Chemistry

Name: Beklau Abebe

5/8/2013

Iodine Clock

Abstract: The purpose of this lab is to determine the orders of reaction and the rate constant of reaction between I- and S2O82- and to examine the effect of catalyst.

Chemical Equations:

3 I-(aq) + S2O82-(aq) I3-(aq) + 2 SO42-(aq)

I3-(aq) + 2 S2O32-(aq) 3 I-(aq) + S4O62-(aq)

I3-(aq) + Starch(aq) Starch—I3- complex

Formulae:

Rate = k[reactant 1]a[reactant 2]b[reactant 3]c…

where: k: rate constant

[reactant 1/2/3/…]: concentration of reactant 1/2/3/…

a/b/c/…: order of reaction with respect to each reactant

k = Ae-Ea/RT or ln k= -EaR1T + ln A

where: A: Arrhenius proportionality factor (unique to each reaction)

R: Universal constant

T: Temperature

Ea: Activation energy

Objective: To understand the orders of reaction and the rate constant

Procedure: Sodium meta-bisulfite (Na2S2O5) undergoes the following transformation when dissolved in water where it dissolves and reacts with the water to form bisulfite (HSO3-) :

Na2S2O5 + H2O --- > 2HSO3-+ 2Na+

When mixed with potassium iodate (KIO3) the following reaction mechanism is proposed leading to the observed color change:

1. Data and calculations:

Table 1. Rates of reactions |

  | Trial | [I-]o (M) | [S2O82-]o (M) | Time 1 (s) | Time 2 (s) | Average time (s) | Δ[S2O82-] (M) | Rate (M/s) |

Part A | 1 | 0.084 | 0.042 | 26.5 | 25.7 | 26.1 | 6.3E-04 | 2.4E-05 |

| 2 | 0.042 | 0.042 | 57.6 | 49.0 | 53.3 | 6.3E-04 | 1.2E-05 |

| 3 | 0.021 | 0.042 | 97.7 | 90.2 | 94.0 | 6.3E-04 | 6.7E-06 |

| 4 | 0.011 | 0.042 | 195.3 | 185.6 | 190.5 | 6.3E-04 | 3.3E-06 |

Part B | 5 | 0.042 | 0.084 | 22.8 | 22.8 | 22.8 | 6.3E-04 | 2.8E-05 |

| 6 | 0.042 | 0.042 | 47.2 | 51.2 | 49.2 | 6.3E-04 | 1.3E-05 |

| 7 | 0.042 | 0.021 | 88.3 | 94.5 | 91.4 | 6.3E-04 | 6.9E-06 |

| 8 | 0.042 | 0.011 | 159.9 | 160.3 | 160.1 | 6.3E-04 | 3.9E-06 |

Part C | 9 | 0.042 |...