S
s block
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Columns 1 and 2 of the periodic table, containing elements in the periodic table over which the s atomic orbitals are being filled.
salt
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An ionic compound that can be formed by replacing the hydrogen ion of an acid with a different cation.
salt bridge
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A union between the two compartments of an electrochemical cell that permits ions to pass but that restricts the flow of solution.
saponification
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The base-catalyzed hydrolysis of an ester; often used in the context of hydrolyzing fats to make soap.
saturated
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Describing 1) a solution that contains the maximum possible equilibrium concentration of a solute, or 2) an organic compound containing no double or triple bonds.
second law of thermodynamics
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A formal statement that any spontaneous process is accompanied by an increase in the entropy (disorder) of the universe.
second-order reaction
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A reaction for which the rate is directly proportional to the square of the concentration of one species or to the product of the concentrations of two species.
secondary structure
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The folding of a protein into sheets and helices held in their shape by ionic attractions and hydrogen bonding.
semiconductor
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A substance having an electrical conductivity intermediate between that of a metal and that of a non-metal.
semipermeable membrane
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A membrane that selectively permits some species to pass through while rejecting others; often one that permits solvent molecules to pass through, but not large molecules such as proteins.
shielding
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The effect of (negatively charged) electrons close to a (positively charged) nucleus in diminishing the attractive force between the nucleus and other electrons in the atom.
SI units
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The international system of units (Système International d'Unité) based on seven fundamental quantities.
sigma bond
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A bond in which the electron density lies on a line between two atoms and is symmetrically distributed around that line; can be formed by the overlap of an s orbital on one atom with any kind of orbital on another atom.
significant figure
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One of the digits in a value that are known with certainty, omitting zeroes that serve only as place holders.
skeletal isomer
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One of two or more compounds having the same chemical composition but differing in the arrangement of the atoms (usually carbon atoms) forming the backbone of the structure of the compounds; also known as chain isomer.
skeletal structure
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A representation of the structure of a species in which lines are drawn to indicate the presence of bonds between atoms.
slit
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A slit is a component of the Spectronic 20 which allows only a fraction of incident light to pass through it
soap
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Salts of fatty acids produced by the saponification of fat.
soft water
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Water from which high concentrations of cations having charge greater than +1 have been removed, usually by ion exchange.
solid
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A state of matter having a specific shape and volume and in which the particles do not change their relative positions.
solubility
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The extent to which a solute dissolves in a solvent; often expressed as the mass of a substance that will dissolve in 100 mL of solvent.
solubility product
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The equilibrium constant expression for the dissolution of an electrolyte; the reactant is a solid and its concentration does not appear in the expression, which is a product of the concentrations of the products (raised the to appropriate powers).
soluble
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Able to dissolve in a solvent.
solute
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The substance added to a solvent to make a solution.
solution
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A mixture of one or more substances dissolved in a solvent to give a homogeneous mixture.
solvent
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The substance to which a solute is added to make a solution.
specific heat
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The quantity of heat required to raise the temperature of one gram of a substance by 1 K ( 1 °C).
spectator ion
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An ion present in a solution when a reaction occurs but which is not a reactant or product in the net ionic equation.
spectrochemical series
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The arrangement of ligands in order by their influence on the electronic spectra of coordination complexes.
spontaneous
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Energetically capable of proceeding without an outside source of energy; referring to a reaction in which the products are thermodynamically favored.
standard electrode potential
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The voltage attributed to a reduction half-reaction under standard conditions; its value is given referenced to the standard hydrogen electrode.
standard hydrogen electrode
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A system in which hydrogen ion and gaseous hydrogen are present in their standard states; used as a reference (of zero) for the values of other standard electrode potentials.
Standard White Tipped Pipet Bulb
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This is a standard white tipped pipet bulb used for pipetting. The silicon attachment is placed over the mouth of the pipet.
standardization
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A chemical procedure to accurately determine the concentration of a solute in a solution.
stereoisomer
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One of two or more compounds that have the same chemical composition and have the same atoms bonded to other atoms, but that differ in the spatial arrangements of the atoms.
stoichiometric coefficient
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The number in front of the formula of a species in a chemical equation that gives the relative number of moles of the species that react or are consumed.
stoichiometry
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The relationship among the amounts of reactants and products in a chemical reaction.
strong acid
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An acid that dissociates completely.
strong base
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A base that dissociates or reacts with water completely.
structural formula
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A representation of the structure of a species that indicates the arrangement of the atoms in space.
sublimation
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The process of vapor forming from a solid without the intermediate formation of a liquid.
substance
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A material having a fixed ratio of elements in its chemical formula.
substitution reaction
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A reaction in which one atom or functional group is replaced by another (distinguished from an addition reaction).
substrate
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The molecule or ion that an enzyme uses as a reactant for the reaction that it catalyzes.
sugar
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A small carbohydrate that either contains five or six carbon atoms or is a dimer of two units, each containing five or six carbon atoms.
superconductivity
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The ability of certain substances at low temperatures to have zero resistance to the conductance of electricity.
supersaturated
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Containing a greater concentration of a solute than under equilibrium conditions.
surface tension
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The combined effect of adhesive and cohesive forces acting at the surface of a liquid to affect the energy required to increase the surface area of the liquid.
syndiotactic
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Having alternately repeating structural units; said of a polymer.
synthesis gas
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A combustible mixture of hydrogen and carbon monoxide produced by passing steam over red hot coke. It is also known as water gas.
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