ACIDS, BASES AND SALTS
- Take solutions of glucose, alcohol, HCl, H2SO4, etc.
- Fix two nails on a cork and place it in a 100 mL beaker. Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch.
- Pour some dilute HCl in the beaker and switch on the current. Repeat with dilute H2SO4.
- In both cases, bulb glows. It means there is an electric current through the acidic solution by ions.
- Repeat the experiment using glucose & alcohol solutions. In these cases, bulb does not glow because glucose & alcohol solutions do not conduct electricity.
What Happens to an Acid or a Base in a Water Solution?Acids produce ions only in aqueous solution. It can be proved by the following experiment.
- Take 1g solid NaCl in a clean dry test tube.
- To this, add some conc. sulphuric acid.
- HCl gas comes out of the delivery tube. [In very humid climate, pass the HCl gas through a guard tube (drying tube) containing calcium chloride to dry the gas].
- When HCl gas is tested with wet blue litmus paper, it becomes red colour. But with dry litmus paper, no colour change occurs.
- It means dry HCl gas (absence of water) cannot produce H+ ions. So it does not behave as an acid.
- HCl solution (presence of water) can produce H+ ions and behave as an acid.
HCl + H2O → H3O+ + Cl–
H+ + H2O → H3O+
Action of base with water:
Bases generate hydroxide (OH–) ions in water.
All bases do not dissolve in water.An alkali is a base that dissolves in
water. They are soapy, bitter and corrosive. Never taste or touch them as they
Acid + Base → Salt + Water
H OH → MX + HOH
H+(aq) + OH– (aq) → H2O(l)
Mixing of acid or base with water:
This process is highly exothermic. E.g.
- Take 10 mL water in a beaker. Add a few drops of concentrated H2SO4 and swirl the beaker slowly.
- Touch the base of the beaker. It is hot. So the reaction is exothermic.
- Repeat this activity with sodium hydroxide pellets. It is also exothermic reaction.