Chemistry:Equivalent
An equivalent (symbol: officially equiv;[1] unofficially but often Eq[2]) is the amount of a substance that reacts with (or is equivalent to) an arbitrary amount (typically one mole) of another substance in a given chemical reaction. It is an archaic unit of measurement that was used in chemistry and the biological sciences (see Equivalent weight § In history). The mass of an equivalent is called its equivalent weight.
Formula
The formula from milligrams (mg) to milli-equivalent (mEq) and back is as follows: [math]\displaystyle{ \begin{align} \text{mg} \to \text{mEq} &: \quad \text{mg } \times \frac{V}{MW} \\[4pt] \text{mEq} \to \text{mg} &: \quad \text{mEq } \times \frac{MW}{V} \end{align} }[/math] where V is the valence and MW is the molecular weight.
For elemental compounds: [math]\displaystyle{ \text{mg} \to \text{mEq} : \quad \frac{\text{element mass [mg]}}{\text{mass fraction}} \times \frac{V}{MV} }[/math]
Common examples
mEq to milligram
| Compound | Chemical formula | Molecular weight (MW) | rowspan=" | Valencies (V) | Sample | ||
|---|---|---|---|---|---|---|---|
| Reference | Elemental uty | Elemental uty to compound weight | |||||
| Potassium (reference) | K | 39.098 g/mol | 1 (K+ ) |
20 mEq potassium | 20*39.098/1=782 mg | ||
| Potassium citrate monohydrate | C 6H 7K 3O 8 |
324.41 g/mol | 3 (K+ ) |
Liquid potassium citrate/gluconate therapy for adults and teenagers taken two to four times a day[3] | 20 mEq potassium | 20*324/3=2160 mg | |
| Potassium gluconate (anhydrous) | C 6H 11KO 7 |
234.245 g/mol | 1 (K+ ) |
Liquid potassium citrate/gluconate therapy for adults and teenagers taken two to four times a day[3] | 20 uty potassium | 20*234.245/1=4685 mg | |
Milligram to mEq
| Compound | Chemical formula | Molecular weight (MW) | Elemental mass fraction | Valencies (V) | Sample | ||
|---|---|---|---|---|---|---|---|
| Reference | Weight | Compound weight to elemental uty | |||||
| Potassium (reference) | K | 39.098 g/mol | 100% | 1 (K+ ) |
3000 mg | 3000*1/39.098=77 uty K+ | |
| Potassium citrate monohydrate | C 6H 7K 3O 8 |
324.41 g/mol | 36.16% | 3 (K+ ) |
Tolerable DRI for potassium dietary supplements[4][5] | 8.3 g (3000/0.3616) | 8296*3/324.41=77 mEq K+ |
| Potassium gluconate (anhydrous) | C 6H 11KO 7 |
234.245 g/mol | 16.69% | 1 (K+ ) |
Tolerable DRI for potassium dietary supplements[4][5] | 18 g (3000/0.1669) | 17975*1/234.245=77 mEq K+ |
Formal definition
In a more formal definition, the equivalent is the amount of a substance needed to do one of the following:
- react with or supply one mole of hydrogen ions (H+
) in an acid–base reaction - react with or supply one mole of electrons in a redox reaction.[6][7]
The "hydrogen ion" and the "electron" in these examples are respectively called the "reaction units."
By this definition, the number of equivalents of a given ion in a solution is equal to the number of moles of that ion multiplied by its valence. For example, consider a solution of 1 mole of NaCl and 1 mole of CaCl
2. The solution has 1 mole or 1 equiv Na+
, 1 mole or 2 equiv Ca2+, and 3 mole or 3 equiv Cl−
.
An earlier definition, used especially for chemical elements, holds that an equivalent is the amount of a substance that will react with 1 g (0.035 oz) of hydrogen, 8 g (0.28 oz) of oxygen, or 35.5 g (1.25 oz) of chlorine—or that will displace any of the three.[8]
In medicine and biochemistry
In biological systems, reactions often happen on small scales, involving small amounts of substances, so those substances are routinely described in terms of milliequivalents (symbol: officially mequiv; unofficially but often mEq[2] or meq), the prefix milli- denoting a factor of one thousandth (10−3). Very often, the measure is used in terms of milliequivalents of solute per litre of solution (or milliNormal, where meq/L = mN). This is especially common for measurement of compounds in biological fluids; for instance, the healthy level of potassium in the blood of a human is defined between 3.5 and 5.0 mEq/L.
A certain amount of univalent ions provides the same amount of equivalents while the same amount of divalent ions provides twice the amount of equivalents. For example, 1 mmol (0.001 mol) of Na+ is equal to 1 meq, while 1 mmol of Ca2+ is equal to 2 meq.
References
- ↑ "CAS Standard Abbreviations & Acronyms". https://www.cas.org/content/cas-standard-abbreviations.
- ↑ 2.0 2.1 American Medical Association, AMA Manual of Style, https://www.amamanualofstyle.com/, retrieved 2019-10-23.
- ↑ 3.0 3.1 "Potassium Supplement (Oral Route, Parenteral Route) Proper Use - Mayo Clinic". https://www.mayoclinic.org/drugs-supplements/potassium-supplement-oral-route-parenteral-route/proper-use/drg-20070753.
- ↑ 4.0 4.1 "Potassium - assessment of suggestd maximum limits in food supplements" (in en). https://vkm.no/english/riskassessments/allpublications/potassiumassessmentofsuggestdmaximumlimitsinfoodsupplements.4.33bc233f15dabfdfa88bdbc1.html.
- ↑ 5.0 5.1 "Proposed maximum levels for the addition of potassium to foods including food supplements". https://www.bfr.bund.de/cm/349/proposed-maximum-levels-for-the-addition-of-potassium-to-foods-including-food-supplements.pdf.
- ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "equivalent entity". doi:10.1351/goldbook.E02192
- ↑ Template:OrangeBook3rd "Chapter 6 - 3: The use of the equivalence concept". http://old.iupac.org/publications/analytical_compendium/Cha06sec3.pdf.
- ↑ "Atome" (in fr), Grand dictionnaire universel du XIXe siècle, 1, Paris: Pierre Larousse, 1866, pp. 868–73
External links
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