Section 19.1 lecture (part B) for Honors & Prep Chemistry

1. Bellwork- concentration review
How many moles of H+ are in 250ml of 3M
HCl?
How many moles of OH- are produced when
25g of NaOH is dissolved in 250ml of
water?
What is the molarity of the NaOH solution?

2. Arrhenius concept
Acids make H+
Bases make OH-

3. The Brønsted-Lowry definition
of
ACIDS AND BASES
Acids donate protons (H+)
HCl  H+ + Cl-
Bases accept protons (H+)
NH3 + H+  NH4+

4. The Bronsted- Lowry model is
more inclusive than the Arrhenius
model.
NH3 + H+  NH4+
Ammonia is a Bronsted-Lowry
base, but does not dissociate to
make OH-

5. 19.1
Why Ammonia is a Base

6. HA + H2O  H3O+ + A-
Acid base conjugate conjugate
acid base
An acid donates a proton forming its
conjugate base. HA  A-
A base accepts a proton forming its
conjugate acid. NH3  NH4+

7. HA  A-
Acid conjugate base
A- is ready to accept a proton, it is a
base.
NH3 + H+  NH4+
Base conjugate acid
NH4+ has a proton to donate. It is an
acid.

8. 19.1
Conjugate Acids and Bases
• A conjugate acid is the particle
formed when a base gains a
hydrogen ion.
• A conjugate base is the particle that
remains when an acid has donated a
hydrogen ion.

9. •A conjugate acid-base pair
consists of two substances related
by the loss or gain of a single
proton.
•A substance that can act as both
an acid and a base is said to be
amphoteric.

10. Water is amphoteric.
Water can be an acid or a base
H2O  H+ + OH-
Water can ionize and donate a
proton.
H2O  H3O+
As a base, water accepts a proton
forming the hydronium ion.

11. A conjugate acid-base pair consists of
two substances related to each other by
the donating and accepting of a proton
Are the following pairs conjugate acid-
base pairs?
a. H2O H3O+
b. OH- HNO3
c. HC2H3O2 C2H3O2-

12. 19.1
Brønsted-Lowry Acids
and Bases

13. Identify conjugate acid base pairs
HCl + NH3  NH4+ + Cl-
HSO4- + OH-  H2O + SO42-
NH3 + H2O  NH4+ + OH-

14. Lewis Acids and Bases
Lewis definition
an acid accepts a pair of electrons
a base donates a pair of electrons.

15. 19.1
Lewis Acids and Bases
• A Lewis acid is a substance that can
accept a pair of electrons to form a
covalent bond.
• A Lewis base is a substance that can
donate a pair of electrons to form a
covalent bond.

16. Animation 25 Compare the three important
definitions of acids and bases.

17. 19.1
Lewis Acids and Bases

18. 19.1 Section Quiz.
1. Which of the following is NOT a
characteristic of acids?
a. taste sour
b. are electrolytes
c. feel slippery
d. affect the color of indicators

19. 19.1 Section Quiz.
2. Which compound is most likely to
act as an Arrhenius acid?
a. H2O
b. NH3.
c. NaOH.
d. H2SO4.

20. 19.1 Section Quiz.
3. A Lewis acid is any substance that
can accept
a. a hydronium ion.
b. a proton.
c. hydrogen.
d. a pair of electrons.

21. pH
The pH scale measures the
hydrogen ion
concentration[H+] of a
solution.
A pH of 7 is neutral

22. A pH less than 7 is acidic (litmus red)
A pH greater than 7 is basic (litmus
blue)
The pH scale ranges from below zero (very
acidic) to above14 (very basic)

23. The pH scale is not linear.
The pH scale is logarithmic.
pH = -log[H+]
[H+] = 1.0 x 10-2 pH = 2 very acidic
[H+] = 1.0 x 10-3 pH = 3 acidic
A solution with pH of 2 contains 10 times
as much H+ as a solution with pH of 3.

24. Acidic = more H+ than OH-
Basic = more OH- than H+

25. From pH 0 to pH 14 the
H+ concentration decreases
100,000,000,000,000 times!!

26. 19.2
Measuring pH
An indicator is a valuable tool
for measuring pH because it
is a different color in acidic
solution than when in base.

27. 19.2
Measuring pH
Phenolphthalein
changes from
colorless to
pink at pH
7–9.

28. 19.2
Measuring pH

29. 19.2
Measuring pH
Universal Indicators

30. 19.2
Measuring pH
– pH Meters

31. Solu%on Red Blue pH paper Universal Acid,
Litmus Litmus indicator Base, or
neutral?
lemon juice
(diluted)
!"#$%&"'( )*+(,&%-$.( /#$*(,&%-$.( 01(020*3( 4'&5*3.2#(&'+&62%"3( 76&+8(/2.*8("3('*$%32#9(
#*-"'(:$&6*(;+&#$%*+<( ( ( ( ( (
baking soda + B(
=2>&'?(."+2(@(1 A ( ( ( ( (
H2O
C32'"(;+&#$%*+<( ( ( ( ( (
,D."#(;+&#$%*+<( ( ( ( ( (
E&'*?23(( ( ( ( ( (
Drano (NaOH)
( ( ( ( ( (
(diluted)
( ( ( ( ( (
(
Lysol (diluted)
Vinegar