentration ofthe acid itself.What is the pH of a 0.5 M solution of HCl? [H+] = [HCl] [H+] = 0.5pH = −log *H+] pH = −log (0.5) pH = 0.3
  13. 13. Example 4For strong acids, that has two hydrogen ions (H+)you need to double the concentration of the acidbefore doing the calculation. What is the pH of a 0.00140 M solution of H2SO4? [H+] = [H2SO4] [H+] = 2 x 0.00140 = 0.00280pH = −log *H+] pH = −log (0.00280) pH = 2.55

×