Chemistry: Electrolytes

Question

After dialysis, the level of magnesium in Amanda's blood was 0.0035 g/dL. What is this value in milliequivalents per liter?

When I tried to solve this, I got 35, but I did not take Mg into account, and I don't know how. I know I need to do a lot of conversions and figure out moles of Mg2+ per liter using its mass. I need to convert deciliters and liters, moles to equivalents (Eq), but I just can't figure out how to start. Please help.

Answer 1

So, you are essentially charged with converting 0.0035 g/dL Mg²⁺ into milliequivalents (mEq) Mg²⁺ / L.

And you are correct that you need to do a series of conversions.

We have 0.0035 g / dL

Convert this to moles Mg / dL: 0.0035 g /dL x 1 mol Mg / 24.31 g = 0.00014397 moles Mg / dL

Convert this to moles Mg / L: 0.00014397 mols Mg / dL x 10 dL / L = 0.0014397 mols Mg / L

Convert this to mmoles Mg / L: 0.0014397 mols Mg / L x 1000 mmols / mol = 1.4397 mmol Mg / L

Finally, convert this to mEq / L: Since the valence on Mg is 2+, each mmole = 2 mEq, so we have...

1.4397 mmol / L x 2 mEq / mmol = 2.879 mEq/L = 2.9 mEq Mg²⁺ / L (2 sig. figs.)

(be sure to check my math)