Group 1 - General Properties and Trends - UNSOLVED PRACTICE SET
Chapter: s-Block Elements Alkali and Alkaline Earth Metals | Topic: Group 1 General Properties and Trends
GROUP 1 - GENERAL PROPERTIES AND TRENDS - UNSOLVED PRACTICE SET
Topic: Group 1 General Properties and Trends
Multiple Choice Questions
Q1. The general electronic configuration of alkali metals is:
- ns²
- ns²np¹
- ns¹
- ns²np⁶
Q2. Which of the following alkali metals has the highest first ionisation enthalpy?
- Li
- Na
- K
- Cs
Q3. The reducing character of alkali metals increases down the group because:
- Ionisation enthalpy decreases
- Atomic radius decreases
- Electronegativity increases
- Electron gain enthalpy becomes more negative
Q4. Alkali metals are stored under kerosene oil because they:
- Are highly reactive with air and moisture
- Are soluble in kerosene
- React with glass containers
- Sublime at room temperature
Q5. The hydration enthalpy of alkali metal ions decreases in the order:
- Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺
- Cs⁺ > Rb⁺ > K⁺ > Na⁺ > Li⁺
- Na⁺ > K⁺ > Li⁺ > Rb⁺ > Cs⁺
- K⁺ > Na⁺ > Cs⁺ > Li⁺ > Rb⁺
Q6. Which alkali metal forms a stable nitride directly on reaction with nitrogen?
- Sodium
- Potassium
- Lithium
- Rubidium
Short Answer Questions
Q7. Why are alkali metals called "alkali metals"? Explain with reference to their reaction with water.
Q8. Arrange Li, Na, K, Rb, Cs in increasing order of:
(a) Atomic radius
(b) Melting point
Give reason for each trend.
Q9. Why is the second ionisation enthalpy of alkali metals much higher than the first? What does this indicate about their preferred oxidation state?
Q10. Explain why alkali metals have low melting and boiling points compared to other metals.
Q11. Your chemistry teacher demonstrates that lithium floats on kerosene but sodium sinks in it. Explain this observation based on the physical properties of these metals.
Q12. Why do alkali metals impart characteristic colours to the flame? Name the colour imparted by sodium and potassium.
Long Answer Questions
Q13. Discuss the general characteristics of alkali metals (Group 1) with respect to:
(a) Electronic configuration and atomic radius
(b) Ionisation enthalpy and its trend down the group
(c) Electropositive character and reducing nature
(d) Reaction with water and air
Illustrate with relevant chemical equations.
Q14. Explain the diagonal relationship between lithium and magnesium. Discuss at least four properties or reactions where lithium behaves differently from other alkali metals but similarly to magnesium. Why does this relationship exist?
Q15. The chemistry of alkali metals has both benefits and hazards in everyday life. Discuss:
(a) Why sodium and potassium are essential for human health
(b) Why uncontrolled reactions of alkali metals with water can be dangerous
(c) The use of sodium in street lamps (sodium vapour lamps) commonly seen on Indian roads
(d) Why potassium is preferred over sodium in some fertilisers used by Indian farmers
Numerical / Application-Based Problems
Q16. The first ionisation enthalpies of Li, Na, K, Rb, and Cs are 520, 496, 419, 403, and 376 kJ/mol respectively.
(a) Calculate the average decrease in ionisation enthalpy when moving from Li to Na, and from Na to K.
(b) Explain why the decrease from Li to Na is smaller than from Na to K.
(c) Predict the approximate first ionisation enthalpy of francium (Fr) based on this trend.
Q17. A sample of an alkali metal chloride (MCl) weighs 5.85 g. When dissolved in water and treated with excess silver nitrate solution, it forms 14.35 g of silver chloride (AgCl) precipitate.
(a) Calculate the molar mass of the metal chloride.
(b) Identify the alkali metal (M).
(c) Write the chemical equation for the reaction.
[Given: Atomic masses: Ag = 108, Cl = 35.5]
Q18. In a flame test experiment, a student observes that 0.23 g of sodium metal produces a bright yellow flame. The same mass of potassium produces a lilac flame.
(a) Calculate the number of moles of sodium and potassium in 0.23 g of each.
(b) If both metals react completely with water, calculate the volume of hydrogen gas evolved at STP from each metal.
(c) Why does the flame colour of potassium appear lilac only when viewed through cobalt blue glass?
[Given: Atomic masses: Na = 23, K = 39; Molar volume at STP = 22.4 L]