Vidaara.orgClass 11 · Chemistry
CodeVID-C11-10-T1-01
Group 1: Alkali Metals — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show full working for Sections B, C and D; only final answers are provided.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The general valence-shell configuration of alkali metals is:
- A.ns2
- B.ns1
- C.ns2np1
- D.ns2np6
2.
The strongest reducing agent among alkali metals in aqueous solution is:
- A.Na
- B.K
- C.Li
- D.Cs
3.
Which alkali metal forms a superoxide on burning in excess air?
- A.Li
- B.Na
- C.K
- D.none of these
4.
Caustic soda is:
- A.Na2CO3
- B.NaHCO3
- C.NaCl
- D.NaOH
5.
Down Group 1, atomic radius:
- A.decreases
- B.increases
- C.stays constant
- D.is irregular
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Why are alkali metals never found free in nature?
7.
Why is the hydration enthalpy of Li+ the highest among alkali metal ions?
8.
Write the reaction of sodium with water.
Section C — Long Answer (3 marks)
2 × 3 = 6 marks
9.
Explain three points of anomalous behaviour of lithium.
10.
Describe the manufacture of sodium carbonate by the Solvay process (key steps).
Section D — Detailed Answer (5 marks)
1 × 5 = 5 marks
11.
Discuss the trends in atomic radius, ionisation enthalpy, hydration enthalpy and reducing power down Group 1, explaining the reasons.
Answer Key
Section A — Multiple Choice Questions
- (B) ns1
- (C) Li
- (C) K
- (D) NaOH
- (B) increases
Section B — Short Answer (2 marks)
- They have very low ionisation enthalpies and are highly reactive, readily losing their ns1 electron, so they always occur combined as salts.
- Li+ is the smallest cation with the highest charge density, so it attracts and binds water molecules most strongly.
- 2Na + 2H2O → 2NaOH + H2; the reaction is vigorous and exothermic.
Section C — Long Answer (3 marks)
- Its small size and high polarising power give covalent compounds (e.g. LiCl in organic solvents); Li2CO3, LiF and Li3PO4 are sparingly soluble; lithium alone reacts with N2 to form Li3N and forms only the oxide Li2O on burning.
- Brine is saturated with NH3, then CO2 is passed: NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl. The NaHCO3 is filtered and heated: 2NaHCO3 → Na2CO3 + H2O + CO2.
Section D — Detailed Answer (5 marks)
- Atomic/ionic radii increase down the group (new shells added). Ionisation enthalpy decreases (electron held more loosely). Hydration enthalpy decreases from Li+ to Cs+ (larger ions are less hydrated). Reducing power in the gas phase rises down the group, but in aqueous solution Li is the strongest reducing agent because of its very high hydration enthalpy, giving the most negative E° (−3.04 V).
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