1. Convert 2.00 g of H₂O to moles.
Usually, to convert from grams to moles we need the molar mass of the compound.
To get the molar mass of any compound we have to look for the atomic masses of the elements present in the molecule. We can use the periodic table.
atomic mass of H = 1.01 amu
atomic mass of O = 16.00 amu
One molecule of H₂O has 2 atoms of of H and 1 atom of O, then the molar mass is going to be:
molar mass of H₂O = 2 * 1.01 + 1 * 16.00
molar mass of H₂O = 18.02 g/mol
This means that the mass of 1 mol of H₂O is 18.02 g.
1 mol of H₂O = 18.02 g of H₂O
We can use that ratio or relationship to solve our problem.
2.00 g of H₂O * 1 mol of H₂O/(18.02 g of H₂O) = 0.111 moles of H₂O
Answer: 0.111 moles of H₂O
6. Convert 0.200 moles of H₂S to grams.
One mol is like a dozen. When we say that we want 1 dozen eggs, we mean that we want 12 eggs. When we say that we want 1 mol of eggs, we mean that we want to buy 6.022 * 10^23 eggs. It's a way of expressing a huge quantity.
The molar mass of a compound is the mass of 1 mol of it. So the molar mass of H₂S is the mass of 1 mol of H₂S. To find the molar mass we need the atomic masses of its elements.
If we look at a periodic table or search it on the web we will find that the atomic masses are:
atomic mass of H = 1.01 amu
atomic mass of S = 32.07 amu
amu means atomic mass unit, it's just the unit of the atomic mass. When calculating the molar mass of an element we replace the unit amu for g.
molar mass of H = 1.01 g/mol
molar mass of S = 32.07 g/mol
One molecule of H₂S has two atoms of H and 1 atom of S. One mol of H₂S molecules will have 2 mol of H atoms and 1 mol of S atoms. So to get the molar mass of H₂S we have to:
molar mass of H₂S = 2 * molar mass of H + 1 * molar mass of S
molar mass of H₂S = 2 * 1.01 g/mol + 1 * 32.07 g/mol
molar mass of H₂S = 34.09 g/mol
We found that the mass of 1 mol of H₂S molecules is 34.09 g.
1 mol of H₂S = 34.09 g of H₂S
We can use that relationship to find the answer to our problem.
0.200 moles of H₂S * 34.09 g of H₂S/(1 mol of H₂S) = 6.82 g of H₂S
Answer: 6.82 g of H₂S