[steph_r]

hello all!
i was given a chemistry worksheet on the mole and no answers. I did my best to work them out (promise you).. but i dont have answers or workings to compare my own with. As you know, the mole is very important in chemistry. Im in yr 11 and guidance would be greatly appreciated. 

here are the questions that i need guidance for to be able to compare:

(a) actual number of atoms in 0.125g of Sulfur Dioxide?
( if number of mole is 0.0020, then do you multiply by avogadro's constant and then by 3 because there are 3 atoms in S02? )

(b) amount of moles present in 20g of water

(c) amount of moles present in 2kg of iron

(d) Amount of hydrogen atoms in 2 moles of Hydrogen, 2 moles of water and 20g of H2PO4

(e) moles of oxygen in: H2O, 1 mole of C02 and 0.2 moles of sulfuric acid

(f) If i have 6 moles of CO2, how many moles of oxygen and carbon atoms do i have?

(g) number of moles present in 88.0g of CO2


THANK YOU IN ADVANCE!

[Astrokel]

( if number of mole is 0.0020, then do you multiply by avogadro's constant and then by 3 because there are 3 atoms in S02? )

Yes!, show your attempts?

[steph_r]

Yes .. here are my attempts (sorry if they're hard to understand)

(a) actual number of atoms in 0.125g of Sulfur Dioxide?

if number of mole is 0.0020, then do you multiply by avogadro's constant and then by 3 because there are 3 atoms in S02?

(b) amount of moles present in 20g of water

n = m/Mr
n = 20/16
n = 1.25mol -  - -  or do you multiply by avogadro's constant? How do you know when to multiply by avogadro's constant?

(c) amount of moles present in 2kg of iron

n = m/Mr
n = 2000(g)/55.85
n = 35.81mol

(d) Amount of hydrogen atoms in:
- 2 moles of Hydrogen  ( 2 x 6.02 x 10^23 = 1.20 x 10^24 ??)
- 2 moles of water ( 2 x 6.02 x 10^23 = 1.20 x 10^24 x 2 = 2.4 x 10^24 ??)
- 20g of H2PO4 (n = m/Mr = 20/95.97 = 0.21 x avogadro's x 2= 2.53 x 10^23 ?)

(e) moles of oxygen in:
- H2O  ( 6.02 x 10^23 ?)
- 1 mole of C02 (1.2 x 10^24 ?)
- 0.2 moles of sulfuric acid (4.82 x 10^23 ?)

(f) If i have 6 moles of CO2, how many moles of oxygen and carbon atoms do i have?

** not too sure about how to do this one


(g) number of moles present in 88.0g of CO2

n = m/Mr
n = 88/44
n = 2  - - -but do you times by Avogadro's constant to get 1.2 x 10^24 or just leave it at 2?

[Sev]

b)
n = m/Mr
n = 20/16
n = 1.25mol -  - -  or do you multiply by avogadro's constant? How do you know when to multiply by avogadro's constant?

There is no need to use the Avagadro constant here.  Use it when converting between moles and molecules etc.
Also, molar mass of water is 18gmol^-1, otherwise procedure is OK 

[steph_r]

Thank you for your help. greatly appreciated

[Astrokel]

(f) If i have 6 moles of CO2, how many moles of oxygen and carbon atoms do i have?

** not too sure about how to do this one

Hey!

1 mole of CO2 contains 1 mole of C atom and 2 moles of O atoms. I guess you know this as can be seen from your understanding of other questions.

So i guess you could work out the moles if there is 6 moles of CO2?