Untitled
Mass conservation
AIM
The aim of this experiment is to show that mass is conserved during a chemical reaction.
The Law of Conservation of Mass, established in 1789 by French Chemist Antoine Lavoisier, states that mass is neither created nor destroyed in any ordinary chemical reaction. Or more simply, the mass of products by a chemical reaction is always equal to the mass of the reactants. (E, Durnford
1999)
The reaction between potassium iodide and lead (II) nitrate under room temperature and atmospheric pressure results with a yellow precipitate. This reaction can be expressed by the equation: 2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
HYPOTHESI ...view middle of the document...
Zero the balance and put both beakers together on the balance (balance is big enough for two beakers). Weigh their total mass accurately.
Record the mass obtained including uncertainties.
Carefully pour the lead (II) nitrate solution into the 100 mL beaker containing the potassium iodide.
Record the observation during the reaction.
Use a glass rod to carefully stir the mixture in order to make sure the reaction is completed. Re-zero the balance. Place both beakers back on balance and weigh their total mass.
Record the mass obtained including uncertainties.
When finished, pour the contents of the beakers into the laboratory sink.
Rinse the beakers and the measuring cylinders under tap water.
Dry the beakers and the measuring cylinders.
Repeat steps 2-12 another four times to maintain accurate results.
RISK ASSESSMENT
CHEMICAL RISKS AND HANDLING:
Lead nitrate is toxic and is categorised as possibly carcinogenic to humans. Potassium iodide is a mild irritant and may be harmful if swallowed and irritating if inhaled. Their product, lead (II) iodide may cause irritation if contacts with skin and eyes. Therefore safety glasses and apron should be worn all the time. Prevent as much ingestion, inhalation and skin contact with the chemicals as possible. Wash hands thoroughly after the practical to eliminate any chemical residue.
PROCEDURAL RISKS AND DISPOSAL:
Beware of holding the beakers while putting them on the balance. Spillage of chemical could make contact with skin and burn the skin. All chemicals should be disposed by pouring them carefully into a sink after the experiment.
EMERGENCY TREATMENT:
Basic treatment of chemical irritation involves by washing the chemical substance off the skin in order to prevent further contact with the offending chemical. If eye irritation occurs, immediate and thorough irrigation of the eye with tap water should be performed in order to prevent damage to the cornea. If a toxic chemical has been swallowed, immediately seek help by calling an ambulance and going to hospital.
Result
Trials
Mass before weighing(�0.001g)
Weight after weighing(�0.001g)
1
138.805g
138.785g
2
139.007g
138.997g
3
138.794g
138.776g
4
138.638g
138.609g
5
138.798g
138.770g
Qualitative data:
Yellow precipitate was produced.
There were some spillages of the product.
Processed data
Trials
Mass difference � 0.002g
Mass difference express as percentage
Random Error
1
0.020
0.014%
0.0014%
2
0.010
0.0072%
0.0014%
3
0.018
0.0013%
0.0014%
4
0.029
0.021%
0.0014%
5
0.028
0.020%
0.0014%
Average
0.021
0.013%
0.0014%
Conclusion
The mass of both the beakers and their contents before the reaction was not the same as the mass after ...
