Question

Preliminary: Key Chemical Equations Reaction 2 Fe3 (a)3 I(a)2 Fe(aq) + I3'(aq) I3(ag) 2 S2032(aq) 3 1a)S4O(0) Reaction 2: + + Prelab Questions 1. List and define any new terms relevant to this experiment 2. Write the general formula for the rate law for Reaction 1 (given above) 3. Write the general formula for calculating average rate bases on the disappearance of thiosulfate (S2O,2) in Reaction 2 (given above) 4. Write the equation used for calculating a concentration after dilution 5. Calculate the concentration of the Fe3 ion if 20 mL of a 0.40 M solution is diluted to 120 mL total volume 6. Calculate the average rate of disappearance of S20,2 if 20.0 mL of a 0.010M solution completely reacts in 9.7 seconds

Answer 1

1. Rate of a reaction: The rate of a reaction is the change in concentration of a reactant or product per unit time. In terms of product the concentration increases er unit time whereas in terms of reactant the concentration decreases per unit time.

2. General formula for the rate law for reaction 1 is

R= -1/2 {d[Fe⁺³]/dt} = -1/3 {d[I^-]/dt} = 1/2 {d[Fe⁺²]/dt} = {d[I^-3]/dt} = k[[Fe⁺³]^a [[I^-]^b

Where a and b are the order of the reaction with respect to the Fe⁺³ and I^- ions respectively.

The (+) symbol is for formation of the product i. e. accumulation of the concentration of the product whereas (-

3. For reaction 2 the average rate of the reaction for disappearance of thiosulphate ion is given by the following expression:

R= -1/2 {d[S₂O₃^-2]/dt}

4. The equation used for calculation of concentration after dilution is M₁V₁ =M₂V₂

Where M₁ is the concentration before dilution and V₁ is the volume taken for dilution from the solution of concentration M₁.

Further, M₂ is the concentration after dilution and V₂ is the final volume after dilution.

5. By using the above equation ,

M₁ = 0.40 M, V₁ = 20 ml, M₂ = ? V₂ = 120 ml

M2 = (M₁V₁ / V₂ ) = (0.40 x 20 / 120) = 0.066 M

The concentration of Fe+3 ion will be 0.066 M.

6. 20 ml = 20/1000 L = 0.02 L

Rate of disappearance of thiosulphate is dc/dt = (0.02 L x 0.010 M) / 9.7 s = 2.061 x 10^-5 mol / sec