Stephen Ashworth

Stephen Ashworth

Teaches chemistry at UEA and communicates science in a small way.

Location University of East Anglia


  • Thanks for letting me know. You will be able to return to the course as often as you like to refresh your memory or repeat parts. We will have to see what the future holds regarding more chemistry courses. (Fingers crossed, thumbs pressed and whatever else one does to ensure good luck.)

  • Stephen Ashworth made a comment

    Thank you all for the comments. Thank you for your suggestions I will definiately make a few changes if the course runs again.

    It sounds as though I had better start polishing up my own website... ;o)

  • Yes, non-bio detergents are without enzymes. The optimum temperature for washing depends on the technology in the washing powder that is being used. The drive for lower temperatures is primarily from a desire to save energy and that is being worked on for both bio and non-bio powders.

  • The enzymes in the potato and the yeast are both doing the same thing. Hydrogen peroxide (H2O2) is being broken down into water (H20) and oxygen (O2) which forms the bubbles. In the case of the potato the enzymes do not have much access to the hydrogen peroxide so that reaction is quite slow. In the case of the yeast the mixing is much more intimate and...

  • You assume correctly - oxygen is being produced from the hydrogen peroxide by the enzymes in the potato. The other product is water.

  • Ketene is a very irritant gas. If the concentration is kept low enough and the exposure time short there should be no problem. If you had to inhale it for a long time or in high concentrations you would eventually suffer pulmonary oedema. The other problem is that the effect is delayed so the lung problems may develop after inhalation has stopped.

  • Stephen Ashworth made a comment

    I would like to thank you all for your kind comments. I am so glad that you have enjoyed doing the course. It sounds as if you has had as much fun doing it as I have had setting it up and being the lead educator.

    I look forward to chatting to you all again if I am asked to put on a second one. ;o)

  • You are quite correct to point it out. I have done something about it now. My apologies that it slipped through the proofreading net! ;o)

  • You are quite correct - I wouldn't either. In fact the yeast probably didn't survive the high concentrations of hydrogen peroxide. One of the enzymes in the yeast was acting as the catalyst and should be able to break down more peroxide after the initial reaction.

  • It looks as though lots of hydrogen peroxide has been reacting this week. It's great to read about what everyone has done.

  • If you are at all worried about it the the most dilute solution (3% or 10 vol) will also show the effect - the reaction will just be much slower.

  • That's the classic demonstration - and name. Great work!

  • You did have lots of water - the foam is made up of it. Although there is gas inside the bubble (oxygen from the reaction) and gas outside the bubble, the material of the bubble itself (like the rubber of a balloon) is mainly water.

    The potato also contains an enzyme which breaks down hydrogen peroxide. Every living thing produces this toxic material just...

  • The molecular formula of hydrogen peroxide is H2O2. The enzymes are breaking this down into water (H2O) and oxygen molecules (O2).

  • For example the claim that something is "chemical free" can be seen to be invalid!

  • These representations do have something of the artwork in them. Some of the even more complex ones are made up of different subunits which come together in a beautifully symmetric fashion.

    You can see lots more at the database site or use the interactive page at to manipulate some for...

  • In principle the reaction will continue for as long as there is acetone vapour and oxygen. I have found, however, that the longest I have managed was about ten minutes.

    The glass did not get very hot, at least not with my arrangement. This is probably because copper is a good conductor of heat and the outer part of the strip is cooled by air. This is not to...

  • The exhaust from a car contains mainly water and carbon dioxide. Unfortunately it also contains small amounts of nitrogen oxides, carbon monoxide and unburnt fuel. What the catalytic converter is doing is speeding up reactions so that carbon monoxide is converted to carbon dioxide, the nitrogen oxides are converted into oxygen and nitrogen, and the unburnt...

  • I hope it will take your mind off things too! ;o)

  • You could well be correct. Ascorbic acid and its derivatives are used to help prevent colour from fading and flavour from changing. The idea is that the ascorbic acid reacts more readily than the colour or flavour compounds. Thus in order to ensure the stated amount of vitamin C they might well decide to use extra.

  • I don't know why we can't get in in the UK. Thus far I have always been able to source it from a local pharmacy, although I have to admit I live in a city, which might help.

    Shortages do occur from time to time. I found it impossible to buy milk of magnesia several months ago - now I ensure that I always have some spare for my science shows.

  • Amazing, isn't it! With one drop you use up the last few molecules of vitamin C and the next drop there is no reaction and the iodine (or better triiodide) is free to combine with the starch to produce a colour.

    A lot of analytical chemistry relies on this concept: it is known as titration (tie-tray-shun).

  • It's hard to say, especially as you tested your starch indicator. I find that I sometimes don't get a nice colour with the starch unless I used boiling water (rather than boiled water that is still hot).

    How much of the vitamin C solution are you using? 5 drops of starch indicator might not be enough for a large volume of vitamin C.

    If you try again,...

  • That's right. The point to remember is that the tincture of iodine contains some iodide too for precisely the reason you have given. That means that we will get the correct colour change even if there is no vitamin C to produce iodide from our added iodine. The converse is also true. The triiodide releases the iodine very quickly so that it can be reduced to...

  • This is indeed an interesting point. I rather like the suggestion that cooking helps release it from the cells. We do have to remember that vitamin C (unlike vitamin A) is soluble in water which is what leaches the vitamin from the cooked material.

  • It does indeed.

  • Yes, the reaction takes place in the presence of oxygen. What you will find is that oxygen is sufficient to oxidise vitamin C. Fortunately the reaction is quite slow but there is an interesting comparison to be drawn between the amount of vitamin C in a fresh sample and one that has been allowed to stand for a considerable time.

  • I understand completely. Perhaps "trivia" is the word to use. It's all those quite interesting things that (in the UK at least) we can learn on QI (

  • It's a good example of the effect of finely dividing a substance, or a very effective demonstration of how much energy there is in food. I used cornflour here (because it is not sticky when clearing up) but I have also used custard powder - which liberates even more energy.

    There are a number of different ways to set this up. The flame can be clamped, for...

  • There is no need to catch up as the material remain available to participants after the course has officially ended.

  • You'll be able to access this course and the material long after the official end of the course. :o)

  • You don't need big goggles, but there are a variety that are available quite cheaply from DIY stores. In fact, there are unlikely to be splashes unless you do this in a particularly spectacular fashion (such as trying for a Coke and Mentos effect). However the small risk is sufficient to warrant the advise.

  • Michael - I have looked at the questions you query and it is in fact quite correct. I could, for example say: "After Michael and I go to the beach, we eat an ice cream." I am describing a sequence of events that occurs regularly but not a specific version of those events such as "On Thursday, after Michael and I went to the beach we ate an ice-cream."


  • If you still have a stain use a little vitamin C solution - that will help to get rid of it by turning the iodine into iodide, which is colourless and will dissolve easily in water.

  • Some great results here! I hope some of you have managed to log them on the Royal Society of Chemistry's website.

  • You are quite correct. The concentration of the iodine in your tincture will make a difference, as will the size of the drop you are able to produce. That's why we all have to calibrate our own equipment.

  • BJ - in cooking a raising agent helps make other things rise, makes them light and fluffy. This is the same, a reducing agent supplies electrons to reduce other things. The reducing agent loses electrons (and becomes oxidised) and the oxidising agent takes up electrons (and becomes reduced).

  • Nothing gets lost during the process. We take an electron from one place (oxidation) and put it in another (reduction). In photosynthesis the energy that the plants absorb from light enable the electrons to be pushed "uphill" in energy terms (a bit like charging a battery). The plant can either store the energy or use it to grow.

  • Yewande gives the explanation I would have given. If we take a substance that has no electrical charge and remove electrons (oxidise) the charge becomes more positive. Remove one electron and it has a charge of +1. If we wish to reduce that charge we arrange for it to accept an electron.

    The logical consequence is that if we have a neutral species and give...

  • Ooops! Thanks for pointing this out. I had better change that..., load up the video editing software.

  • I wish I had the kit for that! ;o)

  • Interesting point. It appears that the precious metals in these devices meant that they are starting to become a target for thieves.

  • Thank you for your positive comments. A lot of these experiments, and some other ones can be found at my Kitchen Chemistry website . Once this course is over I will be able to concentration more on adding new material to that site.

  • Well done, and an interesting application of the filtration technique we met earlier.

  • Great observations and conclusions. I admire your observations and reporting. Keep up the fantastic work!

  • Redox it is! At least an application in a redox titration.

  • Anything that is not too highly coloured and might contain some vitamin C. Apple juice will be fine, the water from boiled (green) cabbage might be interesting, orange juice (freshly squeezed or otherwise) will also be fine. The juices that won't work well are beetroot, blackcurrant and other highly coloured ones. The reason being that we will be looking to...

  • Yes, that's right - in fact it works both ways. Next week we'll be using starch to test for the presence of iodine.

  • More iodine next week too - sorry!

  • Thank you Dave. I hope to be adding some more content when I have the chance. ;o)

  • The main point here is that the vinegar should not be too coloured the detailed concentration will not make a big difference.

  • Yes, I can confidently say that the Milk of Magnesia from South Africa will work. (I have to admit it is one of the only countries apart from the UK where I do have experience of this!)

  • If Remgel soft chews contain magnesium hydroxide and no aluminium hydroxide they should work.

  • I have tried this - the version I used was known as "Cream of Magnesia". It didn't work for me either. I think that is because of the properties of the aluminium hydroxide. I must admit I haven't tried to sort out exactly why this happens - I have simply avoided such preparations when doing these demonstrations.

    Perhaps I need to do a little research on this.

  • When the molecule gives up the H+ it is no longer electrically neutral. The energy of the molecule is lowered if the negative charge that remains can be shared out around the molecule compared to when it can't. The driving force is the lowering of the energy.

  • I like the analogy with the temperature scales - I will have to remember that one.

  • The way to work out the exact pH of a solution is to measure the concentration of H+ in units of moles per litre. The pH is then defined as:

    pH = -log [H+]

    Here log is the logarithm to the base 10, and the square brackets around the H+ mean it is the concentration in units of moles per litre. It is the tricky minus sign that turns everything around. If...

  • Any pH below 7 is called acidic - there are more protons (H+) around than there would be in pure, neutral, water. Any pH above 7 is called alkaline - there are fewer protons (H+) than there would be in pure, neutral, water. Instead there are too many OH- ions.

    At pH of 7 the solution is neutral, everything is balanced. There is a very small amount of H+ but...

  • Red cabbage is the best, as far as I am concerned. The advantage with tea bags, at least for demonstrations when travelling, is that they keep well. Over the course of a week in a hot car red cabbage tends to become unpleasant.

    I like the idea someone suggested in another comment, of making red cabbage ice cubes as a way of storing it.

  • I think the idea of making a chart is excellent - if you know the pH of the solutions you make up to add the indicator to. I suspect it will be somewhat dependent on the exact mix of berries in your fruit tea, but we could all club together to try to find out.

  • I should imagine the juice from the pickled beetroot will work fine. It is likely to be acidic to start with so try adding some base, such as sodium bicarbonate. To avoid having to use too much base I would advise diluting some of your pickle juice in water.

  • I know that broccoli works, so why not artichokes - do an experiment and let us know!

  • Good point. Of course you will have a salt solution whatever proportions of acid and alkali you mix. As you say, which salt will depend on the acid and alkali you choose. For example mixing sodium bicarbonate (alkali) and vinegar (ethanoic acid) will produce a solution of sodium ethanoate and liberate water and carbon dioxide.

  • Oops - (red face). That's me and all the proof-readers - thanks for pointing it out. I will edit it.

  • I try to use both terms because I have learnt through experience that "alkali" is not used the world over. In the contexts we are using here the terms are interchangeable. In the wider context of chemistry "base" is the more general term. While all alkalis are bases not all bases are alkalis.

  • There is a variant one can do with Smarties or M & Ms. Put the paper on a cup or something similar so that it is only touching the edge, place one of the coloured sweets in the middle and drop water onto the sweet. Some of the colour will dissolve and the water then carries it away from the sweet to make a circular chromatogram. Something like this:...

  • Paul makes an interesting point. A lot of the chemicals one would normally try to separate by these means are not coloured. There are a number of methods to make them show up and one of those is to use ultraviolet light.

  • By all means try other papers - toilet paper might work, although it will be a little fragile when wet. You can try it with kitchen towel - I did, but the embossed pattern spoiled the results.

  • The fruits and vegetables from your kitchen cupboards will be used in the second half of the course, so don't lose heart.

  • That's right - the molecules that go fastest and furthest are those that are most soluble in the solvent that is moving: in this case the water.

  • Keep your tincture of iodine handy - you'll need it next week and the week after too!

  • Some of you have (and will) recover crystals from this experiment. If you are interested in crystals you might like to know that this year is the International Year of Crystallography.

  • The sand one finds on a beach usually has a few coloured impurities. The brown colour of the sand I am used to is from iron oxides (like rust). Some of these coloured impurities may dissolve and colour the water you are using. The major component of the sand, however, as Tran says, is silicon dioxide and that is essentially insoluble in water.

  • I don't know about enhancing memory but the guys at Futurelearn assure me that you will be able to access this material long after the course is officially over.

    Several participants have mentioned downloading the material. That certainly ought to be possible - but not just yet! ;o) When I get a chance I'll see what I can arrange.

  • You could mix your own "black" with different food colours and then separate that out. Water soluble felt tip pens, or ink from a fountain pen should also show some separation.

  • This one is a bit like watching paint dry - but time lapse would be cool. The sort of thing that one can see here: .

  • I can understand that! ;o)

  • You will need iodine for subsequent weeks - especially week 5. If nothing else it can be obtained from Amazon . You'll need no more than 30 mL, 25 mL bottle will also be fine. The 2.5% or 3% strength is also what is needed.

  • Yes, as Anthony quite rightly says, you have extracted other molecules from the coffee - the things that dissolve in water to make it brown - and these did not evaporate with the water. This is a common problem when trying to separate out complex mixtures. One approach would be to find a solvent which would dissolve the brown stuff and not the sugar, or...

  • You'll need the iodine again in week 4 but especially in week 5, so it is well worth tracking down.

  • A little bit of searching and I find that the most likely candidate for surfactants in the mustard, at least, are some of the proteins it contains. ( Source:

  • Good point. A fair comparison would try to ensure the delivery methods were all equivalent so that the comparison is with similar amounts of surfactant.

  • Good observations!

  • No they don't contain stearates - at least not many. It is the proteins (in mustard at least) that are stabilising the fat droplets and acting as surfactants. (Source:

  • The oil floats for the same reason our hot water floated - because it is less dense than water. 1 L of oil weighs less than 1 L of water. [Of course, in everyday usage we tend to use "lighter" to mean "less dense" because it is easier to say! ;o) ]

  • You could also try to make an egg swell. Take a fresh egg and dissolve off the shell by leaving in vinegar overnight. There may be some residue which can be wiped off carefully. Then place the now "naked" egg in fresh water and leave it for a while. The higher concentration of salts and proteins inside draws water through the membrane, which will stretch....

  • Great plan - this is an example of a surfactant at work.

  • The mixture that is white coffee is indeed not a solution - it's actually a rather complex mixture. You have, however, dissolved the sugar (the solute) in a solvent (the water of the coffee). There are all sorts of other things, not least the little droplets of milk, that make this not strictly a simple solution.

    Yes, Penelope, because strictly a solution...

  • Amazon appear to have a range available. The Lugols 3% ( currently at £6.75 will be fine. A 30 mL bottle will be enough for our purposes.

  • It is available from Amazon but only get a small bottle (25 mL or 30 mL). We will be using it in week 4 & 5 as well but 25 mL should be enough for everything you need to do.

  • The "official view" is that the dilute solution of ethanoic (acetic) acid is reacting with the sodium bicarbonate to form carbon dioxide, water and a solution of sodium ethanoate (acetate). As the arrangement of atoms is changing this is a chemical change.

    Some observations include the fact that this solution became cooler during the reaction. This is...

  • Yes, when water changes to steam it is a physical change. When that steam changes back to water (liquid) it is a physical change too. When the water is frozen and becomes ice that is another physical change. These are all physical changes because we still have water: gaseous water, liquid water, solid water.

    Only when we change the arrangement of the atoms...

  • The second experiment is predominantly a chemical change as you have correctly identified. It is arguable whether sodium bicarbonate simply dissolving in water is a chemical or a physical change. There are arguments that can be made for both points of view!

  • Ice melting to form water is a physical change. I have the same chemical, in other words the molecules are the same, but the physical state is different. If I put the water in a freezer I get the ice back.

    A chemical change is one in which the molecules have changed. An example is the sodium bicarbonate and vinegar. Here we have rearranged atoms and we can...

  • The majority of the vinegar is water so it is unlikely that, if the experiment is done so that absolutely no liquid escapes, there is less liquid afterwards than before. Indeed the reaction produces some water so there should be (a little) more water at the end than at the beginning.

    With an accurate balance one should, however, be able to observe a loss...

  • You make a good point here. In cooking we use sodium bicarbonate in two ways, one is in baking powder, where it is combined with an acid. When this mixture gets wet the acid is able to react with the bicarbonate as we have done here.

    When sodium bicarbonate is used alone we are relying on the heating effect to decompose the bicarbonate of soda to form...

  • Carbonated drinks have carbon dioxide dissolved in them under pressure. When you open the bottle you are letting the high pressure carbon dioxide out. Not only does this allow the little gas that is in the space above the liquid out, but gas dissolved in the liquid is able to "undissolve" and form bubbles. It is these bubbles that you are seeing.

    If you...

  • The silver effect is a very pretty one. As far as I am aware it is due to a fine layer of air bubbles trapped at the rough surface formed by the soot.

  • That is a real shame - there is a lot of complexity in a flame, but I suppose this is not as spectacular as other flame experiments, such as "Exploding Custard" and "The Whoosh Bottle".

  • The match is relighting the gas formed from the wax. It is actually wax in the gaseous state that is burning, not the liquid wax. Just after the candle is blown out there is a little cloud of wax gas around the wick so the lighted match ignites that gas and does not need to touch the candle wick.