Question

Gold crystallises in a face-centred cubic lattice. How many unit cells are there in a gold sample whose mass is 1.50 grams? The atomic weight of gold is 196.97 g mol^-1.

Select one:

a. 1.15 x 10²¹ unit cells

b. 2.29 x 10²¹ unit cells

c. 3.28 x 10²⁰ unit cells

d. 3.86 x 10²¹ unit cells

e. 9.17 x 10²¹ unit cells

Answer 1

no of moles = mass of gold /atomic weight of gold

                   = 1.5/196.97 = 0.0076 moles

one mole contains 6.023*10²³ atoms

0.0076 moles contains = 0.0076*6.023*10²³ = 4.57*10²¹ atoms

four atoms in one unit cell

4.57*10²¹atoms = 4.57*10²¹/4 = 1.15*10²¹unit cells

fcc contains four atoms = 4.57*10²¹ unit cells/4= 1.15*10²¹ unit cells>>>>>>>answer A