for science students

2. Look at some examples,Look at some examples,
and see if you can figureand see if you can figure
out what an acid is…out what an acid is…
HCl (Hydrochloric acid)HCl (Hydrochloric acid)
HNOHNO33 (Nitric acid)(Nitric acid)
HH22SOSO44 (Sulfuric acid)(Sulfuric acid)
HH33POPO44 (Phosphoric acid)(Phosphoric acid)

3. Acid/Base definitionsAcid/Base definitions
 Definition #1: Arrhenius (traditional)Definition #1: Arrhenius (traditional)
Acid – has hydrogen in the formula, and produces HAcid – has hydrogen in the formula, and produces H++
ions in waterions in water
Base – has OH in the formula, and produces OHBase – has OH in the formula, and produces OH--
ionsions
in waterin water

4. Acids and bases inAcids and bases in
water:water:
 Arrhenius Acid:Arrhenius Acid:
HCl (aq)HCl (aq)  HH++
+ Cl+ Cl--
HCl is an acid because it has H in the formula,HCl is an acid because it has H in the formula,
and increases the amount of Hand increases the amount of H++
in water.in water.
 Arrhenius Base:Arrhenius Base:
NaOH (aq)NaOH (aq)  NaNa++
+ OH+ OH--
NaOH is a base because it has OH in the formulaNaOH is a base because it has OH in the formula
and increases the amount of OHand increases the amount of OH--
in water.in water.

5. The ArrheniusThe Arrhenius
definition had adefinition had a
problem…problem…
 Some bases (like ammonia, NHSome bases (like ammonia, NH33) don’t) don’t
have OH in the formula.have OH in the formula.

6. Bronsted-Lowry definitions:Bronsted-Lowry definitions:
(new and improved(new and improved
definitions)definitions)
Acids are substances thatAcids are substances that give awaygive away hydrogenhydrogen
ions. (This definition is practically the same.)ions. (This definition is practically the same.)
Bases are substances thatBases are substances that acceptaccept hydrogen ions.hydrogen ions.

7. Bronsted-LowryBronsted-Lowry
definition:definition:
Acids are substances that give away hydrogenAcids are substances that give away hydrogen
ions.ions.
Example: HCl gives away hydrogen to water:Example: HCl gives away hydrogen to water:
HCl (aq) + HHCl (aq) + H22OO  HH33O+ (aq) + Cl- (aq)O+ (aq) + Cl- (aq)
Draw the hydrogen ion. What does it consist of?Draw the hydrogen ion. What does it consist of?

8. A hydrogen ion isA hydrogen ion is
simply a proton.simply a proton.
Acids are also called “proton donors.”Acids are also called “proton donors.”

9. Bronsted-LowryBronsted-Lowry
definition:definition:
 A base is a hydrogen ion acceptor.A base is a hydrogen ion acceptor.
Another way of saying the same thing:Another way of saying the same thing:
A base is a proton acceptor.A base is a proton acceptor.

10. An acid is a proton donor
A base is a proton acceptor
acidbase

11. Practice question:Practice question:
 In the reactionIn the reaction
HBr(HBr(aqaq) + NH) + NH33((aqaq))  NHNH44
++
((aqaq) + Br) + Br––
((aqaq))
Identify the acid and the base.Identify the acid and the base.

12. Practice questionPractice question
 In the reactionIn the reaction
HSOHSO44
––
+ H+ H22OO  HH33OO++
+ SO+ SO44
2-2-
Identify the acid and the base.Identify the acid and the base.

13. Practice question:Practice question:
 In the equationIn the equation
HCl(HCl(gg) + H) + H22O(O(ll))  HH33OO++
((aqaq) + Cl) + Cl––
((aqaq))
which formula is a Brønsted-Lowry acid?which formula is a Brønsted-Lowry acid?

14. Tell-tale signs of anTell-tale signs of an
acid:acid:
 sour tastesour taste
(orange juice and lemonade contain(orange juice and lemonade contain
citric acid)citric acid)
 turns litmus paper redturns litmus paper red
(by reacting with a chemical in(by reacting with a chemical in
the litmus paper)the litmus paper)
 reacts with metals to producereacts with metals to produce
hydrogen gashydrogen gas

15. Chemists write the formulas forChemists write the formulas for
acids with the H at the front, soacids with the H at the front, so
they’re easy to identify as acids:they’re easy to identify as acids:
HCl (Hydrochloric acid)HCl (Hydrochloric acid)
HNOHNO33 (Nitric acid)(Nitric acid)
HH22SOSO44 (Sulfuric acid)(Sulfuric acid)
HH33POPO44 (Phosphoric acid)(Phosphoric acid)

16. Tell-tale signs of aTell-tale signs of a
base:base:
 bitter tastebitter taste
 slippery feelslippery feel
 turns litmus paper blueturns litmus paper blue
(Conveniently, base, bitter, and blue all(Conveniently, base, bitter, and blue all
start with B!)start with B!)

17. Some substances,Some substances,
like water act likelike water act like
an acid sometimesan acid sometimes
and act like a baseand act like a base
other times.other times.
Substances that can act as anSubstances that can act as an
acid or a base are calledacid or a base are called
amphoteric.amphoteric.

18. Neutralization reactions:Neutralization reactions:
If you combine an acidIf you combine an acid
with a base…with a base…
Predict the products:Predict the products:
HCl + NaOHHCl + NaOH  ??
Hint: It’s a special kind of double replacementHint: It’s a special kind of double replacement
reaction!reaction!

19. If you combine an acidIf you combine an acid
with a base…with a base…
HCl + NaOHHCl + NaOH  HH22O + NaClO + NaCl
This is called aThis is called a neutralization reactionneutralization reaction
because the acid and base neutralizebecause the acid and base neutralize
each other.each other.

20. If you combine an acidIf you combine an acid
with a base…with a base…
HCl + NaOHHCl + NaOH  HH22O + NaClO + NaCl
The products of any neutralization reactionThe products of any neutralization reaction
are water and a salt.are water and a salt.

21. Acid/Base reactions:
Produce water and a salt (and sometimes carbon dioxide).
Hint: concentrate on the water first. Remember, water
has the formula HOH.
Complete and balance the following:
HCl + KOH →
HCl + Ca(OH)2 →
HOH + KCl
2
Require equal numbers
2HOH + CaCl2

22. 1. Ba(OH)2 + H3PO4 →
2. HC2H3O2 + NaOH →
3. H2SO4 + KOH →
4. H2CO3 + NaOH →

23. Everyday application:Everyday application:
The stomach secretes acids to help digestThe stomach secretes acids to help digest
foods. These acids, which includefoods. These acids, which include
hydrochloric acid, have a molarity ofhydrochloric acid, have a molarity of
about 0.1M.about 0.1M.
Antacids, like Tums, Maalox, Mylanta andAntacids, like Tums, Maalox, Mylanta and
Alka-seltzer are simple bases thatAlka-seltzer are simple bases that
neutralize stomach acids.neutralize stomach acids.

24. Acids and Bases:Acids and Bases:
StrengthStrength
 What makes an acid a strong acid?What makes an acid a strong acid?
It ionizes completely in water!It ionizes completely in water!
 These are strong acids (in order of increasingThese are strong acids (in order of increasing
strength):strength):
1.1. HNOHNO33 (nitric acid)(nitric acid)
2.2. HCl (hydrochloric acid)HCl (hydrochloric acid)
3.3. HBr (hydrobromic acid)HBr (hydrobromic acid)
4.4. HI (hydroiodic acid)HI (hydroiodic acid)
5.5. HH22SOSO44 (sulfuric acid)(sulfuric acid)
6.6. HClOHClO44 (perchloric acid) (the strongest)(perchloric acid) (the strongest)

25. Strong acids:Strong acids:
 HCl + HHCl + H22OO  HH33OO++
+ Cl-+ Cl-
Remember, strong acids ionize completely in
water. The reaction goes all the way to the
right. A single arrow is used. There are
virtually no HCl molecules left intact.

26. One more reminder:One more reminder:
“Weak” does not mean the same“Weak” does not mean the same
thing as “diluted.”thing as “diluted.”
HCl, for example is always aHCl, for example is always a
strong acid. If you add 1000strong acid. If you add 1000
liters of water to it, it will beliters of water to it, it will be
diluted, but still strong becausediluted, but still strong because
what little there is will bewhat little there is will be
completely dissociated.completely dissociated.

27. Electrolytes:Electrolytes:
Acids and bases are both examples ofAcids and bases are both examples of
electrolytes.electrolytes.
Electrolytes are compounds that form ionsElectrolytes are compounds that form ions
when dissolved in water.when dissolved in water.
They’re called electrolytes because theyThey’re called electrolytes because they
can conduct electricity through water.can conduct electricity through water.

28. More on electrolytes:More on electrolytes:
If two wires connected to a light bulb and to a powerIf two wires connected to a light bulb and to a power
source are placed in a beaker of water, the lightsource are placed in a beaker of water, the light
bulb will not glow. If an electrolyte, such asbulb will not glow. If an electrolyte, such as
sodium chloride, is dissolved in the water, the lightsodium chloride, is dissolved in the water, the light
bulb will glow because the solution can nowbulb will glow because the solution can now
conduct electricity. The amount of electric currentconduct electricity. The amount of electric current
that can be carried by an electrolyte solution isthat can be carried by an electrolyte solution is
proportional to the number of ions dissolved.proportional to the number of ions dissolved.
Thus, the bulb will glow more brightly if theThus, the bulb will glow more brightly if the
amount of sodium chloride in the solution isamount of sodium chloride in the solution is
increased.increased.

29. Practice QuestionsPractice Questions

30. Which of these couldWhich of these could
be used to determinebe used to determine
whether a substance iswhether a substance is
a base?a base?
A ThermometerA Thermometer
B Litmus paperB Litmus paper
C BalanceC Balance
D Bunsen burnerD Bunsen burner

31. An element common toAn element common to
all acids is –all acids is –
a. chlorinea. chlorine
b. hydrogenb. hydrogen
c. oxygenc. oxygen
d. sodiumd. sodium

32. The pH Scale…The pH Scale…

33. TheThe pH scalepH scale is a wayis a way
of expressing theof expressing the
concentration of acids.concentration of acids.
Under 7 = acidUnder 7 = acid
7 = neutral7 = neutral
Over 7 = baseOver 7 = base

34. pH is the negative logpH is the negative log
of the Hof the H++
concentration.concentration.

35. pH is the negative logpH is the negative log
of the Hof the H++
concentration.concentration.
What????

36. It’s easier than itIt’s easier than it
sounds!sounds!
If HIf H++
is….is….
1 x 101 x 10-3-3
pH = 3pH = 3
1 x 101 x 10-7-7
pH = 7pH = 7
1 x 101 x 10-12-12
pH = 12pH = 12