In this site we focused on the the areas of science incluod analytical chemisty, general chemistry, inorganic chemistry, organic chemistry, physical chemistry, and spectroscopy.(Online Chemistry Dictionary )

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actinochemistry [CHEM] A branch of chemistry concerned with chemical reactions
produced by light or other radiation.


actinium [CHEM] A radioactive element, symbol Ac, atomic number 89; its longest-
lived isotope is 227
Ac with a half-life of 21.7 years; the element is trivalent; chief use
is, in equilibrium with its decay products, as a source of alpha rays.


actinism [CHEM] The production of chemical changes in a substance upon which elec-
tromagnetic radiation is incident.

actinide series

actinide series [CHEM] The group of elements of atomic number 89 through 103. Also
known as actinoid elements.

acrylonitrile copolymer

acrylonitrile copolymer [ORG CHEM] Oil-resistant synthetic rubber made by polymer-
ization of acrylonitrile with compounds such as butadiene or acrylic acid.

acrylonitrile butadiene styrene resin

acrylonitrile butadiene styrene resin [ORG CHEM] A polymer made by blending acrylo-
nitrile-styrene copolymer with a butadiene-acrylonitrile rubber or by interpolymeriz-
ing polybutadiene with styrene and acrylonitrile; combines the advantages of
hardness and strength of the vinyl resin component with the toughness and impact
resistance of the rubbery component. Abbreviated ABS.


acrylonitrile [ORG CHEM]CH2CHCN A colorless liquid compound used in the manufac-
ture of acrylic rubber and fibers. Also known as vinylcyanide.

acrylic resin

acrylic resin [ORG CHEM] A thermoplastic synthetic organic polymer made by the poly-
merization of acrylic derivatives such as acrylic acid, methacrylic acid, ethyl acrylate,
and methyl acrylate; used for adhesives, protective coatings, and finishes.

acrylic acid or

acrylic acid [ORG CHEM]CH2CHCOOHAn easily polymerized, colorless, corrosive liquid
used as a monomer for acrylate resins.

acrylate resin

acrylate resin [ORG CHEM] Acrylic acid or ester polymer with a CH2 CH(COOR)
structure; used in paints, sizings and finishes for paper and textiles, adhesives, and
plastics. Also known as acrylate.


acrylate [ORG CHEM] 1. A salt or ester of acrylic acid. 2. See acrylate resin.


acrylamide [ORG CHEM]CH2CHCONH2 Colorless, odorless crystals with amelting point
of 84.5 C; soluble in water, alcohol, and acetone; used in organic synthesis, polymer-
ization, sewage treatment, ore processing, and permanent press fabrics.

acrolein test

acrolein test [ANALY CHEM] A test for the presence of glycerin or fats; a sample is
heated with potassium bisulfate, and acrolein is released if the test is positive.

acrolein dimer

acrolein dimer [ORG CHEM]C6H8O2 A flammable, water-soluble liquid used as an inter-
mediate for resins, dyestuffs, and pharmaceuticals.

acrolein cyanohydrin

acrolein cyanohydrin [ORG CHEM]CH2:CHCH(OH)CN A liquid soluble in water and
boiling at 165 C; copolymerizes with ethylene and acrylonitrile; used to modify
synthetic resins. 


acrolein [ORG CHEM]CH2 CHCHO A colorless to yellow liquid with a pungent odor
and a boiling point of 52.7 C; soluble in water, alcohol, and ether; used in organic
synthesis, pharmaceuticals manufacture, and as an herbicide and tear gas.


acriflavine [ORG CHEM]C14H14N3Cl A yellow acridine dye obtained from proflavine by
methylation in the form of red crystals; used as an antiseptic in solution.

acridine orange

acridine orange [ORG CHEM] A dye with an affinity for nucleic acids; the complexes of
nucleic acid and dye fluoresce orange with RNA and green with DNA when observed
in the fluorescence microscope.

acridine dye

acridine dye [ORG CHEM] Any of a class of basic dyes containing the acridine nucleus
that bind to deoxyribonucleic acid.


acridine [ORG CHEM](C6H4)2NCH A typical member of a group of organic heterocyclic
compounds containing benzene rings fused to the 2,3 and 5,6 positions of pyridine;
derivatives include dyes and medicines.

Acree’s reaction

Acree’s reaction [ANALY CHEM] A test for protein in which a violet ring appears when
concentrated sulfuric acid is introduced below amixture of the unknown solution and
a formaldehyde solution containing a trace of ferric chloride.

aconitic acid

aconitic acid [ORG CHEM]C6H6O6 A white, crystalline organic acid found in sugarcane
and sugarbeet; obtained during manufacture of sugar.

acid value

acid value Also known as acid number. [CHEM] The acidity of a solution expressed in
terms of normality. [ORG CHEM] A number indicating the amount of nonesterified
fatty acid present in a sample of fat or fatty oil as determined by alkaline titration.

acid solution

acid solution [CHEM] An aqueous solution containing more hydrogen ions than
hydroxyl ions.

acid salt

acid salt [CHEM] A compound derived from an acid and base in which only a part of
the hydrogen is replaced by a basic radical; for example, the acid sulfate NaHSO4.

acid phosphate

acid phosphate [INORG CHEM] A mono- or dihydric phosphate; for example, M2HPO4
or MH2PO4, where M represents a metal atom.


acidolysis [ORG CHEM] A chemical reaction involving the decomposition of a molecule,
with the addition of the elements of an acid to the molecule; the reaction is compara-
ble to hydrolysis or alcoholysis, in which water or alcohol, respectively, is used in
place of the acid. Also known as acyl exchange.

acidity function

acidity function [CHEM] A quantitative scale for measuring the acidity of a solvent
system; usually established over a range of compositions.


acidity [CHEM] The state of being acid.


acidimeter [ANALY CHEM] An apparatus or a standard solution used to determine the
amount of acid in a sample.


acidification [CHEM] Addition of an acid to a solution until the pH falls below 7.

acidic titrant

acidic titrant [ANALY CHEM] An acid solution of known concentration used to determine
the basicity of another solution by titration.

acidic oxide

acidic oxide [INORG CHEM] An oxygen compound of a nonmetal, for example, SO2 or
P2O5, which yields an oxyacid with water.

acidic dye

acidic dye [ORG CHEM] An organic anion that binds to and stains positively charged



acidic [CHEM] 1. Pertaining to an acid or to its properties. 2. Forming an acid during
a chemical process.

acid heat test

acid heat test [ANALY CHEM] The determination of degree of unsaturation of organic
compounds by reacting with sulfuric acid and measuring the heat of reaction.

acid halide

acid halide [ORG CHEM] A compound of the type RCOX, where R is an alkyl or aryl
radical and X is a halogen.

acid electrolyte

acid electrolyte [INORG CHEM] A compound, such as sulfuric acid, that dissociates into
ions when dissolved, forming an acidic solution that conducts an electric current.

acid dye

acid dye [ORG CHEM] Any of a group of sodium salts of sulfonic and carboxylic acids
used to dye natural and synthetic fibers, leather, and paper.

acid disproportionation

acid disproportionation [CHEM] The self-oxidation of a sample of an oxidized element
to the next higher oxidation state and then a corresponding reduction to lower
oxidation states.

acid chloride

acid chloride [ORG CHEM] A compound containing the radical COCl; an example is
benzoyl chloride.


acid-base titration

acid-base titration [ANALY CHEM] A titration in which an acid of known concentration
is added to a solution of base of unknown concentration, or the converse.

acid-base pair

acid-base pair [CHEM] A concept in the Bro ¨ nsted theory of acids and bases; the pair
consists of the source of the proton (acid) and the base generated by the transfer
of the proton.

acid-base indicator

acid-base indicator [ANALY CHEM] A substance that reveals, through characteristic
color changes, the degree of acidity or basicity of solutions.

acid-base equilibrium

acid-base equilibrium [CHEM] The condition when acidic and basic ions in a solution
exactly neutralize each other; that is, the pH is 7.

acid-base catalysis

acid-base catalysis [CHEM] The increase in speed of certain chemical reactions due
to the presence of acids and bases.

acid azide

acid azide [ORG CHEM] 1. A compound in which the hydroxy group of a carboxylic acid
is replaced by the azido group ( NH3). 2. An acyl or aroyl derivative of hydrazoic
acid. Also known as acyl azide.

acid anhydride

acid anhydride [CHEM] An acid with one or more molecules of water removed; for
example, SO3 is the acid anhydride of H2SO4, sulfuric acid.

acid amide

acid amide [ORG CHEM] A compound derived from an acid in which the hydroxyl group
( OH) of the carboxyl group ( COOH) has been replaced by an amino group ( NH2)
or a substituted amino group ( NHR or NHR2).

acid alcohol

acid alcohol [ORG CHEM] A compound containing both a carboxyl group ( COOH)
and an alcohol group ( CH2OH, CHOH, or COH).

acid acceptor

acid acceptor [ORG CHEM] A stabilizer compound added to plastic and resin polymers
to combine with trace amounts of acids formed by decomposition of the polymers.

by acid

by acid [ORG CHEM] An acid that readily forms stable complexes with aromatic systems.


acid [CHEM] 1. Any of a class of chemical compounds whose aqueous solutions turn
blue litmus paper red, react with and dissolve certain metals to form salts, and react
with bases to form salts. 2. A compound capable of transferring a hydrogen ion
in solution. 3. A substance that ionizes in solution to yield the positive ion of the
solvent. 4. Amolecule or ion that combines with anothermolecule or ion by forming
a covalent bond with two electrons from the other species.

acetyl valeryl

acetyl valeryl [ORG CHEM]CH3COCOC4H9 A yellow liquid used for cheese, butter, and
other flavors. Also known as heptadione-2,3.


acetylurea [ORG CHEM]CH3CONHCONH2 Crystals that are colorless and are slightly
soluble in water. 

N-acetylsulfanilyl chloride

N-acetylsulfanilyl chloride [ORG CHEM]C8H8ClNO3S Thick, light tan prisms ranging to
brown powder or fine crystals with a melting point of 149 C; soluble in benzene,
chloroform, and ether; used as an intermediate in the preparation of sulfanilamide
and its derivatives. Abbreviated ASC. 


acetylsalicylic acid

acetylsalicylic acid [ORG CHEM]CH3COOC6H4COOH A white, crystalline, weakly acidic
substance, with melting point 137 C; slightly soluble in water; used medicinally as
an antipyretic. Also known by trade name aspirin.

acetyl propionyl

acetyl propionyl [ORG CHEM]CH3COCOCH2CH3 A yellow liquid with a boiling point
of 106–110 C; used in butterscotch- and chocolate-type flavors.

acetyl peroxide

acetyl peroxide [ORG CHEM] (CH3CO)2O2 Colorless crystals with a melting point of
30 C; soluble in alcohol and ether; used as an initiator and catalyst for resins.

acetyl number

acetyl number [ANALY CHEM] A measure of free hydroxyl groups in fats or oils deter-
mined by the amount of potassium hydroxide used to neutralize the acetic acid
formed by saponification of acetylated fat or oil.


acetylisoeugenol [ORG CHEM]C6H3(CHCHCH3)(OCH3)(OCOCH3) White crystals with a
clovelike odor and a congealing point of 77 C; used in perfumery and flavoring.

acetyl iodide

acetyl iodide [ORG CHEM]CH3COI A colorless, transparent, fuming liquid with a boiling
point of 105–108 C; soluble in ether and benzene; used in organic synthesis.


acetylide [ORG CHEM] A compound formed from acetylene with the H atoms replaced
by metals, as in cuprous acetylide (Cu2C2).


N-acetylethanolamine [ORG CHEM]CH3CONHC2H4OH A brown, viscous liquid with a
boiling range of 150–152 C; soluble in alcohol, ether, and water; used as a plasticizer,
humectant, high-boiling solvent, and textile conditioner.


acetylenic [ORG CHEM] Pertaining to acetylene or being like acetylene, such as having
a triple bond.

acetylene tetrabromide

acetylene tetrabromide [ORG CHEM] CHBr2CHBr2 A yellowish liquid with a boiling point
of 239–242 C; soluble in alcohol and ether; used for separating minerals and as a

acetylene series

acetylene series [ORG CHEM] A series of unsaturated aliphatic hydrocarbons, each
containing at least one triple bond and having the general formula CnH2n 2.

acetylene black

acetylene black [ORG CHEM] A form of carbon with high electrical conductivity; made
by decomposing acetylene by heat.


acetylene [ORG CHEM]C2H2 A colorless, highly flammable gas that is explosive when
compressed; the simplest compound containing a triple bond; used in organic synthe-
sis and as a welding fuel. Also known as ethyne.

acetyl chloride

acetyl chloride [ORG CHEM]CH3COCl A colorless, fuming liquid with a boiling point
of 51–52 C; soluble in ether, acetone, and acetic acid; used in organic synthesis,
and in the manufacture of dyestuffs and pharmaceuticals.

alfa cetylbutyrolactone

alfa cetylbutyrolactone [ORG CHEM]C6H8O3 A liquid with an esterlike odor; soluble in
water; used in the synthesis of 3,4-disubstituted pyridines.

acetyl bromide

acetyl bromide [ORG CHEM]CH3COBr A colorless, fuming liquid with a boiling point
of 81 C; soluble in ether, chloroform, and benzene; used in organic synthesis and
dye manufacture.

acetyl benzoyl peroxide

acetyl benzoyl peroxide [ORG CHEM]C6H5CO O2 OCCH3 White crystals with a melting
point of 36.6 C; moderately soluble in ether, chloroform, carbon tetrachloride, and
water; used as a germicide and disinfectant.


acetylation [ORG CHEM] The process of bonding an acetyl group onto an organic mole-

acetylating agent

acetylating agent [ORG CHEM] A reagent, such as acetic anhydride, capable of bonding
an acetyl group onto an organic molecule.


acetylacetone [ORG CHEM]CH3COCH2OCCH3 A colorless liquid with a pleasant odor
and a boiling point of 140.5 C; soluble in water; used as a solvent, lubricant additive,
paint drier, and pesticide.



acetyl [ORG CHEM]CH3CO A two-carbon organic radical containing a methyl group
and a carbonyl group.

aceturic acid

aceturic acid [ORG CHEM]CH3CONHCHCH2COOH Long, needlelike crystals with a
melting point of 206–208 C; soluble in water and alcohol; forms stable salts with
organic bases; used in medicine.


acetoxime [ORG CHEM] (CH3)2CNOH Colorless crystals with a chlorallike odor and a
melting point of 61 C; soluble in alcohol, ethers, and water; used in organic synthesis
and as a solvent for cellulose ethers.


acetostearin [ORG CHEM] A general term for monoglycerides of stearic acid acetylated
with acetic anhydride; used as a protective food coating and as plasticizers for waxes
and synthetic resins to improve low-temperature characteristics.


acetophenone [ORG CHEM]C6H5COCH3 Colorless crystals with amelting point of 19.6 C
and a specific gravity of 1.028; used as a chemical intermediate.

acetonyl acetone

acetonylacetone [ORG CHEM]CH3COCH2CH2COCH3 A colorless liquid with a boiling
point of 192.2 C; soluble in water; used as a solvent and as an intermediate for
pharmaceuticals and photographic chemicals.


acetonitrile [ORG CHEM]CH3CN A colorless liquid soluble in water; used in organic

acetone sugar

acetone sugar [ORG CHEM] Any reducing sugar that contains acetone; examples are
1,2-monoacetone-D-glucofuranose and 1,2,6-diacetone-D-glucofuranose. Also
known as acetone glucose.

acetone-sodium bisulfite

acetone-sodium bisulfite [ORG CHEM] (CH3)2C(OH)SO3Na Crystals that have a slight
sulfur dioxide odor and slightly fatty feel; freely soluble in water, decomposed by
acids; used in photography and in textile dyeing and printing.

acetone number

acetone number [CHEM] A ratio used to estimate the degree of polymerization of
materials such as drying oils; it is the weight in grams of acetone added to 100
grams of a drying oil to cause an insoluble phase to form.

acetone cyanohydrin

acetone cyanohydrin [ORG CHEM] (CH3)2COHCN A colorless liquid obtained from con-
densation of acetone with hydrocyanic acid; used as an insecticide or as an organic
chemical intermediate.


acetone [ORG CHEM]CH3COCH3 A colorless, volatile, extremely flammable liquid, mis-
cible with water; used as a solvent and reagent. Also known as 2-propanone.


acetolysis [ORG CHEM] Decomposition of an organic molecule through the action of
acetic acid or acetic anhydride.


acetol [ORG CHEM]CH3COCH2OH A colorless liquid soluble in water; a reducing agent.


acetoin [ORG CHEM]CH3COCHOHCH3 A slightly yellow liquid, melting point 15 C,
used as an aroma carrier in the preparation of flavors and essences; produced by
fermentation or fromdiacetyl by partial reduction with zinc and acid.

acetoacetic acid

acetoacetic acid [ORG CHEM]CH3COCH2COOH A colorless liquid miscible with water;
derived from -hydroxybutyric acid in the body.


acetoacetate [ORG CHEM] A salt which contains the CH3COCH2COO radical; derived
from acetoacetic acid.


acetin [ORG CHEM]C3H5(OH)2OOCCH3 A thick, colorless, hygroscopic liquid with a
boiling point of 158 C, made by heating glycerol and strong acetic acid; soluble in
water and alcohol; used in tanning, as a dye solvent and food additive, and in
explosives. Also spelled acetine.


acetic anhydride

acetic anhydride [ORG CHEM] (CH3CO)2O A liquid with a pungent odor that combines
with water to form acetic acid; used as an acetylating agent.

acetic acid [ORG CHEM]CH3COOH 1. A clear, colorless liquid or crystalline mass with
a pungent odor, miscible with water or alcohol; crystallizes in deliquescent needles;
a component of vinegar. Also known as ethanoic acid. 2. A mixture of the normal
and acetic salts; used as a mordant in the dyeing of wool.

acetate of lime

acetate of lime [ORG CHEM] Calcium acetate made from pyroligneous acid and a water
suspension of calcium hydroxide.

acetate dye

acetate dye [CHEM] 1. Any of a group of water-insoluble azo or anthroquinone dyes
used for dyeing acetate fibers. 2. Any of a group of water-insoluble amino azo dyes
that are treated with formaldehyde and bisulfate to make them water-soluble.


acetate [ORG CHEM] One of two species derived from acetic acid, CH3COOH; one type
is the acetate ion, CH3COO ; the second type is a compound whose structure contains
the acetate ion, such as ethyl acetate


acetanilide [ORG CHEM] An odorless compound in the formof white, shining, crystalline
leaflets or a white, crystalline powder with a melting point of 114–116 C; soluble in
hot water, alcohol, ether, chloroform, acetone, glycerol, and benzene; used as a
rubber accelerator, in the manufacture of dyestuffs and intermediates, as a precursor
in penicillin manufacture, and as a painkiller.


acetaminophen [ORG CHEM]C8H9O2N Large monoclinic prisms with a melting point
of 169–170 C; soluble in organic solvents such as methanol and ethanol; used in
the manufacture of azo dyes and photographic chemicals, and as an analgesic and

acetamidine hydrochloride

acetamidine hydrochloride [ORG CHEM]C2H6N2 HCl Deliquescent crystals that are
long prisms with a melting point reported as either 174 Cor164–166 C; soluble in
water and alcohol; used in the synthesis of imidazoles, pyrimidines, and triazines.


acetamide [ORG CHEM]CH3CONH2 The crystalline, colorless amide of acetic acid, used
in organic synthesis and as a solvent.

acetal resins

acetal resins [ORG CHEM] Linear, synthetic resins produced by the polymerization of
formaldehyde (acetal homopolymers) or of formaldehyde with trioxane (acetal copol-
ymers); hard, tough plastics used as substitutes formetals. Also known as polyacet-


acetaldehyde [ORG CHEM]C2H4O A colorless, flammable liquid used chiefly to manu-
facture acetic acid.


acetal [ORG CHEM] 1. CH3CH(OC2H5)2 A colorless, flammable, volatile liquid used as
a solvent and in manufacture of perfumes. Also known as 1,1-diethoxyethane.
2. Any one of a class of compounds formed by the addition of alcohols to aldehydes.


acephatemet [ORG CHEM]CH3OCH3SPONH2 A white, crystalline solid with a melting
point of 39–41 C; limited solubility in water; used as an insecticide to control
cutworms and borers on vegetables.


acephate [ORG CHEM]C4H10NO3PS A white solid with a melting point of 72–80 C; very
soluble in water; used as an insecticide for a wide range of aphids and foliage pests.


acenocoumarol [ORG CHEM]C19H15NO6 A tasteless, odorless, white, crystalline powder
with a melting point of 197 C; slightly soluble in water and organic solvents; used
as an anticoagulant. Also known as acenocoumarin.


acene [ORG CHEM] Any condensed polycyclic compound with fused rings in a linear
arrangement; for example, anthracene.


acenaphthequinone [ORG CHEM]C10H6(CO)2 A three-ring hydrocarbon in the form of
acetic ester
yellow needles melting at 261–263 C; insoluble in water and soluble in alcohol; used
in dye synthesis.


acenaphthene [ORG CHEM]C12H10 An unsaturated hydrocarbon whose colorless crys-
tals melt at 92 C; insoluble in water; used as a dye intermediate and as an agent
for inducing polyploidy.


acceptor [CHEM] 1. A chemical whose reaction rate with another chemical increases
because the other substance undergoes another reaction.
 2. A species that acceptselectrons, protons, electron pairs, or molecules such as dyes.


accelofilter [CHEM] A filtration device that uses a vacuum or pressure to draw or force
the liquid through the filter to increase the rate of filtration.

accelerator mass spectrometer

accelerator mass spectrometer [SPECT] A combination of a mass spectrometer and
an accelerator that can be used to measure the natural abundances of very rare
radioactive isotopes.

acaroid resin

acaroid resin [ORG CHEM] A gum resin from aloelike trees of the genus Xanthorrhoea in
Australia and Tasmania; used in varnishes and inks. Also known as gum accroides;
yacca gum. { a kə ro ˙ id rez ən}

abstraction reaction

abstraction reaction [CHEM] A bimolecular chemical reaction in which an atom that
is either neutral or charged is removed from a molecular entity. { ab strak shən
re ¯ ak shən}


absorptivity [ANALY CHEM] The constant a in the Beer’s law relation A abc, where A
is the absorbance, b the path length, and c the concentration of solution. Also known
as absorptive power. Formerly known as absorbency index; absorption constant;
extinction coefficient. { əb so ˙ rp tiv əd e ¯ }

absorption tube

absorption tube [CHEM] A tube filled with a solid absorbent and used to absorb gases
and vapors. { əb so ˙ rp shən tu ¨ b}

absorption spectrum

absorption spectrum [SPECT] A plot of how much radiation a sample absorbs over a
range of wavelengths; the spectrum can be a plot of either absorbance or transmit-
tance versus wavelength, frequency, or wavenumber. { əb so ˙ rp shən spek trəm}


absorption spectroscopy

absorption spectroscopy [SPECT] An instrumental technique for determining the con-
centration and structure of a substance bymeasuring the intensity of electromagnetic
radiation it absorbs at various wavelengths. { əb so ˙ rp shən spek tra ¨s kə pe

absorption spectrophotometer

absorption spectrophotometer [SPECT] An instrument used to measure the relative
intensity of absorption spectral lines and bands. Also known as difference spectro-
photometer. { əb so ˙ rp shən spek trə fə ta ¨m ə dər}

absorption peak

absorption peak [SPECT] A wavelength of maximum electromagnetic absorption by
a chemical sample; used to identify specific elements, radicals, or compounds.
{ əb so ˙ rp shən pe ¯ k}

absorption line

absorption line [SPECT] A minute range of wavelength or frequency in the electromag-
netic spectrum within which radiant energy is absorbed by the medium through
which it is passing. { əb so ˙ rp shən lı ¯n}

absorption edge

absorption edge [SPECT] The wavelength corresponding to a discontinuity in the varia-
tion of the absorption coefficient of a substance with the wavelength of the radiation.
Also known as absorption limit. { əb so ˙ rp shən ej }


absorption [CHEM] The taking up of matter in bulk by other matter, as in dissolving
of a gas by a liquid. { əb so ˙ rp shən}

absorptiometric analysis

absorptiometric analysis [ANALY CHEM] Chemical analysis of a gas or a liquid by meas-
urement of the peak electromagnetic absorption wavelengths that are unique to a
specific material or element. { əb so ˙ rp te ¯ ə met rik ə nal ə sis }


absorptiometer [ANALY CHEM] 1. An instrument equipped with a filter system or other
simple dispersing system to measure the absorption of nearly monochromatic radia-
tion in the visible range by a gas or a liquid, and so determine the concentration
of the absorbing constituents in the gas or liquid. 2. A device for regulating the
thickness of a liquid in spectrophotometry. { əb so ˙ rp te ¯ a ¨ məd ər}



absorbency [CHEM] Penetration of one substance into another.


absorbance [PHYS CHEM] The common logarithmof the reciprocal of the transmittance
of a pure solvent.


absorb [CHEM] To take up a substance in bulk.

absolute reaction rate

absolute reaction rate [PHYS CHEM] The rate of a chemical reaction as calculated by
means of the (statistical-mechanics) theory of absolute reaction rates.


absolutemethod [ANALY CHEM] Amethod of chemical analysis that bases characteriza-
tion completely on standards defined in terms of physical properties.

absolute gravity

absolute gravity [CHEM] Density or specific gravity of a fluid reduced to standard
conditions; for example, with gases, to 760 mmHg pressure and 0 C temperature.
Also known as absolute density.

absolute detection limit

absolute detection limit [ANALY CHEM] The smallest amount of an element or com-
pound that is detectable in or on a given sample; expressed in terms of mass units
or numbers of atoms or molecules

absolute configuration

absolute configuration [ORG CHEM] The three-dimensional arrangement of substitu-
ents around a chiral center in a molecule. Also known as absolute stereochemistry.

absolute boiling point [

absolute boiling point [CHEM] The boiling point of a substance expressed in the unit
of an absolute temperature scale.

absolute alcohol

absolute alcohol [ORG CHEM] Ethyl alcohol that contains no more than 1% water.
Also known as anhydrous alcohol.


ABS See acrylonitrile butadiene styrene resin.

Abney mounting

Abney mounting [SPECT] A modification of the Rowland mounting in which only the
slit is moved to observe different parts of the spectrum.

ab initio computation

ab initio computation [PHYS CHEM] Computation of the geometry of a molecule solely
from a knowledge of its composition and molecular structure as derived from the
solution of the Schro ¨ dinger equation for the given molecule.

abietic acid

abietic acid [ORG CHEM]C20H30O2 A tricyclic, crystalline acid obtained from rosin; used
in making esters for plasticizers.

Abel tester

Abel tester [PHYS CHEM] A laboratory instrument used in testing the flash point of
kerosine and other volatile oils having flash points below 120 F (49 C); the oil is
contained in a closed cup which is heated by a fixed flame below and a movable
flame above.

Abegg’s rule

Abegg’s rule [CHEM] An empirical rule, holding for a large number of elements, that
the sum of the maximum positive and negative valencies of an element equals eight.


abalyn [ORG CHEM] A liquid rosin that is a methyl ester of abietic acid; prepared by
treating rosin with methyl alcohol; used as a plasticizer


spectroscopy—The branch of physics concerned with the produc-
tion, measurement, and interpretation of electromagnetic spectra arising from
either emission or absorption of radiant energy by various substances.

physical chemistry

physical chemistry—The branch of chemistry that deals with
the interpretation of chemical phenomena and properties in terms of the
underlying physical processes, and with the development of techniques for
their investigation.

organic chemistry

organic chemistry—The study of the structure, preparation
properties, and reactions of carbon compounds.

inorganic chemistry

inorganic chemistry—The branch of chemistry that deals
with reactions and properties of all chemical elements and their compounds,
excluding hydrocarbons but usually including carbides and other simple carbon
compounds (such as CO2, CO, and HCN).


—The scientific study of the properties, composi-
tion, and structure of matter, the changes in structure and composition
of matter, and accompanying energy changes.

analytical chemistry

analytical chemistry The science of the characteriza
tion and measurement of chemicals; qualitative analysis is concerned
with the description of chemical composition in terms of elements,
compounds, or structural units, whereas quantitative analysis is con-
cerned with the measurement of amount.