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Some Basic Concepts of Chemistry
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13/08/2021 12:07 pm
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A 25.0 mm × 40.0 mm piece of gold foil is 0.25 mm thick. The density of gold is 19.32 g/cm3. How many gold atoms are in the sheet? (Atomic weight : Au = 197.0)
(a) 7.7 × 1023
(b) 1.5 × 1023
(c) 4.3 × 1021
(d) 1.47 × 1022
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13/08/2021 12:35 pm
Correct answer: (d) 1.47 × 1022
Explanation:
Volume of gold foil = 25 × 40 × 0.25 mm3
= 250 × 10-3 cm3
Mass of gold foil = 19.32 × 250 × 10-3 g
= 4.83 g
No. of gold atoms = \(\frac{4.83}{197}\) x NA
= 1.47 × 1022