what are the controls for the following experiments?:
1) to show that there is carbon dioxide in air.
2) to show that there is water vapour in air.
3) to conduct a qualitative experiment to detect the presence of dissolved solids in water samples.
4) to test water for hardness.
None of them need controls?
1) 2 test tubes - lime water in both. Breath in through A and out through B. B tyrns milky, A stays clear. A isnt really a control but more a way of demonstrating its the exhaled air that contains the CO2
3) no control
4) you are testing water for hardness - comparative experiment to test different samples of water