Reference

Quick reference

The numbers and rules you reuse all term, on one page. Values are exact where the SI definition is exact, otherwise rounded to the digits you would use in a first-semester course.

Fundamental constants

The 2019 revision of the SI fixed several of these exactly (the Avogadro and Planck constants, the speed of light, the elementary charge), so they carry no uncertainty; the rest are rounded to the digits a first-semester course needs. Click a value to copy it into a calculator or spreadsheet. The toolkit already builds these in.

Avogadro constant, Nₐ6.02214076 × 10²³ mol⁻¹
Molar gas constant, R8.314462618 J·mol⁻¹·K⁻¹
Molar gas constant, R0.0820573661 L·atm·mol⁻¹·K⁻¹
Speed of light in vacuum, c2.99792458 × 10⁸ m·s⁻¹
Planck constant, h6.62607015 × 10⁻³⁴ J·s
Elementary charge, e1.602176634 × 10⁻¹⁹ C
Faraday constant, F96485.332 C·mol⁻¹
Boltzmann constant, kᵦ1.380649 × 10⁻²³ J·K⁻¹
Standard acceleration of gravity, g9.80665 m·s⁻²
Molar volume of ideal gas (STP, 0 °C, 1 atm)22.414 L·mol⁻¹
Molar volume of ideal gas (SATP, 25 °C, 1 bar)24.790 L·mol⁻¹
Ion-product constant of water, Kᵥ (25 °C)1.0 × 10⁻¹⁴
Zero of the Celsius scale273.15 K

Vapor pressure of water

Any gas collected by displacing water carries water vapor mixed in. Dalton's law gives the dry gas its own pressure: subtract water's vapor pressure at the collection temperature from the total measured pressure, P_gas = P_total − P_H₂O. See Module 14 and the glossary entry for why it rises so steeply with temperature.

Temperature (°C)	Vapor pressure (torr)
0	4.58
5	6.54
10	9.21
15	12.79
20	17.54
21	18.65
22	19.83
23	21.07
24	22.38
25	23.76
26	25.21
27	26.74
28	28.35
29	30.04
30	31.82
35	42.18
40	55.32
45	71.88
50	92.51
60	149.38
70	233.70
80	355.10
90	525.76
100	760.00

Specific heat capacities

The c in q = mcΔT (Module 8) — energy needed to raise one gram of the substance by one degree Celsius. Water's unusually high value is why it resists temperature change so well, and why a metal identified by its measured specific heat is a standard Coffee-Cup Calorimetry extension.

Substance	c (J·g⁻¹·°C⁻¹)
Water (liquid)	4.184
Water (ice, solid)	2.09
Water (steam, gas)	2.01
Ethanol (liquid)	2.44
Air (dry, sea level)	1.01
Aluminum, Al(s)	0.897
Glass	0.84
Iron, Fe(s)	0.449
Zinc, Zn(s)	0.388
Copper, Cu(s)	0.385
Silver, Ag(s)	0.235
Mercury, Hg(l)	0.140
Gold, Au(s)	0.129
Lead, Pb(s)	0.128

Heats of fusion and vaporization

Specific heat (above) tells you the energy to change a substance's temperature; heat of fusion and heat of vaporization tell you the energy to change its phase — melting or boiling a substance takes real energy without moving the thermometer at all, since that energy goes entirely into breaking (not stretching) intermolecular attractions (Module 14). Values are per mole, at 1 atm and the substance's normal melting/boiling point, so pair them with a molar mass conversion, not a direct gram-for-gram use the way specific heat is used. Vaporization always costs far more than fusion for the same substance — boiling fully separates molecules that melting only lets slide past each other.

Substance	ΔH_fus (kJ/mol)	ΔH_vap (kJ/mol)
Water, H₂O	6.01	40.7
Ammonia, NH₃	5.66	23.3
Methanol, CH₃OH	3.2	35.2
Ethanol, C₂H₅OH	4.9	38.6
Acetone, (CH₃)₂CO	5.69	29.1
Benzene, C₆H₆	9.87	30.7
Aluminum, Al	10.7	294
Copper, Cu	13.1	300
Iron, Fe	13.8	340

SI prefixes

A prefix multiplies the base unit by a power of ten. To convert a prefixed quantity to the base unit, multiply by the factor shown; to go the other way, divide. Chained conversions are the safest — write each factor as a fraction equal to one, arranged so the unwanted unit cancels (the method drilled in Module 0).

Prefix	Symbol	Factor
tera	`T`	10¹²
giga	`G`	10⁹
mega	`M`	10⁶
kilo	`k`	10³
hecto	`h`	10²
deca	`da`	10¹
—	`—`	10⁰ (base unit)
deci	`d`	10⁻¹
centi	`c`	10⁻²
milli	`m`	10⁻³
micro	`µ`	10⁻⁶
nano	`n`	10⁻⁹
pico	`p`	10⁻¹²
femto	`f`	10⁻¹⁵

Common polyatomic ions

A polyatomic ion is a covalently bonded group of atoms carrying an overall charge; it stays together through most reactions and keeps its name in the compound. Knowing this set from memory makes writing formulas and naming compounds fast, and it is assumed from Module 2 onward. The charge listed is the charge on the whole ion. Watch the ‑ate / ‑ite pairs: the ‑ate ion has one more oxygen than the ‑ite.

Cations

Name	Formula	Charge
Ammonium	`NH₄⁺`	+1
Hydronium	`H₃O⁺`	+1
Mercury(I) (dimer)	`Hg₂²⁺`	+2

Anions

Name	Formula	Charge
Hydroxide	`OH⁻`	−1
Nitrate	`NO₃⁻`	−1
Nitrite	`NO₂⁻`	−1
Acetate	`CH₃COO⁻ (C₂H₃O₂⁻)`	−1
Hydrogen carbonate (bicarbonate)	`HCO₃⁻`	−1
Hydrogen sulfate (bisulfate)	`HSO₄⁻`	−1
Dihydrogen phosphate	`H₂PO₄⁻`	−1
Cyanide	`CN⁻`	−1
Permanganate	`MnO₄⁻`	−1
Hypochlorite	`ClO⁻`	−1
Chlorite	`ClO₂⁻`	−1
Chlorate	`ClO₃⁻`	−1
Perchlorate	`ClO₄⁻`	−1
Thiocyanate	`SCN⁻`	−1
Carbonate	`CO₃²⁻`	−2
Sulfate	`SO₄²⁻`	−2
Sulfite	`SO₃²⁻`	−2
Chromate	`CrO₄²⁻`	−2
Dichromate	`Cr₂O₇²⁻`	−2
Peroxide	`O₂²⁻`	−2
Oxalate	`C₂O₄²⁻`	−2
Hydrogen phosphate	`HPO₄²⁻`	−2
Thiosulfate	`S₂O₃²⁻`	−2
Phosphate	`PO₄³⁻`	−3
Phosphite	`PO₃³⁻`	−3
Borate	`BO₃³⁻`	−3

Solubility rules (aqueous, ~25 °C)

These generalisations predict whether an ionic compound dissolves appreciably in water, which is what tells you whether mixing two solutions produces a precipitate. Work through the "soluble" list first; if a compound is not covered there, treat it as insoluble. "Slightly soluble" compounds (marked where relevant) still often form a visible solid. Used throughout Module 6.

Generally soluble

Group 1 (Li⁺, Na⁺, K⁺, …) and ammonium (NH₄⁺) salts — all soluble.
Nitrates (NO₃⁻), acetates (CH₃COO⁻), and chlorates (ClO₃⁻) — all soluble.
Chlorides, bromides, iodides — soluble except those of Ag⁺, Pb²⁺, and Hg₂²⁺.
Sulfates — soluble except those of Ba²⁺, Pb²⁺, Ca²⁺, Sr²⁺ (Ag⁺ slightly).

Generally insoluble

Carbonates (CO₃²⁻), phosphates (PO₄³⁻), chromates (CrO₄²⁻) — insoluble except with Group 1 or NH₄⁺.
Hydroxides (OH⁻) — insoluble except Group 1, and Ca²⁺, Sr²⁺, Ba²⁺ (moderately).
Sulfides (S²⁻) — insoluble except Group 1, Group 2, and NH₄⁺.
Oxides — mostly insoluble; soluble ones react with water to give hydroxides.

Solubility-product constants (Ksp, 25 °C)

The solubility rules above are qualitative — "insoluble" really means "so little dissolves it isn't worth calling soluble," not "literally zero." The solubility product, Ksp, is the quantitative version: the equilibrium constant for a sparingly soluble salt dissolving into its ions. A smaller Ksp means less of the solid actually dissolves before the system reaches equilibrium. Beyond this course's own scope — paired here with the qualitative rules it quantifies.

Compound	Ksp
Silver bromide, AgBr	5.4 × 10⁻¹³
Silver chloride, AgCl	1.8 × 10⁻¹⁰
Barium sulfate, BaSO₄	1.1 × 10⁻¹⁰
Calcium carbonate, CaCO₃	3.4 × 10⁻⁹
Calcium fluoride, CaF₂	3.9 × 10⁻¹¹
Magnesium hydroxide, Mg(OH)₂	5.6 × 10⁻¹²
Lead(II) chloride, PbCl₂	1.7 × 10⁻⁵
Lead(II) sulfate, PbSO₄	2.5 × 10⁻⁸

Strong acids & strong bases

"Strong" means essentially 100% ionised in water — every strong-acid molecule donates its proton, every strong-base formula unit releases its hydroxide. There are only a handful; assume anything else (acetic acid, ammonia, carbonic acid, most organic acids) is weak and only partly ionised. This distinction sets how you calculate pH and drives the pH tool.

Strong acids

Name	Formula
Hydrochloric	`HCl`
Hydrobromic	`HBr`
Hydroiodic	`HI`
Nitric	`HNO₃`
Sulfuric (first proton)	`H₂SO₄`
Perchloric	`HClO₄`
Chloric	`HClO₃`

Strong bases

Group	Examples
Group 1 hydroxides	`LiOH, NaOH, KOH, RbOH, CsOH`
Heavier Group 2 hydroxides	`Ca(OH)₂, Sr(OH)₂, Ba(OH)₂`

Activity series of metals

An ordering of metals (and hydrogen) by how readily they give up electrons — that is, how easily they are oxidised. A metal higher in the list will displace the ion of any metal below it from solution and reduce it to the free metal; it will also react with acid (releasing H₂) if it sits above hydrogen. Reactivity decreases from top to bottom. This is the qualitative companion to the quantitative treatment in Module 7.

Li K Ba Sr Ca Na
(most reactive — displace H₂ from cold water)
Mg Al Mn Zn Cr Fe Cd
(displace H₂ from steam or acid)
Co Ni Sn Pb
(displace H₂ from acid, slowly)
H₂
(reference)
Cu Ag Hg Pt Au
(least reactive — do not displace H₂ from acid)

Standard reduction potentials (E°, 25 °C)

The quantitative version of the activity series above, and the number a galvanic cell's cell potential is built from: subtract the anode's value from the cathode's to get the cell's voltage. A more positive value means a stronger oxidizing agent — more eager to be reduced (gain electrons) — which is why this list, read top to bottom, tracks the activity series' order in reverse. Beyond this course's own scope.

Half-reaction	E° (V)
`F₂(g) + 2e⁻ → 2F⁻(aq)`	+2.87
`MnO₄⁻(aq) + 8H⁺ + 5e⁻ → Mn²⁺(aq) + 4H₂O(l)`	+1.51
`Cl₂(g) + 2e⁻ → 2Cl⁻(aq)`	+1.36
`O₂(g) + 4H⁺ + 4e⁻ → 2H₂O(l)`	+1.23
`Ag⁺(aq) + e⁻ → Ag(s)`	+0.80
`Fe³⁺(aq) + e⁻ → Fe²⁺(aq)`	+0.77
`Cu²⁺(aq) + 2e⁻ → Cu(s)`	+0.34
`2H⁺(aq) + 2e⁻ → H₂(g)`	0.00 (reference)
`Pb²⁺(aq) + 2e⁻ → Pb(s)`	−0.13
`Fe²⁺(aq) + 2e⁻ → Fe(s)`	−0.44
`Zn²⁺(aq) + 2e⁻ → Zn(s)`	−0.76
`Al³⁺(aq) + 3e⁻ → Al(s)`	−1.66
`Mg²⁺(aq) + 2e⁻ → Mg(s)`	−2.37
`Na⁺(aq) + e⁻ → Na(s)`	−2.71
`Li⁺(aq) + e⁻ → Li(s)`	−3.04

Naming quick-rules

Name a compound in two steps. First classify it: a metal with a non-metal (or anything containing a polyatomic ion) is ionic; two non-metals together is molecular; a hydrogen-led formula written as an aqueous solution is an acid. Then apply the matching rule below. Formula-writing runs the process backwards, balancing total positive and negative charge to zero. Developed in Module 2.

Situation	Rule
Ionic, metal + non-metal	name the metal, then the non-metal with an ‑ide ending: NaCl = sodium chloride.
Metal with more than one charge	Roman numeral gives the charge: FeCl₂ = iron(II) chloride, FeCl₃ = iron(III) chloride.
Ionic with a polyatomic ion	keep the ion's name: CaCO₃ = calcium carbonate, (NH₄)₂SO₄ = ammonium sulfate.
‑ate vs ‑ite oxoanions	‑ate has one more O than ‑ite: SO₄²⁻ sulfate, SO₃²⁻ sulfite. per‑…‑ate is one more; hypo‑…‑ite is one fewer.
Molecular (two non-metals)	Greek prefixes on both elements (mono‑ dropped on the first): CO = carbon monoxide, N₂O₄ = dinitrogen tetroxide.
Binary acids (HₓX, aqueous)	hydro‑ + root + ‑ic acid: HCl(aq) = hydrochloric acid.
Oxoacids	‑ate anion → ‑ic acid; ‑ite anion → ‑ous acid: HNO₃ nitric acid, HNO₂ nitrous acid.

Abbreviations & symbols

Every acronym and symbol used on this site, expanded in one place. In the course pages the first use of each acronym is also marked in the text — hover or focus it for the same explanation, or select it for more.

Acronyms & initialisms

Acronym	Stands for	Meaning
ACS	American Chemical Society	The largest scientific society for chemistry; publisher of guidelines for safety, ethics, and undergraduate curricula.
AI	Artificial Intelligence	Software that performs tasks — such as generating or summarizing text — that normally require human reasoning.
ATP	Adenosine triphosphate	The cell's main energy-carrying molecule; energy is released when one phosphate group is transferred off.
CIAAW	Commission on Isotopic Abundances and Atomic Weights	The IUPAC commission that evaluates and publishes the standard atomic weights used on the periodic table.
CMS	Content Management System	Software for creating and organizing website content without editing code directly.
CODATA	Committee on Data of the International Science Council	The group that periodically publishes the internationally agreed values of the fundamental physical constants.
DNA	Deoxyribonucleic acid	The double-stranded molecule that stores genetic information; its strands are held together by hydrogen bonds.
EV	Electric Vehicle	A vehicle driven by an electric motor powered from a rechargeable battery pack.
ITO	Indium tin oxide	A transparent electrical conductor used as the electrode layer in touchscreens and flat panels.
IUPAC	International Union of Pure and Applied Chemistry	The body that standardizes chemical nomenclature, atomic weights, units, and terminology worldwide.
LCSS	Laboratory Chemical Safety Summary	A short, student-facing safety summary for a specific chemical, condensed from its Safety Data Sheet.
LED	Light-Emitting Diode	A semiconductor device that emits light when current flows through it; efficient lighting and displays.
LMS	Learning Management System	The online platform (such as Canvas or Moodle) that hosts a course's assignments, grades, and materials.
MRI	Magnetic Resonance Imaging	A medical scan that maps hydrogen nuclei in the body using strong magnetic fields and radio waves.
NIST	National Institute of Standards and Technology	The U.S. metrology institute; source of reference data for constants, spectra, and thermochemistry.
OSHA	Occupational Safety and Health Administration	The U.S. federal agency that sets and enforces workplace-safety standards, including for teaching laboratories.
PDF	Portable Document Format	A fixed-layout document format that displays the same on any device.
PET	Positron Emission Tomography	A medical scan that detects gamma rays from a positron-emitting tracer to image metabolism.
PPE	Personal Protective Equipment	Splash goggles, gloves, lab coat or apron, and closed-toe shoes — the barrier between you and a hazard.
PVC	Polyvinyl chloride	A widely used plastic made from chlorine and ethylene; pipes, insulation, and flooring.
QA	Quality Assurance	The review process that checks course materials for accuracy, clarity, and consistency before release.
RAMP	Recognize hazards · Assess the risks · Minimize the risks · Prepare for emergencies	The American Chemical Society's four-step framework for thinking through safety before any laboratory work.
RTG	Radioisotope Thermoelectric Generator	A power source that converts the decay heat of a radioactive isotope directly into electricity for spacecraft.
SATP	Standard Ambient Temperature and Pressure	25 °C (298.15 K) and 1 bar; one mole of an ideal gas occupies 24.79 L under these conditions.
SDS	Safety Data Sheet	The standardized 16-section document a supplier provides for every chemical: hazards, handling, storage, first aid, and disposal.
SI	International System of Units (Système International d'Unités)	The modern metric system: seven base units (metre, kilogram, second, ampere, kelvin, mole, candela) and their prefixes.
SOP	Standard Operating Procedure	A written, approved step-by-step method for carrying out a specific laboratory task safely and consistently.
STP	Standard Temperature and Pressure	A reference condition for gases. This course uses 0 °C (273.15 K) and 1 atm, at which one mole of an ideal gas occupies 22.41 L.
VSEPR	Valence-Shell Electron-Pair Repulsion	The model that predicts a molecule's shape by placing the electron domains around the central atom as far apart as possible.
WAI	Web Accessibility Initiative	The World Wide Web Consortium effort that develops accessibility guidelines, including WCAG.
WCAG	Web Content Accessibility Guidelines	The international standard for making web content usable by people with disabilities.

Common symbols in equations

Symbol	Meaning
`(s)`	solid
`(l)`	liquid
`(g)`	gas
`(aq)`	aqueous — dissolved in water
`→`	yields / forms (an irreversible reaction)
`⇌`	equilibrium (a reversible reaction)
`Δ`	change in (e.g. ΔH, ΔT) — final minus initial
`∆r / rxn`	of reaction
`° (as in ΔH°)`	standard conditions (1 bar, stated temperature, 1 M solutions)
`[X]`	molar concentration of X
`∥ , \|`	salt bridge / phase boundary in cell notation