The document describes how hydrogencarbonate indicator is used to measure carbon dioxide levels. It changes color from red through orange, yellow, magenta to deep purple as carbon dioxide levels increase or decrease. Experiments show the indicator turning more yellow when exposed to carbon dioxide from respiration or combustion, and more purple when exposed to plants undergoing photosynthesis as carbon dioxide is removed.

1. Hydrogencarbonate Indicator
Increasing CO2 in
indicator
yellow
pH 7.6
orange
pH 7.8
Decreasing CO2 in
indicator
Atmospheric
CO2 level
pH 8.0
red
pH 8.2
pH 8.4
magenta
pH 8.6
pH 8.8
purple
pH 9.0
Hydrogencarbonate indicator is used to measure carbon dioxide levels.
It is red in equilibrium with atmospheric air.
It becomes more orange/yellow with increased carbon dioxide levels.
It changes from red through magenta to deep purple as carbon dioxide is removed.
pH 9.2

2. Carbon dioxide released from a burning candle or a
terrestrial organism can be added to hydrogen
carbonate indicator.

3. Start point
pH 8.4 (cherry red);
0.04% CO2 in atmosphere
Respiration or Combustion
pH 8.0 (yellow); more yellow because of increased CO2 produced
in respiration or combustion (creates carbonic acid).

4. How can we show that plants
use carbon dioxide in
photosynthesis?

5. Result in bright light

6. Start point
pH 8.4 (cherry red);
0.04% CO2 in atmosphere
Photosynthesis
pH 9.2 (purple); more purple because CO2 is being removed from
the indicator for use in photosynthesis.
This reduces the amount of carbonic acid in the solution so it
becomes more alkaline