Homework Help! (Chemistry)

This is precisely why I'm a Communication Studies major...

 

Well, a mole is equal to 6.023X10^23 atoms/molecules/particles.

So, multiplying that by 2.78 = 1.67X10^24, for the first question.

Hopefully, you can do the rest. Good luck.

 

Yes.

Let me know what you get on your homework. Hopefully, I didn't lead you astray.

 

If you need to show your work (you probably do):

given # moles / 1 X 6.02 x 10^23 particles / 1 mole


BTW, all of your given measurements have three significant digits, so your answer should as well. My class has a test on mole problems tomorrow.

 

actually you multiply it by Avogadro 's number (6.023x10(to the 23rd power)). same applies for c. btw.

for b and d, is formula units the molar mass of the molecule or something like that? if so, you get the mass of the molecule and multiply by the number of mols. correct me if i'm wrong btw.

 

Doesn't B only have 2? Its been awhile since I had to figure this out, so I could easily be wrong.

 

No, formula units is functionally equivalent to molecules. It's used for ionic compounds that aren't made of individual molecules like covalently bonded compounds. You would only use a formula mass if the question asked for the number of grams.

 

No, the zero at the end of a number, after the decimal point, is a measured digit. It shows the precision of the measurement. There's a difference in meaning between 0.5 and 0.5000.

 

atoms = Avagadro's number x mol

molecules = mol x molecular mass (m=n x M)

a formula unit is the empirical formula of an ionic or covalent compound and is the lowest whole number ratio of ions

so in this case as KCl and NaI are ionic and in lowest ratio, molecules = formula units

 

This is incorrect. The formula you have given will find mass (m), not the number of molecules.

Also, in my experience, formula unit is only used for ionic compounds, never covalent.

 

Ah, got it, thanks! Like I said it has been awhile, about 15 years.

 

Isn't the answer just "Jesus"?

But seriously folks...

Get really comfortable with Avagadro's number, you'll have it etched in your brain by the time you're done with Moles. It's a bit difficult to get your head around but it's just another unit of measurement. Just like 6.02X10^23 carbon atoms is a mole of carbon, the same number of oranges is a mole of oranges. But, whereas we'd have no idea of how much a mole of oranges weighs, we're lucky in that one mole of any element's atoms will weigh exactly it's molar mass in grams.

 

just double checking. didn't see formula units much.

 

A good way to think of it is as a counting unit, like a dozen, only much, much bigger. Just like a dozen is 12 of something, regardless of what the something is (like eggs, donuts, etc.), a mole is 6.02 x 10^23 pieces of something, regardless of what the thing is.

 

The key here is that a mol or ANYTHING always has the same number of particles. That is the whole point of the "mol". It makes the math really easy. Chemists invented the mol back when no one had calculators. Some smart guy figured out that if you used molls rather then grams you don't always have to divide or multiply buy some ugly number that you really don't know exactly.

Call the number o particles per mol "A" so then 2 mol has 2A particles and 2.435 mol has 2.435A particles and so on.

 

edit: remove dup. (how to dups get in here?)

 

Also delicious in salad.

 

my mistake… whats the formula?

i got the Forumla Unit definition from Wikipedia

 

What do you exactly do with one of those?

 

Become somebody's spokesman.

 

Something about the Ideal Gas Law rings a bell but I'm not sure. Been years since they bestowed that bloody degree on me.