To determine how many molecules are in a sample of a pure solid compound, in addition to Avogadro's number, the student must know:
- The mass of the sample (in grams)
- The molar mass of the compound (the mass of one mole of the compound in grams)
With these two pieces of information, the student can calculate the number of moles in the sample using the formula:
moles=mass of samplemolar mass\text{moles}=\frac{\text{mass of sample}}{\text{molar mass}}moles=molar massmass of sample
Then, the number of molecules can be found by multiplying the number of moles by Avogadro's number (approximately 6.022×10236.022\times 10^{23}6.022×1023 molecules per mole):
number of molecules=moles×Avogadro’s number\text{number of molecules}=\text{moles}\times \text{Avogadro's number}number of molecules=moles×Avogadro’s number
Thus, knowing the molar mass and the mass of the sample, along with Avogadro's number, allows the student to determine the number of molecules in the sample
. The correct choice reflecting this is:
- Molar mass of the compound and mass of the sample
