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Michelle's Design Narrative

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Michelle Norman
1 April 2018

Title:  Extraction of Salt from Rock.

 

Narrator: Teacher of S2 Chemistry, General Science

 

Situation:

A class of S2 pupils in a Science laboratory, double lesson (2 x 50 min.) before lunch on a Monday. Pupils usually tired, hungry and cranky by this time from past experience.  

Task

The aim was to produce as much white salt as possible from dirty brownish Salt Rock that is used to the grit the roads with. In this process the pupils were to practise filtration and evaporation techniques while thinking of ways to maximise salt production.

 

Actions

  1. Pupils watch a demonstration on how to do experiment. Step by step instructions on the board.
  2. Pupils had to collect their equipment and samples of rock to process. This seemed to take a while - due to everyone forming a bottleneck around some bits of equipment. Action taken was to spread the trays out around the room.
  3. The rock had to be ground down into a powder using a mortar and a pestle. On the whole this worked well. Will however ensure that some of the larger lumps are broken down and that each group gets the same amount of salt next time.
  4. The rock powder was then dissolved into some water. Did not specify amount of water on purpose but might have to in future as some put loads of water in – ended up with very dilute salt solutions, which in turn meant lots to boil off. Bit time consuming.  
  5. The solution was then filtered using a funnel and filter paper. Some groups had brown filtrate instead of clear filtrate. Had to discretely go around and remind them how to fold paper correctly and not to poke wet filter paper with their spatulas.
  6. The filtrate was poured into a crucible and then heated until no more water remained. Some groups heated it too much and, in the process, lost some salt when it popped out of the crucible. Stopped them and showed them how to do it without losing salt or getting burnt by hot salt in the process.
  7. The salt was then scrapped out of the crucible and onto some filter paper for quality inspection and weighing. Class become quite competitive at this point.
  8. Pupils cleaned equipment and put all practical stuff away where they had found them.
  9. Plenary – Class discussion: Evaluated effectiveness of techniques and ways in which they could improve both the quality and the amount of salt produced.

Results

All groups managed to produce some salt at the end of the lesson. The quality and amounts varied per group. This then provided some of the points for discussion in the plenary. Through this process the groups did practise the techniques of filtration and evaporation. By working together in groups, they also practised and built on communication and teamwork skills. The teamwork also helped the less confident learners a chance to take part without the fear of failure or loss of face.

 

Reflections

On reflection I will need to ensure that for a large class all the equipment needed is in clear marked trays that are spread around the room to avoid bottlenecks. Maybe a pre-set tray per group.  It might in hindsight be a good idea to provide laminated step by step instruction cards with diagrams. These cards could also have hints/tips /clues on how to produce good quality salt. Each group should also have a Health and Safety card. Groups could have been also selected with more care and each person given a role to play to ensure that all did their fair share of work

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