Reaction Rates
Objective: Investigate the effect of varying sodium thiosulfate concentration on the reaction time and the rate of the
reaction between sodium thiosulfate and hydrochloric acid.
Safety: HCl is corrosive, sodium thiosulfate is irritating to tissue
Na2S2O3 (aq) + 2 HCl
(aq)
↔ S(s) + SO2 (g) + 2 NaCl (aq) + H2O (l)
Procedure:
A. Add 5 mL of 2.0 M HCl to 50mL of varying molar concentrations of Na2S2O3 .
B. Begin timing how long it takes for the solution to become opaque. This is accomplished by placing a black
X behind the beaker containing the solution and timing how long it takes for the X to disappear.
Data:
Beaker Volume .15 M
Na2S2O3
Volume H2O
Total volume solu- Molarity Na2S2O3
tion
Reaction time in
seconds
Reaction rate (1/
time, sec-1)
1
2
3
4
5
1. Calculations for molarity of Na2S2O3.
M 1V 1= M 2V 2
Beaker
1
2
3
4
5
2. Calculations for reaction rate ( 1/time in sec)
1
2
3
4
5
( M1 molarity of Na2S2O3 ; V1 = volume Na2S2O3 ; V2= total volume of solution)
3. Graph the concentration of Na2S2O3 (x axis) versus time in seconds (y axis). Don’t forget a title!
4. Graph the concentration of Na2S2O3 (x axis) versus the Reaction rate (1/sec-1) (y axis).
5. Identify the relationship between the concentration of Na2S2O3 and time in seconds, and explain.
6. Identify the relationship between the concentration of Na2S2O3 and reaction rate, and explain.
Conclusion: based on your observations Prove what the relationship is between the concentration and the
time for the reaction to occur compared to the relationship between the concentration and the reaction rate.