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