Monday, November 16, 2009

Chemistry: Moles!?

1. How many grams are there is 3.4 x 1024* molecules of NH3?

* 24 is superscript

2. How many moles are present in 2.45 x 1023* molecules of diphosphorus pentoxide?

* 23 is superscript

Can you leave molecules they way they are (in the 1st question), or do you have to convert them to moles?

Please show your work! Thank you!

Chemistry: Moles!?
Reply:I will not do your work for you. But I can tell you how to do it (you'll need a periodic table and a scientific calculator (has EXP button)

1)First of all, yes, you must convert the molecules to moles. (by dividing molecules by Avogadro's constant)

Next, you multiply moles by the molar mass of NH3 (15g/mol)

That's it!

2) Just divide molecules by Avogadros (6.02 time ten to the 23)to get mol.
Reply:To convert from molecules to grams, you first have to convert to moles. I'll try my best to explain this for the first question. Then try to see if you can do the second one on your own. :)

1. You are given 3.4 x 10^24 molecules of NH3. To do this question, you need to find the atomic mass of NH3. Nitrogen's mass is 14, and hydrogen is 1, so the total mass is 17. Anyway, try to set up an equation in which you can cancel out terms, like this:

(3.4x10^24 molecules NH3) x (1 mol NH3/6.02 x 10^23 molecules) x (17 grams/1 mol).

If you don't already know, 6.02 x 10^23 is known as Avogadro's Number. 1 mol of any compound will have 6.02 x 10^23 molecules (or atoms if you are referring to an element). Dividing your given by this term is what allows you to convert to moles, and from there you can use the atomic mass to convert from moles to grams.

Hope that helps.
Reply:3.4X10*24 /(6.02X10*23)X17=.......

the second is the same as the first one

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