More on stoichiometric ratio
Please don't read what follows if you are not really fluent in these calculations, as it may confuse you.
The interesting thing when using ratios, is that once you know what you are doing, you can alter the numbers of moles and masses in your setup to make calculations easier and faster. Or you can change the way ratios are created.
Let's get back to the calcium carbonate example and calculate, what is the mass of calcium carbonate that reacts with 0.3 mole of HCl?
|100.1 g||:||2 moles|
|x g||:||0.3 mole|
Ratio looks this way:
100.1 g : 2 moles = x g : 0.3 mole
and x = 15.01 g
The same can be solved with ratio set as
100.1 g : x g = 2moles : 0.3 mole
which is a side effect of proportion properties.
You don't have to use the same units in all columns, but in every column you must use only one unit - be it mole or mass. However, for calculations invloving both moles and masses dimensional analysis can be better, as it makes mistakes more difficult.
Also note, that once you've decided to use masses, then it doesn't matter what units you use. You can enter grams in first row, and tons in the second, the results will be correct. Once again, dimensional analysis makes mistakes more difficult, but if you have mastered ratio calculations you will probably finish them faster.