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### Topic: Calculating Amounts of substances Moles  (Read 15368 times)

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#### jamesbrown

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##### Calculating Amounts of substances Moles
« on: January 23, 2016, 12:14:13 PM »
Hello I was just wanting to check if I got this question right.

How much sulphur dioxide would be made from 320 tonnes of sulfur.
If the equation is S+O2=SO2
that would mean the ratio would be 1 : 1 : 2
Also the mass would be 32 : 32 : 64
Which means that i would have to double the amount of Sulphur so it would be 320*2 = 640 tonnes
Is that right?
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#### Hunter2

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##### Re: Calculating Amounts of substances Moles
« Reply #1 on: January 23, 2016, 01:25:19 PM »
Yes corrrect. Better is to calculate via mole. 320 t Sulphur  corresponds 10000 kmol.  This correspond also to the SO2 . With the molar mass of 64 kg/kmol gives 640 t.

#### jamesbrown

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##### Re: Calculating Amounts of substances Moles
« Reply #2 on: January 23, 2016, 01:49:38 PM »
If 48 tonnes of iron ore is used in a blast furnace what would the the mass of iron be. If the equation is:
Fe2O3 + 3CO = 2Fe + 3CO2

Would I find the moles of iron oxide.
But I'm not really sure what to do after that?

Thanks
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Hunter2

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##### Re: Calculating Amounts of substances Moles
« Reply #3 on: January 23, 2016, 02:17:33 PM »
You calculate the moles of the 48 t Iron oxide.

If you have that then you can see the ratio of the moles of iron oxide to iron in the equation.

With the new mole value you calculate backwards to the mass of iron.

You need the molar masses of iron oxide and iron itself.
« Last Edit: January 23, 2016, 02:51:46 PM by Hunter2 »

#### AWK

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##### Re: Calculating Amounts of substances Moles
« Reply #4 on: January 23, 2016, 04:19:52 PM »
Just read the balanced reaction - one mole of Fe2O3 gives 2 moles of Fe.
AWK

#### jamesbrown

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##### Re: Calculating Amounts of substances Moles
« Reply #5 on: January 23, 2016, 04:23:51 PM »
So the moles of Iron oxide is 300000
So does that mean iron has 120000 moles
and oxygen has 180000 moles
and because in the equation we are making 2 iron does that mean the moles of iron is 120000*2=240000
then we need to find the mass of it so would it be i don't know could someone help?
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Hunter2

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##### Re: Calculating Amounts of substances Moles
« Reply #6 on: January 23, 2016, 04:42:40 PM »
No you get 300000 mole Fe2O3. This correspond according the equation to the double amount of iron. So the moles of Fe is 600000 moles.

This you have to calculate back to the mass of iron.

#### jamesbrown

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##### Re: Calculating Amounts of substances Moles
« Reply #7 on: January 23, 2016, 05:56:27 PM »
Can someone just give me a step by step method on how do do mole questions like these. I'm really trying to understand but Its quite complicated in my opinion. Here are a list of the question that I have to do. So yeah. Thank you for trying to help someone dumb like me.
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Burner

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##### Re: Calculating Amounts of substances Moles
« Reply #8 on: January 23, 2016, 10:02:55 PM »
If I am not mistaken,

(Number of moles)=(mass)/(molar mass)

So, (mass)=(Number of moles)*(molar mass)

Moreover, we uses mole ratio directly from the balanced equation. Take question 2 as an example, you have 300000 mol of Fe2O3. From the balanced equation, mole ratio of Fe2O3 and Fe is 1:2, i.e. 1 mol of Fe2O3 gives 2 mol of Fe. Thus, 300000 mol of Fe2O3 gives 600000 mol of Fe. Then, you have to multiply that 600000 mol of Fe with its molar mass, which is 56. Finally, you get 600000*56=33600000g of Fe, or 33.6 tonnes of Fe.

Year 1 science student in HKUST and a Chemistry geek.
If I make any mistakes in the forum, please don't hesitate to correct me as I want to learn.

#### Hunter2

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##### Re: Calculating Amounts of substances Moles
« Reply #9 on: January 24, 2016, 07:01:56 AM »
Generally the steps are:
1. Write chemical equation if it is not given.
2. Calculate the given mass into moles as described n = m/M, n [mole], m [mass] and M [molar mass]
3. Check how much moles correspond to the material what you looking for (Fe2O3 to Fe here 1:2)
4. Calculate back to the mass with the formula given in 2.
« Last Edit: January 24, 2016, 07:32:13 AM by Hunter2 »

#### jamesbrown

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##### Re: Calculating Amounts of substances Moles
« Reply #10 on: January 24, 2016, 08:13:20 AM »
For question 3 I have worked out the amount of moles for sodium chloride which is 136752.1368
but then for the ratio would it be 3:2:1 so i would have 91168.0912 moles of sodium and then i would have 45584.0456 mole of chlorine.
Is this right I don't know.
Then if this is right what would i do next?
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Hunter2

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##### Re: Calculating Amounts of substances Moles
« Reply #11 on: January 24, 2016, 08:29:25 AM »
First calculate the mole NaCl  n = 16000 kg/58,5 kg/Kmol =273,5 kmol

In the equation you can see that the mole amount of sodium is the same like the NaCl. So the given moles multiplited with the molar mass of sodium gives 6290,59 kg

For the Chlorine you see its the half it gives then 9695,73 kg

#### jamesbrown

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##### Re: Calculating Amounts of substances Moles
« Reply #12 on: January 24, 2016, 08:53:50 AM »
Hunter why did you not convert the mas into grams and why did you not work out the moles for 2nacl because you only worked out the moles for nacl
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A: It went OK.

#### Hunter2

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##### Re: Calculating Amounts of substances Moles
« Reply #13 on: January 24, 2016, 09:00:34 AM »
What do you mean, I didn't convert the mass in gram. The mass is given in gram. 16 t = 16000 kg and this is equal to 273,5 kmol.

The equation is 2 NaCl => 2 Na + Cl2

So 2 NaCl correspond to 2 Na. This  is the same like NaCl correspond to Na. You can erase the 2 on both sides.

And 2 NaCl to Cl2 is the same like NaCl to 0.5 Cl2

#### jamesbrown

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##### Re: Calculating Amounts of substances Moles
« Reply #14 on: January 24, 2016, 09:04:18 AM »
Sorry i meant why did you convert it to kg not grams
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.