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.