How to use cabbage to make a pH indicator

Making indicator strips at home

Safe­ty pre­cau­tions

Ob­serve safe­ty mea­sures when work­ing with heat­ing equip­ment and hot liq­uids. When work­ing with house­hold chem­i­cals, wear pro­tec­tive gloves, eye­wear, and a mask.

Reagents and equip­ment

  • 300 g red cab­bage;
  • 1 heat-re­sis­tant glass;
  • 1 cof­fee fil­ter;
  • 1 pipette;
  • cot­ton wool;
  • a fun­nel;
  • a cup;
  • a knife;
  • a cut­ting board;
  • 250 mL fresh­ly-boiled wa­ter;
  • 9% vine­gar;
  • wa­ter;
  • 10% bak­ing soda so­lu­tion;
  • drain clean­er (usu­al­ly a 10% so­lu­tion of sodi­um hy­drox­ide).

Step-by-step in­struc­tions

Dice 300 g red cab­bage. Trans­fer the cab­bage to your heat-re­sis­tant glass and add 250 mL hot wa­ter. Let stand 30 min­utes. Drain the so­lu­tion into the sec­ond glass through the fun­nel with cot­ton wool to fil­ter out the cab­bage slices. Use the pipette to ap­ply the so­lu­tion to the cof­fee fil­ter, then let the fil­ter dry at room tem­per­a­ture for 30 min­utes. Cut into strips. Cal­i­brate us­ing reagents you like­ly have on hand: vine­gar cre­ates an acidic medi­um, which turns the strip red; wa­ter cre­ates a neu­tral medi­um, so the strip stays pur­ple; the 10% bak­ing soda so­lu­tion cre­ates a ba­sic en­vi­ron­ment, which caus­es the stip to turn blue; drain clean­er (usu­al­ly a 10% so­lu­tion of sodi­um hy­drox­ide) cre­ates a strong­ly ba­sic medi­um, which turns the strip first green, then yel­low.

Process de­scrip­tion

Red cab­bage con­tains pig­ments known as an­tho­cyanins. An­tho­cyanins can also be found in many fruits, veg­eta­bles, and berries, such as blue­ber­ries, red grapes, red onions, and so on. They change col­ors in ac­cor­dance with the acid­i­ty of their en­vi­ron­ment – a prop­er­ty that can help you de­ter­mine the pH of var­i­ous sub­stances around you! They turn red in acidic medi­ums such as vine­gar, pur­ple in weak­ly acidic and neu­tral medi­ums such as wa­ter, blue in weak­ly ba­sic medi­ums such as a so­lu­tion of bak­ing soda, and green, then yel­low in strong­ly ba­sic so­lu­tions such as drain clean­er.