Question

(a) Calculate the number of oxygen molecules and the number of oxygen atoms in 34.5 g of O₂.

oxygen molecules =

×

10

      oxygen atoms =

×

10

Enter your answers in scientific notation.

(b) Calculate the mass of 8.99

×

10¹⁴ SO₃ molecules.

×

10

g

Enter your answer in scientific notation.

Answer 1

1)

Molar mass of O2 = 32 g/mol

mass(O2)= 34.5 g

number of mol of O2,

n = mass of O2/molar mass of O2

=(34.5 g)/(32 g/mol)

= 1.078 mol

number of molecules = number of mol * Avogadro’s number

number of molecules = 1.078 * 6.022*10^23 molecules

number of molecules = 6.49*10^23 molecules

number of atoms = 2*number of molecules

= 2*6.49*10^23 atoms

= 1.30*10^24 atoms

2)

number of mol of SO3 = number of molecules / Avogadro’s number

= (8.99*10^14) / (6.022*10^23)

= 1.493*10^-9 mol

Molar mass of SO3,

MM = 1*MM(S) + 3*MM(O)

= 1*32.07 + 3*16.0

= 80.07 g/mol

mass of SO3,

m = number of mol * molar mass

= 1.493*10^-9 mol * 80.07 g/mol

= 1.20*10^-7 g

Answer: 1.20*10^-7 g