As we stated earlier, the unit of moles can act as a bridge that connects together the other units. So here we can see that moles rise right in the middle between grams and all the terms that we collectively call particles. Now if we take a look here at this example question, it says how many grams of CL2 contain 9.25×1024 molecules of CL2.
All right. So we're going to start out with our given amount which is 9.25×1024 molecules of CL2 and we have to get to our end amount over here. Now remember, we're going to say in order to get there, we're going to have to utilize some conversion factors and our end amount that we want to get to is grams of CL2. So if we take a look here, we need to get rid of molecules first. So our first conversion factor, we're going to say that we do 6.022×1023 molecules of CL2. And remember that connects us to Moles.
So for every one mole of CL2, then we're going to realize that molecules are out. Now we have moles. We're not there yet though, because we don't want moles at the end as our answer. We want grams. So our second conversion factor, which we saw earlier, would be that one mole of CL2 here on the bottom is 70.90 grams of CL2 here on the top here are moles would cancel out and we'd have our answer in grams.
Now when you do the math, make sure you put these in parentheses, otherwise your calculator may give you the incorrect answer. So we do 9.25×1024 * 70.90 divided by Avogadro's number here. Now, if you did this correctly, what you get initially is 1089.048 grams of CL2. But realize at this point we have three sig figs in our original value given to us. So we need this answer also to be in three sig figs. So we'd write that in scientific notation as 1.09×103 grams of CL2.
So here, writing it in scientific notation gives us our three significant figures which we had in the original question. 9.25×1024 given to us has three sig figs. So our answer must have three sig figs.
