Finding Mass % Composition

[Jared Limqueco 3E]

So everytime there is a mass % comp question, I always just find each % using g/mol instead of converting everything to just grams first. I still get the right answer this way. It saves time and reduces the chances of a calc error, in my opinion.

I'm wondering if there is any scenario where converting everything to grams first is a necessary step? My TA and the textbook converts everything to grams first when dealing with these problems, so on the back of my mind I've been kinda doubting what I've been doing. Thanks in advance

[Benjamin Chen 1H]

What do you mean by "using g/mol"?

It seems like you're taking moles and turning it into grams if you're multiplying by g/mol (probably a molar mass?).

What would you do if you had gram sample? Like a 1.00 g sample has 0.112 grams of H and 0.888 grams of O, and you wanted to find the empirical formula?

[Jared Limqueco 3E]

What do you mean by "using g/mol"?

It seems like you're taking moles and turning it into grams if you're multiplying by g/mol (probably a molar mass?).

What would you do if you had gram sample? Like a 1.00 g sample has 0.112 grams of H and 0.888 grams of O, and you wanted to find the empirical formula?

Oh my b I was very unclear about my process. So let's say I was given just a formula, CH5O. I find the total g/mol first. Then, for each element, I take their g/mol and divide it by the total, so it would be something like C5 in g/mol divided by CH5O in g/mol, same for the rest. I don't convert anything to grams.

[SamayaJoshi1A]

Hi! I don't think this is a necessary step for any of the questions. Dr. Lavelle just does this to show that there is a ratio and that the percentages should add up to 100 percent.

[Moura Girgis 1F]

Hi! I don't think this is a necessary step for any of the questions. Dr. Lavelle just does this to show that there is a ratio and that the percentages should add up to 100 percent.

I agree, Dr. Lavelle just tries to show us the w=actual process, but it is not necessary.