Precision regarding molecular weights

[Melinda Luo 2G]

Whenever I am finding the molecular weight of an atom/molecule, is it crucial/necessary that I use the exact values from the periodic table, or would it be fine to round a little bit? For example, if I needed the molecular weight of carbon, can I just round the weight to 12 g, or do I have to do 12.011 g? In another instance, does chlorine have to be 35.45 g, or can I get away with using 35.5 g?

[Gabriel McDonald 1J]

I think a little rounding is okay. I generally go by what Dr. Lavelle uses in class (for example, 12.01 g/mol for carbon, 1.01 g/mol for hydrogen, etc.). But if I haven't seen an example from him using a particular element, or if I'm confused or not sure what to round to, I usually just round using sig figs.

[Neelaj Das 3I]

Using around 3-4 significant figures is standard I think. You probably don't want to go from 12.011 to 12, but using 12.01 is perfectly fine I think.

[Tammy Shen 2L]

I've been rounding to 4 significant figures and it's worked for me in completing the Achieve homework. Usually in class, Dr. Lavelle will round to 4 as well.

[Jason Ho 2L]

I would use what the periodic table gives up to 2 decimal places. Carbon has a molar mass of 12.011 g/mol, but I use 12.01 g/mol. It might not make a difference now, but rounding can make a huge difference later on when we are dealing with really small or large amounts.

[Syrah Tamola 3C]

Whenever I'm doing the homework, I refer to the periodic table that is listed in the additional resources in a question. But yes, I normally round to 3-4 sig figs.

[Kaethe Zappacosta 2L]

Whenever I use molecular weight I usually round to the hundredths place, and this seems to work pretty well. However, when solving something like empirical or molecular formula, I use as many sig figs as possible. This is because you have to find a molar ratio, so the molar mass of each atom must be precise.

[Hailey Sarmiento 3E]

Personally, I just copy the molar masses straight from whatever periodic table is closest, but rounding to the ones place for cases like .01 wouldn't hurt, as long as you don't need a number with specific decimals and you can find an answer closest to yours.

[Benicio Rivera 1F]

When we get the molecular weight where should we round? How many Sig Figs is too many sig figs?

[Mia Hansen 2I]

I don't think you need to round it if you're using the molecular weight mid problem. If it's your final answer, you need to make sure it's the appropriate amount of sig figs.

[Cassidy Chiong 2J]

I typically use 4 significant figures since that is the number of sig figs I normally see on periodic tables. I think the more sig figs, the better (in terms of elements) in order to end with the most precise answer as possible. So, it is okay to round to a certain extent, but I personally don't round to the point where my answer is inaccurate within the hundredths/thousands place.