help with some sciency stuff:-) (moles)?

Question

can someone giv me a hand in explaining what moles are, and how you work out how many moles there are per ml(or wateva) coz we did it in science today and im not completely sure about it...can someone explain kinda the whole topic in kinda easy-to-understand terms

thanx xxxxxxxxx

Answer 1

I'm glad you're asking - the whole idea of 'moles' and 'Molar' confuses more people in the lab than almost anything else. OK; the previous answers gave you good theoretical definitions. Here's some practical stuff:
1. For lab purposes, 1 'mole' of a solid material is the formula weight (FW) or molecular weight (MW) in grams. For instance, you get a jar of Sodium Chloride (NaCl) and want to find out how much 1 mole is: on the label, it says "FW 58.44", meaning that when you add the atomic weights of Sodium (Na) and Chlorine (Cl) together, you get 58.44 (22.99+35.45=58.44). So, 1 mole of NaCl weighs 58.44g.
Why is this useful? Well, often in the lab you'll see a reference to "Molar" as a measure of concentration (like "a 4 Molar solution of NaCl"). "Molar", by the way, is generally abbraviated as capital M. "Mole" is generally abbreviated as "mol" with a small M.
A 1 Molar (1M) solution is 1 mole of material dissolved in 1 liter of water (or other solvent). A 4 Molar solution would be 4 moles of material per 1 liter of solvent.
Suppose you were asked to make a 4M aqueous solution of NaCl ("aqueous" meaning "dissolved in water")?
Easy, now you know what it means, right?
So, let's work it out - 1 mol of NaCl is 58.44g, so 4 mols would be 233.76g, right? So, you would weigh out that much NaCl and dump it into some water and stir it until it dissolves. Then you would carefully add more water until your final volume was 1 liter. 4 mols/L = a 4M solution.
Congratulations! You've made a lab reagent!
Now, how much NaCl would you need to make a 1/2 liter aqueous solution of 2M NaCl? (*tick* *tick* *tick*)

Answer 2

Avogadros constant is how many atoms that are in one mole. On the periodic table the weight of each element equals 1 mole.
So 1 mole of oxygen weights 16 grams.

I think you are talking about Avogadro's Law though.

Volume(1)/ Number of moles (1) = Volume (2)/ Number of moles (2)

The Volume and number of moles vary directly with each other. When one increases, so must the other. If you are given a chemical equation such as 3O(2) -> 2O(3), and you are told you have 1/2 mol of O(2), you can find how many moles of O(3) you need.

1/2 moles O(2) (2 moles O(3)/ 3 moles O(2))
The moles of O2 cancel out, leaving you .33 moles of O3.

Answer 3

A mole is the number of atoms or molecules which are the gram equivalent of the atomic (or molecular) weight. For example, the molecular weight of O2 is 16 * 2 = 32. Thus a mole of O2 weighs 32 grams.

The number of particles is Avogadro's number, 6.02 * 10^23

Answer 4

It's very easy really, but often badly explained by teachers, but this question should have been posted in 'chemistry'.
A 'mole' is 6.02 x 10^23. So, a mole of something, is 6.02 x 10^23 of it. It doesn't matter what that something is.
For example, a mole of marbles is 6.02 x 10^23 marbles (602,000,000,000,000,000,000,000 marbles). A mole of bricks is 6.02 x 10^23 bricks.
Why 6.02 x 10^23? It's called 'Avogadro's number, and it is chosen to allow atomic weight to be expressed in grams).

For example. What is the atomic weight of hydrogen?
1 gmol^-1 (The atomic mass is usually listed on the periodic table). So, 1 mole of hydrogen ATOMS is 6.02 x 10^23 of them. How much does 6.02 x 10^23 hydrogen atoms weigh?
1 g.

Another one: What is the atomic weight of carbon?
12 gmol^-1. So, 1 mole of carbon atoms is 6.02 x 10^23 of them. How much does that weigh?
12 g.

What is the MOLECULAR weight of H2?
2 gmol^-1. So, 1 mole of H2 MOLECULES is 6.02 x 10^23 of them. How much does that weigh?
2g.

Answer 5

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