FORMING HYDRONIUM IONS
The proton (H+) has been transferred from the HCl molecule to a water molecule. form a hydronium (H3O+) ion and a Cl- ion. This type of reaction is called ionization (because ions are being formed).
• Complete Question 1 on page 4 of your notes.
BRONSTED-LOWRY DEFINITIONOF ACIDS AND BASES
An acid is any substance which donates (gives) a proton (H+) to another substance.
A base is any substance which accepts (takes) a proton from another substance.
A Bronsted Acid is a proton donor
A Bronsted Base is a proton acceptor
BRONSTED-LOWRY DEFINITIONOF ACIDS AND BASES
We see that the HCl is donating the proton and the water is accepting the proton.
Therefore HCl is the Bronsted acid and H2O is the Bronsted base.
HCl + H2O H3O+ + Cl-
acid base
BRONSTED-LOWRY DEFINITIONOF ACIDS AND BASES
Let’s look at another example:
NH3 + H2O NH4+ + OH-
base acid acid base
Bronsted Bases
Strong Bases- yellow
Oxide O2-
Amide NH2-
PO43-
Weak Bases
SO32-
CN-
CO32-
NH3
Incr
easi
ng
stre
ngt
hacids bases
The two Bronsted strong bases. They are found on the right bottom area of the acid chart -p 334
H+
H+
O2- + H2O OH-
NH2- + H2O NH3
Again, all bases make OH-
means strong
+ OH-
+ OH-
Strong Bases
Note all bases make OH-
Ra(OH)2 Ra2+ + 2OH-
Sr(OH)2 Sr2+ + 2OH-
KOH K+ + OH-
LiOH Li+ + OH-
means strong
There are 11 Arrhenius strong bases - Group I and Group II hydroxides
Strong bases completely ionize in water to produce OH-
Be(OH)2(s) ⇄ Be2+ + 2OH-
Zn(OH)2(s) ⇄ Zn2+ + 2OH-
Arrhenius Weak Bases
A weak base is one that partially reacts with water to produce OH-.
Whether you consider Arrhenius or Bronsted-Lowry, BASES act the same way: They all make OH- by accepting a proton from water!
NH3 + H2O ⇄ NH4+ + OH-
C6H5O73- + H2O ⇄ HC6H5O7
2- + OH-
H+
H+
Write the Kb expression for the following 3 weak bases
Kb =
[HF][OH-]
[F-]
[HC2O4-][OH-]
[C2O42-]
Kb =
Kb =[H2CO3][OH-]
[HCO3-]
AMPHIPROTIC SUBSTANCES
Some substances (ex: H2O) are capable of acting as an ACID (when surrounded by a stronger base) OR acting as a BASE (when surrounded by a stronger acid).
Substances that act as acids or bases are called amphiprotic.
AMPHIPROTIC SUBSTANCESOther amphiprotic substances:
• H2O
• H2PO4-
• HCO3-
+ H+ - H+
• Example: H3PO4 H2PO4
- HPO42-
AMPHIPROTIC SUBSTANCES
In general, amphiprotic substances…
Have a negative charge and
An easily removable hydrogen.
AMPHIPROTIC SUBSTANCES
Identify the acid and base in the reactants of the following reactions:
H2S + HCO3- H2CO3 + HS-
NH4+ + H2O H3O+ + NH3
HCOOH + HSO3- H2SO3 + HCOO-
CONJUGATE ACID-BASE PAIRS
Conjugate acid – the species with one more proton (ex. HIO3)
Conjugate base - the species with one less proton (ex. IO3
-)
*There will always be 2 conjugate pairs
POLYPROTIC ACIDSThe formula of an acid tells us how many protons (H+) the acid can
donate.
An acid that can supply:
– ONE proton (ex: HCl) = monoprotic acid
– TWO protons (ex: H2SO4) = diprotic acid
– THREE protons (ex: H3PO4) = triprotic acid
– More than ONE proton = polyprotic acid