Where does the chemistry teacher start with chemistry? The typical traditional start in UK schools was with the destructive nature of the Bunsen burner with safety to introduce practical work and then onto elements, mixtures and compounds (which is quite a difficult concept) with separation techniques.
The Vis-Chem video of the macro event at the beginning of the video shows the traditional test tube reaction. The colourless solutions have been already prepared and then mixed with a white precipitate forming.
Now watch the microscale version. Here is the line of silver and chloride ions coming together to form a precipitate. This microscale version though shows the addition of the solids to the puddle and in the space of just over a minute, the whole macro process that the Vis-Chem video describes (and more because this procedure shows the dissolving process) takes place in front of the student in under 2 minutes.
- All displacement reactions, where a more reactive metal displaces a less active metal ion from the solution.
- Some displacement reactions such as magnesium on metal salt solutions, eg iron(II) sulfate, result in the formation of the less active metal but at the same time, bubbles (of hydrogen gas) are seen along with the formation of iron(II) hydroxide precipitate. So there are competing reactions as shown below with electrons reacting with water and with iron(II) ions.
- There is the "puzzling" reaction when zinc and copper metal ae attached together and placed in a dilute acid. The bubbles of hydrogen appear on the copper metal as the electrons move from the zinc to the copper and react with the acid on the surface but it is the zinc metal that dissolves. There must be a lower kinetic barrier for this mechanism as rather than zinc reacting directly with acid. The copper is effectively acting as a catalyst.
Aishling Flaherty of Limerick University presented a plenary address on 1st year University students find "curly arrow" explanation of organic chemistry reactions difficult. ‘Twas ever thus. I did it in 1964 and it was tricky to many then. But chemistry then was taught as physical, organic and inorganic with distinct rivalries. Is it still?
Unless the Big Idea of electron movement (with electrons falling into a hole or even a depression “a partial hole”) is used in both inorganic and organic chemistry, we shall still be struggling with the understanding of these concepts. VisChem also looks at some simple organic reactions.
When the questions are asked how and why does this happen, then the Big Ideas of entropy increase and conservation of energy come into being, with the proviso that there may be a kinetic barrier. The molecular shape and intermolecular forces between molecules, especially in water at school level, are crucial in the mechanisms in which electron pairs are attracted to electron deficient (holes) species. There is periodicity because I can carry out these reactions with compounds of elements in the same groups. And it all happens because matter is made up of very tiny particles. It is all very holistic.
Looking for connections in inorganic chemistry reactions and indeed, between different branches of chemistry, is a form of “chunking”, a process (see diagram below) in which “individual pieces of information are bound together into a meaningful whole” (Wikipedia). Instead of learning loads of separate facts, you apply basic ideas from which you can ascertain an answer to an exam question. Would it were so simple!
Exams are so important that students are scared of being wrong and teachers are worried for their jobs because they may be blamed for exam failures. It is safer to students to have many “fact cards” to learn by heart.
Application of present knowledge to new situations really throws students, A recent UK examination question about boiled carrots caused consternation because “we had not studied carrots” but they had studied osmosis in potatoes! And osmosis all about matter consisting of very tiny particles, invisible to the naked eye, the first of P W Atkins big ideas.