Results:
Observation:
As the calcium reacted with the water, I observed the calcium effervescing, and the calcium moved up and down in the cylinder during the reaction. As the reaction progressed, the piece of calcium gradually dissolved smaller and smaller until it was completely dissolved in the water.
Discussion:
Possible Sources of Error:
- Parallax error- I may have read the level of water in the measuring cylinder incorrectly because it was inverted and I may have not been looking parallel to the markings.
- Experimenter’s error- My reaction time in recording the results may not have been quick enough which would cause an incorrect reading in time.
- Experimenter’s error- The trough was not cleaned before usage, and tap water was used in the experiment instead of distilled water. The fact that the apparatus may have contained impurities may have affected the results.
Summary of Chemical Concepts:
Calcium has a higher position then hydrogen in the reactivity series. This means that calcium is more reactive than hydrogen and reacts readily when it comes into contact with water. When the metal (calcium) was added to the water, the metal hydroxide (calcium hydroxide) and hydrogen were formed. As the reaction progressed, the hydrogen caused a pressure and gradually displaced the water and pushed it out of the measuring cylinder. As the calcium reacted, more hydrogen was produced, and the water level in the measuring cylinder decreased because of the hydrogen displacing the water. At the end of the reaction, the calcium dissolved in the water leaving an aqueous solution of calcium hydroxide.
2Ca(s) + 2H20(l) 2Ca(OH)2(aq) + H2(g)
Calcium Water Calcium Hydroxide Hydrogen
Conclusion:
The rate of reaction was fastest in the first 40 seconds and slowest in the last 40 seconds. This shows that as the reaction went on, the products were used up and the rate of reaction was slowed down.
Time/sec Volume of H2/cm
0 0
40 1.5
80 2.5
120 3.2
160 3.7
200 3.8
240 3.8
