Question

Define pH value. What would you say about the pH of a solution in which
(i) H+ aq. ions = OH- ions
(ii) evolves CO2 when heated with Na2CO3
(iii) OH-ions > H+ aq. ions.

July 30, 2024

Answer

pH is defined as the negative logarithm [to the base 10] of the hydrogen ion concentration expressed in moles/litre. Thus, pH = -log₁₀H⁺. It represents the strength of acids and alkalis, expressed in terms of hydrogen ion concentration [H⁺ aq.]

(i) When, H⁺ ions = OH^– ions, the solution is neutral with pH = 7.

(ii) When the solution evolves CO₂ when heated with Na₂CO₃, it is acidic in nature with pH less than 7.

(iii) when, OH^–ions > H⁺ aq. ions, the solution is basic in nature with pH more than 7.

💡 Some Related Questions

The questions below refers to the following salt solutions listed A to F:
A: Copper nitrate
B: Iron [II] sulphate
C: Iron [III] chloride
D: Lead nitrate
E: Magnesium sulphate
F: Zinc chloride
(i) Which soln. becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it.
(ii) Which solution gives a white precipitate with excess ammonium hydroxide solution.

Write balanced equations for — (a) Aluminium (b) Zinc — is warmed with NaOH [caustic soda] soln.

Give reasons for the following:
Sulphurous acid forms two types of salts on reaction with an alkali.

Give reasons for the following:
Acetic acid does not form an acid salt but forms a normal salt.

Give reasons for the following:
In the preparation of an insoluble salt from another insoluble salt by precipitation [double decomposition], dilute nitric acid and not dilute sulphuric acid is generally used.

Give reasons for the following:
An aqueous solution of the salt ammonium chloride is acidic in nature while an aqueous solution of sodium chloride is neutral.

Give reasons for the following:
Concentrated sulphuric acid is a weaker acid compared to dilute sulphuric acid.

The diagram represents the preparation of sodium sulphate salt from dil. H2SO4 acid and sodium hydroxide.

1. Name the apparatus ‘A’.
2. Name the substance ‘X’ placed in ‘A’ and the substance ‘Y’ placed in B.
3. State the reason for conducting the titration using the apparatus ‘A’ and ‘B’.
4. State which solution is transferred to the evaporating dish and evaporated to point of crystallization for obtaining the salt.
5. State why titration is not conducted for the preparation of copper [II] sulphate crystals by neutralization.

Give balanced equations for the preparation of the following salts:
1. Calcium oxide ⟶ Calcium chloride ⟶ Calcium carbonate
2. Zinc sulphide ⟵ Zn ⟶ Zinc sulphate
3. Iron [II] chloride ⟵ Fe ⟶ Iron [III] chloride
4. Lead [II] oxide ⟶ Lead nitrate ⟶ Lead sulphate
5. Copper [II] oxide ⟶ Copper [II] sulphate ⟵ Copper [II] hydroxide

State which of the following methods is generally used for preparing the salts 1 to 5 given below:
A: Neutralisation — insoluble base and dil. acid
B: Neutralisation — alkali and dil. acid
C: Simple displacement — active metal and dil. acid
D: Direct combination
E: Precipitation [double decomposition]
1. PbCO3
2. Zn(NO3)2
3. NaCl
4. Cu(NO3)2
5. FeS