The mass of a quantity of NiCl2 is 24.6 g. How many formula units are in the sample?
A. 3.2 3 1023 NiCl2 formula units
B. 5.3 3 10–21 NiCl2 formula units
C. 1.1 3 1023 NiCl2 formula units
D. 1.9 3 1027 NiCl2 formula units
To determine the number of formula units in a sample of a substance, you need to use Avogadro's number and the molar mass of the substance.
First, find the molar mass of NiCl2 by adding the atomic masses of each element:
Ni: 58.69 g/mol
Cl: 35.45 g/mol
Molar mass of NiCl2 = 58.69 + 2(35.45) = 129.59 g/mol
Next, calculate the number of moles in the given mass of NiCl2 by dividing the mass by the molar mass:
Number of moles = 24.6 g / 129.59 g/mol = 0.19 mol
Now, use Avogadro's number (6.022 x 10^23 formula units/mol) to convert from moles to formula units:
Number of formula units = 0.19 mol x (6.022 x 10^23 formula units/mol) = 1.14 x 10^23 NiCl2 formula units
Therefore, the correct answer is C. 1.1 x 10^23 NiCl2 formula units.
mols = grams/molar mass
In this case formula unit is that for NiCl2 in what I've called molar mass above. In this case, mols = formula units.