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### E. 23 b

Posted: **Tue Oct 27, 2020 7:31 pm**

by **asalest 2K**

why don't we divide by Avogadro's to get moles for b in:

E.23 Calculate the amount (in moles) of (a) Cu21 ions in 3.00 g of CuBr2; (b) SO3 molecules in 7.00 3 102 mg of SO3; (c) F2 ions in 25.2 kg of UF6; (d) H2O in 2.00 g of Na2CO3?10H2O.

### Re: E. 23 b

Posted: **Tue Oct 27, 2020 8:03 pm**

by **Kimiya Aframian IB**

asalest 2K wrote:why don't we divide by Avogadro's to get moles for b in:

E.23 Calculate the amount (in moles) of (a) Cu21 ions in 3.00 g of CuBr2; (b) SO3 molecules in 7.00 3 102 mg of SO3; (c) F2 ions in 25.2 kg of UF6; (d) H2O in 2.00 g of Na2CO3?10H2O.

Hi! so solve for moles for b, the first step is to convert mg to g. Now use the molar mass of SO3 to convert g to mol.

If you continue to solve for molecules, then you need to multiply by Avogadro's number (it's multiplication not division so that you can cancel out your units and get molecules. Hope this helps!

### Re: E. 23 b

Posted: **Tue Oct 27, 2020 8:07 pm**

by **Marisa Gaitan 2D**

You only use avogadro's number when converting to/from number of atoms/molecules. Since this question asks you to go from mg to moles, you simple go from mg to g to moles of SO3.

### Re: E. 23 b

Posted: **Tue Oct 27, 2020 8:09 pm**

by **Marisa Gaitan 2D**

Disregard my answer, I misread the question. The person above me has the correct answer. So sorry!!