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The Strong vs. The Weak
The Strong vs. The Weak
The Jekyl and Hyde of Acids and Bases
Review- The pH scaleReview- The pH scale
0 7 14Acid Neutral Base
The pH scale is based on the number of H+ and OH- ions
Which side has the most H+?
Which side has the most OH-?
And where are they just about equal?
Most H+
(little OH-)
Most OH-
(little H+)
Equal H+ and
OH-
H+ and OH- again• Another way of showing the H+/OH-
concentrations is this diagram:
PH
[H+]
1o-1 1o-14
H+
OH-
1 14Ph 7
10-7
General Properties- IonicsGeneral Properties- Ionics
Ionic compounds ionize in aqueous solution– Which means… they break into ions
Inorganic acids and bases are ionic– So, they ionize in water too
NaCl(s) Na+ + Cl-
HCl H+ + Cl-
The few, the strong...The few, the strong...
What makes an acid a strong acid? A strong acid has a very low pH Which means it has a lot of free H+ ions
- In chemistry, we say that it “dissociates” a lot
Strong acids are also the ones which can do massive damage to your skin, eyes...
And the weak onesAnd the weak ones
What makes an acid a weak acid? A weak acid has a pH which is fairly close to 7 Which means it doesn’t have many free H+ ions
- it only dissociates slightly
Strong and Weak IonizationStrong and Weak Ionization
Strong Acids and Bases completely ionize
Weak ones only ionize a little- making an equilibrium with ions and the compound
CH3COOH CH3COO- + H+
HCl H+ + Cl-
Which is Which?Which is Which?
pH0
1
2
3
4
5
6
7
pH
NitricAcid
BoricAcid
SulfuricAcid
Take a look at the chart to the left and pick out the acid which has the most free H+ ions
How did you know?
Nitric
It has very low pH
So, it’s a strong acid
Strength and BasesStrength and Bases
Bases are similar Strong bases have HIGH pH (lots of OH- ions and not a lot of H+ ions)
- They dissociate a lot
-Also, just like strong acids, strong bases can really damage your skin or eyes...
Weak bases have a pH close to 7
- They dissociate very little
Try it againTry it again
Which one is the weak base?
pH0
2
4
6
8
10
12
14
pH
Ammonia
NaOH
KOH
Ammonia (pH closest to 7)
So, ammonia would be the least dangerous because it has very few free OH- ions
Give and TakeGive and Take
And, you know that acids start with H, so they
and bases
0 7 14
Strong Acid Weak Acid Weak Base Strong BaseN
eutral
donate H+
accept H+ to make HOH
donate H+ ions accept H+ ions
Fancy New scienceWord
Of the day
AMPHIPROTIC:
Substance that can act as an acid (H+ donor) or a base (H+ acceptor)
Example: H2O can become H3O+ or OH-
Fancy new scienceWord of
The day #2
Conjugate Pair:
2 Substances which differ by one H+. One acts as an acid (H+ donor) and one as a base (H+
acceptor) .
Example: HCl/Cl-
SummarySummary
0 7 14Acid Neutral Base
Strong Acid
Dissociates well
Lots of free H+ ions
Weak Acid
Dissociates slightly
Few free H+ ions
Weak Base
Dissociates slightly
Few free OH- ions
Strong Base
Dissociates well
Lots of free OH- ions
The EndThe End