Acids, Bases, Salts

1. Acids - Bases - Salts

2. Acids
• An acid is a substance that provides H+
ions in water.
• Here are some examples of substances
that are acids;
• HCl: hydrochloric acid
• HNO3: nitric acid
• H2SO4 : sulphuric acid
• H3PO4: phosphoric acid.

3. Bases
• A base is a substance that provides OH-
ions in water.
• Here are some examples of bases:
• NaOH: Sodium hydroxide
• KOH: Potassium hydroxide
• Ba(OH)2: Barium hydroxide

4. Ionic equations- Acids
• When acids dissolve in water they
produce hydrogen (H+) ions. We say that
the ions are in aqueous solution and write
(aq) in the equation to tell the state of the
reaction. Different acids can produce
different numbers of H+ ions.
• Let us look at the representation for each
of the following acids.

5. Ionic equations- acids
• HCl (g) → H+
(aq) + Cl-
(aq)
• Hydrochloric acid dissolves in water to produce hydrogen
ions and chloride ions.
• Another example; Sulphuric acid dissolves in water
to produce in the first instance hydrogen ions and
hydrogen sulphate ions then further dissociates in
water to form hydrogen ions and sulphate ions.
Therefore, we can say that when sulphuric acid
dissolves in water it produces 2 moles of H+ ions.
Sulphuric acid is a dibasic acid.
• H2 SO4(l) → H+(aq) + HSO4- (aq) → H+(aq) + SO4 2 –
(aq).

6. Ionic equations - bases
• When bases dissolve in water they
produce OH- ions.
• The following are examples of what
happens when bases dissolve in water.
• Sodium hydroxide : NaOH(s) → Na+
(aq) + OH- (aq)
• ( lye or caustic soda)
• Potassium hydroxide: KOH (s) → K+
(aq) + OH- (aq)

7. Ionic equations- bases
• Similar to the number of ions that can be
produced by a dibasic acid a similar thing
can occur with a dibasic acid a similar
thing can occur with a diacidic base.
• Barium hydroxide :
Ba (OH )2 (s) → Ba 2+
(aq) + 2 OH-
(aq)
• Barium hydroxide is a diacidic base !

8. Acid-base neutralization process
Acid-base neutralization reactions in which
an acid reacts with a base to yield water
plus an ionic compound called a salt.
• Let’s look at the neutralization that occurs
between hydrochloric acid and aqueous
sodium hydroxide to yield water and
aqueous sodium chloride.
HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)

9. Salts
• Salts can also be formed by precipitation
reactions.
• When precipitation reactions occur, soluble
reactants yield an insoluble solid product that
drops out of the solution (precipitates!). As this
precipitate forms it drives the force of the
reaction. When positive ions and negative ions
change positions in two reacting compounds
precipitation occurs. The product that
precipitates is called an insoluble salt.

10. Salts
• For example:
• Lead nitrate is formed when an aqueous
solution of lead II nitrate reacts with an
aqueous solution of potassium iodide. This
can be represented in an equation;
Pb(NO3)2 (aq) + 2 KI (aq) → PbI2 + 2 KNO3 (aq)

11. A neutralization reaction
• In a neutralization reaction Anions and
cations react in proportion to produce
water and a salt.
• The anion of the salt ( A-
) comes from the
acid, and the cation of the salt ( M+
) comes
from the base:

12. Neutralization cont’d
• This can be represented as follows:
• HA (aq) + MOH (aq) → H2O (l) + MA (aq)
• Acid Base Water A salt.

13. Strong acids / strong bases
• Let us look at the reaction between a
strong acid and a strong base in water.
• We will now write the ionic equation for
these reactants and products.
H+
(aq) + A-
(aq) + M+
(aq) + OH-
(aq) → H2O (l) + M+
(aq) + A-
(aq)

14. Ionic equations-neutralization
Cancel the ions on both sides that are similar
H+
(aq) + A-
(aq) + M+
(aq) + OH-
(aq) → H2O (l) + M+
(aq) + A-
(aq)
Equation:
H+
(aq) + OH-
(aq) → H2O (l)
Or we could also write the equations as follows:
H3O + (aq) + OH-
(aq) → 2 H2O (l)

15. Ionic equations-neutralization
• Or we could also write the equations as follows:
• H3O + (aq) + OH-
(aq) → 2 H2O (l)

16. Summary of acid – bases – salts
Acids liberate hydrogen ions (protons) in aqueous
solution.
• The basicity of an acid is the number of ionisable
hydrogen atoms it contains in its molecule.
• Acids react with: (i) metals to give hydrogen (ii) bases to
give a salt and water only (iii) carbonates to give a salt,
water and carbon dioxide.
• Acidity and Alkalinity are measured on the pH scale
• The pH scale runs from 1 to 14. Ranges between 1 and
7 are acid. Ranges between 7 and 14 are alkaline or
basic. A range of 7 is neither acidic nor basic.

17. Summary of acid – bases – salts
• Normal salts contain no ionisable hydrogen atoms
• Acid salts contain one or more ionisable hydrogen
atoms.
• Bases are substances which accept protons ( they are
often oxides or hydroxides)
• A solution of a salt is an electrolyte. An electrolyte can
conduct electricity when molten or in solution.
• Strong acids and strong bases are completely ionised
in solution.
• Weak acids and weak bases are incompletely ionised
in solution.