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.
Compare the alkali metals and alkaline earth metals with respect to
(i) ionization enthalpy
(ii) basicity of oxides and
(iii) solubility of hydroxides.
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.
Discuss the various reactions that occur in the Solvay process.
Why are lithium salts commonly hydrated and those of the other alkali metal ions usually anhydrous?
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 ?
When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain the reasons for this type of colour change.
In what ways lithium shows similarities to magnesium in its chemical behaviour?
Why is Li2CO3 decomposed at a lower temperature whereas Na2CO3 at higher temperature?
Find the oxidation state of sodium in Na2O2.
Explain why is sodium less reactive than potassium?
How do you account for the formation of ethane during chlorination of methane?
What are hybridisation states of each carbon atom in the following compounds ?
(i) CH2=C=O,
(ii) CH3CH=CH2,
(iii) (CH3)2CO,
(iv) CH2=CHCN,
(v) C6H6
What will be the minimum pressure required to compress 500 dm3 of air at 1 bar to 200 dm3 at 30°C?
Calculate the molecular mass of the following:
(i) H2O
(ii) CO2
(iii) CH4
Assign oxidation number to the underlined elements in each of the following species:
(a) NaH2PO4
(b) NaHSO4
(c) H4P2O7
(d) K2MnO4
(e) CaO2
(f) NaBH4
(g) H2S2O7
(h) KAl(SO4)2.12 H2O
What is the basic theme of organisation in the periodic table?
Explain the formation of a chemical bond.
Choose the correct answer. A thermodynamic state function is a quantity
(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.
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?
Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.
Calculate the amount of carbon dioxide that could be produced when
(i) 1 mole of carbon is burnt in air.
(ii) 1 mole of carbon is burnt in 16 g of dioxygen.
(iii) 2 moles of carbon are burnt in 16 g of dioxygen.
Calculate the enthalpy change for the process
CCl4(g) → C(g) + 4 Cl(g)
and calculate bond enthalpy of C – Cl in CCl4(g).
ΔvapH0(CCl4) = 30.5 kJ mol–1.
ΔfH0 (CCl4) = –135.5 kJ mol–1.
ΔaH0 (C) = 715.0 kJ mol–1 , where ΔaH0 is enthalpy of atomisation
ΔaH0 (Cl2) = 242 kJ mol–1
Considering the elements F, Cl, O and N, the correct order of their chemical reactivity in terms of oxidizing property is:
(a) F > Cl > O > N
(b) F > O > Cl > N
(c) Cl > F > O > N
(d) O > F > N > Cl
At a certain temperature and total pressure of 105 Pa, iodine vapour contains 40% by volume of I atoms
I2(g) ↔ 2l (g)
Calculate Kp for the equilibrium.
A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill.
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?
What will be the pressure exerted by a mixture of 3.2 g of methane and 4.4 g of carbon dioxide contained in a 9 dm3 flask at 27 °C ?
An element with mass number 81 contains 31.7% more neutrons as compared to protons. Assign the atomic symbol.
In three moles of ethane (C2H6), calculate the following:
(i) Number of moles of carbon atoms.
(ii) Number of moles of hydrogen atoms.
(iii) Number of molecules of ethane.
What do you understand by bond pairs and lone pairs of electrons? Illustrate by giving one example of each type.