Using a demonstration of strong and weak acids, Australian researchers studied the effectiveness of using cognitive conflict strategy with Year 11 chemistry students

A woman surrounded by books and thinking

Researchers from the University of Western Australia, Maree Baddock and Robert Bucat, explored the effectiveness of using cognitive conflict strategy with 66 Year 11 chemistry students.1 Cognitive conflict arises when students observe an event which is at odds with their current understanding. The students are then encouraged to think about possible explanations and work towards a meaningful understanding of the phenomenon.  

In the three-year project the researchers used information gathered from the teaching of a lesson in one year to help modify the teaching in the following year to enhance students' learning. The researchers used a demonstration which showed the colour of methyl violet indicator in hydrochloric acid of concentrations 1 M, 0.1 M, 0.01 M and 0.001 M and 1 M ethanoic acid.  

In the first year's lesson the teacher showed students the colours of the indicator with the hydrochloric acid solutions and asked them to predict the colour of the indicator in ethanoic acid. The demonstration was chosen to surprise students by showing them that the colour of the indicator with 1 M ethanoic acid is not yellow as with 1 M HCl but purple, which is similar to the result with 0.01 M HCl. The students had to write a report on the lesson to include what they thought was the aim of the demonstration and explain what they had observed and what they had learnt. The researchers found that the students could not relate the difference between the two 1 M acid solutions to the different hydrogen ion concentrations.  

The following year, based on the findings of the first year, the researchers encouraged the teacher to support the learning by providing a similar group of students with the formulae of the acids and the hydrogen ion concentrations of the hydrochloric acid solutions. Analysis of the second cohort's reports showed that this support produced the desired cognitive conflict but the students still could not formulate a reasonable explanation for the result.  

In the third year, the teacher tried to lead the class by initially talking about the ionisation of hydrochloric acid and again writing the hydrogen ion concentrations on the board. But even with this level of support the students could not make the leap to the correct explanation for why ethanoic acid is a weak acid.