Color-changing milk

Milk, sev­er­al drops of dye and… soap! What will hap­pen? Find out in our ex­per­i­ment!

Safe­ty pre­cau­tions

Warn­ing! Only un­der adult su­per­vi­sion

Equip­ment

• plate with milk;
• alu­minum foil;
• food col­or­ings;
• liq­uid soap;
• pipettes.

Step-by-step in­struc­tions

Pour some milk into a plate. Make four strips out of sev­er­al lay­ers of alu­minum foil, bend them at right an­gles, and set them in the milk. Drip some food col­or­ing into the milk, then add a drop of soap right in the cen­ter. The soap spreads over the sur­face of the milk, form­ing a thin film, and the food col­or­ing be­gins to spread along with it.

Process de­scrip­tion

Why does this hap­pen? On the one hand, the soap spreads out­wards as it strives to be in con­tact with as much liq­uid (in this case, milk), and as lit­tle soap, as pos­si­ble. On the oth­er hand, due to its spe­cial molec­u­lar struc­ture, soap tends to stay on the liq­uid’s sur­face. When the soap droplet comes into con­tact with the sur­face of the milk, it thus be­gins to spread out across its en­tire sur­face, push­ing the food col­or­ing out­ward and form­ing beau­ti­ful pat­terns.

A sim­i­lar ex­per­i­ment is in­clud­ed in the MEL Chem­istry sub­scrip­tion!