Moles to molecules?

Hello,





I'm quite in a pickle here, I'm really confused about moles, molecules and atoms. I have 20 questions on this assigned for homework and I don't get any. My textbook does not even explain anything.





Here are some.


How many moles of water does 6.02 x 10^23 molecules represent?


I really don't understand this... Could somebody reply with the way they would do this and the answer?





Here is another one.


How many moles of CaCl2 does 2.41x10^24 formula units represent?





I really don't understand this one either.








Thanks A TON.

Moles to molecules?
The first one is easy, and I hope this explains it for you. A mole consists of an "Avogadro's Number" of atoms, molecules, or whatever. That number is 6.02 x 10²³ So if you have 6.02 x 10²³ molecules of water, then you have EXACTLY one mole of it.





So let's look at Calcium Chloride (CaCl).


We have more than 6.02 x 10²³ molecules, so let's divide what we do have by 6.02 x 10²³ and see what we get.


When you divide powers of ten, just subtract the exponents to make it easier.


Now we have 24.1/6.02, or about 4 moles of CaCl.
Reply:A mole is defined as the quantity of a substance that has the same number of particles as are found in 12.000 grams of carbon-12. This number, Avogadro's number, is 6.022x1023. The mass in grams of one mole of a compound is equal to the molecular weight of the compound in atomic mass units. One mole of a compound contains 6.022x1023 molecules of the compound. The mass of 1 mole of a compound is called its molar weight or molar mass. The units for molar weight or molar mass are grams per mole. Here is the formula to determing the number of moles of a sample:





mol = weight of sample (g) / molar weight (g/mol)
Reply:The first one is 1. 6.02x10^23 is one mol, so that many water molecules is one mol of water.


I don't know about the second one, I don't have a calculator with me.





A mol is a set number used to easily find the exact number of molecules in a sample of an element... the atomic weight of an element (usually just under the element's atomic symbol) corresponds to real-world measurements.


for example, instead of one carbon atom weighing 12.010 amu (atomic weight units), 12.010 grams of carbon would be 6.02x10^23 atoms of carbon.





It's really a very useful number, I like it.
Reply:First you need Avogadro's number. I think it's 697-9567. No I'm just joking. It's 6.022 X 10^23. That is how many molecules that are in a single mole of anything.


Now, to find how many moles are in 2.41x10^24 form. units


You need to divide by Avogadro's number.


Here's why you should divide.


2.41 molecules 1 mole


---------------------- x -----------------------


1.0000000000 6.022 molecules


As you can see the molecules cancel and you are left with moles!