Analysis of the Driver R et al (1994) report also suggested some other additional misconceptions, which I had not drawn from my interviews. These were that, hydrogen gas is produced during the neutralisation reaction of acids and alkalis. Also the amount of hydrogen that is displaced from the reaction is proportional to the strength of the acid used in the reaction. This is because pupils believe the stronger an acid is, the greater the number of hydrogen bonds it has to break.
Additional data also reveals the importance that pupils place upon acids is also suggested by both Carr M (1984) and Driver et al (1994). They suggest that pupils’ knowledge of acids are obtained from their sensory perceptions, such as acids taste sour and from crime stories about acid baths. Similar findings were also reported from a survey carried out by Vidyapati and Seetharamappa (1995), on higher secondary school students. When pupils were asked to identify an acid, 63% and 69.3% gave fruit and soda pop, respectively. Hand and Treagust (1998) in (Driver et al 1994) found that pupils believed that, acids can burn and eat materials away; that the stronger the acid the faster it eats it away; and that the reactions of metal and carbonates with acids, is a result of the acid eating it away. Furthermore, they also identified one pupil who believed that “a base is something that makes up an acid”. Consistent with this data, is that reported by Toplis R(1998), that when pupils were asked the question ‘It is alkaline?’(in terms of an acid) even after a period of study they still stated that ‘acids can be alkaline or neutral’. Underlining the fact that pupils’ constructed beliefs still persist, even following a period of study (Driver (1983), (Nussbaum 1980).
Cros et al (1986) survey of university students also confirms the data from Carr M and Driver et al, that although students could easily identify acids, 43% of students could not name more than two bases. They also identified a further problem that 17% of students believed that pH scale was a measurement of the degree of acidity and not a measurement for the alkalinity of a solution as well. Ross and Munby (1991) further strengthen the Cros survey, with the acknowledgment by one student, who revealed that pH was a level of acidity and another pupil who incorrectly identified antacids as a chemical which does not react with an acid Vidyapati, T.J. and Seetharamappa, J.(1995).
Further data revealed from my interviews (KIP), is that pupil’s think that the word salt refers only to table salt. This is probably from the fact that most salts formed are colourless and soluble. Also identified are the problems that pupils seem to have with naming of chemicals and the products that forms following a reaction.
Additionally identified are pupil problems with the concept of the reactivity series (JOR). If they are given data from previous experiments, pupils find it hard to identify the fact that from this, they can predict other related experiments, which contain the same starting reactants. Pupils also have a problem with relating displacement reactions to the reactivity of a metal, again something, which is based upon predicting the reactivity of reactants.
Balancing word equations also seems a problem for pupils (JOR). It is not understood that for a word equation to be correctly written that both the reactants and the products must be equal on both sides.
Teaching and learning activities to address these difficulties
The following paragraphs identify key learning and teaching activities, which have been suggested by the teachers interviewed, to address the difficulties that pupils have with the metal, acid and bases topic.
To address the issue that pupils have with the naming of salts formed during neutralisation reactions, by always identifying the salt as NaCl (KIP). Teacher activities could include the idea of salt cards and ask pupils to decide and select an appropriate metal or metal compound, which they believe, could form the salt. Pupils gain practice in distinguishing salts from different compounds, one possible activity to address this issue suggested by KIP, is to perform experiments upon the salts produced by the reactions. In order to demonstrate to pupils that each of the salts has different properties (Aird D et al (1994).
To address the issue that pupils have about acids eating materials away is to reinforce the use of the correct term, corrode, giving reference to the corrosion of materials in the environment where pupils may have encountered such reactions.
Displacement of metals as a topic can be addressed, as linked to the transfer of an object from one reactant to another. The activity which was suggested to me is the Pokemon and mobile phone worksheet, where Pokemon are compared too metals of different strength or reactivity. The strongest or most reactive Pokemon always ends up with the mobile phone. Also hand puppets based upon this theme can also be used to address the issue of transfer of material to the strongest.
When addressing the strength and weakness of acids, one must identify the properties of two acids, such as ethanoic and hydrochloric acid. These as well as demonstrating the strength of acids will also address the issue that not all acids are poisonous and harmful as well as showing that some acids can be ingested. It would also be a good time to identify 5 common alkalis that pupils write down in their books and are quizzed at varying opportunities to name them. Repeating the correct spelling of acids will also draw pupils from making the mistake that hydraulic acid is the correct term for hydrochloric acid.
Pupils could also construct concept maps of their understanding. Then teachers can perceive pupils learning through the perusal of such maps.
To address the issue of balancing equations, pupils are given a few examples on the board, and then asked to write their own equations for metal of their choice. Other ideas include card sorts for pupils to match up the equations. Another way to help pupils understanding of word equations is the use of a seesaw model as a balance and using balls for the different weights for the elements and compounds. The pupils are given the initial equation and the balls placed accordingly on the sides of the seesaw. Pupils are then encouraged to come up and balance the seesaw, thus giving pupils a way of visualising how to balance equations.
Rationale for teaching order
The first part of the topic is to recap the understanding that pupils have of acids and bases from year 7 teaching. The idea of this is to determine pupils’ prior knowledge of what an acid or an alkali is and then to use universal indicator, to classify solutions based upon their knowledge of the pH scale as a measure of the acidity/alkalinity of the solution, (Sc1. 2a, 2f, 2k, 2n). Pupils may also use a pH meter to measure the pH of buffer solutions and relate them to colour. The use of natural indicators such as red cabbage and beetroot, could also help pupils to find which of these natural indicators is the best at identifying solutions, based upon their prior knowledge and work. From the use of universal indicator pupils should be encouraged to produce a summary table or chart to show colour changes, related to the pH. For this topic it is important that pupils first understand what an acid and alkali is, in order to identify the reaction that occur later in this topic.
Following their observation of the use of U.I to determine the pH of solutions, pupils use this information to determine the end point of reactions, such as neutralisation. Pupils’ use the information gained from this experiment to construct word equations for the salt formed in the reaction. Then pupils can carry out experiments using the application of neutralisation. This could be carried out using the treatment of indigestion, or demos for the manufacture of soil and fertilisers. Pupils must first learn the simple experiments that occur when acids and alkalis react together, in order to construct word equations and begin to get a prior understanding of such word equations. Without this basic understanding pupils will not be able to predict, more complex reactions or equations, which occur later in the topic. Pupils will then be able to look at the reactions of acids with other materials such as metals, bases, including carbonates. But due to the complexity of some of the reactions pupils cannot “jump” into this section without the knowledge gained from neutralisation reactions as previously stated.
From the information gathered on the reactivity of acids and possibly their subsequent ability to recognise patterns in reactivity, pupils were then taught how acids in the atmosphere, “acid rain”, can lead to the corrosion of some metals and how chemical weathering occurs as a result. The knowledge gained from the above experiments should allow pupils to understand and express the reactions in terms of both word and chemical equations.
Pupils should now have gained knowledge of the way in which metals reacts with acids and from this information pupils will have the basic understanding of how metals react. This knowledge should allow pupils to identify that some metals would react faster than others. Without this prior understanding it is again a large jump from one unit to another, this prior knowledge allows pupils to gather information on reactivity series of metals, whilst observing the reactions of acids. Pupils are also gaining insight into how metals react, without questioning the reasons for such experiments. This therefore allows a swift transition from one unit to another without confusing pupils. From the observations of the reactivity of metals with acids, pupils should be encouraged to identify that this data can be used to predict other reactions, such as the reactions with oxygen and water. To further consolidate this information pupils should now be encouraged to investigate this through Sc1 investigations such as the trip to Venus, which reinforces their understanding of the reactivity series.
Understanding of the reactivity series of metals is a prerequisite of the next unit within this topic. Without the knowledge of the prior reactions and construction of word equations, pupils will not understand the principle of displacement. To understand this part of the topic pupils must has secure knowledge that the most reactive metal kicks out the weakest metal. It is therefore very important that this is the last unit within the topic as it consolidates the rest of the topic and pupil understanding is at a premium.
References
Aird D et al (1994) Teaching Physical Science: A manual for teachers. London Macmillan Press
Carr M (1984), Model confusion in chemistry. Research in Science education. Vol. 14, 97-103
Cros et al (1986) Conceptions of first year university students’ of the constituents of matter and the notions of acids and bases. European Journal of Science Education, 8, 305-313.
Driver R et al (1983) The pupil as scientist? Milton Keynes: Open University Press.
Driver R et al (1994) Making Sense of Secondary Science research into children’s ideas London: Rouledge
Hand and Treagust (1998) in Driver et al 1994
Nussbaum, J. (1980). Towards a diagnosis by science teachers of pupils’ misconceptions: an exercise with student teachers. In Cognitive development research in science and mathematics. Proceeding of an international Seminar, ed. Archenhold, W.F., Driver, R.H., Orton, A. and Wood-Robinson, C. Leeds: University of leeds.
Ross, B. and Munby, H. (1991) Concept mapping and misconceptions: a study of high schol students’ understandings of acids and bases. International journal of science education, 13, 11-23.
Toplis, R. (1998) Ideas about acids and alkalis. School Science Review 30, (291), 67-70
Vidyapati, T.J. and Seetharamappa, J.(1995) Higher secondary school students’ concepts of acids and bases. School science Review, 77(278), 82-84.
