15 posts • Page 1 of 1
When trying to find the molecular formula & we put the molar mass of molecular formula over the mass of the empirical formula we found, is the number supposed to be a whole # or can it be like 1.23? If it can be 1.23, do we round when we multiply it by the subscript of the elements in empirical formula??
The molecular formula should be complete multiples of the empirical formula, or very close to whole numbers. The questions should be designed so that there is little ambiguity.
Yeah, it should be a whole number when you multiple it. If you get a decimal of some sort I believe it should be so close to a whole number value. Ex: 4.98-5.01 (would round up or round down respectively to get 5)
Yea, it should be a whole number. The questions are usually phrased in a way in which the multiple of of the molecular to empirical formula is easy to work with. However, there may be examples where the multiple is "3.99" or "4.02". In this case, you would round to the nearest whole number.
The factor that you get after dividing the molecular mass by the empirical mass should be an integer, or really close (I think if you can round from the hundredths place to an integer it's close enough). If you don't get an integer than re-check the empirical formula or empirical mass. It's really easy to type something in wrong on your calculator and mess up the whole problem!!
The video modules he has posted on his websites are very helpful. For this question he explains why there has to be a whole number for the empirical formula and if you multiply one number you have to do the same to the rest. Highly recommend if you have not checked it out.
How do you go from the molecular formula to the empirical formula if you aren't given a molar mass by mass spectrometry to compare to (and divide by) the molar mass you calculate using the molecular formula? In other words, how would we know what factor the empirical formula was multiplied by in order to get to the molecular formula?
Who is online
Users browsing this forum: No registered users and 1 guest