Foundations of chemistry

Why this chapter exists

• Everything you make is a chemical system — it reacts with disinfectant, sweat, saline, oxygen, heat
• Measurement in medicine is overwhelmingly chemical — most tests measure a concentration
• The workshop is a chemical environment — solvents, adhesives, fluxes, resins

Chapter three applies these ideas to the molecules of life and to your materials.

Inside an atom

• Nucleus: protons (positive) and neutrons; almost all the mass
• Electrons: almost all the volume; about 1/1836 of a proton's mass
• Atomic number — the proton count — defines the element
• Chemistry is the behaviour of the outer electrons
• Atoms lose, gain, or share electrons to reach a full outer shell

The gas laws

• PV = nRT — temperature always in kelvin
• Boyle: expand the chest, pressure falls, air flows in
• Dalton: each gas contributes its share of the pressure
• Oxygen in dry air at sea level: about 159 mmHg; in the warm, wet trachea about 149
• Henry: dissolved gas is proportional to partial pressure

The mole: counting atoms in batches

• One mole = 6.022 × 10²³ particles
• Mass of one mole in grams = molecular mass
• Water 18 g/mol · sodium chloride 58.4 · glucose 180
• Reactions care about moles, not grams

Equilibrium: the body's carbon dioxide buffer

• Forward and reverse rates equal; composition steady
• Le Chatelier: disturb it and it shifts to partly counteract
• CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
• Breathe off CO₂ → pH rises; retain it → pH falls
• Never mix cleaners: bleach plus acid releases chlorine gas

Batteries and thermal runaway

• Energy is roughly voltage × capacity: 3.7 V × 2 Ah ≈ 7.4 Wh
• Lithium-ion: high energy density, needs protection circuitry
• Lithium iron phosphate: lower density, more thermally stable
• Coin cells: a serious swallowing hazard
• Thermal runaway is a positive-feedback loop

The analytical workflow

• Question — what must we know, and how well?
• Sample — collect, label, store, chain of custody
• Prepare — weigh, dissolve, dilute, extract
• Separate — chromatography, centrifugation, filtration
• Detect and quantify — against calibration standards and controls
• Report — result, units, uncertainty, traceability

A result's quality belongs to the whole chain, not the instrument at the end.

Where a maker contributes

• Teaching instruments: LED colorimeters, conductivity and pH loggers
• Open-source potentiostats for teaching and research
• Lab fixtures and racks: machined, sheet metal, moulded, laser-cut — chemically compatible
• Scientific glassblowing and custom apparatus
• Lab automation and instrument-to-LIMS data scripts

Best first build: an LED colorimeter — Beer–Lambert, calibration, and noise in one afternoon.

Worked example: a dispenser for chlorine tablets

• Tablet: 1.5 g available chlorine; policy 1,000 ppm = 1 g/L → 1.5 L per tablet
• The real product: an unambiguous fill mark, not a mixer
• Solution decays — show when it was made up
• Polypropylene or HDPE; not aluminium
• Distinct shape and colour so it is never used for acids

Perhaps best of all — propose a pre-made product. Then measure whatever is built.

Workshop exercise and exit criteria

• Build a calibration curve from a food-dye dilution series
• Clinical arithmetic with units: saline, dextrose, glucose, alcohol
• Make a zinc–copper cell; watch a galvanic couple corrode
• Identify plastics by density; note what FTIR would add
• Audit five workshop substances from their safety data sheets

What this chapter does not establish

• You are literate in chemistry, not a chemist
• A straight calibration line is a teaching instrument, not a validated method
• Reading an SDS is not a risk assessment for someone else's workplace
• Accelerated ageing supports a claim; it is not shelf-life proof

Next — Chemistry and molecular biology for the maker.