Chem II Lab 14- A Clock Reaction

reaction rates depend on

the nature of the reactants, the concentration of the reactions, the temperature, and the presence of a catalyst

increasing the concentration of reactants increases

particles for unit volume and number of collisions

increasing the temprature increases

average kinetic energy and velocity

rate of disappearance formula

- change in concentration/ change in time

rate of appearance formula

change in concentration/ change in time

rate law equation

rate= k[A]^x[B]^y

when the solution turns blue-black what has been formed ?

I² (iodine), which reacts with the starch that we added previously to become blue-black

when the solution turns blue-black what has been consumed ?

S2O3^2- (thiosulfate), which turns the I² to I^- to break its bond with starch, once the reaction is blue-black again it indicates the thiosulfate is no longer effective

when the solution is clear what is present ?

2I^- (aq) + 2S₂O₈^2-

when the solution is blue-black what is present?

I² (aq) + 2 SO4^2- + starch

what is the formula for the reaction we are testing ?

2 I^- (aq) + S₂O₈^2- (aq) → I² (aq) + 2SO₄^2- (aq)

if doubling the concentration of a reactant quadruples the rate then the order is

2

if double the concentration if a reactant doubles the rate the order is

1

what is the role of KNO₃

maintains ionic strengths and balances changes in KI by maintaining relative number of ions in the solution, add spectator ions to make sure solutions are the same

what is the role of KI

to provide and disassociate its I^- ions to react with the peroxydisulfate (Na₂S₂O₈)

role of starch

to react with iodine (I²) to make a blue-black complex

role of sodium thiosulfate (Na₂S₂O₃)

to consume iodide (I²) produced and bring it back to (I^-)

how does a catalyst effect the reaction rate

it changes the ration pathway so that less energy is needed per collision and (energy of activation is lowered

reaction rate units

mol./s

instantaneous rate

the rate of a given point in time (derivative of a curve

how to calculate rate constant w/ rate equation, rate, and the concentrations of the reactants

k= rate/ [A]x[B]y

how to find orders of reactants from rate and concentrations at different experiments

divide rates at two different experiments, and the concentration of one reactant to find coefficient

what part of the rate law equation do we determine in the experiment?

x,y, and k

peroxydisulfate

S₂O₈^2-

sulfate

SO₄^2-

iodide

I^-

Iodine

I²

what was the source of I^- ?

KI, potassium iodide

what was the source of S₂O₈^2-?

Na₂S₂O₈

what components were in solution A ?

KI, KNO₃, Na₂S₂O₈, EDTA, Starch

what components were in solution B ?

Na₂S₂O₈

role of EDTA

takes out chemical impurities that messes up rxn

which two components create the clock reaction ?

sodium thiosulfate (S₂O₃^2-) and starch

how does the clock creation work

when I^- becomes I², it reacts with the starch to make a blue-black complex, when the sodium thiosulfate (S₂O₃) is added to the reaction, I² returns to I^- and the reaction starts over

how did we calculate the moles of Thiosulfate (S₂O₃^2-)

L in aliquots (0.0004) 0.4 mol/L =1.6×10^-4

how do we calculate moles of Disulfate ? (S₂O_8)?

mol S₂O₃ × 1mol I² /2mol S₂O₃ × 1mol/1mol = molS₂O₈ (0.8 × 10^-4)

units of the slope in mols/time graph

mol/s

what are the units of rate ?

M/s or mol/L

how do we convert a slope to the rate ?

divide it by the total volume of the solution

what equation do we use to calculate concentrations in reactions ?

m₁v₁=m₂v₂