WordNet

a representation of a substance using symbols for its constituent elements (同)chemical_formula
a group of symbols that make a mathematical statement (同)expression
a conventionalized statement expressing some fundamental principle
a liquid food for infants
derived from experiment and observation rather than theory; "an empirical basis for an ethical theory"; "empirical laws"; "empirical data"; "an empirical treatment of a disease about which little is known" (同)empiric
relying on medical quackery; "empiric treatment" (同)empirical

PrepTutorEJDIC

(あいさつなどの)『決まった言い方』;空虚な言葉 / (…の)習慣的なやり方,決まった方法《+『for』+『名』(do『ing』)》 / (…の)製法,調理法,処方せん《+『for』+『名』》 / (…の)『公式』,式《+『for』+『名』》
経験を基礎とする,実験に基づいた

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/02/14 22:58:27」(JST)

wiki en

[Wiki en表示]

In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound.^[1] A simple example of this concept is that the empirical formula of sulfur monoxide, or SO, would simply be SO, as is the empirical formula of disulfur dioxide, S₂O₂. This means that sulfur monoxide and disulfur dioxide, both compounds of Sulfur and Oxygen will have the same empirical formula.

An empirical formula makes no mention of the arrangement or number of atoms. It is standard for many ionic compounds, like CaCl₂, and for macromolecules, such as SiO₂.

The molecular formula, on the other hand, shows the number of each type of atom in a molecule. Also the structural formula shows the arrangement of the molecule. It is possible for different types of compounds to have equal empirical formulas.

Examples

Glucose (C₆H₁₂O₆), ribose (C₅H₁₀O₅), acetic acid (C₂H₄O₂), and formaldehyde (CH₂O) all have different molecular formulas but the same empirical formula: CH₂O. This is the actual molecular formula for formaldehyde, but acetic acid has double the number of atoms, ribose has five times the number of atoms, and glucose has six times the number of atoms.
The chemical compound n-hexane has the structural formula CH₃CH₂CH₂CH₂CH₂CH₃, which shows that it has 6 carbon atoms arranged in a chain, and 14 hydrogen atoms. Hexane's molecular formula is C₆H₁₄, and its empirical formula is C₃H₇, showing a C:H ratio of 3:7.

Calculation

Suppose you are given a compound such as methyl acetate, a solvent commonly used in paints, inks, and adhesives. When methyl acetate was chemically analyzed, it was discovered to have 48.64% carbon (C), 8.16% hydrogen (H), and 43.20% oxygen (O). For the purposes of determining empirical formulas, we assume that we have 100 g of the compound. If this is the case, the percentages will be equal to the mass of each element in grams.

Step 1: Change each percentage to an expression of the mass of each element in grams. That is, 48.64% C becomes 48.64 g C, 8.16% H becomes 8.16 g H, and 43.20% O becomes 43.20 g O.

Step 2: Convert the amount of each element in grams to its amount in moles.

Step 3: Divide each of the found values by the smallest of these values (2.7)

Step 4: If necessary, multiply these numbers by integers in order to get whole numbers; if an operation is done to one of the numbers, it must be done to all of them.

Thus, the empirical formula of methyl acetate is C₃H₆O₂. This formula also happens to be methyl acetate's molecular formula.

References

^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Empirical formula".

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. アレルギー疾患リスクのある乳児への粉ミルクおよび固形食の導入 introducing formula and solid foods to infants at risk for allergic disease
2. 早産児のための母乳の栄養組成および人工乳 nutritional composition of human milk and preterm formula for the premature infant
3. 低ナトリウム血症患者におけるナトリウム欠乏の評価 estimation of the sodium deficit in patients with hyponatremia
4. 早産児のための授乳および強化母乳栄養 human milk feeding and fortification of human milk for premature infants
5. 中等症から重症熱傷患者に対する栄養所要量および経腸栄養剤 nutritional demands and enteral formulas for moderate to severe burn patients

English Journal

Preparation and structure investigation of novel Schiff bases using spectroscopic, thermal analyses and molecular orbital calculations and studying their biological activities.

Zayed EM1, Zayed MA2, El-Desawy M3.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.Spectrochim Acta A Mol Biomol Spectrosc.2015 Jan 5;134:155-64. doi: 10.1016/j.saa.2014.06.014. Epub 2014 Jun 14.
Two novel Schiff's bases (EB1 and L1) as new macrocyclic compounds were prepared via condensation reactions between bisaldehyde (2,2'-(ethane-1,2-diylbis(oxy))dibenzaldehyde): firstly with hydrazine carbothioamide to give (EB1), secondly with 4,6-diaminopyrimidine-2-thiol to give (L1). EB1 has a gen
PMID 25016203

Giant piezoresistivity in aligned carbon nanotube nanocomposite: account for nanotube structural distortion at crossed tunnel junctions.

Gong S1, Zhu ZH.
Nanoscale.Nanoscale.2014 Dec 10. [Epub ahead of print]
High piezoresistivity is critical for multifunctional carbon nanotube polymer composites with sensing capability. By developing a new percolation network model, this work reveals theoretically that a giant piezoresistivity in the composites can be potentially achieved by controlled nanotube alignmen
PMID 25492244

Invited Commentary: Agent-Based Models for Causal Inference-Reweighting Data and Theory in Epidemiology.

Hernán MA.
American journal of epidemiology.Am J Epidemiol.2014 Dec 5. pii: kwu272. [Epub ahead of print]
The relative weights of empirical facts (data) and assumptions (theory) in causal inference vary across disciplines. Typically, disciplines that ask more complex questions tend to better tolerate a greater role of theory and modeling in causal inference. As epidemiologists move toward increasingly c
PMID 25480820