Determine the number of moles of atoms in a 15.78 g sample of a metal whose molar mass is 72.59 g·mol–1.

Question

BlackTom AI · Accepted Answer

To determine the number of moles of atoms in a given mass, we use the formula n = mass / molar mass.

Option 1: '4.600 mol' — If this were correct, the corresponding mass would be n × M = 4.600 mol × 72.59 g/mol ≈ 333.0 g, which does not match the given 15.78 g. This is therefore incorrect.

Option 2: '4.371 × 10^25 mol' — This is an extremely large number of moles, far exceeding any practical quantity for a 15.78 g sample. Such a value would imply an astronomically large mass, so this option is not feasible for the given mass and molar mass.

Option 3: '0.2174 mol' — Compute n = 15.78 g / 72.59 g/mol ≈ 0.2174 mol. This matches the calculation directly and is consistent with the given mass and molar mass, making it the correct result.

Option 4: '1.309 × 10^23 mol' — This is another extremely large number of moles, which would imply a mass far greater than 15.78 g when multiplied by the molar mass. It does not align with the provided mass, so it is incorrect.

Option 5: '7.639 × 10^−24 mol' — This is an impossibly tiny amount of substance for the given mass and molar mass; the result would correspond to a fraction of a molecule, which is not meaningful in this context. Therefore it is incorrect.

Determine the number of moles of atoms in a 15.78 g sample of a metal whose molar mass is 72.59 g·mol–1.单项选择题

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