Skip to 0 minutes and 1 secondMARK LANGLEY: Welcome to the question and answer session for Teaching Practical Chemistry course from STEM Learning. We've had some very interesting questions come through and we've valued your responses to all the sections of the course we've gone through. You've raised some interesting points. And the responses you've given to support each other have been excellent.
Skip to 0 minutes and 19 secondsTIM BRADBURY: So first off, we'll start with a question from Maureen regarding some issues making sure that you get the correct chemicals from chemical suppliers. The example given being a mix up between hexane and hexene. And one of the easiest ways to make sure that you do source the correct chemical would be when ordering to use the structural formula of the compound that you would like to make sure that you get the correct chemical.
Skip to 0 minutes and 47 secondsMARK LANGLEY: Some of the other issues can be ordering appropriate quantities of chemicals. So it may be worth checking with suppliers about the amount of chemicals you order. Because if you're only going to be using 1 or 2 grammes, it's not worth buying larger stocks of chemicals. Not only because of expense, but it can also mean that some chemicals will degrade over time. You also may be limited to how much of certain chemicals you can have at any one time. So for instance, holding limits for flammable liquids are often restricted by local regulations. Simon asks a very interesting question. Is there a downside to using micro scale for chemistry practicals?
Skip to 1 minute and 24 secondsThere are a few times where you want students to be able to use larger scale equipment such as boiling tubes, test tubes, funnels, et cetera because they will need to be able to manipulate these if they go into further study. And they're also the types of equipment that may be seen in assessments such as exams. However, the micro scale does come into its own to allow students to work on their own. But it's also particularly useful when you're dealing with chemicals that may be hazardous in larger quantities or expensive. So one of the ways we can use micro scale is to minimise waste by doing common reaction to show the migration of ions in an aqueous solution.
Skip to 1 minute and 59 secondsSo we're taking a laminated sheet which has circles printed on it. And what we will do is take a small sample of lead nitrate and potassium iodide. And the lead compounds are particularly hazardous. If you do this on a larger scale, then you do have to keep the waste for disposal because you can't just discharge into the environment. If we take using a splint, a wooden splint, a very tiny amount of lead nitrate and put it in a circle, and we take an equally small amount of potassium iodide, we place that in the circle. We can then add a drop of water in the circle in between.
Skip to 2 minutes and 47 secondsAnd we can push our two compounds together so they touch the circle at the same time.
Skip to 2 minutes and 57 secondsAnd then watch to see the resulting reaction. The disposal for this is quite easy. We can just take a paper towel, wipe it off, and put it in the bin. And any remaining chemical that's on here can be moved carefully with a spatula back into the small bottles. And you can also give students much smaller bottles of chemicals to use so they're not tempted to use larger amounts. It's also possible to print alternating white and black circles when you laminate so you can clearly see compounds that you've place on the paper.
Skip to 3 minutes and 27 secondsTIM BRADBURY: Next we have a question from John who would like some explanation about the bubbles that were given off during the production of copper sulphate from copper oxide and sulphuric acid. The explanation for the formation of the bubbles would simply be the nucleation of gas from within the solid, and also from within the sulphuric acid solution. So as the copper oxide powder is added, the gas that's dissolved in the sulphuric acid comes out of solution. So this is not the formation of the product through the equation. The equation for the reaction would be copper oxide plus sulphuric acid going to form copper sulphate plus water. So we don't have any gaseous products from this reaction.
Skip to 4 minutes and 14 secondsMARK LANGLEY: Kerry asked an interesting question about obtaining the empirical formula for magnesium oxide by burning magnesium in a crucible covered in a lid. This is the standard way of doing it in schools. But it doesn't always give the best results. There is a better way that can be found on the STEM Learning Centre website, which is an experiment used by the Royal Society of Chemistry. This involves using two bottle lids made of metal which are held together with the magnesium oxide inside by wrapping nichrome wire around the outside. This allows much better penetration of heat and oxygen without losing some of the magnesium oxide.
Skip to 4 minutes and 52 secondsHowever, thought has to be given to whether this is actually the best practical to explain this. Because if he induces errors then that raises questions of how we talk to students about the results of the experiment. We've had an interesting question about the use of indicators in electrolysis and whether this might lead to some confusion among students. The indicator that we used in the sodium chloride electrolysis, which is universal indicator, does help students understand what is going on because it's much easier for them to be able to see the reactions of the gases produced at the anode and cathode.
Skip to 5 minutes and 29 secondsHowever, it does mean that they need to understand the universal indicator and what the colour changes mean and also some of the reactions of chlorine, such as the bleaching of the indicator. If you use other indicator solutions such as, for example, during the electrolysis of potassium iodide, using starch and phenolphthalein mixture as the indicator, this requires some additional chemistry as one of the products is a starch iodine complex which goes black. However, students may have come across this if they've done, for example, the starch testing in leaves.
Skip to 5 minutes and 59 secondsTIM BRADBURY: We have some comments on the course which have picked up on the use of 1.4 moles of sulphuric acid. And concerns have been raised regarding the high concentration of that acid. To refer back to health and safety guidelines, certainly in England, Wales, and Northern Ireland, the CLEAPSS guidance states that anything below 1.5 molar sulphuric acid were classed as moderate hazard. Anything above 1.5 molar or 1.5 molar and above, should I say, would class as corrosive and therefore would require the use of indirectly vented goggles. The same guidance can be found for Scotland through SSERC. However, if you are outside the United Kingdom, always seek advice from your local regulatory provider.
Skip to 6 minutes and 46 secondsMARK LANGLEY: As we picked up during the course, of the issues of concentration and quantity of chemicals is quite important in chemistry. For example, as Tim mentioned, using 1.4 molar sulphuric acid is perfectly acceptable in this circumstance because it enables an almost saturated solution of copper sulphate to be formed, which minimises the amount of copper oxide remaining and makes it much easier and quicker for crystals to be obtained in the lab. For other use, such as reactions with metals, then much lower concentrations would be much more sensible to use. And often using hydrochloric acid rather than sulphuric, for example, reduces the risk even further.
Skip to 7 minutes and 23 secondsA very interesting comment and discussion during the course about how you work with analogies with special educational needs students who may grasp the analogy and mix it up with the science. I love that it takes great care in choosing appropriate analogies. A better approach may be to use everyday examples of where the chemistry occurs, and then just stick to using the basic science to help students explain it. Analogies can confuse students, especially if they involve abstract thought as well. So sometimes you need to look at particular examples of how you might approach this so that students feel comfortable with the science they're understanding.
Q&A with Mark and Tim
The Q&A sessions on courses from the National STEM Learning Centre provide you with the opportunity to ask more about the course content and issues from your own classroom practice.
Mark and Tim recorded their answers to a selection of your questions on 30 October. The video was uploaded on 1 November. A transcript will be uploaded as soon as it is processed.
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