1. Acids and Bases

2. Acids and Bases
pH < 7 pH > 7
taste sour taste bitter
react w/bases react w/acids
proton (H1+) donor proton (H1+) acceptor
turn litmus red turn litmus blue
lots of H1+/H3O1+ lots of OH1–
react w/metals don’t react w/metals
Both are electrolytes.

3. Acid vs. Base Base Different Alike Different Topic Topic Acid
Affects pH
and
litmus paper
pH < 7
pH > 7
Topic
Topic
sour taste
Related to
H+ (proton)
concentration
bitter taste
Acid
Base
Acids
A substance with at least one hydrogen atom that can dissociate to form an anion and an H+ ion (a proton) in aqueous solution, thereby forming an acidic solution
Bases
Compounds that produce hydroxide ions (OH–) and a cation when dissolved in water, thus forming a basic solution
Neutral
Solutions that are neither basic nor acidic
react with
metals
pH + pOH = 14
does not
react with
metals

4. Properties ACIDS BASES electrolytes electrolytes sour taste
bitter taste
turn litmus red
turn litmus blue
react with metals to form H2 gas
slippery feel
vinegar, milk, soda, apples, citrus fruits
ammonia, lye, antacid, baking soda
ChemASAP

5. Properties of acids and bases Acids – Sour taste
– Turns blue litmus paper red
– Reacts with some metals to produce H2
– Dissolves carbonate salts, releasing CO2
Bases
– Bitter taste
– Turns red litmus paper blue
– Slippery to the touch
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

6. Common Acids and Bases Strong Acids (strong electrolytes)
Strong Bases (strong electrolytes)
NaOH sodium hydroxide
KOH potassium hydroxide
Ca(OH) calcium hydroxide
HCl hydrochloric acid
HNO3 nitric acid
H2SO4 sulfuric acid
Phosphoric acid, H3PO4, is another acid commonly found in the laboratory. It is on the borderline between a strong and weak acid.
Weak Base (weak electrolyte)
NH4OH ammonia
Weak Acids (weak electrolytes)
CH3COOH ethanoic acid
H2CO3 carbonic
Weak Base (weak electrolyte)
NH ammonia inwater
NH3 + H2O  NH4OH
Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 145

7. Acid + Base  Salt + Water
Orange juice + milk  bad taste
Evergreen shrub + concrete  dead bush
Under a pine tree + fertilizer  white powder
HCl + NaOH  NaCl + HOH
salt water

8. Neutralization of Bug Bites
Wasp - stings with base
Red Ant - bites with acid
(neutralize with lemon juice or vinegar)
(neutralize with baking soda)

9. Conjugate Acids/Bases/Pairs

10. Acid Dissociation + 1- HCl Cl Conjugate base Acid Conjugate pair H
When a strong acid dissolves in water, the proton that is released is transferred to a water molecule that acts as a proton acceptor or base.
Resulting H3O+ ion is called the hydronium ion.
Bases that do not contain the hydroxide ion accept a proton from water, so small amounts of OH– are produced—water acts like an acid by donating a proton.
Substances that can behave as both an acid and a base are said to be amphoteric.
Products of an acid-base reaction are also an acid and a base. The acid product is the conjugate acid of the base, and the base product is the conjugate base of the acid.
All acid-base reactions involve two conjugate acid-base pairs.
Conjugate base
Acid
Conjugate pair
Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 280

11. Acid Dissociation + 1- HCl Cl Conjugate base Acid Conjugate pair H
When a strong acid dissolves in water, the proton that is released is transferred to a water molecule that acts as a proton acceptor or base.
Resulting H3O+ ion is called the hydronium ion.
Bases that do not contain the hydroxide ion accept a proton from water, so small amounts of OH– are produced—water acts like an acid by donating a proton.
Substances that can behave as both an acid and a base are said to be amphoteric.
Products of an acid-base reaction are also an acid and a base. The acid product is the conjugate acid of the base, and the base product is the conjugate base of the acid.
All acid-base reactions involve two conjugate acid-base pairs.
Conjugate base
Acid
Conjugate pair
Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 280

12. Conjugate Acid-Base Pairs
conjugates
base
acid
HCl H2O H3O Cl-
acid
base
conjugates
Two species that differ by only a proton constitute a conjugate acid-base pair.
1. Conjugate base has one less proton than its acid; A– is the conjugate base of HA
2. Conjugate acid has one more proton than its base; BH+ is the conjugate acid of B
• In the reaction of HCl with water, HCl, the parent acid, donates a proton to a water molecule, the parent base, forming Cl–; HCl and Cl– constitute a conjugate acid-base pair.
• In the reverse reaction, the Cl– ion in solution acts as a base to accept a proton from H3O+, forming H2O and HCl; H3O+ and H2O constitute a second conjugate acid-base pair. Any acid-base reaction must contain two conjugate acid-base pairs, which in this example are HCl/Cl– and H3O+/H2O
• HCl (aq) H2O (l)  H3O+ (aq) Cl– (aq)
parent acid parent base conjugate acid conjugate base
HCl H2O H3O Cl-
acid base CA CB

13. Conjugate Acid-Base Pairs
conjugates
acid
base
NH H2O NH OH-
base
acid
conjugates
base acid CA CB
NH H2O NH OH-

14. Water is Amphoteric HCl + H2O H3O+ + Cl- NH3 + H2O NH41+ + OH-
Amphoteric or Amphiprotic substances:
Substances which can act as either proton donors (acids) or
proton acceptors (bases) depending on what substances are present.
HCl H2O H3O Cl-
acid base CA CB
Water is amphiprotic: it can act as an acid by donating a proton to a base to form the hydroxide ion, or as a base by accepting a proton from an acid to form the hydronium ion, H3O+
Structure of the water molecule
1. Polar O–H bonds and two lone pairs of electrons on the oxygen atom
2. Liquid water has a highly polar structure
base acid CA CB
NH H2O NH OH-

15. A substance that can act as either an acid or a base.
Amphoteric
A substance that can act as either an acid or a base. 1- 1+ + +
H2O
H3O+
HSO4-
H2SO4
water
hydronium ion
hydrogen sulfate
ion
sulfuric acid 1- +
sulfate ion
SO42-
water
H2O
hydrogen sulfate
ion
HSO4-
hydroxide ion
OH- 2-

16. A substance that can act as either an acid or a base.
Amphoteric
A substance that can act as either an acid or a base. 1- + 1+ +
sulfuric acid
H2SO4
water
H2O
H3O+
HSO4-
hydronium ion
hydrogen sulfate
ion
(HSO4- as a base)

17. A substance that can act as either an acid or a base.
Amphoteric
A substance that can act as either an acid or a base. 1- +
sulfate ion
SO42-
water
H2O 2- 1- +
HSO4-
OH-
hydrogen sulfate
ion
hydroxide ion
(HSO4- as an acid)

18. Conjugate Acid-Base Pairs
conjugates
base2
acid2
HC2H3O H2O H3O C2H3O2-
acid1
base1
conjugates
acid base CA CB
HC2H3O H2O H3O C2H3O2-
The reaction proceeds in the direction such that the stronger acid
donates its proton to the stronger base.

19. Strong vs. Weak Acid
A salt can dissolve in water to produce a neutral, basic, or acidic solution, depending on whether it contains the conjugate base of a weak acid as the anion (A–) or the conjugate acid of a weak base as the cation (BH+), or both.
• Salts that contain small, highly charged metal ions produce acidic solutions in water.
• The most important parameter for predicting the effect of a metal ion on the acidity of coordinated water molecules is the charge-to-radius ratio of the metal ion.
• The reaction of a salt with water to produce an acidic or basic solution is called a hydrolysis reaction, which is just an acid-base reaction in which the acid is a cation or the base is an anion.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 508

20. A- H+ A- H+ A- H+ A- H+ A- H+
Acids: Concentration vs. Strength
CONCENTRATED
DILUTE
H+ A- H+ A- H+ A- H+ A- HA
A- H+ A- H+ A- H+ A- H+ A -
H+ A- HA H+ A- H+ A- H+ A-
A- H+ A- H+ A- H+ A- H+ A- H+
H+ A - H + A - H + A - HA H + A -
A- H+ A- H+ A- H+ A- H+ A–
H+ A- H+ A- H+ A- H+ A- H+
A- H+ A- H+ A- H+ A- H+ A-
HA A- H+ A- H+ A- H+ A- H+
H+ A H+ A HA
A H+ A - H A –
H+ A H+ A H+
A HA H A -
H+ A H+ A H+
STRONG ACIDS
Dissociate nearly 100%
HA H A-
WEAK ACIDS
Dissociate very little
HA H A-
STRONG
HA HA H+ A- HA HA HA
HA HA HA HA HA H+ A-
H+ A- HA HA HA HA HA
HA HA H+ A- HA HA HA
HA HA HA H+ A- HA HA
H+ A- HA HA HA HA HA
HA HA HA H+ A- HA HA
H+ A- HA HA HA HA HA
HA HA H+ A- HA HA HA
HA HA HA HA
HA HA HA
H+ A HA HA
HA HA H + A –
HA H + A – HA HA
Strong acids react essentially completely with water to give H+ and the corresponding anion.
Strong bases dissociate essentially completely in water to give OH– and the corresponding cation.
Both strong acids and strong bases are strong electrolytes.
Only a fraction of the molecules of weak acids and weak bases react with water to produce ions and are, therefore, weak electrolytes.
No correlation between solubility in water and whether a substance is a strong or a weak electrolyte.
WEAK

21. Range and Color Changes of Some Common Acid-Base Indicators
pH Scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Indicators
Methyl orange red – yellow
Methyl red red yellow
Bromthymol blue yellow blue
Neutral red red yellow
From F. Brescia et al., Chemistry: A Modern Introduction, W. B. Saunders Co., 1978.
Adapted from R. Bates, Determination of pH, Theory and Practice, John Wiley & Sons, Inc., New York, 1964.
Choosing the correct indicator for an acid-base titration
1. For titrations of strong acids and strong bases (and vice versa), any indicator with a pKin between 4 and 10 will do
2. For the titration of a weak acid, the pH at the equivalence point is greater than 7, and an indicator such as phenolphthalein or thymol blue, with pKin > 7, should be used
3. For the titration of a weak base, where the pH at the equivalence point is less than 7, an indicator such as methyl red or bromcresol blue, with pKin < 7, should be used
Phenolphthalein colorless red colorless beyond 13.0
Bromthymol blue indicator would be used in titrating a strong acid with a strong base.
Phenolpthalein indicator would be used in titrating a weak acid with a strong base.
Methyl orange indicator would be used in titrating a strong acid with a weak base.

22. pH
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

23. Common pH Indicators
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 520

24. Edible Acid-Base Indicators
COLOR CHANGES AS A FUNCTION OF pH
INDICATOR pH
RED APPLE SKIN
BEETS
BLUEBERRIES
RED CABBAGE
CHERRIES
GRAPE JUICE
RED ONION
YELLOW ONION
PEACH SKIN
PEAR SKIN
PLUM SKIN
RADISH SKIN
RHUBARB SKIN
TOMATO
TURNIP SKIN *
Source: Volume 62, Number 4, April 1985 pg 285 (Not sure of magazine title)
*YELLOW at pH 12 and above

25. Ethanol (drinking alcohol) Ethanoic acid (vinegar)