Some more Questions
·
Define solubility product?
The solubility product of a salt at a given temperature may be define as the product of molar concentrations of the ions raised to the power equal to the number of times each ion occurs in the equation for the solubility equilibrium.
· What will be the pH of 1 MNa2SO4 solution?
Sodium sulphate is a salt of strong acid and a strong base and thus, its aqueous solution will be neutral. Its pH will be seven.
· Define an acid and a base according to Arrhenius theory.
An acid is a substance which provides H+ ion in aqueous solution whereas base is a substance which provide OH- ion in aqueous solution.
· Give two limitations of Arrhenius theory.
(i) It fails to give the acidic and basic properties of substances in solvents other than water.
(ii) It fails to give the acidic properties of substances such as CO2, SO2 which do not contain hydrogen.
· Why it is necessary to add NH4Cl before adding NH4OH for precipitation of group III cation.
Group III cations (Fe3+ , Al3+ ) are precipitation as metal hydroxides. Their Ksp values are low. To keep ionic product low, the OH- ion concentration is decreased i.e. the ionisation of NH4OH is suppressed by the addition of NH4CL.
· Why it is necessary to add dilute HCl before passing H2S for precipitating group II cation.
Group II cations ( Cu+2 , Cd2+ ,As+3 etc.) are precipitated as their sulphides. Their Ksp values are low. To keep ionic product low, the S2- ion conc. Is decreased i.e. the ionisation of H2S is suppressed by the addition of HCl.
· Which substance makes a buffer with acetic acid? What happens to the pH when small quantity of hydrochloric acid is added to such a mixture .
CH3COONa. When a small quantity of HCl is added to this buffer, then H+ ions react with acetate ion from sodium acetate.
CH3COO- + H+ CH3COOH.
Acetic acid is very poorly ionised and not change the pH appreciably.
· Aqueous solution of sodium acetate is basic. Where as that of sodium chloride is neutral. Explain.
Sodium chloride being a salt of strong acid and strong base is not hydrolysed in water. On the other hand, sodium acetate is basic in aqueous solution as it is a salt of strong base and weak acid and provides more OH- ions in aqueous solution.
· Why NH4Cl is used along with NH4OH for precipitation of III(A) metal hydroxides?
NH4Cl is used to suppress the ionisation of NH4OH so that the OH- concentration falls. It is due to common ion effect.
NH4OHDNH4+ +OH-
NH4C NH4+ + Cl-
The increase in conc. Of NH4+ ion shifts the equilibrium (i) in the backward direction. Thus, the precipitation of higher group metal hydroxides will be prevented and only III group metal hydroxide will precipitate. It may be noted that Ksp value of III group metal hydroxides are low.
· What is the difference between solubility and solubility product?
(i) Solubility is applicable to all solutes where as solubility product is applicable to all electrolytes.
(ii) The solubility product (Ksp) of an electrolyte is fixed at a given temperature where as solubility of an electrolyte decreases by the addition of salt having a common ion.
· Why is the solution containing sodium acetate and acetic acid called a buffer solution.
An equimolar mixture solution of weak acid and acetic acid and its salt with strong base is called buffer solution. Here CH3COOH is weak acid and CH3COONa is its salt with strong base.
· The ionic product of water is 0.11×10-14 at 273K; 1×10-14 at 295K and 51×10-14 at 373K. Deduce from this data whether the ionisation of water to H+ ion and OH- ion is exothermic or endothermic in nature.
With the rise in temperature, the ionic product increases. It means that more ions will be formed i.e. rate of forward reaction increases. Hence, according to Le-chatelier’s principles, reaction is endothermic in nature.
Define solubility product?
The solubility product of a salt at a given temperature may be define as the product of molar concentrations of the ions raised to the power equal to the number of times each ion occurs in the equation for the solubility equilibrium.
· What will be the pH of 1 MNa2SO4 solution?
Sodium sulphate is a salt of strong acid and a strong base and thus, its aqueous solution will be neutral. Its pH will be seven.
· Define an acid and a base according to Arrhenius theory.
An acid is a substance which provides H+ ion in aqueous solution whereas base is a substance which provide OH- ion in aqueous solution.
· Give two limitations of Arrhenius theory.
(i) It fails to give the acidic and basic properties of substances in solvents other than water.
(ii) It fails to give the acidic properties of substances such as CO2, SO2 which do not contain hydrogen.
· Why it is necessary to add NH4Cl before adding NH4OH for precipitation of group III cation.
Group III cations (Fe3+ , Al3+ ) are precipitation as metal hydroxides. Their Ksp values are low. To keep ionic product low, the OH- ion concentration is decreased i.e. the ionisation of NH4OH is suppressed by the addition of NH4CL.
· Why it is necessary to add dilute HCl before passing H2S for precipitating group II cation.
Group II cations ( Cu+2 , Cd2+ ,As+3 etc.) are precipitated as their sulphides. Their Ksp values are low. To keep ionic product low, the S2- ion conc. Is decreased i.e. the ionisation of H2S is suppressed by the addition of HCl.
· Which substance makes a buffer with acetic acid? What happens to the pH when small quantity of hydrochloric acid is added to such a mixture .
CH3COONa. When a small quantity of HCl is added to this buffer, then H+ ions react with acetate ion from sodium acetate.
CH3COO- + H+ CH3COOH.
Acetic acid is very poorly ionised and not change the pH appreciably.
· Aqueous solution of sodium acetate is basic. Where as that of sodium chloride is neutral. Explain.
Sodium chloride being a salt of strong acid and strong base is not hydrolysed in water. On the other hand, sodium acetate is basic in aqueous solution as it is a salt of strong base and weak acid and provides more OH- ions in aqueous solution.
· Why NH4Cl is used along with NH4OH for precipitation of III(A) metal hydroxides?
NH4Cl is used to suppress the ionisation of NH4OH so that the OH- concentration falls. It is due to common ion effect.
NH4OHDNH4+ +OH-
NH4C NH4+ + Cl-
The increase in conc. Of NH4+ ion shifts the equilibrium (i) in the backward direction. Thus, the precipitation of higher group metal hydroxides will be prevented and only III group metal hydroxide will precipitate. It may be noted that Ksp value of III group metal hydroxides are low.
· What is the difference between solubility and solubility product?
(i) Solubility is applicable to all solutes where as solubility product is applicable to all electrolytes.
(ii) The solubility product (Ksp) of an electrolyte is fixed at a given temperature where as solubility of an electrolyte decreases by the addition of salt having a common ion.
· Why is the solution containing sodium acetate and acetic acid called a buffer solution.
An equimolar mixture solution of weak acid and acetic acid and its salt with strong base is called buffer solution. Here CH3COOH is weak acid and CH3COONa is its salt with strong base.
· The ionic product of water is 0.11×10-14 at 273K; 1×10-14 at 295K and 51×10-14 at 373K. Deduce from this data whether the ionisation of water to H+ ion and OH- ion is exothermic or endothermic in nature.
With the rise in temperature, the ionic product increases. It means that more ions will be formed i.e. rate of forward reaction increases. Hence, according to Le-chatelier’s principles, reaction is endothermic in nature.
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