Question

What mass of oxygen is contained in 5.5g of KClO3, and how many atoms of oxygen are there in this mass?

Answer 1

Can you find the moles of KClO3?

Answer 2

Yes. I worked it out this way but I am not sure if it right.
Number of moles of KClO3 =\[\frac{ mass of KClO3 }{ molar mass of KClO3 }\]
=\[\frac{ 5.5g }{ 122.64 }\]
= 0.045

Answer 3

Awesome! That's what I get.

Answer 4

Now, how many moles of O are there in 1 compound?

Answer 5

I suppose I have to work out the mole ratio, right?
K : Cl : O
1 : 1 : 3 x 0.045
Hence 0.135 moles of O

Answer 6

Sweet!

Answer 7

Now, can you convert to mass of oxygen from moles of oxygen?

Answer 8

Hint* you need the molar mass

Answer 9

0.135mol x16g =2.16. Is that right?

Answer 10

That's what I get :)

Answer 11

Do you know how to do the second part?

Answer 12

39.17 % of oxygen is contained in KClO3 molecule

Answer 13

The question asked for mass, not mass percent...

Answer 14

39.17% of 5.5 g = 2.16 g

Answer 15

By this way u can do it quickly

Answer 16

From moles of O you can use Avogadro's number to find number of atoms.

Answer 17

I am not sure how to do the second part, I need help please!

Answer 18

Calculate the moles of O [by dividing 2.16 by atomic mass of O] and then multiply the result by Avagadro number

Answer 19

0.135 mol O * (6.022x10^23 atoms O/1 mol O) = ? atoms O

Answer 20

0.135 mol x 6.02x10^23 = 8.127x10^22 atoms of oxygen

Answer 21

\(\huge\checkmark\)

Answer 22

Everything clear now ?

Answer 23

Perfect! :)

Answer 24

Thank you very much Abhisar and Joanna.

Answer 25

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Answer 26

and

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Answer 27

No worries :)

Answer 28

If were possible for me I would voted for both answers. You have tremendously helped me you both.

Answer 29

ahhan..!
It's okay..glad to help :)

Answer 30

@JoannaBlackwelder deserved it more :)

Answer 31

Thanks, @Abhisar for your help too! :)

Answer 32

No problem :)

Answer 33

\[Numbber of moles of KClO3=\frac{ mass of KClO3 }{ Molar mass of KClO3 }\

=\frac{ 5.5g }{ 122.64g/mol }\] = 0.045moles

mole ratio; K : Cl : O
1 : 1 : 3
number of moles O2 atoms = 0.045 x 3 = 0.135 moles
Mass of O2 in 5.5g of KClO3 = mole x molar mass
= 0.135 x 16g
= 2.16g

Number of O2 atoms = 0.135 x 6.02x10^23 = 8.127x10^22