Neco Model Questions Vol1 2022 Chemistry Question 3

Practice essay / theory question 3 from the 2022 Neco Model Questions Vol1 Chemistry examination. This question covers Chemical Bonding, Ionic structures, Coordination numbers, Crystal lattice calculations .

Neco Model Questions Vol1 2022 Chemistry Essay / Theory
Topics: Chemical Bonding Ionic structures Coordination numbers Crystal lattice calculations
Question 3 NECO_MODEL_QUESTIONS_VOL1 • 2022 • CHEMISTRY • essay

A solid compound X is formed between a metal M and a non‑metal N. The metal M forms a +3 ion and the non‑metal N forms a –2 ion. In the crystal each M ion is surrounded by six N ions in an octahedral arrangement, while each N ion is tetrahedrally coordinated to four M ions. The crystal adopts the rock‑salt structure in which each cubic unit cell of edge length 0.5 nm contains four formula units of X.

Question Parts

( a )
Write the empirical formula of X based on the charges of the ions.
( b )
Explain why X has a high melting point, referring to the type of bonding and the crystal structure.
( c )
Using the given coordination numbers, determine the ratio of M to N ions in the lattice and show that it is consistent with the formula obtained in part (a).
( d )
If 1.00 g of X contains 0.025 mol of M ions, calculate the total number of N ions present in that gram of X. Assume the rock‑salt structure described above (four formula units per unit cell). Express your answer in scientific notation to two significant figures.

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About This Question

This is Neco Model Questions Vol1 2022 Chemistry Question 3. It is one of the essay questions from the 2022 Neco Model Questions Vol1 Chemistry examination.

The question covers Chemical Bonding, Ionic structures, Coordination numbers, Crystal lattice calculations .

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