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Skip to 0 minutes and 10 secondsRates of reactivity can be quite a challenge to teach students as it requires quite a depth of understanding. And some of the techniques used can be quite difficult for students to grasp. So in this video we're going to start looking at different ways of actually teaching some of these approaches.

Skip to 0 minutes and 27 secondsWe're going to start off by actually looking at rates of reaction that involve a little bit of temperature change. So we've got some light sticks, which we can use, which are broken and allow a chemical reaction to happen. And in that reaction we get light produced rather than heat. And we can put these into different temperature solutions. So we have some iced water, some water at room temperature, and we've got some water from a kettle which we're going to fill the last beaker. So it's just off the boil, about 80 degrees.

Skip to 0 minutes and 53 secondsAs well as being able to use commercial light sticks that are often used for parties or used as distress flares, we can also see some very cheap ones that are available from the shops. And when these are cracked inside, a chemical is released, which mixes to give us some bright background. What we're going to do now is dim the lights and put some of these into different temperature water. OK, so we're going to take our glow sticks and we're not going to crack them. We're going to shake them, which mix the chemicals together. And as you can see, they're glowing about the same.

Skip to 1 minute and 28 secondsAnd now we're going to put one into our ice cold water, we're going to put one in at room temperature, and one into our really hot water. And then after a few minutes we should be able to see how the brightness changes with the different temperature. We can very quickly see that the temperature is having an effect on the reaction. And that's what most pupils would suggest would happen. They have this experience from primary schools that the higher the temperature that something is, the more you heat it up, the quicker the reaction will happen.

Skip to 1 minute and 57 secondsAnd what we need to do in science is we need to be able to pull that down to actually at a particle and an atomic level as to why these reactions happen.

Qualitative to quantitative progression

In practical work, we often teach the physical skills of setting up equipment, at the same time as expecting students to take and record measurements, analyse and evaluate. However, students need to be guided from simple experiments and qualitative observations, to those with quantative measurements, where they may use numbers generated for further analysis, including calculations involving molarities.

As students develop their practical skills, they should be able to apply them better particularly if they understand why they are doing something in a certain way. For example, using a burette allows a greater degree of precision (to ±0.05cm3) than a measuring cylinder (at 1cm3 at best). There should be opportunities for students to choose their equipment that suits the measurements they want to take.

This means that we have to provide steps for progression with practical skills, in the same way as we develop subject knowledge. As we looked at in Week 1, it is good if we can move away from just recipe following for students, and rates of reaction is a good way to develop some investigative skills. Consider allowing students a choice over equipment, or ranges taken. If students have grasped the basic techniques, then they could be given different reactions to investigate, with less direct support for more able students.

Qualitative example

As a starter, in the video above we are using some glowsticks. These are chemical reactions that give out light. Inside are two solutions, one is contained inside a glass vial. When this is broken the solutions will mix and react together forming light (fluorescence).

We are putting the glowsticks into water at room temperature, hot water (from a kettle) and ice-cold water. Ask the students to predict what will happen before lowering in the glowsticks. Most will suggest that the hotter the water, the brighter the glowstick.

It is worth asking about “how long they will last” as well. The idea that the coldest one lasts longest and elicit ideas of what is going on (the hotter the water, the quicker the reactants are “used up”). This can lead into discussions about the factors that alter rates of reaction and some of the particle theory behind them: then students can start to explore in more detail how they affect the rate of a reaction.

  • Temperature
  • Concentration (or pressure of a gas)
  • Surface area (of a solid)
  • Presence of a catalyst

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This video is from the free online course:

Teaching Practical Science: Chemistry

National STEM Learning Centre

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