The new task | Specialists from Science Section ERI and their experts | EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA 1/2016
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SCHOOL
SCIENCE
IN SHOR
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EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA | ebis.ibe.edu.pl | ebis@ibe.edu.pl | © for the article by the Authors 2016 © for the edition by Instytut Badań Edukacyjnych 2016
The new task
of the Science Section
of the Educational Research Institute
Presented task is prepared by the Science Section of Educational Research Institute for the third and fourth stage of education. Presented task has not been previ-ously published. It is valuable mostly because of the sig-nificant practical context: touching real problems that students may encounter in everyday life.
Chemistry – Marsh gas
Task
Adam has read that methane may be produced by bacteria in the process of decomposition of organic matter. This process can be observed for instance in the marshes – gas bubbles which are rising to the surface include methane.
In order to confirm this information, Adam has developed the system shown in the figure below. He placed marshy soil in an Erlenmeyer flask. The flask was connected by a glass pipe to a graduated cylinder filled with water.
After several hours, the graduated cylinder was filled with the colorless gas, which displaced water from it.
Whether on the basis of this experiment can you
draw the following conclusions? Statements
Can you deduced this from the experiment?
1. The gas in the graduated cylinder has
a lower density than water. Yes / o No 2. The gas in the cylinder is poorly
soluble in water. Yes / o No 3. The gas in the cylinder is flammable. o Yes / No
Commentary
A skill measured in this task is the reasoning on the basis of results of experiment. This is one of the most important and also one of the most difficult skills that student should acquire in the course of teaching
chem-The authors:
CHEMISTRY – author of the item: Magdalena Czugała; author of the commentary: Małgorzata Musialik
Specialists from Science Section ERI and their experts
The new task | Specialists from Science Section ERI and their experts | EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA 1/2016
89
SCHOOL
SCIENCE
IN SHOR
T
EDUKACJA BIOLOGICZNA I ŚRODOWISKOWA | ebis.ibe.edu.pl | ebis@ibe.edu.pl | © for the article by the Authors 2016 © for the edition by Instytut Badań Edukacyjnych 2016
istry. To solve the task correctly, it should be noted that at the beginning of the experiment a reversed upside down graduated cylinder was completely filled with water, and after several hours it has filled at the top with the gas that partially displaced water from it. Then, it should be deduced that this gas – methane – must be poorly dissolved in water, since it was accumulated over the surface (2nd statement) and that it has a density lower
than water, and therefore it was raised to the surface (1st
statement). After collecting the gas in the graduated cylinder, none experiment was performed to verify its flammability, for example by insertion lighted torch into the graduated cylinder, and although methane is the combustible gas, it is not demonstrated in this particular experiment.
This item was tested on a group of 118 graduates from lower secondary school. The following table shows the percentage distribution of their responses (the correct answers are marked in bold, percentages do not sum up to 100% because some students did not indi-cate any response).
Statements
Students’ responses [%]
1. The gas in the graduated cylinder has a lower density than water.
Yes (71,2%) / No (28,0%) 2. The gas in the cylinder is poorly soluble
in water.
Yes (72,0%) / No (27,1%) 3. The gas in the cylinder is flammable. Yes (43,2%) / No (55,9%)
The whole item was successfully solved by 39% of students participating in the study. Three quarters of the students had no major difficulties with the assessment of 1st and 2nd statement, while only 56% of the students
indicated the correct answer in the case of 3rd
state-ment, which means they could not interpret the results
of experiment or did not notice that the evidence for this statement can be found in the description of experiment. The item was difficult for the students, and rather poor-ly differentiated in terms of their skill level, i.e. the total score obtained by the student in the entire test.
The item is compliant with the following require-ments of the core curriculum for chemistry at ISCED 2 level:
General aims of education – learning outcomes:
II. Reasoning and application of acquired knowledge to solve problems.
2.1 The student describes the properties of substan-ces and explains the course of simple chemical processes; knows the relationship between the properties of various substances and their appli-cations, and their impact on the environment (...). III. Mastering the practical activities.
3.2 The student designs and carries out a simple che-mical experiments.
Learning content – specific requirements:
Substances and their properties. A student:
1) describes properties of substances being the main components of daily use products, e.g. rock salt, sugar, flour, water, copper, iron; carries out exper-iments in which properties of selected substances are tested;
8. Carbon and its compounds with hydrogen. A stu-dent:
4) observes and describes physical and chemical pro-perties (combustion reactions) of alkanes on the example of methane and ethane;
