BR chemistry

[yingao88]

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Given two compounds A and 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 ?

A. Mixture of 1.0 g of compound A and 1 g of compound B
B. mixture of 1 ml compound A with 1ml compound B.

 

[ih371990]

Given two compounds A and 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 ?

A. Mixture of 1.0 g of compound A and 1 g of compound B
B. mixture of 1 ml compound A with 1ml compound B.

Try plugging in arbitrary numbers for A and B and calculate. Say like 100g/mol for B and 1g/mol for A. And 100g/ml for A and 1g/ml for B. Should be a relatively fast calculation for you to compare statement A and B (convert to moles, calculate mole fraction).

I think a lot of these types of questions can be approached this way, as long as the numbers you are plugging in are true according to the premise in the given question.

 

[shoehornlettuce]

Given two compounds A and 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 ?

A. Mixture of 1.0 g of compound A and 1 g of compound B
B. mixture of 1 ml compound A with 1ml compound B.

For choice A: If you have 1.0g of each compound A and B and compound B has a higher molecular mass, then you will have more molecules of compound A in 1.0g and thus a greater mole fraction.

For choice B: Same as above, you will have a greater mole fraction of A, however, I think this is the answer they are looking for. The question asks for the "greatest" mole fraction of A implying that A can have the greater mole fraction in both scenarios. Because A is more dense than B, you can fit more raw weight of A in a specific volume than you can B and so it will have the greatest mole fraction of the two scenarios shown.

Kind of a tricky question but I think that is what they are looking for.

 

[chem4ever]

Given two compounds A and 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 ?

A. Mixture of 1.0 g of compound A and 1 g of compound B
B. mixture of 1 ml compound A with 1ml compound B.

When I was doing this question, it drove me crazy. Then I figured it out. Best feeling ever.

For answer B, since A is denser than B, then you get more grams A per mL of A than grams of B per mL of B. So in this mixture, you have more grams of A then grams of B.

Now without even going to the next step mathematically, think about this conceptually. If you have more grams of A than grams of B, then compared to answer A, you will definitely have a higher mole fraction of A. In fact, you can change the two answer choices to this:

A. Mixture of 1.0 g of compound A and 1 g of compound B
B. mixture of more grams of compound A than grams of compound B.

If in answer choice A, there's an equal number of grams of A and B, and in answer choice B, there's more grams of A than grams of B, then which one will have the higher mole fraction?

Now, the molecular mass thing is a little confusing. I don't remember the other two choices off hand but I believe you need the molecular mass thing to eliminate the other choices.

 

[Temperature101]

Given two compounds A and 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 ?

A. Mixture of 1.0 g of compound A and 1 g of compound B
B. mixture of 1 ml compound A with 1ml compound B.

This question is somewhat similar with a question in the Phase Change chapter...I mised 3 out of 7 question in that passage alone.