Chemical Properties of Acids

  1. Acids have the following chemical properties:
    1. Acid + Reactive Metal  Salt + Hydrogen gas
    2. Acid + Metal Carbonate  Salt + Water + Carbon Dioxide gas
    3. Acid + Base oxide  Salt + Water
    4. Acid + Alkali  Salt + Water

Acid + Reactive Metal

  1. Acids react with metals that is more electropositive than hydrogen in the electrochemical series to produce salt and hydrogen gas.
  2. Acids do not react with copper and silver.
  3. This is actually a displacement, where the metals that are placed above hydrogen in Electrochemical Series displace hydrogen from acid.
Acids + Reactive Metal  Salt + Hydrogen Gas

Example:

Sulphuric acid + Zinc
H2SO4 + Zn → ZnSO4 + H2
Nitric acid + Lead
2HN3 +Pb→Pb (NO3)2 + H2

Example of Experiment

Procedure

  1. About 5 cm³ of dilute sulphuric acid is poured into a test tube.
  2. One spatula of zinc powder is added into the acid.
  3. A burning wooden splinter is placed at the mouth of the test tube.
  4. The observations are recorded.

Observation

Colourless gas is released. A “pop” sound produced when the wooden splinter is placed at the mouth of the test tube.


Inference

Hydrogen gas is released

Chemical Equation
H2SO4 + Zn → ZnSO4 + H2

Acid + Carbonate

Acids react with metal carbonates produces salt, water and carbon dioxide

Acids + Metal Carbonate  Salt + Water + Carbon Dioxide Gas

Example:

Sulphuric acid + Lime Stone
H2SO4 +CaCO3 → CaSO4 + CO2 + H2O
Nitric acid + Copper(II) Carbonate
2HNO3 +CuCO3 → Cu(NO3)2 +CO2 + H2O

Example of Experiment

Procedure

  1. About 5 cm³ of dilute sulphuric acid is poured into a test tube.
  2. One spatula of calcium carbonate powder is added into the test tube.
  3. The gas released is passed through lime water as shown in the diagram above.
  4. The observations are recorded


Observation
Colourless gas is released. The gas turn lime water chalky.

Inference

Sulphuric acid reacts with calcium carbonate.
The gas released is carbon dioxide.

Chemical Equation:

H2SO4 +CaCO3 → CaSO4 +CO2 + H2O

Acid + Base Oxide

Acids react with bases produces salt and water

Acids + Base Oxide  Salt + Water (Neutralisation)


Example
:

Sulphuric acid + Iron(II) Oxide
H2SO4 + FeO→FeSO4 + H2O

Hydrochloric acid + Magnesium Oxide

2HCl + MgO → MgCl2 + H O


Example of Experiment

Procedure

  1. One spatula of copper(II) oxide powders is added to 5cm³ of hydrochloric acid in a test tube.
  2. The mixture is heated slowly and stirred with a glass rod.
  3. The observations are recorded.


Observation

  1. The black solid dissolves.
  2. The colourless solution turns blue.

Inference

  1. The copper(II) oxide powder (the black powder) has reacted with the hydrochloric acid.
  2. The blue colour solution contain copper(II) ions.


Chemical Equation

2HCl + CuO → CuCl2 + H2O

Acid + Alkali

  1. Acids react with alkali produces salt and water only.
  2. This is called a neutralisation reaction.
Acids + Alkali  Salt + Water (Neitralisation)

Example:

Ethanoic Acid + Sodium Hydroxide

CH3COOH + NaOH → CH3COONa + H2O

Hydrochloric Acid + Ammonia Solution

HCl + NH3 → NH4Cl

Writing Ionic Equation of the Reactions of Acids

Steps in writing the ionic equation of the reactions of acids:

  1. Write the chemical equation of the reaction.
  2. List down all the ion presence below the equation.
  3. Cancel the ions that do not change in the reaction.
  4. Rewrite the equation with only the ions that have changed in the reaction.
Example

Write the ionic equations for the following reactions:
a. Acids + Zinc
b. Acids + Metal Carbonate
c. Acids + Base Oxide
d. Acids + Alkali

Answer:
a. Acids + Zinc
We can use any acid for the reaction, as it will not affect the ionic equation at the end.
In this case, let’s use hydrochloric acid for the chemical equation.

Step 1: Writing the Chemical Equation
   2HCl + Zn → ZnCl2 + H2
Step 2: List down the ions
   2H+ + 2C l + Zn → Zn2+ + 2C l + H2
Step 3: Cancel the ions that do not change
   2H+ + 2C l + Zn → Zn2+ + 2C l + H2
Step 4: Rewrithe the equation
   2H+ + Zn → Zn2+ + H2

b. Acids + Metal Carbonate

Let’s use hydrochloric acid and calcium carbonate
Step 1:
   2HCl + CaCO3 → CaCl2 + CO2 + H2 O
Step 2:
   2H+ + 2C l + Ca2+ +CO32− → Ca2+ + 2C l + CO2 + H2O
Step 3:
   2H+ + 2C l + Ca2+ +CO32− → Ca2+ + 2C l + CO2 + H2O
Step 4:
   2H+ +CO32− →CO2 + H2O

c. Acids + Base Oxide
Let’s use Hydrochloric acid and Zinc Oxide
Step 1:
   2HCl + ZnO → ZnCl2 + H2O 
Step 2:
   2H+ +2C l − + Zn2+ + O2− → Zn2+ + 2C l− + H2O 
Step 3:
   2H+ + 2C l + Zn2+ + O2− → Zn2+ + 2C l + H2
Step 4:
   2H+ + O2− → H2
d. Acids + Alkali
Step 1:
   HCl + NaOH → NaCl + H2
Step 2:
   H+ + C l +Na+ + OH → Na+ + C l + H2
Step 3:
   H+ + C l + N a+ + OH− → Na + + C l + H2
Step 4:
   H+ + OH → H2O