Values for Molar Mass

[Amy Jordan 2A]

Hi! I noticed that sometimes for certain elements different molar masses are used (rounded and not rounded), so I was wondering if it matters which value I use? Thanks so much!

[Cory Poon 3G]

I'm not too sure about this, but I think you usually select the values rounding to the hundredth place. Hydrogen would be 1.01, Carbon would be 12.01, Oxygen would be 16.00, Nitrogen would 14.00, and Chlorine would be 35.35.

[Madison Rhynhart 3H]

Hi I typically use the data given by the periodic table, as they are the most precise and will lead to a more precise answer later on. However you have to based the values for molar mass off of the significant digits you would like to get.

[Elena Chan 2L]

I think you should try to keep as many decimal places for molar masses as possible, but you must consider the amount of significant figures that the problem provides in the beginning. I would try to make it as specific as possible for calculating with molar mass and then adjusting the significant figures at the end.

[elletruchan2I]

Hi Amy!
I think when given the option you should always use the not rounded molar masses so that you can maintain a certain amount of significant figures/accuracy, but if you need a reliable resource for the periodic table and molar masses, I would suggest just using the one Dr. Lavelle provides on his website. That way your answers should always match up with what he gives.

[Vance Liu]

I usually keep two decimal places after each mass (H=1.01,c=12.01, etc.). That's just how I did it in HS chem and it keeps it precise enough without being ridiculously precise.

[Reece Fong 2k]

Just FYI, if you guys are using a scientific calculator, you can store values in it. For example, Avogadro's Constant: You can type 6.022E23 and then hit the STO button and then Alpha[Choose a Letter] and it will store it in that variable for future use. So instead of writing 6.022E23 every time, you can just put A.

[Sarthika Chimmula 3H]

Hi Amy! I would keep as many digits/significant figures in your molar masses as possible when doing calculations so that your answer is as precise as possible (I typically write out the molar mass to the thousandths place when calculating values). Your answer will typically end up having as many significant figures as the value that they provide to you in the problem, so it does not matter how many sig figs you use in your molar mass, but I would recommend being as precise as possible!

[Neha Mukund]

I would usually not round the molar masses before doing the problem because that could cause the final answer to be less precise. You could adjust the significant figures at the very end after doing all of the calculations. I have been using the periodic table on Professor Lavelle's website for all of our work.

[Simone Byun 1F]

I would use as many significant digits as you can for as long as possible. You can always round at the end.

[Alaura Dis 1H]

Hi, I typically go by the number of significant figures given in the problem, but if no numbers are given in the question, I usually round to the hundredths place. Mostly I just try to be consistent with how much I am rounding by.

[Harbaksh Kaur 3E]

I'd recommend using the most decimal places as you can because I've found that it usually gives me a more accurate answer!

[Minh Nguyen 3H]

Personally, I try to be consistent with how I round if the problem doesn't give me a specific number (if the problem does, then I just use the exact same number). This usually means I round to the thousandths place for all the numbers that I use.

[Kavya Anand 2B]

Hi, usually there’s no harm in being as specific and using as many sig figs as your given, you could also match it to the number of sig figs that are used in the problem.

[Jessica Servoss 1H]

I think for a more accurate answer, use what the periodic table provides directly- unless the question or problem states the molar mass as a rounded number.

[Coraly De Leon]

Hi,

Personally, I go with the exact number given in the periodic table to be more precise. Yet, I'm pretty sure in some scenarios, the problem will ask to round to a specific decimal place.

[Nishan Reddy 3K]

From what I have noticed from my discussion section, you can use whatever values of molar mass that you want (most likely the one from the given periodic table) as long as you round to the proper significant figures of the given values in the problem at the end of all of your calculations.

[Mia Orr 3B]

I usually use whatever value is given in the periodic table so my answer can be as accurate as possible, and save the rounding for my final answer. The only occasions where I don't do that is when the molar masses are stated in a problem, then I use the values given and go from there. Hope this helps! :)

[Hope Galarneau 1A]

Hi! I think as long as you round to either the hundredths or thousandths place your calculation should still be good depending on the number of significant figures you need. I would just make sure that you round the molar masses to the same decimal place to keep your final answer as error free as possible. However, if you do not want to round, having more sig figs in the molar masses shouldn't cause errors in your final answer. Thus, I would either round the molar masses to an appropriate number of sig figs or just keep it as it is when doing calculations.

[Lizzy Bulla 3K]

I would try not to round for as long as possible when you are doing your calculations until the very end.

As for the periodic table, there is one on Lavelle's chem14a website which I assume would be a good one to use for this class

[Mahika Saoji 3K]

Hi! I was confused about this at first too because my TA would round/wouldn't round for some numbers, but I found that being more specific/using the most decimals is the best way to go because it will give you an accurate answer!

[405479701]

Not rounding is better in order to get more accurate results/ solutions.

[Meia Schram 1J]

I would agree with a vast majority of these responses in that keeping the true value of the periodic table is best, especially a periodic table provided by Dr. Lavelle. When the sig figs of a problem are less than a possible molar mass of an element, that is the only time I would round.