To convert grams (g) of a substance to moles (mol), you need to divide the mass by the molar mass of the substance.
The molar mass of Be(NO2)2 can be calculated by adding the molar masses of its constituent atoms, which are:
The molar mass of Be: 9.01 g/mol
The molar mass of N: 14.01 g/mol
The molar mass of O: 16.00 g/mol (there are two oxygen atoms in the nitrite ion, NO2-)
So the molar mass of Be(NO2)2 is:
9.01 g/mol (Be) + 2(14.01 g/mol (N) + 2(16.00 g/mol (O)) = 9.01 g/mol + 28.02 g/mol + 32.00 g/mol = 69.03 g/mol
Now we can use this molar mass to convert 11.9 g of Be(NO2)2 to moles:
moles = mass/molar mass
moles = 11.9 g / 69.03 g/mol
moles ≈ 0.1727 mol
Therefore, 11.9 g of Be(NO2)2 is equivalent to approximately 0.1727 moles.