### Moles

Posted:

**Wed Oct 02, 2019 3:16 pm**How do you find the amount in moles of F- ions in 25.2 kg of UF6?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=26&t=45933

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Posted: **Wed Oct 02, 2019 3:16 pm**

How do you find the amount in moles of F- ions in 25.2 kg of UF6?

Posted: **Wed Oct 02, 2019 3:20 pm**

You can use dimensional analysis on this problem. If you are starting with 25.2 kg of UF6, you can convert to g by multiplying by the conversion: 1000 g/1 kg. From there you can use the molar mass of UF6 to convert to moles by multiplying by the conversion: 1 mol UF6/352.0194 g. Then, in a molecule of UF6, there are 6 moles of F- ions, so you can multiply by the conversion: 6 mol F-/1 mol UF6. This will give you the number of moles of F- ions in 25.2 kg of UF6.

Posted: **Wed Oct 02, 2019 3:23 pm**

First you would have to convert 25.2 kg to grams, and then convert grams to moles.

Second use stoichiometry to find the amount of moles multiplied by 6 which will tell you the amount of F ions

25.2 kg * 1000g/1 kg* 1 mol UF6/Molar Mass UF6 * 6 mol F- ions/1 mol UF6

Second use stoichiometry to find the amount of moles multiplied by 6 which will tell you the amount of F ions

25.2 kg * 1000g/1 kg* 1 mol UF6/Molar Mass UF6 * 6 mol F- ions/1 mol UF6

Posted: **Wed Oct 02, 2019 3:29 pm**

using dimensional analysis:

25.2 kg UF6*(1000g/1kg)*(1mol/352.03g UF6)(6molF-/1mol UF6)=429.51 moles F- =430 moles of F- ions (3 sig figs)

first I wrote what I was given, then multiplied by a conversion factor to convert kg to g. then I multiplied by the molar mass of UF6 and then multiplied by the mole ratio of F- ions per molecule of UF6 (there are 6 F- ions per molecule). from then your units will be moles of F- ions.

25.2 kg UF6*(1000g/1kg)*(1mol/352.03g UF6)(6molF-/1mol UF6)=429.51 moles F- =430 moles of F- ions (3 sig figs)

first I wrote what I was given, then multiplied by a conversion factor to convert kg to g. then I multiplied by the molar mass of UF6 and then multiplied by the mole ratio of F- ions per molecule of UF6 (there are 6 F- ions per molecule). from then your units will be moles of F- ions.

Posted: **Wed Oct 02, 2019 5:07 pm**

I would begin by converting 25.2 kg to grams, or 25.2 x 10^3 grams. From there I would find the moles of the UF6 by dividing the grams of UF6 by the molar mass. From there multiply the moles by 6 because there are 6 F- ions in each molecule of UF6, so you can get the number of moles of F- ions in the entire sample.

Posted: **Thu Oct 03, 2019 12:05 am**

A key component to remember how to solve for the moles of F- ions in 25.2 kg of UF6 is to understand the idea of the molar ratio. That means that for ever one atom of U there are 6 atoms of F, so your conversion factor is 1 to 6. So, that means you could solve this by first solving for the moles for UF6 and then using the conversion factor.

For example, first you should convert your units, so 25.2kg becomes 25200g (because 1kg=1000g) and then put that value over the molar mass (352.02g/mol). You would then get the number 71.5868417 moles (remember take sig figs at the end) . This number is the number of moles of UF6, but we are trying to find specifically how many moles of F- there are. So we take our mole number and multiply it by 6 because that was from the original ration (1 to 6), and we get the number 429.52105, which, if we use our sig fig rules, rounds to 430 moles.

For example, first you should convert your units, so 25.2kg becomes 25200g (because 1kg=1000g) and then put that value over the molar mass (352.02g/mol). You would then get the number 71.5868417 moles (remember take sig figs at the end) . This number is the number of moles of UF6, but we are trying to find specifically how many moles of F- there are. So we take our mole number and multiply it by 6 because that was from the original ration (1 to 6), and we get the number 429.52105, which, if we use our sig fig rules, rounds to 430 moles.