Cleaning Chemistry and Agents
What the exam tests
Chemistry questions ask you to choose an agent by pH, charge, and soil type, then predict what it will do to the fiber and dye. The exam favors practical decisions: which pre-spray, which spotter, which bleach, and when to use water at all.
Core rules
- pH governs fiber risk. Wool and silk prefer mildly acidic to neutral (about pH 4.5–6.5). Cotton and other cellulosics tolerate mild alkali, but alkaline residue plus slow drying causes browning. Nylon and acid-dyed fabrics can shift color at high pH.
- Surfactant charge matters. Anionic surfactants lift particulate soil; nonionic surfactants emulsify oils and are compatible with most systems; cationic surfactants are germicidal and antistatic but can precipitate anionic detergent and leave residue. Never mix incompatible concentrates.
- Solvents dissolve what water cannot. Volatile dry solvent lifts grease, tar, and oil-based ink; perchloroethylene is the standard dry-cleaning solvent. Water-based detergents remove sugars, salts, and water-soluble soils.
- Bleaches are last resort. Oxidizing bleaches (hydrogen peroxide, sodium percarbonate) attack organic color; reducing bleaches (sodium bisulfite) strip oxidized color and can help dye bleed. Test both on a hidden area.
- Spotting is stain-specific. Protein stains (blood, egg, milk) need cold water and enzyme/protein spotter; tannin stains (tea, coffee, wine) respond to acid; rust needs an acid rust remover; oil needs solvent.
Worked example
A customer points to a brown mark on a cotton-blend seat. You test with a tannin spotter: the mark lightens. That supports a tannin stain, not rust (rust would not respond) and not blood (blood would respond to protein spotter, and hot water would set it). You apply acid tannin spotter, rinse, extract, and dry quickly.
Traps
Using hot water on protein stains; mixing chlorine bleach with ammonia or acid (toxic gas); over-alkalizing wool; leaving detergent residue that resoils; bleaching a dye that will bleed.