how many molecules are in 1.00g of iodomethane?

Question

how many molecules are in 1.00g of iodomethane?

Answer 1

The molecular mass of Iodomethane (CH3I) is 141.94 g/mol.

1g/141.94g/mol = 0.007 moles.

.007 x 6.02 x 10^23 = 4.21 x 10^21 molecules.

Answer 2

Atomic weights: C=12, H=1, I=127. Iodomethane is CH3I, so molecular weight is 142. Start with the 1.00gCH3I. Multiply by 1molCH3I/127gCH3I. The gCH3I cancel, and you get moles CH3I. Next multiply by 6.02x10^23 molecules CH3I/1molCH3I. The molsCH3I cancel, and you get number of molecules. 6.02x10^23 is Avogadro's number, so that's where that comes from. It helps to express 127 as 1.27x10^2, so you use exponential notation throughout.