"Photosynthesis" experiment

How to make oxygen with the help of a plant

Here is an in­ter­est­ing and en­ter­tain­ing ex­per­i­ment that lies on the bor­der­line of two sci­ences – chem­istry and bi­ol­o­gy. You can eas­i­ly re­peat it at home and amaze your friends and fam­i­ly.

Reagents and equip­ment

  • so­lu­tion of bak­ing soda (5 g/l);
  • wa­ter plant (in our case it is wa­ter­weed);
  • beaker;
  • fun­nel;
  • test tube;
  • match or splin­ter;
  • lamp.

Step-by-step in­struc­tions

Place the wa­ter plant in the beaker, cov­er it with a fun­nel and fill the beaker with the salt so­lu­tion, then place a test tube con­tain­ing wa­ter in the fun­nel. Turn on a bright light and wait for around two to three hours. Af­ter the test tube fills com­plete­ly, care­ful­ly re­move it from the fun­nel and hold a smol­der­ing splin­ter or match up to it. Watch the splin­ter burn.

Pro­cess­es de­scrip­tion

Pho­to­syn­the­sis is a com­plex bio­chem­i­cal process in which light en­er­gy trans­forms into the en­er­gy of chem­i­cal bonds, or more sim­ply it is a process in which car­bon diox­ide and wa­ter trans­form into or­gan­ic sub­stances and oxy­gen un­der the im­pact of light:

СО₂ + Н₂О → Or­gan­ic sub­stances + О₂

It is easy to prove the pres­ence of oxy­gen – just low­er a smol­der­ing splin­ter or match into the test tube, and it will im­me­di­ate­ly flare up, as oxy­gen is a gas that sup­ports com­bus­tion.

Why the so­lu­tion of bak­ing soda is re­quired: as the car­bon diox­ide in the air dis­solves poor­ly in wa­ter, to in­crease its con­cen­tra­tion we can use car­bon­ates or bi­car­bon­ates, which by their na­ture are salts of car­bon­ic acid (CO₂・H₂O).