Chemistry: formulas and the periodic table

Molar mass. Type a formula: H2O, Ca(OH)2, K4[Fe(CN)6], hydrates as CuSO4·5H2O (or * / . for the dot), and charges as SO4^2-, Fe{3+}, Fe+3, MnO4- or superscripts (SO₄²⁻). D and T stand for deuterium and tritium. The molar mass is the sum of IUPAC standard (abridged) atomic weights; the table splits it by element. Enter a quantity in grams, moles, or particles to convert between them (Avogadro constant 6.022 140 76 × 10²³ mol⁻¹).

Balance equations. Write reactants and products separated by →, →, or =. Any coefficients you type are ignored. The balancer solves the element (and charge) conservation equations exactly — the null space of the composition matrix, in rational arithmetic — and scales to the smallest whole numbers. Ionic and redox equations work as long as every charge is written, and electrons can be added as e^-. A plain trailing sign means ±1, so write Fe^2+ rather than Fe2+ (which would read as two iron atoms with a +1 charge).

Empirical formula. Enter mass percentages (or masses in grams). Moles per 100 g are divided by the smallest, then multiplied by the smallest whole number (up to 12) that makes every ratio within 0.1 of an integer. Add the compound’s molar mass to get the molecular formula.

Periodic table. Click an element for its data; colour the table by category, block, state, electronegativity, or melting point. Values in brackets are the mass number of the most stable or best-known isotope. Melting and boiling points are at 1 atm where known; carbon and arsenic sublime, so only the sublimation temperature is given.

Electrochemistry

Galvanic cell. Pick two half-reactions from the table of standard reduction potentials (25 °C, 1 mol/L, against the standard hydrogen electrode). The lower one is the anode, where oxidation happens; the cell EMF is E°(cathode) − E°(anode), and ΔG° = −nFE° with n the electrons in the balanced overall reaction. Zinc against copper gives −0.76 V and +0.34 V, about 1.10 V. The Li, Zn, Fe, H₂, AgCl/Ag, Cu and O₂ values are the book’s (Appendix C); Mg, Al, Ni, Sn, Pb, Ag, Pt and Au are from the CRC Handbook and Bard, Parsons & Jordan, Standard Potentials in Aqueous Solution (1985). Real cells read less, and in sea water or body fluid what corrodes is set by the galvanic series in that fluid — the table is a starting point, not a prediction.

Faraday’s law. The mass deposited or dissolved is m = Q·M / (n·F), with Q = I·t, F = 96,485.332 C/mol and n the electrons per ion. The two book examples are one click away: 1 A for 10 minutes (600 C) plates about 0.67 g of silver; a corrosion current of 1 µA for a year (31.6 C) dissolves about 9.1 mg of iron as Fe²⁺. Give an area to see the average thickness — corrosion concentrated in a pit or crevice goes far deeper. 100 % current efficiency is assumed.

Companion to Chapter 2, Basic chemistry (electrochemistry, Faraday’s law and the zinc–copper cell exercise) of Human Biology for the Medical Maker; the potentials table is its Appendix C.

For learning and planning. Check critical work against authoritative references (IUPAC, CRC Handbook, NIST).

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You can also write a link by hand with the readable parameters formula — for example ?formula=C6H12O6. formula fills the molar-mass calculator; eq fills the equation balancer (add #balance).

Electrochemistry

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