Teaching Separation of Substances Without a Laboratory in Karnali
At a rural school in Karnali, a Grade 6 science teacher has 38 students, one 40-minute science period per week, and no laboratory. The prescribed textbook activity for “separation of substances” asks students to filter a kerosene–water mixture using filter paper, a funnel and a glass beaker; to evaporate salt water; and to use a magnet. The school has no kerosene, filter paper, funnels, beakers or magnets, but it has sand, gravel, salt, cloudy water, cloth, plastic bottles and one metal spoon. The annual examination will include a 5-mark question asking students to describe filtration and evaporation with examples. The teacher is also two weeks behind the curriculum grid.
1. Redesign the activity using available materials while preserving the curriculum competencies and preparing students for the examination question. Show the sequence and the science reasoning.
Read the worked answer
The competencies are not ‘use filter paper’; they are understanding that mixtures can be separated by physical methods chosen according to the properties of the components, and being able to describe filtration and evaporation with examples. The materials can change if the reasoning stays.
Sequence:
- Engage: Give each group a bottle of cloudy water with sand and a separate salt–water sample. Ask: how can we get clear water, and how can we get salt back?
- Filtration with local materials: Cut plastic bottles into funnels. Use cloth as the filter medium. Students pour cloudy water through cloth, then through a bottle packed with gravel and sand. They compare turbidity. The science reasoning is that the filter has small gaps that trap solid particles while allowing water through. Cloth and sand are not filter paper, but the principle is the same.
- Evaporation: Stir salt into water until it dissolves. Put a small amount on the metal spoon and heat it carefully over a candle or safe heat source, or leave it in a shallow lid in the sun. Students observe the water disappearing and salt crystals remaining. The reasoning is that water evaporates and the dissolved salt does not.
- Magnetic separation: If no magnet is available, use a borrowed magnet or demonstrate with one; otherwise, discuss a local example such as separating iron nails from sand and ask students to explain why a magnet works only for magnetic materials.
- Exam link: Students write the method, draw a labelled diagram of the bottle filter, and give one example each of filtration and evaporation. They compare their local method with the textbook method and explain why both work.
This covers the concept, the process and the examination language without pretending that the missing equipment is essential.
2. What safety and classroom-management issues arise in this redesigned activity, and how would you address them?
Read the worked answer
The main risks are hot water or hot metal, crowded groups around a heat source, ingestion of salt water or dirty water, and cuts from cut plastic bottles. With 38 students and one 40-minute period, the teacher must plan the room and the groups before the lesson.
Safety measures: use only small quantities; heat the spoon over a controlled candle or a safe stove at a demonstration table, not in student groups; keep hair and loose clothing away; have a water bucket and cloth for burns; forbid tasting; wash hands after handling soil and salt water; cut bottles in advance or use blunt scissors under supervision. Students with cuts should not handle broken plastic.
Management: form six groups of six or seven, each with a named materials manager, recorder and reporter. Give a clear sequence on the board. Use a 5-minute teacher demonstration for the heating step, then rotate groups through filtration and observation stations. Keep the heat station teacher-supervised. Set a visible timer for each station.
Because the period is short, set up the materials before class and use a quick exit ticket rather than a long written report. The judgement is to preserve student investigation while keeping the most hazardous step under teacher control.
3. How would you assess whether students can transfer the concept rather than memorise the textbook procedure?
Read the worked answer
I would use a near-transfer and a far-transfer task. Near transfer: give students a new mixture - muddy water with salt dissolved in it - and ask them to design a two-step method to obtain clear water and salt. They should choose filtration first and evaporation second, and explain why the order matters. Far transfer: ask them to explain how a tea strainer or a water filter used at home works, or why a magnet can separate iron pins from sand but not salt.
I would assess three things: the chosen method, the explanation of properties, and the use of correct terms. A labelled diagram and a short oral explanation would allow students with weaker writing to show understanding. I would also include one item that asks them to compare their cloth-and-bottle filter with the textbook’s filter paper and state what is the same and what is different. Memorised answers usually describe the textbook steps only; transfer answers adapt the method to the new mixture and justify the choice.
I would record results on a simple rubric: method appropriate, reasoning accurate, vocabulary correct, safety awareness. The data would tell me whether to reteach the principle or move on to solutions and suspensions.