Question

Chalcopyrite, the principal ore of copper (Cu), contains 34.63 percent Cu by mass. How many atoms of Cu can be obtained from 5.11 x 103 kg of ore? A) 1.68 x 1028 Cu atoms B) 1.68 x 1025 Cu atoms C) 6.77 x 1031 Cu atoms D) 6.77 x 1034 Cu atoms

Answer 1

Answer:

A) 1.68 x 10²⁸ Cu atoms.

Explanation:

∵ The mass of Cu in the chalcopyrite ore = mass of the ore x weight fraction of Cu.

• Weight fraction of Cu = Weight % / 100 = 34.63 /100 = 0.3463.

∴ The mass of Cu in the chalcopyrite ore = mass of the ore x weight fraction of Cu = (5.11 x 10³ kg)(0.3463) = 1.77 x 10³ kg.

• We need to calculate the no. of moles of Cu atoms:

n of Cu = mass/atomic mass of Cu = (1770 x 10³ g) / (63.54 g/mol) = 27.853 x 10³ mol.

• We have that every mole of an element contains Avogadro's no. of atoms (6.022 x 10²³).

∴ 27.853 x 10³ mol of Cu contains = (27.853 x 10³ mol)(6.022 x 10²³) = 1.677 x 10²⁸ Cu atoms ≅ 1.68 x 10²⁸ Cu atoms.