Question

Using the average atomic masses from the periodic table, calculate how many moles the following masses represent: a) 4.65g of C2H5OH, b) 7.94g of barium nitrate

Answer 1

Mole conversion: to get one unit you need to start with one unit.
a) start with the grams of ethanol: 4.65g
Then with your periodic table add up the weight: Carbon is 12 and there are 2 of them so 24g/mol + 6g/mol of hydrogen + and 16g/mol of oxygen = the molar mass of ethanol is 46.0g/mol. Now do the following:
4.65g of ethanol x 1 mol / 46.0g = 0.101 mol

4.65 has 3 sig figs and so does 46.0 therefore the answer has 3 sig figs