Mass percentage

breannasung_1K
Posts: 30
Joined: Fri Apr 06, 2018 11:05 am

Mass percentage

How do you do a mass percentage problem if the percentages for the given elements do not equal 100?

annie_finneran_1K
Posts: 37
Joined: Fri Apr 06, 2018 11:02 am

Re: Mass percentage

I would say most likely that wouldn't happen as that does not make sense. If they do not add up to 100 maybe double check your math, or maybe another element is simply not being mentioned.

Brynne Keyser 1B
Posts: 31
Joined: Fri Apr 06, 2018 11:03 am

Re: Mass percentage

You have to find the mass of the elements that are given and convert the masses to percentages, assuming that it is out of 100%. It should always add up to 100 if you carry out the problem in this fashion.

Hope this helps!

Isabel Jabara 1C
Posts: 34
Joined: Fri Apr 06, 2018 11:03 am

Re: Mass percentage

Mass percentages should always add up to 100%. If yours don't, maybe you calculated something wrong, or maybe the question did not explicitly give you all the information. For example, if it is a combustion problem, the question might not have given you information about the O2 that is in the reactants, and you might have to calculate this mass percentage by yourself.

Chiara Berruto 1K
Posts: 29
Joined: Fri Apr 06, 2018 11:01 am

Re: Mass percentage

It should always add to 100% but I remember Dr. Lavelle stating that it is a combustion reaction and the mass percentages given do not add up to 100 then it is likely the oxygen that is being left out and will make up the difference.

Posts: 15
Joined: Mon Apr 09, 2018 1:39 pm

Re: Mass percentage

I am pretty sure if it is a combustion problem you just assume whatever % is left is the oxygen, but for any other problem I believe it should add up to 100.

Rummel Requerme 1E
Posts: 35
Joined: Fri Sep 25, 2015 3:00 am
Been upvoted: 1 time

Re: Mass percentage

There should be no loss of mass, as stated in the law of conservation of mass. If there were a case in which it does not add up to 100%, for instance, combustion, then it's safe to assume the missing portion is oxygen.

Hope_Pham_1G
Posts: 29
Joined: Fri Apr 06, 2018 11:04 am

Re: Mass percentage

100 grams is merely a value that facilitates the conversion from mass percentage composition to actual mass composition. Rather than multiplying the percentage by 100 (and essentially only moving decimal points), you multiply by the specific given grams of the sample.

juliaschreib1A
Posts: 29
Joined: Fri Sep 29, 2017 7:06 am

Re: Mass percentage

The mass percentages have to equal 100% because all the elements together must add up to the total molecule. However, you may be confused for the next step in solving an empirical formula problem, when we are asked to assume that the elements are part of a 100 gram sample. This simply just makes the math easier and quicker.