2014: kinetics 02

SECTION EUROPEENNE Epreuve spécifique de sciences physiques en anglais. How to protect a metal from corrosion?

The primary function of a rain gutter is to direct water from the roof of a home to the ground in such a way that it does not damage the building or lawn. Document 1: acid rain

Document 2: Zinc is a metal, which is corroded by an acidic environment, according to the following reaction: Zn(s) + 2 H3O+ (aq) → Zn2+ (aq) + H2 (g) + 2 H2O (l) In order to study the influence of experimental factors on the corrosion of zinc, a sulphuric acid solution is poured into an Erlenmeyer containing zinc powder. The Erlenmeyer flask is kept in a constant-temperature bath. The conditions and results of three experiments are given below: Temperature Initial mass of zinc Zinc form Volume of sulphuric acid solution Initial concentration of H3O+ in the solution Reaction half-time t1/2

Experiment 1 25°C 0,50 g Powder 75 mL

Experiment 2 25°C 0,50 g Powder 75 mL

Experiment 3 25°C 0,50 g Powder 75 mL

0,50 mol.L-1

0,25 mol.L-1

0,40 mol.L-1

32 min

48 min

37 min





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2014: kinetics 02 Document 3: Study of the influence of the form of zinc In wet weather conditions, zinc is progressively coated with a thin layer of zinc carbonate that gives it a natural patina aspect, so that it doesn’t require any protective painting. Three experiments have been carried out at 25°C, from 0.50g of zinc power (experiment A), 0.50 g of zinc small chips (experiment B), and 0.50 g of zinc small chips coated with a thin layer of zinc carbonate. The volume of sulphuric acid solution and the initial concentration in oxonium ions are identical. The progress of the reaction versus time is plotted on the graph below for each of these three experiments. A

A B

C

Task: Imagine you are a technical salesman who works for a rain gutter company. The rain gutters you sell are made of zinc and constructed in one seamless continuous piece. Use the results of these experiments to describe the advantages of the zinc gutters made by your company and try to convince your clients (the jury) of their long lifespan. For the sake of clarity, please define all the technical words pH, half-time, progress of the reaction… that you use during your presentation.



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2014 : kinetics 01

SECTION EUROPÉENNE Épreuve spécifique de sciences physiques en anglais

How to make some bread? Doc 1: the recipe of bread

1.

In a large bowl, mix warm water, yeast, and 1/3 cup honey. Add 5 cups white bread flour which is principally made of starch, and stir to combine. Let set for 30 minutes, or until big and bubbly

2.

Mix in 3 tablespoons melted butter, 1/3 cup honey, and salt. Stir in 2 cups whole wheat flour. Flour a flat surface and knead with whole wheat flour until not real sticky. Place in a greased bowl, turning once to coat the surface of the dough. Cover with a dishtowel. Let rise in a warm place until doubled.

3.

Punch down, and divide into 3 loaves. Place in greased 9 x 5 inch loaf pans, and allow to rise until dough has topped the pans by one inch. Then bake at 175 degrees C for 30 minutes; do not overbake. Cool completely.

Vocabulary : Starch : amidon Yeast : levure Dough: pate Knead: pétrir Sticky: gluant Pans: casseroles

Doc 2: the reactions inside the dough





Doc 3: The gas produced during the reaction Bubble through lime water (CaOH) and turns into cloudy.

ethanol

Doc 4 : Yeasts are considered as catalysts for the reaction of fermentation. You could find them inside the baking powder and have been used by bakers for hundreds of years to make bread. The gas bubbles formed in the dough as it is cooked cause the bread to rise. Doc 5: curve of the quantity of gas produced in different conditions against time



1 : with yeast 2 : Without yeast 3 : without yeast in the fridge Task : Pauline wants to make some bread at home but she doesn’t know how to do it… On the web, she has found a recipe but she doesn’t really understand why she has to follow these steps …. Help her to bake some bread, and explain to her the interest of using yeast.

Feel free to use or not the previous documents to make your presentation. • • •

Explain why the bread is rising and why the dough produce some bubbles. Why is it interesting to use some yeast during this reaction? Do you know other methods you could use in order to increase the rate of reaction?