NEET Practice Questions (MCQs) with Answers & Solutions

(d) Key Idea More the extent of hydration, lesser is the ionic mobility.

Ionic mobility of alkali metal ions is lowest when aqueous solutions of their salts are put under an electric field. In all the alkali metals, Li⁺ ion is smallest thus, extent of hydration is maximum in Li⁺ ion i.e. The dissolution of Li⁺ in water occurs and get hydrated. Smaller the size of a cation, greater is the extent of hydration and lesser is the ionic mobility.

(c) Aqueous solution of slaked lime is called lime water whereas suspension solution of slaked lime is called milk of lime.

(c) Beryllium salts are covalent in nature because of very small Be²⁺ ion and its high polarising power, so it is easily hydrolysed, e.g. BeCl₂+2H₂O$\to$ Be(OH)₂ + 2HCl

(c) The "Sodium pump" is also known as a sodium-potassium pump. This pump is an important contributor to action potential produced by nerve cells. The process of moving sodium and potassium ions across the cell membrane is an active transport process involving the hydrolysis of ATP to provide the necessary energy. This process is responsible for maintaining the large excess of Na⁺ outside the cell and the large excess of K⁺ ions on the inside.

Solubility of the sulphates. The sulphates becomes less soluble as you go down the group i.e.

                            Mg > Ca > Sr > Ba

The magnitude of the lattice energy remains almost constant as the size of the sulphate ion is so big that small increase in the size of the cation from Be to Ba does not make any difference. However, the hydration energy decreases from Be²⁺ to Ba²⁺ appreciably as the size of the cation increases down the group. The significantly high solubility of ${\mathrm{MgSO}}_4$ is due to high enthalpy of solvation of the smaller Mg ions.

Order of thermal stability is

K₂CO₃>Na₂CO₃>CaCO₃>MgCO₃

Hence, MgCO₃ releases CO₂ most easily

MgCO₃ $\stackrel{∆}{\to }$MgO + CO₂

Li is the alkali metal which forms only normal oxide Li₂O when heated in air.

    2Li+1/2 O₂$\to$Li₂O

Sodium, when heated in air, forms peroxide while heavier alkali metals form superoxide as the major product.

(b) Being hygroscopic, sodium dichromate, Na₂Cr₂O₇ cannot be used in volumteric analysis. All other given statements are true.

(a) Ca(OCl)₂, calcium hypochlorite is the active ingredient in bleaching powder which releases chlorine.

(b) Key Idea Hydration energy varies inversely with size and in sulphates of alkaline earth metals lattice energy remains almost constant.

The order of size of alkaline earth metals is

                Be²⁺<Ca²⁺<Sr²⁺<Ba²⁺

Thus, the order of hydration energy is

                Be²⁺>Ca²⁺>Sr²⁺>Ba²⁺

Hence, BeSO4 has the hydration enthalpy higher than the lattice enthalpy.