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Question
Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is 9.1×10–28 g). Which one is heavier?
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Solution
Mass of 1 mole of aluminium atom = 27g mol−1
Al − 3e− → Al3+ (3 moles of electrons)
Mass of 3 moles of electrons
= 3 × (9.1 × 10−28) × 6.022 × 1023 g
= 0.00164g
Molar mass of Al3+ = 27 − 0.00164g mol−1
= 26.9984g mol−1
Difference = 27 – 26.9984
= 0.0016 g
1 mole of Al atoms is heavier than 1 mole of Al3+ions.
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