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Stage 2 Chemistry: Design Investigation: Rates of Reactions (Research…
Stage 2 Chemistry: Design Investigation: Rates of Reactions
Research Questions
What is a lethal dose of "cyanide"?
Does sodium thiosulphate have health risks in high concentrations?
How do I know when the reaction is complete?
Known Factors
Na2S203 + 2HCl -> S(s) + 2NaCl + SO2(g) + H2O(l)
2M HCl is available
0.15M Na2S2O3
Possible Hypotheses
As the concentration of sodium thiosulphate increases, then the rate of the reaction will increase
If the temperature of sodium thiosulphate is increased, then the rate of reaction will also increase
Limitations of Design
The SO2 gas produced is quite toxic and causes irritation, low volumes will have to be used
Dilutions require time to prepare, which means less time for the experiment
Temperature using the provided equipment is hard to maintain and can change during the course of a reaction, affecting the results
Controlled Variables
Volume of the HCl (constant as 10 mL)
Concentration of the HCl (2M or 1M more realistically)
Volume of sodium thiosulphate (kept at 10 mL)
Uncontrolled Variables
Temperature of the room
Affects the rate of the reaction
Independent Variable
Concentration of sodium thiosulphate, (0.5M initially)
Concentrations used are (0.5M, 0.4M, 0.3M, 0.2M, 0.1M)
Temperature interval of sodium thiosulphate. room temp., 30, 40, 50, 60,
Dependent Variable
The time taken until the "x" disappears from view (obscured)