In a solution at constant H+ concentration, iodide ions react with hydrogen peroxide to produce iodine.
H+ + I- + 1/2H2O2 --> 1/2I2(aq) + H2O
The reaction rate can be followed by monitoring the appearance of I2. The following data were obtained:
[I-]____[H2O2]____Initial rate (M/min)
.015____ .030 ____.0022
.035____ .030 ____.0052
.055____ .030 ____.0082
.035____ .050 ____.0087
a) Write a rate expression for the reaction.
My answer --> rate= K[I-][H2O2]
b) Calculate K.
My work/answer -->
.0022 M/min= K[.015M][.030M]
.0022 M/min= 4.5 E-4 M^2 * K
4.9 1/M*min= K
c) What is the rate of the reaction when 25.0 mL of a .100 M solution of KI is added to 25.0 mL of a 10.00% by mass solution of H2O2 (d= 1.00 g/mL)? Assume volumes are additive.
My answer -->
I have been unable to figure out this part. I know KI is just used to introduce I- into solution, but I don't know how to go about solving it. Any help would be appreciated.
To calculate the rate of the reaction when 25.0 mL of a 0.100 M solution of KI is added to 25.0 mL of a 10.00% by mass solution of H2O2, we can follow these steps:
1. Calculate the moles of KI:
Since the volume is given in milliliters, we need to convert it to liters:
25.0 mL = 0.0250 L
Now, we can calculate the moles of KI using its molarity:
Moles of KI = Molarity x Volume
= 0.100 mol/L x 0.0250 L
= 0.00250 moles
2. Calculate the mass of H2O2:
The concentration of H2O2 is given as a percentage by mass. This means that for every 100 g of the solution, 10.00 g is H2O2.
Therefore, the mass of H2O2 in 25 mL (or 25 g, since the density is 1.00 g/mL) is:
Mass of H2O2 = (10.00 g/100 g) x 25 g
= 2.50 g
3. Calculate the moles of H2O2:
Since the molar mass of H2O2 is 34.02 g/mol, we can calculate the moles of H2O2:
Moles of H2O2 = Mass / Molar Mass
= 2.50 g / 34.02 g/mol
= 0.0736 moles
4. Use the rate expression to calculate the rate of the reaction:
As given in the question, the rate expression is: rate = K[I-][H2O2]
Substitute the values into the rate expression:
rate = K x [0.00250 moles] x [0.0736 moles]
rate = 0.182 K
Therefore, the rate of the reaction when 25.0 mL of 0.100 M KI is added to 25.0 mL of a 10.00% by mass solution of H2O2 is 0.182 K.