Name:_________________
Chemistry 12
Unit
4A.3-4A.4 Protons and Brønsted-Lowry Acids and Bases
4A-3
4A-4
Hebden P. 115-119
D2
D3
By the end of this lesson I will be able to
define Brønsted-Lowry acids and bases
identify Brønsted-Lowry acids and bases in an equation
identify an H3O+ ion as a protonated H2O molecule that can be represented in shortened form as H+
Homework: Unit 4 Workbook pg 3-5
For extra practice: Hebden pg.
 Hydronium
 Brønsted-Lowry acid
Vocab
 Brønsted-Lowry base
 Monoprotic acid
 Diprotic acid
 Triprotic acid
 Polyprotic acid
 Amphiprotic acid
A) What is Hydrogen?
Hydrogen consists of a proton surrounded by a single electron.
However that hydrogen often loses its one electron to become the H+ hydrogen ion.
A hydrogen ion is just a proton! It also loses that BIG
of 1 proton.
electron cloud to become a very tiny nucleus
+1 charge
Hydrogen ion: (very very very small space) = Very large charge density
Lithium ion
+1 charge
𝑟𝑒𝑙𝑎𝑡𝑖𝑣𝑒𝑙𝑦 𝑙𝑎𝑟𝑔𝑒𝑟 𝑠𝑝𝑎𝑐𝑒
= Normal charge density
This means H+ is very strongly attracted to any region where negative charges exist.
4.3-4.4 Notes
5
B) Hydronium
Recall from Chem 11:
A water molecule looks like this:
The “non-binding orbitals” of water have a
partial negative charge -. The H+ ions are
attracted to this and will attack it to create a
bond.
ALL of the H+ ions will attack the water molecules to create hydronium ion or the hydrated proton.
Definition: Hydronium Ion / Hydrated Proton
H+ + H2O ↔ H3O+
Essentially
E.g.
is now:
H+ = H3O+
HCl (g)
→ H+(aq) + Cl-(aq)
HCl (g) + H2O(l) → H3O+ (aq) + Cl-(aq)
Practice
1. 1. Write equations which show how the following acids dissociate in water to give H3O+(aq)
a) HClO ____________________________________________________________________________________________________
b) H3PO4 ____________________________________________________________________________________________________
c) HMnO4 ____________________________________________________________________________________________________
d)
HSO3-
____________________________________________________________________________________________________
4.3-4.4 Notes
6
C) Brønsted-Lowry Theory of Acids and Bases
Arrhenius’s Theory is useful but is now considered incomplete with the knowledge of equilibrium reactions.
The Bronsted-Lowry Theory is more general and includes the concepts of equilibrium.
Definition: Acid
Arrhenius Acid: A substance that releases H+ (aq) in water.
Brønsted-Lowry Acid: a substance that DONATES A PROTON to another substance
 an acid is a PROTON DONOR ( Gives away an H+)
Definition: Base
Arrhenius Base: A substance that releases OH- (aq) in water.
Brønsted-Lowry Base: a substance that ACCEPTS A PROTON from another substance
 a base is a PROTON ACCEPTOR (receives an H+)
General Formula
HX + Y → X + HY
To find out which one is the acid/base, look for two chemical species that are most similar:
HX compare to X: HX → X
 HX has lost a proton, therefore HX is an ACID
Y compare to HY: Y → HY
Y has gained a proton, therefore Y is a BASE
Example:
NH3 + H2O ↔ NH4+ + OHForward Reaction
NH3



H2O



GAINS a proton (and + charge)
PROTON ACCEPTOR
Acts as a BASE
LOSES a proton (and + charge)
PROTON DONOR
Acts as an ACID
Reverse Reaction
NH4
+
OH-
 LOSES a proton (and + charge)
 GAINS a proton (and + charge)
 PROTON DONOR
 PROTON ACCEPTOR
 Acts as an ACID
 Acts as a BASE
In every Bronsted-Lowry reaction there is an acid and base on both sides.
NH3
base
In conclusion: Each
+
H2O
acid
↔
NH4+ +
acid
OHbase
side must have both and ACID and a BASE.
4.3-4.4 Notes
7
Some more definitions
Monoprotic acid
Diprotic acid
Triprotic acid
Polyprotic acid
an acid that can donate only 1 proton
an acid that can donate up to 2 protons
an acid that can donate up to 3 protons
any acid that can donate more than 1 proton
Practice
2. For each of the following reactions, which reactant acts as an acid and which acts as a base?
a) HNO3 + H2O ↔ NO3- + H3O+
d) H3PO4 + CH3COO- ↔ H2PO4- + CH3COOH
acid:__________
acid:__________
base: ____________
base: ____________
b) HCO3- + SO32- ↔ CO32- + HSO3e) HCO3- + HF ↔ H2CO3+ Facid:__________
acid:__________
base: ____________
base: ____________
2c) HS + H2PO4- ↔ H2S + HPO4
acid:__________
base: ____________
3. Consider the acids: H3PO4, HF, H2S, H4P2O7 , H2CO3, HCN
a) Which of the acids are monoprotic?
____________________________________
b) Which of the acids are diprotic? _____________________________________
c) Which of the acids are triprotic? _____________________________________
d) Which of the acids are polyprotic? _____________________________________
NOTE: Substances can be both an ACID and a BASE depending on what they are reacting with.
a) HS- + H2PO4- ↔ H2S + HPO42- :
H2PO4- acts as an acid
b) H2S- + H2PO4- ↔ HS- + H3PO4
H2PO4- acts as a base
These substances that can act as both acids and bases are called: AMPHIPROTIC
e.g. H2O and many species from polyprotic acids like H2PO4-, HCO3-, HS+𝐻 +
H3PO4 ←
−𝐻 +
H2PO4+𝐻 +
H2S
←
→
HPO42-
−𝐻 +
HS-
→
S2-
A substance is AMPHIPROTIC if:
a) it has a NEGATIVE (-) charge …. AND
b) has a removable hydrogen
c) or it is H2O
Practice
4. Circle the following compounds that are amphiprotic.
HCl
HSO4-
HCr2O7-
PO43-
H2O
4.3-4.4 Notes
HPO42-
NH3
NH4+
CH3COOH
8