how many molecules are there in 5.0g of methyl alcohol, CH3OH?

Question

Please! Help! I suck at chemistry!!! THANKS!!!

Answer 1

This is easy:

The molecular weight of methanol is 32.04 grams per mole. You have 5.0 grams, which means you have 5.0/32.04 moles

5.0/32.04 = 0.156 moles

But one mole of ANYTHING (atoms, molecules, bottle caps, aluminum cans, rocketships, planets, etc.) is 6.023x10^23 items.

You have 0.156 moles, so:

0.156 * 6.023x10^23 = 9.4 x 10^22 molecules.

Answer 2

Well, you remember Avogadro's number don't you? That is the number of molecules in a mole of an element or compound with a value of 6.022 x 10^23 molecules/mole. From here you want to determine the molar mass of the compound in question, in this case methyl alcohol. You can look this up in a CRC Handbook or on www.chemfinder.com. If you want to do it the long way you can use your handy dandy periodic table and add up the atomic mass of each atom in the compound. With methyl alcohol you have 1 carbon at 12.01 grams/mole, 4 hydrogens at 1.01 grams/mole, and 1 oxygen at 16 grams/mole for a total molar mass of 32.04 grams/mole. Your question is in regards to 5 grams, right? Well, 5 grams of methyl alcohol is 0.156 moles (5 grams/32.04 grams). Now we can use Avogadro's number to determine the number of molecules in 5 grams of methyl alcohol. Just take how many moles of stuff you have (0.156 moles) and multiply it by 6.022 x 10^23 molecules/mole to get your final answer; 9.39 x 10^22 molecules. I took the long route so that you will understand the process. I hope this helps.