Physical and Chemical Properties of Bases | Extra Documents, Videos & Tests for Class 10 PDF Download

PHYSICAL PROPERTIES OF BASES
(i) Taste They are sharp bitter in taste.
(ii) Effect on skin They give a feeling of soapy touch and all alkali have a mild corrosive action on skin.
(iii) Effect on Indicator They affect the indicators as given below

Fig: Bases show various physical properties

Chemical Properties of Bases
2. Reaction with Metals
(i)

(ii)

2. Reaction of Bases with Non-metallic oxide
Base react with non-metallic oxide to form their respective carbonates and water.
(i)

(ii)

Some of the alkalis like sodium hydroxide (NaOH) are called deliquescent because they absorb carbon dioxide from the air and its strength decreases with time.

3. Reaction of Bases with Acids
They neutralise the acids to form salt and water.
Acid + Base → Salt + Water

4. Reaction of Bases with ammonium salt
Bases react with ammonium salt to evolve ammonia gas.

(i)

(ii)

5. Reaction of Bases with Salt
Bases react with salt solution to form another base and another salt.

(i)

(ii)

USES OF BASES

COMPARISON BETWEEN PROPERTIES OF ACIDS & BASES

Q.1. What do All Acids and Bases have in Common?
Ans. A common thing for all the acids is that they produce hydrogen ions [H⁺ (aq.)] when dissolved in water. For Ex, Acids like HCl, H₂SO₄, HNO₃, CH₃COOH etc. show acidic character because they dissociate in aqueous solution to produce hydrogen ions. But all the compounds containing hydrogen are not acids such as glucose (C₆H₁₂O₆) and alcohol (C₂H₅OH) also contain hydrogen but they do not show acidic character.

Activity: To find the characteristics common between acids and bases.

Materials required: Dilute hydrochloric acid, Dilute sulphuric acid, Dilute solution of sodium hydroxide, Ethanol, Glucose solution & Beaker, Carbon electrodes, Dry cells, bulb 1.5 V, Key.

Procedure: Take a beaker and place two carbon electrodes into it.
Connect the electrodes to a battery bulb through a key and a dry cell. Pour dilute hydrochloric acid into the beaker and press the key. Did the bulb glow? Perform similar experiment with all the given solutions, and record your observations.

Observation

Solution	Bulb glows	Bulb does not glow	Nature of solution
Dil. Hydrochloric acid		×	Conducting
Dil Sulphuric acid		×	Conducting
Dil. Sodium hydroxide		×	Conducting
Ethanol	×		Non- Conducting
Glucose solution	×		Non- Conducting

Conclusion: The solutions of acids and bases are good conductors of electricity. The solution of glucose and ethanol are a nonconductor of electricity.

Bases: A common thing for all the bases (or ) is that they all produce hydroxide ions (OH^-) when dissolved in water. For Example - NaOH, Mg(OH)₂, Ca(OH)₂ and NH₄OH are all bases because they dissolve in water to produce hydroxide ion (OH^-)

Acids or Bases (Alkali) in Water Solution-
The acidic behavior of acids due to the presence of hydrogen ions. H⁺ (aq) ions, in them. The acids produce hydrogen ions only in the presence of water. So, in the absence of water, a substance will not form hydrogen ions and hence will not show its acidic behavior.

Activity: To show that acids furnish H⁺ (aq) ions only in the presence of water.
Materials required:  Common salt, Conc. sulphuric acid, anhydrous calcium chloride, blue litmus paper, boiling tube, delivery tube packed with anhydrous calcium chloride.

Procedure:  Take 0.5g of dry common salt in a dry boiling tube. Add a few drops of concentrated sulphuric acid over common salt in the boiling tube. What do you see? A colourless, irritating gas is evolved. Fit a cork carrying a calcium chloride packed delivery tube into the mouth of the boiling tube.

Bring a dry blue litmus paper near the opening of the calcium

chloride tube. Observe, if there is any change in colour. Colour of the litmus paper remains unchanged. Now, bring a moistened blue litmus paper near the mouth of the calcium chloride tube. Do you observe any change in the color of litmus paper? Yes, blue litmus has changed to red.

From the above activity, following conclusion can be drawn :-

Conclusion: Dry HCl gas on coming in contact with dry blue litmus paper does not produce H⁺ ions, and hence the color of litmus paper does not change. so, we can say that separation of H⁺ ions form acid takes place only in the presence of water.

Q.2. Why should water be never added to dilution of an Acid?
Ans. Mixing of water in acid is an exothermic process and more heat has produced that splashing of water. In order to avoid this. We must add acid into water and not water into acid.

Moreover, acid must also be added to water in small lots and not in one installment. 

Q.3. How Strong are Acid or Base Solution?
Ans. Acids and bases on dilution with water, decreases the concentration of H⁺(aq) or OH^-(aq) ions in the acidic and basic solutions respectively.

If we find quantitatively, the amount of H⁺(aq) / OH^-(aq) ions present in a solution, we can judge how strong an acid or a base is?

We can do this by the help of a universal indicator, which is a mixture of several indicators. The universal indicator shows different colors at different concentration of hydrogen ions or pH values in solution.