Question

Moles of zn(no3)2 in 151.50 g of this substance.

Answer 1

moles = mass / molar mass

moles = 151.50 g / 189.4188 g/mol

moles = 0.80 mol

Answer 2

The number of moles,n, may be calculates as the mass in grams divided by the molar mass

n = mass / molar mass

The molar mass is calculated adding the masses of all the elements in the molecular formula.

In this case

Element Number of atoms(N) atomic mass (am) N*am

Zn 1 65.4 g/mol 65.4 g
N 1*2 = 2 14.0 g/mol 2*14.0 = 28.0 g
O 3*2 = 6 16.0 g/mol 6*16.0 = 96.0 g

Molar mass = total = 65.4 g/mol + 28.0 g/mol + 96.0 g/mol = 189.4 g/mol

n = mass / molar mass = 151.50 g / 189.4 g/mol = 0.80 moles