Question

determine the number of oxygen atoms in 8.18ng of Ba(NO3)2.

Answer 1

Molar mass of Ba(NO3)2,

MM = 1*MM(Ba) + 2*MM(N) + 6*MM(O)

= 1*137.3 + 2*14.01 + 6*16.0

= 261.32 g/mol

mass(Ba(NO3)2)= 8.18 ng = 8.18*10^9 g

number of mol of Ba(NO3)2,

n = mass of Ba(NO3)2/molar mass of Ba(NO3)2

=(8.18*10^-9 g)/(261.32 g/mol)

= 3.13*10^-11 mol

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

number of molecules = 3.13*10^-11 * 6.022*10^23 molecules

number of molecules = 1.885*10^13 molecules

1 molecule of Ba(NO3)2 has 6 oxygen atoms

so,

number of oxygen atoms = 6* 1.885*10^13

= 1.131*10^14

Answer: 1.131*10^14