Just as the mole connected the connection to particles, we can use moles as the connection to mass. Now we're going to say here 1 mole of a substance is equal to the molar mass of that substance. Remember the term molar mass? We can use molar weight, molecular weight, or molecular mass. They all mean the same thing.
Here we're told that one mole of still chlorine weighs 70.90 grams. What does that 70.90g come from? Well, if you look on the periodic table, you'll see chlorine, and you'll see that underneath chlorine or above it, you'll see a value of 35.45. That's the mass of 1 chlorine. But here we're dealing with two chlorines, so that would be 35.45 * 2, which gives us that value of 70.90.
Now here again, this can serve as a conversion factor in itself, where one mole of CL2 is 70.90 grams CL2, and since it's a conversion factor, we can also flip it where 70.90 grams of CL2 on top and one mole of CL2 on the bottom. Remember, we do this based on if we need to cancel out certain units. So just remember the moles can serve as a bridge to connect us to the mass of element or compound.
Now that we've seen this, let's move on to our example problem.