Class 11 Chemistry - Chapter The s Block Elements NCERT Solutions | Why are alkali metals not found in natur

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.

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.

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.

Why is Li₂CO₃ decomposed at a lower temperature whereas Na₂CO₃ at higher temperature?

In what ways lithium shows similarities to magnesium in its chemical behaviour?

Find the oxidation state of sodium in Na₂O₂.

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.

Explain why BeH₂ molecule has a zero dipole moment although the Be–H bonds are polar.

Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches the equilibrium:

2BrCl (g) ↔ Br₂ (g) + Cl₂ (g) for which K_c= 32 at 500 K.

If initially pure BrCl is present at a concentration of 3.3 × 10^–3 mol L^–1, what is its molar concentration in the mixture at equilibrium?

Explain why pure liquids and solids can be ignored while writing the equilibrium constant expression?

Consider the reactions:

(a) H₃PO_2(aq) + 4 AgNO_3(aq) + 2 H₂O_(l) → H₃PO_4(aq) + 4Ag_(s) + 4HNO_3(aq)

(b) H₃PO_2(aq) + 2CuSO_4(aq) + 2 H₂O_(l) → H₃PO_4(aq) + 2Cu_(s) + H₂SO_4(aq)

(c) C₆H₅CHO_(l) + 2 [Ag (NH₃)₂]⁺_(aq) + 3OH^-_(aq) → C₆H₅COO^-_(aq) + 2Ag_(s) + 4NH_3(aq) + 2 H₂O_(l)

(d) C₆H₅CHO_(l) + 2Cu²⁺_(aq) + 5OH^-_(aq) → No change observed.

What inference do you draw about the behaviour of Ag⁺and Cu²⁺from these reactions?

Pressure of 1 g of an ideal gas A at 27 °C is found to be 2 bar. When 2 g of another ideal gas B is introduced in the same flask at same temperature the pressure becomes 3 bar. Find a relationship between their molecular masses.

Give the number of electrons in the species , H2 and

Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation:

N2(g) + H2(g) → 2NH3(g)

(i) Calculate the mass of ammonia produced if 2.00 × 103 g dinitrogen reacts with 1.00 × 103 g of dihydrogen.

(ii) Will any of the two reactants remain unreacted?

(iii) If yes, which one and what would be its mass?

Do you observe any soil pollution in your neighbourhood? What efforts will you make for controlling the soil pollution?

What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen? Provide justification with suitable examples.

Discuss the consequences of high enthalpy of H-H bond in terms of chemical reactivity of dihydrogen.