Question

What is the number of formula units in a 4.27 mol sample of CaO ? formula units

Suppose you have two samples that are equal in weight, 32.332.3 g MoMo and 32.332.3 g Al2O3Al2O3.

Calculate the number of moles of each substance.

MoMo:

molmol

Al2O3Al2O3:

mol

Answer 1

1)

use:

number of formula units = number of mol * Avogadro’s number

= 4.27 * 6.022*10^23 units

= 2.571*10^24 units

Answer: 2.57*10^24 units

2)

a)

Molar mass of Mo = 95.95 g/mol

mass(Mo)= 32.3 g

use:

number of mol of Mo,

n = mass of Mo/molar mass of Mo

=(32.3 g)/(95.95 g/mol)

= 0.3366 mol

Answer: 0.337 mol

b)

Molar mass of Al2O3,

MM = 2*MM(Al) + 3*MM(O)

= 2*26.98 + 3*16.0

= 101.96 g/mol

mass(Al2O3)= 32.3 g

use:

number of mol of Al2O3,

n = mass of Al2O3/molar mass of Al2O3

=(32.3 g)/(1.02*10^2 g/mol)

= 0.3168 mol

Answer: 0.317 mol