f Block - Lanthanides and Properties - UNSOLVED PRACTICE SET

Q7. Why are lanthanides called inner transition elements? Explain with reference to their electronic configuration.

Q8. Most lanthanides show a +3 oxidation state. Explain why this oxidation state is particularly stable.

Q9. Why do lanthanides have very similar chemical properties? What makes their separation difficult?

Q10. What is meant by the "lanthanide contraction"? Mention one consequence of this phenomenon.

Q11. Why are lanthanide ions (Ln³⁺) generally coloured? Explain the origin of colour in terms of f-f transitions.

Q12. Cerium (Ce) shows a +4 oxidation state in addition to +3. Explain why Ce⁴⁺ is stable.

Section C: Long Answer Questions

Q13. (a) What are lanthanides? Write their general electronic configuration.

(b) Why are they called f-block elements?

(c) Describe the trends in atomic and ionic radii across the lanthanide series.

(d) Why do lanthanides show limited variable oxidation states compared to transition elements?

Q14. (a) Explain why lanthanides are paramagnetic. How does magnetic susceptibility vary across the series?

(b) Describe the colour of lanthanide ions. Why do some lanthanide ions appear colourless?

(c) Why are lanthanide compounds generally less coloured than transition metal compounds?

Q15. (a) Describe the extraction of lanthanides from monazite sand.

(b) Why is the separation of individual lanthanides difficult? Describe one method used for their separation.

(c) List four important uses of lanthanides in modern technology.

Q16. The following table gives data for lanthanide elements:

(a) Plot a graph of ionic radius vs. atomic number for Ln³⁺ ions.

(b) Calculate the total decrease in radius from La³⁺ to Lu³⁺. What is the percentage decrease?

(c) Why is the decrease in radius not perfectly smooth? (Consider Eu and Gd.)

(d) Explain why Gd has a slightly larger radius than expected from the trend.

(e) How does this steady decrease in radius affect the properties of elements that come after the lanthanides (e.g., Hf)?

Q17. Lanthanides have numerous applications in modern technology:

(a) Neodymium is used in making powerful magnets (Nd₂Fe₁₄B). Why are neodymium magnets the strongest permanent magnets known?

(b) Europium and terbium are used in fluorescent lamps and TV screens. What property of these elements makes them useful for this application?

(c) Cerium is used in catalytic converters in cars. What reaction does it catalyse? Why is it effective?

(d) Lanthanum is used in nickel-metal hydride (NiMH) batteries for hybrid cars. What role does lanthanum play in these batteries?

(e) A smartphone contains about 0.03 g of neodymium, 0.01 g of europium, and 0.005 g of terbium. If 1 billion smartphones are produced in a year, calculate the total mass of each lanthanide required annually.

Q18. In a school project on "Rare Earth Elements in Daily Life," students research the uses of lanthanides.

(a) A student finds that the colour TV in her home uses europium (red phosphor) and terbium (green phosphor). Explain how these elements produce colour when excited by electrons.

(b) Another student learns that his father's camera lens contains lanthanum glass. Why is lanthanum added to optical glass? What property does it improve?

(c) A third student discovers that the spark plugs in her mother's car contain yttrium (often grouped with lanthanides). Why are lanthanides used in spark plugs?

(d) The students visit a wind farm and learn that the generators use neodymium magnets. Why are these magnets preferred over conventional magnets in wind turbines?

(e) The teacher asks: "China produces about 60% of the world's lanthanides. Why is this concentration of supply a concern for other countries?" Discuss the geopolitical and environmental implications.