Question

A patient is supplementing their potassium intake by taking 75 mL of a 3.5% (w/v) potassium bicarbonate solution daily. How many milliequivalents of potassium ion is the patient consuming daily?

KHCO3 MW 100

K+ MW 39

HCO3- MW 61

Answer 1

A milliequivalent is equal to the number of univalent counter ions (H+ or OH) which will be needed to react with one molecule of the substance

When an atom has a valence of one ( e.g. Na+, K+, CI, etc.) a mEq of that ion is equal to the atomic weight of the atom in milligrams. For example, one mEq of sodium (Na+) with an atomic weight of 23 (AW) weighs 23mg.

When an atom has a valence of two or more (e.g. Mg+2, Ca+2, Al+3) a mEq of that ion is equal to the atomic weight of the atom in milligrams divided by the atom's valence. For example, one mEq of calcium (Ca+2) with an atomic weight of 40 weight 20 mg.

Because in chemical compounds or salts ions always come in pairs, (positive and negative ions are always together in salts like NaC1 and CaC12) we can never weigh or measure just one ion.

When both ions have a valence of one (e.g. NaC1), one millimole (the molecular weight (MW) of the compound in milligrams) of he compound contains one mEq of each ion.)

The atomic weight (AW) of K+ = 39 and the AW of C1 = 35.5. The molecular weight of (MW) of KC1 = 74.5 mg

Since both ions have a valence of one, 74.5 mg KC1 (the weight of one millimole contains 1 mEq of K and 1 mEq of C1.

Therefore, 20 mEq of KC1 is 20 x 74.5 mg = 1490 mg.

If one or both of the ions in the pair has a valence of two or more (e.g. CaC12), one millimole of the compound contains two or more mEq's of each ion.