Milliequivalent and millimole calculations and conversions

Definitions & Calculations

Note: Use of equivalents and milliequivalents is valid only for those substances that have fixed ionic valences (e.g. sodium, potassium, calcium, chlorine, magnesium bromine, etc). For substances with variable ionic valences (e.g. phosphorous), a reliable equivalent value cannot be determined. In these instances, one should calculate millimoles (which are fixed and reliable) rather than milliequivalents.

Term Definition Calculations
Mole Gram molecular weight of a substance (a.k.a. molar weight) 6.022 x 1023 entities
Millimole (mM) Milligram molecular weight of a substance (a millimole is 1/1000 of a mole) Weight of a substance (milligrams) Milliequivalents (valence of ion) Moles x 1000
Equivalent weight Gram weight of a substance which will combine with or replace 1 gram (1 mole) of hydrogen; an equivalent weight can be determined by dividing the molar weight of a substance by its ionic valence. Moles x valence of ion
Miilliequivalent (mEq) Milligram weight of a substance which will combine with or replace 1 milligram (1 millimole) of hydrogen (a milliequivalent is 1/1000 of a equivalent) Millimoles x valence of ion Equivalents x 1000 [Molecular weight (grams) / valence] x [1/1000]

Valences And Atomic Weights Of Selected Ions

Note: The molecular weight of phosphorus only is approximately 31 grams, and sulfur only is 32 grams.

Substance Electrolyte Valence Molecular weight (grams)
Calcium Ca2+ 2 40
Chloride Cl- 1 35.5
Magnesium Mg2+ 2 24
Phosphate HPO4 - (80%) 1.8 961
Phosphate pH = 7.4 H2PO4 - (20%) 1.8 961
Potassium K+ 1 39
Sodium Na+ 1 23
Sulfate SO4 - 2 961

Milliequivalents

Milliequivalent conversation equations are shown in the table below. Selected approximate milliequivalents and weights of selected ions are also listed below.

Milliequivalent converstion desired Conversion equation
Mg/100mL --> mEq/L [(mg/100mL) x 10 x valence] / atomic weight = mEq/L
mEq/L --> mg/100mL [(mEq/L) x atomic weight] / 10 x valence = mg/100mL
mEq/L --> volume of percent of a gas [(mEq/L) x 22.4 / 10] = volume percent
Salt mEq/g Salt mg Salt/mEq
Calcium carbonate [CaCO3] 20 50
Calcium chloride [CaCl2 * 2H2O] 14 74
Calcium gluceptate [Ca(C7H13O8)2] 2 245
Calcium gluconate [Ca(C6H11O7)2 * H2O] 5 244
Calcium lactate [Ca(C3H5O3)2 * 5H2O] 7 154
Magnesium gluconate [Mg(C6H11O7)2 * H2O] 5 216
Magnesium oxide [MgO] 50 20
Magnesium sulfate [MgSO4] 17 60
Magnesium sulfate [MgSO4 * 7H2O] 8 123
Potassium acetate [K(C2H3O2)] 10 98
Potassium chloride [KCl] 13 75
Potassium citrate [K3(C6H5O7) * H2O] 9 108
Potassium iodide [KI] 6 166
Sodium acetate [Na(C2H3O2)] 12 82
Sodium acetate [Na(C2H3O2) * 3H2O] 7 136
Sodium bicarbonate [NaHCO3] 12 84
Sodium chloride [NaCl] 17 58
Sodium citrate [Na3(C6H5O7) * 2H2O] 10 98
Sodium iodine [NaI] 7 150
Sodium lactate [Na(C3H5O3)] 9 112
Zinc sulfate [ZnSO4 * 7H2O] 7 144

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