© 2017 by Emily Rose Seeber. 

  • Emily Rose Seeber

Safer Chemicals, Better Practicals: 5 experiments for A-level organic chemistry


I don't know about anyone else who teaches A-level organic chemistry, but the CLEAPSS booklet 'Safer Chemicals, Safer Reactions' has been my bible over the last few years in terms of running exciting organic practicals which are safe for students. However, CLEAPSS simply provide the list of instructions, and if this is all that students are provided with, then these practicals which are an opportunity for rich and engaging learning experiences, are being wasted.

In this blog I explain how I use five of the organic chemistry practicals listed in 'Safer Chemicals, Safer Reactions':

  1. Phenol reactions

  2. Nitration of benzene

  3. Reduction of nitrobenzene

  4. Phenylamine reactions

  5. Extraction of caffeine

I also provide links to resource sheets for each of them.

1. Phenol reactions

I really believe in students thinking during practical work and not simply following instructions. This becomes particularly important at A-level where we expect students to really understand the reasoning behind each step in a mechanism, and also to be able to link the theory effectively with their observations. In this first practical, a pre-lab is used to frame the learning question: is the inductive effect or the mesomeric effect more important in determining the reactivity of phenol. The students make predictions about what they will observe in either case. This means that they need to link their understanding of the reactivity of benzene to the phenol case. It also means that they are intellectually invested in the outcome of each test. This approach sets up the practical as a 'crucial experiment' to provide 'conflict' in the lesson and make the learning more meaningful for the students.

The students then complete the practical using methyl 4-hydroxybenzoate. As they complete the practical, students use their observations to assess the two theories and come up with some conclusions about the bonding in phenol. This whole approach contextualises the students' learning and gives them the 'top-down' structure they need for conceptual chunking.

The post-lab task is designed also designed to ensure that students are able to situate their learning in what they have already learned. In the first task students are comparing and contrasting different functional groups which provides them with the scaffolding they need for more advanced tasks which require them to select the right approach to the problem. The second task asks them to build on their understanding of the mechanism for aromatic electrophilic substitution with a different surface context: amino acids. This requires students to use their knowledge as part of the deeper problem solving structure and leads to better understanding of the abstract ideas.

The worksheet for the entire practical is available here.

2. Nitration of benzene

In this practical the learning objectives really need to be about safe working practice because even this safer version uses extremely hazardous acids. The pre-lab for this practical gives students the instructions and asks them to analyse these from a practical perspective in advance.

This "how" approach ensures that when the students are completing the practical they have a good idea about how to complete each step safely and efficiently.

During the lab, students are asked "why" questions about the method they are using. This asks them to think more deeply about the practical principles involved, encouraging understanding of abstract ideas about practical skills.

After the practical, students need an opportunity to express what they have learned. For this practical I provide students with choice about the kind of task they think will be the most effective for furthering their learning. All of the tasks require students to think about the deep structure of the practical: the method and principles, rather than learning each step. The students need to see how the pieces all fit together to perform well at A-level.

The worksheet for the entire practical is available here.

3. Reduction of nitrobenzene

This practical uses a range of different apparatus and has various practical stages, so I really encourage students to focus on the apparatus and drawing and documenting each stage. I give the students a practical sheet which has space for a diagram with each step and require them to draw a scientific diagram before they start. Reading instructions and drawing a diagram to represent them has been shown to strengthen neural connections and make students more likely to remember the practical.

Here is an example with diagrams from an earlier version of this task (scanned in so apologies for the lopsidedness!):

During the practical I have students take photographs of the stages of the practical. The afterwards, for homework, students make a photo-strip showing all of the different stages of the reaction with instructions and comments about their observations to help them recall the stages and link theory and practice. All of the new A-level specifications require students to really understand why a particular set-up is used in each case, and making sure that students move from instructions to diagrams, then photos back to theory, helps them to access this deeper learning.

The worksheet for the entire practical is available here.

4. Phenylamine reactions

By the time students look at phenylamine, they have usually already covered phenol, so I generally use this as a quick practical to test students' understanding of the effect of the lone pair on the nucleophilicity of the aromatic ring. The students' first task is to predict what they will observe in each of the reactions, and explain their reasoning:

Once students have either had their predictions confirmed or denied, they need to have an opportunity to embed the correct understanding of the reactions of phenylamine and the correct explanations. This is Task A. In Task B, students compare and contrast the reactions of phenol and phenylamine more explicitly which is known to help students access the deep structure of the learning, i.e. that the lone pair overlaps and increases electron density in the aromatic ring. This makes it more likely that students will be able to predict the reactivity of other substituted benzene rings, such as methoxybenxene, correctly, as they have a grasp of the abstract principles, not just the examples.

The worksheet for the entire practical is available here.

5. Extraction of caffeine

This practical is really difficult for students to understand if they do not have a firm grasp of solubility. The solvent extraction is complicated by the fact that the propan-1-ol layer is only immiscible with the aqueous layer when the aqueous layer is a saturated salt solution. For this reason, the pre-lab is designed to get students thinking about solubility of propan-1-ol in water and a simple solvent extraction so that they can apply their understanding to the practical task.

Throughout the practucal, students need to be encouraged to relate the stages back to their understanding of solubility, so the practical section has questions associated with each step (these are "why" questions wherever possible). The practical takes about 2.5 hours (two lessons in most schools).

At the end of the practical, I use a post-lab activity which really drives home the learning objectives about solubility and solvent extraction. The students watch a video about an alternative method using dichloromethane and make their own resource sheet for this version of the practical, which has some significant differences (e.g. the students are not required to add salt). This means that students are looking at the same techniques, but with a slightly different perspective which has been shown to help students transfer their learning more effectively in different situations.

The worksheet for the entire practical is available here.

I hope you have found my methods for the Safer Chemicals, Safer Reactions tasks helpful. Please feel free to share this post with others and use my resources in your own lessons.

#practical #pedagogy #PCK

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