School Science Review, March 2004, 85(312) 47 Howarth Snail shells and acid rain Snail shells and acid rain – an alternative to marble chips and acid Sue Howarth A novel class investigation for GCSE coursework or a key stage 3 project. It works, it’s simple, covers both biological and chemical topics and it’s fun! ABSTRACT An original project carried out by a UK year 9 (13–14 year-old) science class is described. The reaction between acid and snail shells was investigated, and the effects of different acids, acid concentration, temperature and shell size were studied. The results were related to the effects of acid rain on snails in the wild. Students responded with interest and the project not only encompassed many chemical and biological ideas but encouraged teamwork and the development of good practical skills. It could equally well be a useful project after key stage 3 SATs or the basis of GCSE coursework. This article describes an alternative approach to the standard marble chips and acid investigation. Like most schools, our chemistry syllabus includes a study of rates of reactions and, like many other schools, my class were going to do the ‘usual’ marble chips and hydrochloric acid investigation. However, to make it more interesting, and because I also teach them biology, we extended the topic by studying snail shells, another source of calcium carbonate, and created a combined biology and chemistry project. Another inducement for introducing an alternative to the ‘usual’ practical was to do some ‘real’ science. We know how marble chips react with acid after several million replicate ‘experiments’ but most of us probably cannot predict exactly how snail shells will react, making the outcome much more interesting for student and teacher (Box 1). As a result of the marble chips and hydrochloric acid investigation becoming almost a mandatory piece of coursework in the UK, there are now numerous sites on the Internet (220 ‘hits’ using the search engine Google for ‘marble chips’ + ‘hydrochloric acid’ + ‘coursework’, April 2003) providing exemplar write- ups of this practical. Three such sites are listed at the end of this article. The existence of these on-line reports makes it harder for teachers to be certain of the origin of coursework submitted for examination credit at GCSE. Though most of the sites carry warnings about plagiarism, the material is still there for our students. One site actually says ‘add or make up your results here’! By using the variation on an existing practical suggested here, students are not only involved in real research but must also depend on results and ideas generated themselves. Marble is, of course, important in terms of acid rain damage to buildings and statues, but using snail shells allows consideration of the effects of acid rain on the biotic environment, too. The non-uniformity of shells allows considerable discussion of ‘anomalous’ results, leading into areas as diverse as genetics, variation, taxonomy and biodegradation. I teach in limestone country (Bath) where the snail population is enormous. The many dry-stone walls provide shelter for snails and it is easy to pick up large numbers of empty shells from gardens (Figure 1). Shells were collected, washed, dried and used by my year 9 class, a group of mixed-ability students, for their investigation. We had started the practical work, using the shells and hydrochloric acid, when serendipitously the Salters’ Chemistry Club newsletter arrived with the announcement that they would be running a ‘Project by Post’ competition for years 8 and 9 (see Salters website). Their category, ‘Everyday Chemistry’,