TBR Gen Chem Chapter 1 Question 47

[INOHELP]

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Given two compounds,Compound A and Compound B, and the fact that B has a higher molecular mass than A, but A is denser than B, which of the following mixtures would have the greatest mole fraction of A?

So in this case, having 1 gram of A and 1 Gram of B as well as 1 ml of A and 1 ml of B leads to a mole fraction that is greater than .5.

How do we know that the 1 ml of A and 1 ml of B leads to a greater mole fraction? It seems to me that if the molecular mass of A is small enough, it can have a high mole fraction of A?

 

[FeinMS]

Given that A is denser than B, you can tell that 1ml of A contains more g of A than 1ml of B contains g of B. Also note that B has larger molecular mass than A. To compare mole fractions of A and B, we can just compare moles of A and B in this case. mole=mass/molecular mass. moles of A has larger numerator and smaller denominator than B meaning moles of A > moles of B. Correct me if I'm wrong.

 

[DrBTS]

What an elegant question

 

[INOHELP]

I am still confused.

My question isn't answered.. unless I am just not interpreting it..

 

[Inygma]

Hey... I originally had your question, but figured it out.

It is true that 1g of A would have a higher than .5 mole ratio when mixed with 1g of B since A has smaller molecular mass. (EQUAL MASS OF A and B)

The reason C is the correct answer is because since we know A is more dense than B, we know there is more mass of A in 1 mL than there is mass of B in 1 mL. (MORE A than B)

Since we know mole ratio of A is greater than .5 when the mass of A and B is equal, we know that the mole ratio will be even greater for A if there is more mass of A than there is for B.

Does that explain it clear enough?