Testing for carbon dioxide with limewater
Make carbon dioxide from marble chips and acid, then bubble it, your breath and fresh air through limewater to see which turn it milky.
Core concept
Carbon dioxide turns limewater milky
Topic: Air and gases
carbon dioxide: A gas we breathe out. Plants take it in to make their food. All key words is a colourless gas with no smell, so you cannot see it. Chemists test for it with limewater, a clear solution: A mixture where one substance has dissolved completely in a liquid, like salt water. All key words of calcium hydroxide. When carbon dioxide bubbles through limewater, it reacts to form tiny particle: A tiny piece that matter is made of, far too small to see. All key words of chalk (calcium carbonate), which make the limewater milky. In the laboratory, carbon dioxide is made by adding dilute hydrochloric acid: A substance that tastes sour, like lemon juice or vinegar. It turns blue litmus red. All key words to marble chips.
What you will learn
- Describe how carbon dioxide is prepared from marble chips and dilute acid.
- Use the limewater test to identify carbon dioxide.
- Show that the air we breathe out contains more carbon dioxide than fresh air.
Before you start
- Know that bubbles of gas can be evidence of a chemical reaction.
Materials
- Marble chips (calcium carbonate)
- Dilute hydrochloric acid
- Limewater
- Drinking straw and air pump
Equipment
- Conical flask with a delivery tube
- 3 test tubes in a rack
Procedure
- Add dilute hydrochloric acid to the marble chips in the flask to make carbon dioxide.
- Bubble carbon dioxide from the flask through the limewater in Tube A.
- Breathe out gently through a straw into the limewater in Tube B.
- Pump fresh air through the limewater in Tube C.
- Compare the three tubes.
How this simulation is simplified
- Fresh air contains a little carbon dioxide (about 0.04%), too little to turn limewater milky in a short test.
- Bubbling gas does not change the liquid volume.