Asked in Premeth Test 19 — Solids

A substance has a density of 2 kg dm-3 and it crystallizes in a fcc lattice with an edge length equal to 700 pm, then the molar mass of the substance is:

Correct answer: B. 103.30 g mol-1

  • A. 74.50 g mol-1
  • B. 103.30 g mol-1
  • C. 56.02 g mol-1
  • D. 65.36 g mol-1

Explanation

To find the molar mass of the substance in an fcc lattice, use the formula:M = (density × NA × a3) / Z, where:Density = 2 kg dm-3 = 2000 g dm-3a = edge length = 700 pm = 700 × 10-12 mNA = Avogadro's number = 6.022 × 1023 mol-1Z = number of atoms per unit cell for an fcc lattice = 4Convert the edge length to dm: a = 700 × 10-10 dm.Plug these values into the formula to calculate M:M = (2000 × 6.022 × 1023 × (700 × 10-10)3) / 4 = 103.30 g mol-1.Therefore, the correct answer is 103.30 g mol-1.Other options result from incorrect calculations due to errors in unit conversion, misapplication of the formula, or incorrect assumptions about the lattice structure.

Written and checked by , M.Phil ChemistryLast updated
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Solids are classified by particle arrangement and bonding into crystalline, ionic and molecular forms. Questions cover crystal lattices, the shapes and properties of ionic crystals, and lattice energy, including how ion charge and ionic size affect the strength of attractions within an ionic solid.

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