FORMULA SHELF
18 of 370
The arithmetic behind the work: what to measure, what to type in, and what the answer comes out as. Every formula says what the symbols mean and gives a worked example, so you can check it against a job you have already done.
SHELVES
Chemistry
18 formulas
The rule that lets you scale up a gas reaction - a bottle of gas and a cylinder of gas behave the same way.
Double the moles in a fixed vessel and you double the pressure.
Each one holds the other two constant. A cold bottle warms in the sun and the pressure goes up, which is why a bottle left in a hot shed can go off.
Gas at 10 C in a bottle warms to 30 C and its pressure rises by about 7%.
How a milk, a must, or a soil stays at a steady pH while things are added to it. A brine is a buffer, and so is the lime in a soil.
A phosphate buffer with pKa 6.8 and equal parts has a pH of 6.8.
Every time you mix a concentrate with water, for a spray, a disinfectant or a test solution. Always add the concentrate to the water, never the other way round.
50 mL of 5 mol/L acid made up to 500 mL = 0.5 mol/L.
Why a compost heap gets hot, why a lime slurry in a slurry tank warms, and why a soaking cold feed makes the animal cold.
Fermenting fruit releases heat; the vat warms by a few degrees.
Why salt melts ice on a road, why a brine freezes below zero, and why a freezer with a brine tank is colder than one with water.
A 10% salt brine freezes at about -6 C.
The rule behind a pressure cooker, a tyre, a gas cylinder and a fermenting barrel. Pressure rises with temperature and with the amount of gas, and falls as the volume grows.
A 20 L bottle at 20 C and 2 bar holds roughly 0.8 moles.
The reason a sealed compost bin gains mass (it gains the carbon dioxide that leaves) and the reason a fire seems to lose mass - the carbon dioxide and water vapour have left the shed.
A burning log loses mass as gases escape, not because matter vanished.
The standard way to say how strong a solution is. A 1 mol/L solution of sodium hydroxide is 40 g of it in a litre of water.
50 g of NaOH (40 g/mol) in 2 L = 0.625 mol/L.
Convenience only. Double-check the result against the worked example or a second method before you use it.
The bridge between grams and reactions. Every recipe that uses chemicals is really counting molecules.
36 g of water is 2 moles, because H2O is 18 g/mol.
Convenience only. Double-check the result against the worked example or a second method before you use it.
For trace elements in soil and feed, nitrate in water, and anything described as 'trace'. A soil test of 30 ppm copper is very different from 30 percent.
1 g per tonne = 1 ppm.
For a 2% milk replacer mix, a 1% iodine solution, a 5% bleach mix or a salt brine. Note that the denominator is the solution, not the water.
25 g of powder in 1 litre of water is about 2.4% w/v.
How well a process actually ran. A lime neutralisation that only reaches 80% means you need more lime than the label says.
You need 50 kg of chalk and get 41 kg of product = 82% yield.
For making a solution of a known strength, for a lime neutralisation calculation, and for anything where the reaction has to be right rather than roughly right.
CaCO3 + 2HCl gives CaCl2, so 1 mole of chalk needs 2 moles of acid.
For working out the strength of a bought solution, and for checking a soil or water test against the method. The end point is the colour change, so get it right before you read the burette.
25 mL of unknown acid neutralised by 20 mL of 0.1 mol/L alkali is 0.08 mol/L.
To decide whether a borehole needs a softener, and why soap will not lather and the kettle furs up.
40 mg/L of calcium gives 100 mg/L of hardness.
Soil, water, antacids and preserves. A change of one unit is ten times more or less acid, which is why a small pH change matters so much. See Soil Ph And Lime.
pH 6 is ten times more acid than pH 7.
For checking that a caustic solution is strong enough, and for understanding why a wash and a rinse need different strengths.
A solution at pH 12 has pOH 2.
SOURCES & PROVENANCE
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This page is an AI-organised index. The label means the grouping and cross-links were compiled with AI; the information itself comes from the public-domain books, reports and manuals listed below. Open any source to read the local copy or follow the link to the original publication.