Experimental techniques

An experimental technique is an introductory topic from the chemistry section in Grade11-12. It exposes learners to basic separating methods such as, filtration, evaporation, crystallization, heating, paper chromatograph, simple and fractional distillation. From its name (experimental techniques), this is supposed to be a practical topic but mostly these concepts are taught theoretically due to lack o f conventional materials suggested for use in the syllabus. For the purposes o f this study, the focus will be on fermentation (which is one o f the organic chemistry competencies) and distillation. I now discuss each o f these below.

Fermentation

According to Campbell (1990), alcoholic fermentation can be defined as a metabolic process whereby yeast converts CH12O6 to ethanol (CH3CH2OH) and carbon dioxide gas, in the absence o f oxygen. Such a chemical reaction is referred to as anaerobic. Fermentation is a chemical

process that involves the breaking down o f organic materials such as glucose/sugar by m icro­ organism such as yeast to produce ethanol and carbon dioxide gas. During the separation process the organic materials (fruits) are soaked in the water. Due the presence of glucose/sugar the mixture begins to ferment after a few days. During fermentation, glucose from plants is turned into ethanol by enzymes (biological catalysts) such as those contained in yeast, the process is shown below:

Enzymes

Glucose ^ Ethanol + Carbon dioxide + Energy Enzymes/yeast

C6H12O6 ^

2

2

The rate o f fermentation is determined by the amount o f sugar and the temperature involved. Thus, fermentation is practiced in everyday activities such as making Ombike and Oshikundu using indigenous fruits and vegetables, such as: Berries; Palm fruits. Eeshegele, Eenyandi, W ater Melon; Dates, Raisins, Cane sugar and other natural sugars. My assumption is that referring to everyday activities when teaching scientific concepts such as fermentation might help learners to understand and see the relevance o f the content. I now discuss the concept of distillation.

Distillation

Atkinson (1985) defines distillation as the process o f boiling to form vapour and the cooling of the vapour (condensation) which changes to liquid. Furthermore, fractional distillation is defined as a process separating two liquids by distillation, the distillate being collected as fractions which boil at different temperatures (ibid). Dube, Gordon, Jeoffreys, Khalieli, Molapo and Odara (2012) point out that the component with the lowest boiling point is reached first as it evaporates first. In this case, the mixture o f water and alcohol is collected first because it has the lower boiling point of 78°C compared to pure water which is 100°C at sea level. The two components (water and alcohol) are separated from one another by the vaporization process. The component with the lowest boiling point rises to the top o f the container and goes to the delivery tube until it reaches the condenser where the vapour is condensed to the liquid form and collects (Dube, et al., 2012).

Distillation plays a vital role in oil and alcohol industries. In Namibia, distillation is used in the purification o f sea water, in the separation o f sugar and salt and is also a common practice in making Ombike a traditional alcoholic drink made especially in the villages. Ombike can be used as a bio-fuel, Thamilvanan and SenthamilSelvi (2013).This alcohol is an eco-friendly and can be used to recover our fuel shortage and during combustion ethanol relatively releases a low emission o f volatile organic compounds, carbon dioxide (CO2) and nitrogen oxides (NO). This emission o f toxicity o f ethanol is lower than those o f fossil fuels such as petroleum, diesel and so forth (ibid). Thus, such indigenous practices/indigenous technologies can be used for environment sustainability.

Yet, many Physical Science teachers lack the pedagogical content knowledge o f how to teach these topics. As a result, learners do not understand the scientific processes involved in distillation as revealed in the Exam iners’ reports (2014-2015) (also see Table 1ink Chapter 1).Thus, it is against this backdrop that this research explored how Physical Science teachers teach the concepts on experimental techniques - fermentation and distillation conventionally and through the inclusion o f indigenous practice o f making Ombike. Since learners are already familiar with the materials, as argued by Asheela, Ngcoza and Enghono (2015) and some have assisted their knowledgeable others to prepare Ombike it will be easy for teachers to help learners cross the border from IK to WS. In the next section I discuss the role o f practical work/activities.

2.2.5 Practical work/activities

Practical activities/work refer to the theory which deals with concrete evidence/real life situations. M illar (2004) define practical work as those teaching and learning activities in science which involves student or learners at some point in handling or observing real objects or materials. Based on the definition above, practical work came to be seen as a means of allowing pupils ‘to find out things for themselves’ (Gott & Duggan, 1996). Furthermore, (Asheela, 2017; Maselwa & Ngcoza, 2003; Woodley, 2009) argue that practical work helps learners to acquire skills such as: manipulating equipment; making predictions, observing, recording, and analysing data, and drawing conclusions. They further added that the practical work approach in science teaching and learning is helpful for the learners in acquiring a better understanding o f science (ibid). These scholars suggest that, practical work enhances conceptual understanding.

In contrast, Gott and Duggan (2004) cautioned that the assumption than an understanding of scientific evidence will emerge as a result o f doing practical work, without being specifically taught or structured is questionable. They, thus regard practical work as having a key role in the teaching o f evidence but only if the type o f practical work is selected with care and with a clear purpose in mind (ibid).