problems with The Mole?

Question

Does anyone know how to calculate how many moles there are in something?

e.g i have been set a couple of questions by my tutor and i'm not sure where to start.

how many moles are present in the following?

5 g of copper CU
10 g of zinc
1 kg of potassium

how do you do the calculations?

thanks for any help.

Answer 1

For an element,

1 mole = the mass number expressed in grams

(Mass number can be found at the bottom of the symbol of the element in the periodic table)

http://www.iupac.org/reports/periodic_table/

For example, the mass number of copper is 64. Therefore:
1 mole of Cu = 64 grams

For compounds, simply add together the mass numbers. Then,
1 mol of the compound = the sum of all mass numbers

For example, water (H20) has 2 hydrogen and 1 oxygen atoms.
The mass number of hydrogen is 1, the molar mass of oxygen is 16. Therefore the mass of 1 mole of water is: (2 *1) + 16 = 18 grams.

After you know the above facts, it is easy.

To find the mole of Cu in 5g, simply divide 5g by 64 g, which is the mass of 1 mole of Cu. The answer is 0.078.

Do the same for all the others: simply divide the given mass by the mass number. When doing the last one, keep in mind that the mass is 1kg, which translates to 1000g.

Hope that helped

Answer 2

What you need to know is that:
no. moles = mass (g) / molecular weight

this is because all a mole is, is the molecular weight of the substance in grams. So Copper (Cu) has a molecular weight of 64, 1 mole of Cu weighs 64 g.

So using the formula: 5 g / 64 = 0.08 moles of Cu.

Taking the next one zinc: it's molecular weight = atomic mass (from the periodic table) is 65. Use the formula: 10 g / 65 = 0.15 moles of Zn.

Last one you can do yourself!!! It's always good to talk to your teacher though if you don't understand! :)

Answer 3

no. of moles=no. of grams/mass of one mole

a)5g of Cu--5/64=0.078125moles
b)10g of Zn--10/65=2/13 moles
c)1000g of K--1000/39= 25 wholes 25/39 moles

Answer 4

let Atomic Mass of Cu=M
then no: of moles =5g/M
Slry, No of moles of zinc=10g/M1
No:of moles of pottasium=1000g/M2
Where M1and M2 are the respective atomic masses
Thus, no:of moles is equal to no of grams of particles that conaines atomic mass or molecular mass

Answer 5

I think that if you are paying a tutor, they should at least ensure that you know how to do your homework. Either you are telling them you understand something when you don't or you need to get a tutor who actually teaches you stuff.

Answer 6

Divide mass by the atomic weight

Answer 7

http://www.gcsechemistry.com/imoles.htm
this site is about all mole calculations!!

http://dbhs.wvusd.k12.ca.us/webdocs/Mole/Grams-to-Moles.html

Answer 8

I'm having a problem with the question, LOL