86.2 grams C2H4 to moles (explain steps please)?

Question

86.2 grams C2H4 to moles

0.943 mole H20 to molecules

7.74 x 10^26 formula units Al2O3 to moles

91.9 grams NH4IO3 to formula units

6.63 x 10^23 molecules C6H12O6 to moles

Answer 1

find mass of C2H4
C = 12 x 2 = 24
H = 1 x 4 = 4
mass = 28

86.2 / 28 = moles

moles x Avogadro's number = number of molecules
0.943 x (6.02 x 10^23) = molecules

units divided by Avogadro's number = moles
7.74 x 10^26 / (6.02 x 10^23) = moles

91.9 g divided by mass = moles
moles x Avogadro's number = formula units

6.63 x10^23 divided by Avogadro's number = moles

Answer 2

Each element and compound has a "molecular weight". The molecular weight is just how many grams are needed to make one "mole". A "mole" is a fixed number of atoms, 6.023 x 10^23.

The atomic weight of carbon is 12. One mole of carbon weights 12 grams. The molecular weight of oxygen is 16, there are 16 grams of oxygen per mole.

If you want to make carbon monoxide, CO, you need one atom of carbon and one atom of oxygen. Unfortunately, we can't measure or count individual atoms, but we can measure the weight of things very accurately.

If you weigh out 12 grams of carbon, and 16 grams of oxygen, you have one mole of each, and each mole has 6.023 x 10^23 atoms in it, so you have exactly enough carbon and oxygen to react to CO with none leftover.

In real life, no one reacts exactly one mole of anything, instead they weigh out what they need, and divide by the molecular weight to calculate how many moles they actually have.

So if you had only 9 grams of carbon instead of 12, you have 9/12 = 0.75 moles of carbon. To make CO you need 0.75 moles of oxygen. Multiply 16 grams/mole x 0.75 moles = 12 grams of oxygen needed for this reaction.

Always try to look up the molecular weight in a reference table. Although many elements have a molecular weight very close to a round number, you need the EXACT molecular weight for stoichometry calculations.

So first thing you usually need to do, is look up the molecular weights of your element or molecules.


For C2H4 (ethylene gas, or ethene) the molecular weight is 28.05 grams/mole.

86.2 grams C2H4 / 28.05 grams/mole = 3.07 moles


One mole of H2O (water) contains 6.023 x 10^23 molecules. You only have 0.943 moles of water.

6.023 x 10^23 molecules/mole x 0.943 moles = 5.68 x 10^23 water molecules


Al2O3 is aluminum oxide. You have 7.74 x 10^26 molecules. A mole only contains 6.023 x 10^23 molecules.

7.74 x 10^26 / 6.023 x 10^23 = 1,285 moles of aluminum oxide


NH4IO3 is "Iodic acid (HIO3) ammonium salt", with a molecular weight of 192.94 grams/mole. You have only 91.9 grams.

91.9 grams / 192.94 grams/mole = 0.48 moles of NH4IO3

0.48 moles x 6.023 x 10^23 = 2.9 x 10^23 molecules


C6H12O6 is a carbohydrate (sugar), which particular one, is not specified.

One mole = 6.023 x 10^23 molecules. You have 6.63 x 10^23 molecules.

6.63 x 10^23 molecules / 6.023 x 10^23 molecules / mole = 1.1 moles of this sugar.