So IUPAC now reports a range for the molar mass. If you really want to know a precise molar mass for some experiment, you should measure the isotope composition of your sample. That's long been known (and i have had students ask about the issue). The molar mass for the element depends on the isotopic composition - and that varies.

In fact, there is a real problem with molar masses, that has caused IUPAC to make a major change in how they are reported. Molar masses are known to ridiculous precision.

But any good scientist would not approximate and actually look up the conversion, there by making the conversion the most precise thing in your calculations. If you use approximations, then no shit it will not be precise. There is a known conversion with way more precision you will ever be using in the lab, which is why it is not considered for sig figs. It doesn’t matter if you going from metric to American either. It’s a known rule in chemistry that, unless you are working at a particle accelerator, the molar mass contains way more precision than what you are measuring, therefore, you do not use it as a limiting factor for sig figs.Īlso, conversions are EXACT measurements. Even the masses on periodic tables are rounded to 3 or 4 decimal places, but known values extend way further. No measurement you will ever make in lab will ever even be close to this precision, so the sig figs of the molar mass are not considered. A screenshot is preferable to a picture of your laptop screen.Īlright Mr. Please do not ask for help acquiring, preparing, or handling illicit substances or for help with any activity that does not fall within the confines of whatever laws apply to your particular location.īonus points: If submitting a picture please make sure that it is clear. Any infractions will be met with a temporary ban at the first instance and a permanent ban if there is another. It is also important that you describe the specific part of the problem you are struggling with. It is OK if you are a little (or a lot!) stuck, we just want to see that you have made an effort. Please complete any questions as much as you can before posting. We will not do your homework for you, so don't ask. Please flair yourself and read over the rules below before posting.

What is molar mass on periodic table