Lithium Carbonate Math Question

[hopefulpharmd]

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I can't seem to wrap my mind around this question, any help would be much appreciated. Thank you!

Your patient is receiving lithium carbonate (Li2CO3) capsules but needs to change to a liquid form (lithium citrate; Li3C6H5O7). MW: Li=7, C=12, H=1, O=16.

If the patient's dose of lithium carbonate was 300mg a day, how many millimoles of lithium did the patient receive in a day?

 

[cycloketocaine]

I can't seem to wrap my mind around this question, any help would be much appreciated. Thank you!

Your patient is receiving lithium carbonate (Li2CO3) capsules but needs to change to a liquid form (lithium citrate; Li3C6H5O7). MW: Li=7, C=12, H=1, O=16.

If the patient's dose of lithium carbonate was 300mg a day, how many millimoles of lithium did the patient receive in a day?

This is one of those out of that problem set.....did you see the explanation in back?

 

[Pink11]

I know you have to divide the MW of Lithium carbonate by 2 because there is a 2 after Li2CO3, but I don't thoroughly understand why. Anyone else can help?

 

[Pink11]

This is one of those out of that problem set.....did you see the explanation in back?

I read the explanation at the end but still don't understand why MW has to be divided by 2.

 

[hopefulpharmd]

Yeah, I don't understand why it's divided by 2 either. I'm probably lacking some fundamental knowledge. 🙁

 

[All4MyDaughter]

The molecular weight of Lithium Carbonate is 74... So 74 mg of Lithium Carbonate is equal to one mMol of Lithium Carbonate. But since there are two Lithium atoms in every Lithium Carbonate, there are two mMol of Li in 74 mg of Lithium Carbonate.

You just set up the proportion and solve for X. X being the # of moles of Lithium in 900 mg of Lithium Carbonate.

The key thing to understand:

74 mg = 1 mMol of Lithium Carbonate molecules
74 mg = 2 mMol of Lithium atoms

Lithium Carbonate = Li2CO3
I know it's hard to see without subscript but it's 2 Lithium atoms, 1 carbon atom and 3 oxygens...

 

[hopefulpharmd]

Thank you so much for your help!

 

[All4MyDaughter]

Thank you so much for your help!

I hope it helps. It would be easier to explain in person where I could write on the board, etc.

 

[hopefulpharmd]

I hope it helps. It would be easier to explain in person where I could write on the board, etc.

It does help, thank you! Just to clarify, if the question had asked for millimoles of lithium carbonate, you would NOT have to multiple by 2 to account for the 2 lithiums, correct?

 

[pfaction]

I learned that 300 mg LiCarb = 8.12 mEq of lithium.

300 / 72.89 * 2 Li = 8.12.

 

[All4MyDaughter]

It does help, thank you! Just to clarify, if the question had asked for millimoles of lithium carbonate, you would NOT have to multiple by 2 to account for the 2 lithiums, correct?

Correct!

 

[Pink11]

Correct!

Thank you!