3. Strong Acid (SA)
• an acid that dissociates completely into ions
in water
Ex. All molecules of HCl(aq) dissociate into
H+ and Cl- ions
▫ H+ ions that are formed bond with H2O to form
H3O+
HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
7. Weak Acid (WA)
• an acid that dissociates very slightly into
ions in water
Ex. not all molecules of CH3COOH(aq) break
apart, some remain intact
• only about 1% of acetic acid molecules
dissociate
8. Dissociation (Weak Acid)
1% of acetic acid molecules dissociate. In solution
there are mostly acetic acid molecules and only some
ions.
9.
10. Concentration
• the concentration of H3O+(aq) ions, [H3O+],
in a dilute solution of a SA is equal to the
concentration of the acid, [acid]
[H3O+] = [strong acid]
• Ex. In a sample of 1.0 mol/L HCl(aq)
[H3O+] = 1.0 mol/L
Recall: C = n
square bracket V
Molar Concentration
11. Concentration
• the concentration of H3O+(aq) ions, [H3O+],
in a dilute solution of a WA is much less
than the concentration of the acid, [acid]
• Ex. In a sample of 1.0 mol/L CH3COOH (aq)
[H3O+] <<< 1.0 mol/L
• That is, [H3O+] < [weak acid]
12. Strong Base (SB)
• a base that dissociates completely into
ions in water
Ex. all molecules of NaOH(aq) dissociate into
Na+ and OH- ions
• other SB’s are…
KOH
Ca(OH)2
Ba(OH)2
13. Weak Base (WB)
• most bases are weak
• WB dissociates very slightly into ions in
water
▫ Ex. Ammonia [OH1-] < [weak base]
14. Concentration
• the concentration of OH1-(aq) ions, [OH1-],
in a dilute solution of a SB is equal to the
conc. of the base, [base]
[OH1-] = [strong base]
Ex. In a sample of 1.0 mol/L NaOH(aq)
[OH1-] = 1.0 mol/L
17. Measuring Strength – pH Scale
• In pure water,
[H3O+] = [OH-] = 1.0 x 10-7 mol/L
• In acidic solution, [H3O+] > [OH-]
• In basic solution, [H3O+] < [OH-]
18.
19. 19
pH and acidity
The pH values of several
common substances are
shown at the right.
Many common foods are
weak acids
Some medicines and many
household cleaners are
bases.
20. Indicators
• An acid-base indicator is a substance that
changes colour in acid and base solutions. It is
used to determine if neutralization is complete.
• ex. litmus
phenolphthalein (phth)
bromothymol blue (BTB)
universal indicator
21. pH Scale Review
• Now that we know when an acid or base is dissolved in
water it will produce either:
▫ OH-
▫ H+
• pH measures the concentration (how many) of H+ in the
solution
• When pH is 7 that means the concentration of OH- is
equal to H+
• When pH is less than 7 we have a higher concentration of
H+
• When pH is bigger that 7 we have a higher concentration
of OH-
23. Neutralization
• Adding a base to an acid neutralizes the acid’s
acidic properties.
• This is called a neutralization reaction.
▫ Ex. for an upset stomach, use an ANTACID
25. Example
1. In an experiment, 15.85 mL of HCl(aq) completely
neutralizes 25.00 mL of 0.125 mol/L KOH(aq).
Calculate the concentration of this acid.
26. Example 2
2. What volume of 0.185 mol/L H2SO4(aq) will react
completely with 25.00 mL of 0.225 mol/L KOH(aq)?
27. Learning Check
3. What mass of aluminum hydroxide will react
completely with 27.50 mL of 0.255 mol/L
H2SO4(aq)?
28. Learning Check 2
4. What is the molar concentration of phosphoric
acid if 17.50 mL of this acid reacted with 3.22 g
of magnesium hydroxide?
29. Titration
• lab procedure involving neutralization, used to
determine an unknown concentration
• progressive addition of a solution (called titrant)
from a graduated tube (called burette) to a known
volume or mass of a second solution, until the
endpoint
▫ endpoint is indicated by a colour change of an added
indicator
• at equivalence point, nH+ = nOH-
▫ given the concentration of one sol’n, you can calculate
the concentration of the other sol’n
