When carrying out mole conversions use the following formula;
n = m / M
n = moles
m = mass (g)
M = molar mass (gmol^-1)
e.g. convert 0.116 mol of NO2 into mass (g)
m(NO2) = n(NO2) x M(NO2)
= 0.116mol x [(1 x 14) + (2 x 16)]gmol^-1
m(NO2) = 5.336 g
the second part of your question can be solved by using the Avogadro's constant;
N(subscript A) = 6.02 x 10^23 mol^-1
Avogadro's number is the number of particles present when the amount of material is the same as the atomic weight (or relative molecular mass, or relative atomic mass or weight) expressed in grams. This is one mole of the substance. For example, with water, H2O, the relative molecular mass is 18 (16 for oxygen and 1 for each of the two hydrogens), so in 0.036 lb (18 g) of water there are 6.023 x 1023 HOH molecules. With a gas there is a slight difference because the gas may be encountered in the diatomic state in the atmosphere. For example, oxygen and nitrogen in the atmosphere are generally encountered as O2 and N2 respectively. With these diatomic molecules, there is an Avogadro's number of diatomic molecules in the amount of gas that is equivalent to the relative molecular mass. There may be an ambiguity if correct terminology is not applied. One mole of oxygen could refer to one mole of oxygen atoms (6.023 x 10 23 atoms) or it could refer to one mole of diatomic, gaseous oxygen, one mole of oxygen molecules (12.046 x 1023 oxygen atoms). The first case is elemental oxygen and the latter is molecular oxygen. A mole of anything contains the Avogadro number of those objects, whether it be a mole of atoms, molecules, or ions.
e.g. 8.17*10^24 molecules of NH3
M(NH3) = 17gmol^-1
This number, 17, is the mass of one mole of NH3. One mole of NH3 is 6.022 x 10^23 molecules of NH3 (Avogadro's number).
=8.17*10^24 molecules of NH3 / 6.022 x 10^23
=13.56692129 moles of NH3
As a result, there are 8.17*10^24 molecules of NH3 in 13.56692129 moles of NH3 .
hope this helps:-)
· 1 decade ago