Molar Mass

[Shana Patel 1C]

When a question requires us to calculate anything that needs molar masses, should we use the molar mass on the periodic tables that we have? e.g H- 1.00794 (6 sig figs)
Is there a specific amount of sig figs we should use or it just depends on the periodic table given?

[Simi Kapila_3E]

In his examples, he usually uses 4 or 5 sig figs (usually 3 numbers after the decimal place), so I would say stick to that amount.

[Jonathan3B]

Usually weather you put in the precise molar mass (EX: O-15.99), round it ( EX: O from 15.99 to 16), or "simplify" it (EX: O from 15.99 to 15.9) you will still be able to get the correct answer, so I think its up to personal preference and the specific molar mass. So for me I will enter C as 12.01 instead of 12.011 because it is easier and the difference is minimal.

[AntonioZarich2E]

I generally leave the numbers as they are on the periodic table in my calculator, and then round to the hundredths in the answer. This worked for the Sapling homework.

[Sondia Luong 1C]

Thanks for asking this question because I never considered significant figures when calculating the molar mass! I've never had any accuracy issues in my solution due to round off errors in molar mass. It should be fine if you round off the mass of the elements on the periodic table to the nearest hundredth.

[Armen_Isayan_2L]

Hello! When a question requires us to calculate anything that needs molar mass, I personally use the precise numbers on the periodic table and then round to the number of sig figs necessary. As others have mentioned the number of sig figs which are usually utilized is 4 or 5, which is a solid amount to follow, depending on if there is a decimal point or not.

[Bai Rong Lin 2K]

When a question requires us to calculate anything that needs molar masses, should we use the molar mass on the periodic tables that we have? e.g H- 1.00794 (6 sig figs)
Is there a specific amount of sig figs we should use or it just depends on the periodic table given?

I believe the specific amount of sig figs you use for problems revolves around the numbers it gives you within that problem if I am correct.

[Sydney Jensen 3L]

I generally will stick to around five significant figures, but if the numbers are slightly different, there is not a huge impact on the final answer, especially when we have to round and cut it off at a certain number of significant figures for the final answer.

[Savannah Torella 1L]

Usually while calculating, I use all of the decimals given on the periodic table. I don't know how different it is for every table, but mine has three number after the decimal point. I use all of those decimal until the very end. I then round my answer by the same amount of decimal places given to other numbers in the problem. If no other problems are given, it is usually safe to round your answer to the hundredth place.

[Charlie Russell 2L]

Don't consider significant figures until you have your final answer. You will use the number of sig figs of the numerical data provided in the question, using THAT number of sig figs for your final answer. Be as precise as possible during computation ex. using the detailed molar masses provided on the periodic table when obtaining an answer (and yes, the periodic table values should suffice in our problems).

[Rayna Irving 2C]

The way I usually do it is I copy exactly what is written on the periodic table when calculating molar mass and wait to deal with significant figures until I get my final answer for the problem. Usually what I've found is that any rounding errors are so small they're insignificant and don't really affect the final answer.

[Madeline Ogden 3B]

I always check how many sig figs are being asked for and then add 1 or 2 extra when doing my calculations. For example, if the problem asks you to give an answer with 4 sig figs, I would do my calculations with 5 to 6. I think of it a lot like a haircut; you can always take more off but you can never add more on. In a similar way, you can always take a couple of sig figs off of your answer after rounding but you can never add more/make it more precise if you rounded before making your calculations. Hope this helps!

[Ruth Rosales 3D]

Hello!

When solving a problem, I use the periodic table given in the cover of the textbook. Regardless of the sig. figs. in the problem, I use the full value when doing the math, and once I get the final answer I round it up to the sig. figs. given in the problem.

[Gabriel Nitro 1E]

Hi,

Honestly, it depends on the situation. If you were provided a problem which gives you a specific variation of the molar mass of an atom, I would use that. If during the exam you were given an entire periodic table for the length of the test, I would use that. However, despite the variation, as long as the math is correct you should still get the same answer whether or not the molar masses of two different references are off by a 1000th of a place.

Hope this helps! :)

[Ashley Wagner 2A]

Hi!
I usually use the full molar mass on the periodic table when calculating unless the molar mass was given in the question. If it wasn't given then keep the full molar mass until the end where I finally apply sig. figs. to the answer.

[Kristina Krivenko 3I]

I usually write 3 numbers after the decimal place. That way it's precise enough for the calculations but also not too long to write down / memorize (so over time you memorize molar masses of most commonly used elements, such as carbon, oxygen, hydrogen, etc). After I'm done with the calculations, I refer back to the problem to check how many sig figs I should have in my answer.

[Adam Bustamante 1I]

During my calculations I write down whatever the periodic table has for molar masses and don't round until I get to my final answer (this prevents any errors or wrong number of significant figures). Then, I just look at the problem and find the lowest number of sig figs used and round the final answer to whatever that may be.

[Alexandra Salata 2L]

Yeah I think using the molar masses on the periodic table that he's given us for the midterm would be the most accurate. As for the sig figs, I think once you've calculated the answer, 3 sig figs will do. In your calculations, however, I would probably use the number exactly as it's given in the periodic table to make sure I don't mess up the next steps in the calculation.

[Shana Patel 1C]

Thank you for clarifying for me.

[Adrienne Yuh 2B]

I think the best way to do molar mass, and to be as accurate as possible, is to first take all the numbers without rounding and then do the calculations. At the end, you can round to get the most exact answer.

[emmaferry2D]

What I normally do is use the amount given on the periodic table, then focus on the sig figs given in the equation to make my final answer. So basically calculate with the full molar mass without rounding, then round based on sig figs at the end of the problem.

[Gicelle Rubin 1E]

What I normally do is use the entire number from the periodic table and after I'm done with calculations, I round. :)

[Karina Grover 1A]

I don't believe that there are a specific number of significant figures that you should always use, but I find it better to use the molar masses specified on the periodic table to ensure that I yield the most accurate results always.

[Violet Kwan 3H]

For homework or sapling, I usually use two decimal places for molar mass. But on tests, I tried to be a precise as possible (for Oxygen I used 15.9994 instead of 16) and then find sig figs at the very end.