speech transcript

Liceo Scientifico Giordano Bruno - Mestre / Venezia

deep purple

chemical reactions and their different speed rates

in accordo con il

Ministero dell’Istruzione, Università, Ricerca

e sulla base delle

Politiche Linguistiche della Commissione Europea

percorso formativo a carattere

tematico-linguistico-didattico-metodologico

scuola secondaria di secondo grado

teacher

Donata Cesare

Deep Purple

Chemical Reactions and Their Different Speed Rates

Today we are going to talk about chemical reactions and their different speed rates: some are very fast, some are very slow.

The speed rate depends on the nature of the reactants but there are other factors such as the concentration of the reactants, the presence of a catalyst and the temperature.

You will see the effects of some factors in the reaction of potassium permanganate on oxalic acid.

In the lab you will use the following glassware: test tubes, beakers, graduated cylinders, glass stirring rods, pipettes.

You will need 4 hot plates with 4 magnetic stirrers, 4 stopwatches and 4 thermometers, some spatulas and some containers of distilled water.

The goal of our experiment is to verify how a redox between potassium permanganate (KMnO4) on oxalic acid (C2H2O4) is influenced by the following factors:

  • gradual decrease in the concentration of the reactants
  • presence of a catalyst
  • gradual increase in the temperature

By mixing the 2 solutions containing the reactants a chemical reaction occurs. It produces manganous sulphate (MnSO4),potassium sulphate (K2SO4), carbon dioxide (CO2) water (H2O) as you can read on the blackboard:

  • 2KMnO4 + 5C2H2O4 + 3H2SO4 2MnSO4 + K2SO4 +10CO2 + 8H2O

Next you will add 20mL, then 40mL and eventually 60mL of water.

How long does the discolouring take?

The reaction speed rate is timedwith a stopwatch.

The gradual discolouring process in the purple solution goes through the following stages:

  • purple
  • red
  • orange
  • yellow
  • colourless

From the chart and the graph you can see that the discolouring time of the reaction increases with the decrease in concentration.

The same reaction takes place as before, but you can see that in the presence of a catalyst the discolouring time of the reaction decreases…….. therefore, the reaction is faster.

The last experiment concerns a reaction affected by a change in temperature:

25°C, 35°C, 45°C, 55°C

If you use solutions of potassium permanganate with the same concentration, but the reaction is produced in a beaker with water at different temperatures, you can notice that the higher the temperature, the faster the discolouring, as you can see from the temperature and time values we have recorded:

24.6 °C2’ 14”

34.7 °C0’ 51”

43.9 °C0’ 24”

54.8 °C0’ 10”

The discolouring times of the various tests carried out at increasing temperature appear in the graph below.

Materiale sviluppato da eniscuola nell’ambito del protocollo d’intesa con il MIUR