So I did a kinetics lab on the rate of reaction of peroxydisulfate ion with iodide ion. Part 1 was the effect of concentration. One of the questions asked is to calculate the amount of thiosulfate consumed in moles.
My results for trial 1 were
(Times taken for consumption of 1.0ml aliquots of Na2S2O3 in reaction of peroxydisulfate with iodide):
1.o ml---1:45(min:sec)
2.0ml---3:34
3.0ml---5:58
4.0ml---8:48
5.0ml---11:35
the concentrations of solutions and amounts used:
Na2S2O3 0.20M 1.0ml
KI 0.25M 10.0ml
(NH4)S2O8 0.25M 10.0ml
KNO3 0.25M 27.0ml
I've been working on this for awhile now, and I can't figure out what to do with all of this information that I have. MY lab instructor won't help me..Please help!
To calculate the amount of thiosulfate consumed in moles, we need to use the balanced equation for the reaction:
(NH4)S2O8 + 6KI + 6H2O -> 4SO4^2- + 6KOH + 2NH4+ + 5I2
From the equation, we see that 6 moles of thiosulfate (S2O3^2-) are consumed for every mole of (NH4)S2O8.
First, let's convert the time measurements from minutes and seconds to seconds only:
1.0 ml --- 1 minute : 45 seconds = 1 * 60 + 45 = 105 seconds
2.0 ml --- 3 minutes : 34 seconds = 3 * 60 + 34 = 214 seconds
3.0 ml --- 5 minutes : 58 seconds = 5 * 60 + 58 = 358 seconds
4.0 ml --- 8 minutes : 48 seconds = 8 * 60 + 48 = 528 seconds
5.0 ml --- 11 minutes : 35 seconds = 11 * 60 + 35 = 695 seconds
Next, we need to calculate the reaction rates for each trial. The reaction rate can be calculated by taking the reciprocal of the time it takes for the thiosulfate to be consumed:
Reaction rate (in seconds^-1) = 1 / time (in seconds)
For trial 1:
Reaction rate = 1 / 105 = 0.0095 seconds^-1
For trial 2:
Reaction rate = 1 / 214 = 0.0047 seconds^-1
For trial 3:
Reaction rate = 1 / 358 = 0.0028 seconds^-1
For trial 4:
Reaction rate = 1 / 528 = 0.0019 seconds^-1
For trial 5:
Reaction rate = 1 / 695 = 0.0014 seconds^-1
Now, to calculate the moles of thiosulfate consumed, we need to use the reaction rate and the initial concentration of (NH4)S2O8. We will use the first trial as an example:
Initial moles of (NH4)S2O8 = volume (in L) * concentration (in M) = 10 ml * 0.25 M * (1 L / 1000 ml) = 0.0025 moles
Moles of thiosulfate consumed = reaction rate * initial moles of (NH4)S2O8
= 0.0095 seconds^-1 * 0.0025 moles = 0.00002375 moles
Repeat this calculation for each trial to find the moles of thiosulfate consumed.