Class 11 Chemistry - Chapter The s Block Elements NCERT Solutions | Comment on each of the following observa
Comment on each of the following observations:
(a) The mobilities of the alkali metal ions in aqueous solution are Li+ < Na+ < K+ < Rb+ < Cs+
(b) Lithium is the only alkali metal to form a nitride directly.
(c) E° for M2+(aq) (where M = Ca, Sr or Ba) is nearly constant.
(a) On moving down the alkali group, the ionic and atomic sizes of the metals increase. The given alkali metal ions can be arranged in the increasing order of their ionic sizes as:
Li+ < Na+ < K+ < Rb+ < Cs+
Smaller the size of an ion, the more highly is it hydrated. Since Li+ is the smallest, it gets heavily hydrated in an aqueous solution. On the other hand, Cs+ is the largest and so it is the least hydrated. The given alkali metal ions can be arranged in the decreasing order of their hydrations as:
Li+ > Na+ > K+ > Rb+ > Cs+
Greater the mass of a hydrated ion, the lower is its ionic mobility. Therefore, hydrated Li+ is the least mobile and hydrated Cs+ is the most mobile. Thus, the given alkali metal ions can be arranged in the increasing order of their mobilities as:
Li+ < Na+ < K+ < Rb+ < Cs+
(b) Unlike the other elements of group 1, Li reacts directly with nitrogen to form lithium nitride. This is because Li+ is very small in size and so its size is the most compatible with the N3- ion. Hence, the lattice energy released is very high. This energy also overcomes the high amount of energy required for the formation of the N3- ion.
(c) Electrode potential (E°) of any M2+/M electrode depends upon three factors:
(i) Ionisation enthalpy
(ii) Enthalpy of hydration
(iii) Enthalpy of vaporisation
The combined effect of these factors is approximately the same for Ca, Sr, and Ba. Hence, their electrode potentials are nearly constant.
More Questions From Class 11 Chemistry - Chapter The s Block Elements
- Q:-
Compare the alkali metals and alkaline earth metals with respect to
(i) ionization enthalpy
(ii) basicity of oxides and
(iii) solubility of hydroxides.
- Q:-
Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals.
(a) Nitrates (b) Carbonates (c) Sulphates.
- Q:-
Discuss the various reactions that occur in the Solvay process.
- Q:-
Why are lithium salts commonly hydrated and those of the other alkali metal ions usually anhydrous?
- Q:-
State as to why
(a) a solution of Na2CO3 is alkaline ?
(b) alkali metals are prepared by electrolysis of their fused chlorides ?
(c) sodium is found to be more useful than potassium ?
- Q:-
When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain the reasons for this type of colour change.
- Q:-
In what ways lithium shows similarities to magnesium in its chemical behaviour?
- Q:-
Why is Li2CO3 decomposed at a lower temperature whereas Na2CO3 at higher temperature?
- Q:-
Find the oxidation state of sodium in Na2O2.
- Q:-
Explain why is sodium less reactive than potassium?
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(i) CH2=C=O,
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(iv) CH2=CHCN,
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Assign oxidation number to the underlined elements in each of the following species:
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(b) NaHSO4
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(d) K2MnO4
(e) CaO2
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(i) used to determine heat changes
(ii) whose value is independent of path
(iii) used to determine pressure volume work
(iv) whose value depends on temperature only. - Q:-
A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.
a) What is the initial effect of the change on vapour pressure?
b) How do rates of evaporation and condensation change initially?
c) What happens when equilibrium is restored finally and what will be the final vapour pressure? - Q:-
Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.
Recently Viewed Questions of Class 11 Chemistry
- Q:-
The first (ΔiH1) and the second (ΔiH) ionization enthalpies (in kJ mol–1) and the (ΔegH) electron gain enthalpy (in kJ mol–1) of a few elements are given below:
Elements ΔiH1 ΔiH ΔegH I 520 7300 -60 II 419 3051 -48 III 1681 3374 -328 IV 1008 1846 -295 V 2372 5251 +48 VI 738 1451 -40 Which of the above elements is likely to be :
(a) the least reactive element.
(b) the most reactive metal.
(c) the most reactive non-metal.
(d) the least reactive non-metal.
(e) the metal which can form a stable binary halide of the formula MX2, (X=halogen).
(f) the metal which can form a predominantly stable covalent halide of the formula MX (X=halogen)?
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Also, mention whether change will cause the reaction to go into forward or backward direction.
(i) COCl2 (g) ↔ CO (g) + Cl2 (g)
(ii) CH4 (g) + 2S2 (g) ↔ CS2 (g) + 2H2S (g)
(iii) CO2 (g) + C (s) ↔ 2CO (g)
(iv) 2H2 (g) + CO (g) ↔ CH3OH (g)
(v) CaCO3 (s) ↔ CaO (s) + CO2 (g)
(vi) 4 NH3 (g) + 5O2 (g) ↔ 4NO (g) + 6H2O(g)
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Write the general outer electronic configuration of s-, p-, d- and f- block elements.
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Considering the elements B, C, N, F, and Si, the correct order of their non-metallic character is:
(a) B > C > Si > N > F
b) Si > C > B > N > F
(c) F > N > C > B > Si
d) F > N > C > Si > B - Q:-
Give the number of electrons in the species
, H2 and 
- Q:-
How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?
- Q:-
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- Q:-
One mole of H2O and one mole of CO are taken in 10 L vessel and heated to 725 K. At equilibrium 40% of water (by mass) reacts with CO according to the equation,
H2O (g) + CO (g) ↔ H2 (g) + CO2 (g)
Calculate the equilibrium constant for the reaction.
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