The Science of Laundry

Louise from the Ontario Science Centre introduces an experiment to determine the best conditions for removing different types of stains. She explains the concepts of constants (fabric type, water) and variables in an experiment, demonstrating with an old cotton t-shirt cut into squares and a bowl as a stand-in for a washing machine.

The video focuses on oil stains and explains why oil and water don't mix. It delves into the molecular structure of water (H2O), which is polar due to electron distribution, forming hydrogen bonds. Oil, on the other hand, is non-polar, with long carbon chains where electrons are evenly distributed, making it immiscible with water.

The first variable tested is temperature. Oil-stained fabric squares are washed in cold water (10-12°C) and hot water (50°C+). The results show that while mixing and agitation spread the stain, neither cold nor hot water alone effectively removes the oil stain. Hot water might make it slightly lighter but isn't a significant improvement.

The video then introduces laundry detergent and explains its function. Detergent molecules are amphiphilic, possessing a polar (hydrophilic) head attracted to water and a nonpolar (hydrophobic) tail attracted to oil. This dual nature allows detergent to encapsulate oil within micelles, enabling it to be washed away with water.

The oil stain experiment is repeated, this time adding laundry detergent directly to the stain. Fabric samples are washed in cold water with detergent and hot water with detergent. The results show that cold water with detergent significantly removes the stain, and hot water with detergent completely removes it, indicating that warmer water and detergent are the best for oil stains.

The video moves on to a tough stain: egg yolk, which contains proteins and fats. It explains that proteins are chains of amino acids, which can be polar or nonpolar, and their folding is influenced by water. The video then demonstrates how heating an egg causes protein denaturation and aggregation, making them insoluble in water, as seen when egg white turns opaque.

The egg yolk stain experiment is conducted in two sets: one washed in water alone (cold and hot) and another with detergent (cold and hot). Cold water alone removes most of the egg yolk stain, leaving a faint yellow residue from fats. Hot water alone leaves a definite dark yellow stain due to insoluble protein aggregates. Cold water with detergent almost completely removes the stain, while hot water with detergent leaves a noticeable yellow ring from set proteins.

The experiment concludes that the best conditions for removing egg yolk stains are cold water and detergent. The video then offers practical laundry tips: always check fabric care labels, treat stains immediately to prevent them from setting, pretreat unknown stains with detergent in cold water first (to avoid setting protein stains), and air dry stained items as hot air from a dryer can set stains.