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- Capable of reacting with an acid to form a salt. Lavoisier classified lime, baryta, alumina, and silica as "salifiable earths".
- salt bridge.
- A tube (often filled with ion-laced agar) that allows two solutions to be in electrical contact without mixing in an electrochemical cell.
- saponification. saponify; saponified; saponifies.
- The hydrolysis of esters using hot sodium hydroxide solution to produce the salt of a carboxylic acid. Usually saponification refers to the hydrolysis of esters of fatty acids to manufacture soaps.
- SATP. standard ambient pressure and temperature. Compare with STP and standard state.
- Used to describe a substance at standard pressure and a temperature of 25°C (298.15 K).
- saturated fat. Compare with unsaturated fat.
- A lipid that contains no carbon-carbon double bonds. Animal fats like butter and lard are composed of saturated fat. Saturated fats tend to be waxy or greasy solids.
- saturated solution. Compare with supersaturated solution.
- A solution which does not dissolve any more solute. When a saturated solution is placed in contact with additional solute, solute neither dissolves nor is deposited from a saturated solution.
- scientific method.
- An inefficient but highly successful method of knowledge construction based on experimental testing of hypotheses.
- scientific notation. exponential notation.
- A system for reporting very small or very large numbers by writing the number as a decimal number between 1 and 10, multiplied by a power of 10. For example, 602000000000000000000000 is written in scientific notation as 6.02 x 1023. 0.000323 is written in scientific notation as 3.23 x 10-4.
- second. (s)
- The second (s) is the base unit of time in the SI system of units, defined as the duration of 9,192,631,770 cycles of the radiation associated with a certain color of light emitted by the cesium atom.
- second ionization energy. (IE,IP) second ionization potential. Compare with first ionization energy, adiabatic ionization energy, vertical ionization energy, electronegativity, and electron affinity.
- The energy needed to remove an electron from an isolated +1 ion. The third ionization energy would be the energy required to remove an electron from an isolated +2 ion, and so on.
- second law. second law of thermodynamics.
- The second law states that every spontaneous process causes a net increase in the entropy of the universe. Many alternative statements are possible, including: Heat cannot be converted to work via an isothermal cycle. Heat cannot be converted to work with 100% efficiency. Heat cannot flow from a cold object to a warmer object without doing outside work.
- second order reaction. Compare with zero order reaction and first order reaction.
- A reaction with a rate law that is proportional to either the concentration of a reactant squared, or the product of concentrations of two reactants.
- Separation of a dense material (usually a solid) from a less dense material (usually a liquid) by allowing the denser material to settle out of the mixture.
- semipermeable membrane.
- A membrane that allows some but not all of the components in a mixture to pass through it. Semipermeable membranes are used in dialysis.
- serine. (Ser, HOCH2CH(NH2)COOH)
- A naturally occuring amino acid with an hydroxyl group on its side chain.
- shell. Compare with subshell.
- A set of electrons with the same principal quantum number. The number of electrons permitted in a shell is equal to 2n2. A shell contains n2 orbitals, and n subshells.
- shielding. Compare with penetration.
- Electrons in orbitals with high penetration can shield the nucleus from less penetrating electrons. Because they are closer to the nucleus on average, they repel those farther away and lessen the effective nuclear charge for the more distant electrons.
- short term memory.
- Short term memory is a mechanism for storing temporary information, such as where you parked your car or numbers in a simple arithmetic problems.
- siemens. (S, upside-down ) absolute ohm; ohm-1; reciprocal ohm; mho. Compare with conductance.
- The SI unit of electrical conductance. A material has a conductance of one siemens if one ampere of electric current can pass through it per volt of electric potential.
- 1. A negatively charged ion containing silicon and oxygen, usually SiO3-2, Si2O7-6, and Si3O7-2. 2. A compound containing positively charged metal ions combined with negatively charged ions made of silicon and oxygen.
- single displacement. single replacement reaction; single displacement reaction; single replacement. Compare with double displacement.
- A reaction of the form A + BC = B + AC. For example, zinc displaces hydrogen from hydrochloric acid in the following reaction: Zn(s) + 2 HCl(aq) = ZnCl2(aq) + H2(g).
- sigma bond. ( bond) Compare with pi bond.
- In the valence bond theory, a sigma bond is a valence bond that is symmetrical around the imaginary line between the bonded atoms. Most single bonds are sigma bonds.
- significant figure. significant digit; significant.
- A convention for recording measurements. Measurements are rounded so that they contain only the digits up to and including the first uncertain digit, when the number is written in scientific notation.
- SI. Systeme Internationale; International System.
- Le Systéme Internationale (SI) is a system of units introduced to remove barriers to international trade, based on the older metric system. It is now used in science and technical communications worldwide.
- A salt of a fatty acid. For example, sodium stearate is a soap made by neutralizing stearic acid. Commercial soaps are mixtures of fatty acid salts.
- A colloid with solid particles suspended in a liquid. Examples are protoplasm, starch in water, and gels.
- A solid is a relatively dense, rigid state of matter, with a definite volume and shape. Molecules in solids are often packed close together in regularly repeating patterns, and vibrate around fixed positions.
- solubility. solubilities; equilibrium solubility; solubleness.
- The solubility of a substance is its concentration in a saturated solution. Substances with solubilities much less than 1 g/100 mL of solvent are usually considered insoluble. The solubility is sometimes called "equilibrium solubility" because the rates at which solute dissolves and is deposited out of solution are equal at this concentration.
- solubility product. (Ksp) ion product; solubility product constant; Ksp.
- The equilibrium constant for a reaction in which a solid ionic compound dissolves to give its constituent ions in solution.
- solubilizing group.
- A group or substructure on a molecule that increases the molecule's solubility. Solubilizing groups usually make the molecule they are attached to ionic or polar. For example, hydrocarbon chains can be made water-soluble by attaching a carboxylic acid group to the molecule.
- soluble. Compare with insoluble.
- Capable of being dissolved in a solvent (usually water).
- soluble salt.
- An ionic compound that dissolves in a solvent (usually water).
- A substance dissolved in a solvent to make a solution.
- solution. homogeneous mixture. Compare with heterogeneous mixture.
- A sample of matter consisting of more than one pure substance with properties that do not vary within the sample. Also called a homogeneous mixture.
- The most abundant component in a solution.
- solvent extraction.
- Solvent extraction is a method for separating mixtures by exploiting differences in the solubilities of the components. For example, a coffee machine extracts the soluble components of ground coffee with water, and leaves the insoluble components behind. The sample is shaken or mixed with solvent (or with two immiscible solvents) to effect the separation. The "like dissolves like" is a useful guide for selecting solvents to use in the extraction. Nonpolar substances are usually successfully extracted into nonpolar solvents like hexane or methylene chloride. Polar and ionic substances are often extracted with water.
- sorption. Compare with adsorption and absorption.
- Assimilation of molecules of one substance by a material in a different phase. Adsorption (sorption on a surface) and absorption (sorption into bulk material) are two types of sorption phenomena.
- specific gravity. specific gravities. Compare with density.
- The mass of a unit volume of a substance relative to the mass of a unit volume of water. Temperature must be specified when reporting specific gravities, since the density of the substance and of water change with temperature. Specific gravities are often reported relative to water at 4°C; at that temperature, water has a density of 1.00000 g/mL and the specific gravity of a substance is equal to its density in g/mL.
- specific heat. Compare with heat capacity.
- The heat required to raise the temperature of 1 g of a substance by 1°C is called the specific heat of the substance. Specific heat is an intensive property with units of J g-1 K-1.
- specific volume. Compare with density.
- The volume of a unit mass of substance. For example, the specific volume of water at 4°C is 1.00000 mL/g. Specific volume is the reciprocal of density.
- spectator ion.
- A spectator ion is an ion that appears as both a reactant and a product in an ionic equation. For example, in the ionic equation
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) = AgCl(s) + Na+(aq) + NO3-(aq) the sodium and nitrate ions are spectator ions.
- An instrument for measuring the amount of light absorbed by a sample.
- spectrophotometry. spectrophotometric.
- Determination of the concentration of a material in a sample by measurement of the amount of light the sample absorbs.
- spectroscope. spectrometer.
- An instrument for measuring the spectrum of light or radiation.
- spectroscopy. spectrometry; spectroscopic.
- Spectroscopy is analysis of the interaction between electromagnetic radiation and matter. Different types of radiation interact in characteristic ways with different samples of matter; the interaction is often unique and serves as a diagnostic "fingerprint" for the presence of a particular material in a sample. Spectroscopy is also a sensitive quantitative technique that can determine trace concentrations of substances.
- 1. A sequence of colors produced by passing light through a prism or diffraction grating. 2. A range of wavelengths of electromagnetic radiation. 3. A plot that shows how some intensity-related property of a beam of radiation or particles depends on another property that is related to dispersal of the beam by a prism, a magnet, or some other device. For example, a plot of light absorbance vs. wavelength is an absorption spectrum; a plot of ion abundance vs. mass is a mass spectrum.
- Electrons have an intrinsic angular momentum that is similar to what would be observed if they were spinning. Electron spin is sometimes called a "twoness" property because it can have two values, referred to as "spin up" and "spin down". Nuclei can have spins of their own.
- spin pair. () paired spins; electron pair; paired electrons. Compare with unpaired spin.
- Two electrons with opposite spins, usually occupying the same orbital.
- spontaneous. spontaneity; spontaneous process; spontaneous reaction.
- A spontaneous process occurs because of internal forces; no external forces are required to keep the process going, although external forces may be required to get the process started. For example, the burning of wood is spontaneous once the fire is started. The combination of water and carbon dioxide to reform the wood and oxygen is NOT spontaneous!
- A substance that makes a mixture more stable. Antioxidants and antiozonants are examples of stabilizers; stabilizers are added to paints to prevent the components of the mixture from separating over time.
- standard deviation. (s,BESD,)
- The standard deviation is a statistical measure of precision. The best estimate of the standard deviation s for small data sets is calculated using
where xi is the measurement from the i-th run, x-bar is the mean of all the measurements, and N is the number of measurements. For very large data sets, the standard deviation is the root-mean-square deviation from the true mean, and is usually written as to distinguish it from the best estimate standard deviation s used for small data sets.
- standard entropy of reaction. (Srxn°) entropy of reaction.
- A change in entropy associated with a reaction involving substances in their standard states. A superscript circle (°) distinguishes standard enthalpy changes from enthalpy changes which involve reactants and products that are not in their standard states.
- standard enthalpy change. (H°) standard enthalpy. Compare with enthalpy change.
- A change in enthalpy associated with a reaction or transformation involving substances in their standard states.
- standard enthalpy of formation. (Hf°) standard heat of formation; heat of formation; enthalpy of formation.
- The change in enthalpy when one mole of compound is formed from its elements in their most stable form and in their standard states.
- standard enthalpy of reaction. (Hrxn°) standard heat of reaction.
- A change in enthalpy associated with a reaction involving substances in their standard states.
- standard hydrogen electrode. SHE.
- A platinum electrode that runs the half reaction 2 H+(aq, 1M) + 2 e- H2(g, 1 atm), chosen as a reference for cell voltages. The electrode potential of the standard hydrogen electrode is defined to be zero volts.
- standard molar entropy. (S°)
- The entropy of one mole of a substance in its standard state.
- standard molar volume.
- The volume of 1 mole of an ideal gas at STP, equal to 22.414 liters.
- standard reduction potential. (E°)
- The voltage associated with a reduction process at standard state. The reduction potential of 2H+(aq, 1M) + 2 e- H2(g, 1 atm) is taken as exactly zero volts.
- standard solution.
- A solution of precisely known concentration.
- standard state. (° or
- A set of conditions defined to allow convenient comparison of thermodynamic properties. The standard state for a gas is the the state of the pure substance in the gaseous phase at the standard pressure, with the gas behaving ideally. The standard state for liquids and solids is the state of the most stable form of the substance at the standard pressure. Temperature is not included in the definition of standard state and must be specified, but when not given a temperature of 25°C is usually implied.
- standard pressure. (P° or P
- Standard pressure is a pressure of 1 bar. Before 1982, the standard pressure was 1 atm (1 atm = 1.01325 bar).
- A polysaccharide used by plants to stockpile glucose molecules. The most common forms are amylose and amylopectin.
- state function.
- A property that depends only on the condition or "state" of the system, and not on the path used to obtain the current conditions. Energy, enthalpy, temperature, volume, pressure, and temperature are examples of state functions; heat and work are examples of non-state functions.
- state of matter.
- There are three common states of matter: gases, liquids, and solids. States of matter differ in the way the molecules are arranged at the molecular level, but not in the structure of the molecules themselves. Other states (the plasma and Bose-Einstein condensate states) are uncommon on Earth.
- stationary phase.
- A stationary phase is a substance that shows different affinities for different components in a sample mixture in a separation of the mixture by chromatography. The mobile phase (a solution containing the sample) flows over or through the stationary phase to effect the separation.
- An alloy of iron and carbon. Steel contains anywhere between 0.2% carbon (for soft wire and sheet steel) and 1.5% carbon (for cutting tools), with small amounts of many other elements often present.
- steradian. (str)
- A solid angle with vertex at the center of a sphere of radius r that encompasses an area of r2 on the surface of the sphere.
- Stereochemistry is the study of how the properties of a compound are affected by the spatial positions of groups within its molecules. Stereochemistry is also concerned with determining the structure of stereoisomers.
- Molecules with the same atoms and bond structure, but different three dimensional arrangements of atoms. For example, the CH3 groups in CH3CH=CHCH3 can be placed on the same side of the double bond in one stereoisomer and on opposite sides in another.
- stoichiometric coefficient.
- The coefficients given before substances in a balanced chemical equation. For example, the stoichiometric coefficient of carbon dioxide in the following reaction is 4:
2 C2H6(g) + 7 O2(g) 4 CO2 + 6 H2O
- 1. Ratios of atoms in a compound. 2. Ratios of moles of compounds in a reaction. 3. A branch of chemistry that quantitatively relates amounts of elements and compounds involved in chemical reactions, based on the law of conservation of mass and the law of definite proportions.
- STP. standard temperature and pressure. Compare with SATP and standard state.
- Used to describe a substance at standard pressure and a temperature of 0°C (273.15 K).
- Stripping is a technique for removing volatile components in a mixture by bubbling a stream of an chemically unreactive gas (like nitrogen) through the sample, and then 'scrubbing' the nitrogen through a solution or solid adsorbent that can recover the volatile materials.
- strong acid. Compare with weak acid.
- A strong acid is an acid that completely dissociates into hydrogen ions and anions in solution. Strong acids are strong electrolytes. There are only six common strong acids: HCl (hydrochloric acid), HBr (hydrobromic acid), HI (hydroiodic acid), H2SO4 (sulfuric acid), HClO4 (perchloric acid), and HNO3 (nitric acid).
- strong base.
- A strong base is an base that completely dissociates into ions in solution. Strong bases are strong electrolytes. The most common strong bases are alkali metal and alkaline earth metal hydroxides.
- strong electrolyte. Compare with weak electrolyte.
- A strong electrolyte is a solute that completely dissociates into ions in solution. Solutions of strong electrolytes conduct electricity. Most soluble ionic compounds are strong electrolytes.
- strong ligand. strong field ligand. Compare with weak ligand.
- A ligand that causes a large crystal field splitting which results in a low-spin complex.
- structural formula. Compare with molecular formula and empirical formula.
- A structural formula is a diagram that shows how the atoms in a molecule are bonded together. Atoms are represented by their element symbols and covalent bonds are represented by lines. The symbol for carbon is often not drawn. Most structural formulas don't show the actual shape of the molecule (they're like floor plans that show the layout but not the 3D shape of a house).
- sublimation. sublimate; sublimating.
- Conversion of a solid directly into a gas, without first melting into a liquid.
- subshell. sublevel.
- A set of electrons with the same azimuthal quantum number. The number of electrons permitted in a subshell is equal to 2 + 1.
- substitution. substitution reaction.
- A reaction in which an atom or fragment within a molecule is replaced with another.
- A substance that is acted upon by an enzyme during a biochemical reaction.
- A carbohydrate with a characteristically sweet taste. Sugars are classified as monosaccharides, disaccharides, or trisaccharides.
- sulfate. (SO42-) sulphate.
- 1. The SO42- ion, formed by reaction of sulfuric acid with a base. 2. A compound containing the SO42- ion.
- sulfite. (SO32-) sulphite.
- 1. The SO32- ion, formed by reaction of sulfurous acid with a base. 2. A compound containing the SO32- ion.
- sulfuric acid. (H2SO4) oil of vitriol; sulphuric acid.
- An oily, corrosive liquid that acts as a strong acid when dissolved in water. Sulfuric acid has so many industrial uses that sulfuric acid production was once used as an index of industrial productivity. Salts of sulfuric acids are called sulfates.
- sulfurous acid. (H2SO3) sulphurous acid.
- A colorless liquid that acts as a weak acid when dissolved in water, sometimes used as a bleach. Salts of sulfurous acid are called sulfites.
- The ability of certain materials to carry an electric current with zero electrical resistance.
- supercritical fluid.
- A fluid state that occurs when the pressure and temperature exceed the substance's critical pressure and critical temperature. Supercritical fluids fill their containers like gases but dissolve substances like liquids, which makes them very useful as solvents. Their density and other properties are intermediate between gases and liquids.
- superoxide. superoxide ion.
- A binary compound containing oxygen in the -½ oxidation state. For example, KO2 is potassium superoxide, an ionic compound containing the superoxide ion, O2-.
- supersaturated solution. supersaturated.
- A supersaturated solution has concentration of solute that is higher than its solubility. A crystal of solute dropped into a supersaturated solution grows; excess solute is deposited out of the solution until the concentration falls to the equilibrium solubility.
- supercooling. supercooled; supercool.
- Liquids at temperatures below their normal freezing points are said to be "supercooled".
- surface tension.
- The work required to expand the surface of a liquid by unit area.
- A material that spreads along a surface, changing the properties of the surface. For example, soap spreads over a water surface and lowers its surface tension.
- surroundings. Compare with system.
- In thermodynamics, the surroundings refer to the universe outside the system.
- A heterogenous mixture in which droplets or particles are suspended in a liquid.
- synthesis. synthesize; synthetic reaction. Compare with decomposition.
- Formation of a complex product from simpler reactants. For example, water can be synthesized from oxygen and hydrogen gas: H2(g) + ½O2(g) H2O().
- synthetic. synthetic material; artificial; artificial substance.
- A substance manufactured by chemical synthesis.
- system. Compare with surroundings.
- In thermodynamics, the system is the part of the universe that is of interest.
- systematic error. determinate error. Compare with random error, gross error and mistake.
- Systematic errors have an identifiable cause and affect the accuracy of results.
- A molecular shape that results when there are 3 bonds and 2 lone pairs around the central atom in the molecule. The atoms bonded to the central atom lie at the ends of a "T" with 90° angles between them. ICl3 has a T-shaped molecular geometry.