A student studied the clock reaction described in this experiment. She set up re

Question

A student studied the clock reaction described in this experiment. She set up reaction mixture 2 by mixing 20 ml 0.010 m kl, 10 ml 0.010 M Na_2O_2, 10 ml 0.040 M KBrO_3 and 10 ml 0.10 M HCl using the procedure given. It took about 45 seconds for the color to turn blue. a. Find the concentrations of each reactant in the reacting mixture by noting that the number of moles of each reactant do not change when that reactant is mixed with the others, but that its concentration does. For any reactant A, moles A =M_Astock times V_stock = M_A mixture times V_mixture The volume of the mixture was 50 ml. Revising the above equation: M_Amixture = M_Astock items V_Astock(mL)/50mL Find the concentrations of each reactant by using the above equation. b. Calculate the relative rate of reaction for Mixture 2.(1000/t). Knowing the relative rate of reaction for Mixture 2 and the concentrations of 1, BrO_3, and J^+ in the mixture (question 1a), set up Equation 6, relative rate - K'(1^-) =(BrO_3)"(H't,) for the relative rate of the reaction. The only unknown quantities are k,m, n,and p. The student found that relative rate for Mixture 1.

Explanation / Answer

1)First we have to know the given data:

KI : 20mL   0.010M

Na2SO3 : 10mL    0.001M

KBrO3 : 10mL     0.040M

HCl : 10mL    0.10M

Total volume = (20 +10 + 10 + 10)mL = 50 mL

We can find molarity of each reactant with this equation:

MAmixture = [A ] = (MAstock x VAstock) /50mL

[ I-] = (MI-stock x VI-stock) /50mL = (0.010M x 20mL)/50mL = 0.0040M

[ BrO3-] = (MBrO3-stock x VBrO3-stock) /50mL = (0.040M x 10mL)/50mL = 0.0080M

[ H+] = (MH+stock x VH+stock) /50mL = (0.10M x 10mL)/50mL = 0.020M

b) Relative rate of the reaction for mixture 2 can be found using

Relative rate = 1000/t = 1000/45sec = 22 sec-1   .

c) Relative rate equation can be calculated by:

Relative rate = k`(I-)m(BrO3-)n(H+)p .

If we plug in calculated concentrations values:

Relative rate = k`(0.0040)m(0.0080)n(0.020)p = 22sec-1 .

2) In mixture 1 we can calculate relative rate using the equation:

Relative rate = 1000/t = 1000/85 sec = 11.8sec-1   .

If we both equation for relative rate we have the following:

(22sec-1/11.8sec-1) = [k`(0.0040)m(0.0080)n(0.020)p ]/ [k`(0.0020)m(0.0080)n(0.020)p ]

And canceling out the common terms:

1.9 = 2m .

Rounding 1.9 = 2

21 = 2m    and m = 1. First order reaction for I-

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