Chemistry from day today life and application of science in energy saving cooking
Posted on March 2nd, 2013

Dr Hector Perera                London

Sometimes the students need some day today examples to remember certain things in chemistry. To some students this subject chemistry is little mysterious to understand because the name also sounds like che-mystry. There are plenty of reactions taking place in the surrounding, including at home but unless they are explained in simple ways, some students find it difficult to convince themselves.

I mentioned about the reaction of metals with oxygen, gave metal oxides and some common examples, iron oxide, copper oxide and aluminium oxide. The point is if these metals do not form oxide with oxygen they should be shinning all the time but sometimes the surface goes dull due oxide formation. Then I asked to give examples of water soluble oxides. To my surprise a few said, iron oxide and copper oxide. This is where simple day to day examples are needed to convince them.

If iron oxide was water soluble, George Stephan wouldn’t be able to discover steam railways because as soon as the oxide is formed it dissolves away. Imagine it happened to the steam train while climbing, “Kadugannawa Hill” then what? The railway lines also rusts to some extent due to oxide formation then heavy rains and floods would have dissolved the railway lines but they don’t, that means iron oxide is not soluble in hot or cold water. 

Most of the shops glass frames of windows are made out of aluminium but loses the shiny surface due to oxide formation. If aluminium oxides are water soluble, the fames would have dissolved in heavy rains and all glass windows would have fallen down. What about some aluminium saucepans and kettles, they would have long gone by dissolving in hot water. There is a possibility of dissolving some aluminium when pots and pans are used for cooking curries with certain acidic ingredients such as tamarind and “goraka” that is a different issue. That means these acids react with aluminium to some extent. There are research backings to say that aluminium metal is responsible for a disease called Alzheimer. In an aging adult, forgetfulness beyond the normal rate may be a symptom of a disease like Alzheimer’s disease or vascular dementia.

Some students told me copper oxide would dissolve in hot water but they have forgotten that radiator pipes that carry hot water from the boiler are made out of copper. In cold weather countries they need radiators to keep the houses warm. If copper oxides were to dissolve in hot water how would they carry hot water to radiators? I have seen in Sri Lanka some tea boutiques with copper boilers and they happily worked, never dissolved away. When you walk past a church, just look at the roof, you would notice some are slightly blue due to copper oxide because of copper roofing. Have a look at some status in the park or in some public places, they are made out of a mixture of metals, copper and tin then called it bronze. The statues have a dull surface due to oxide formation but it does not dissolve away. I think some coins are made out of copper but they have a dull surface due to the oxide formation. This mixture of metals is called an alloy then bronze is an alloy of copper and tin or even zinc.  You must be wondering why we use alloys for making things that is because pure copper is too soft, it dents easily. Now have I got to say again that copper oxide does not dissolve either in cold water or in hot water? Gold never rusts but how often ladies have to gold plate their jewellery? That is because they are not pure gold. Some copper is mixed with pure gold to make it stronger as pure gold is too soft to make jewellery. Archimedes discovered the law of flotation when he sat naked in the bath tub.

What metals are used for making air crafts? Certainly cannot be iron because too heavy to lift off. They use an alloy called Magnalium which is a mixture of Magnesium, Copper and Nickel or Tin. Small amount of Magnesium makes it corrosive resistant, durability and lightness. 

Let me mix some mystery, chemistry with some history. In the history of Sri Lanka there was an incident where a King called Rawana who abducted the wife of King Rama as a vengeance for cutting the nose of his sister Surpanakha. That time he came on a special plane made out wood, called “Dandu Monare”.

 Fire works

Certain metals such as Magnesium, Calcium, Potassium, Sodium and Copper have coloured flames. One might think you need to go to a chemistry laboratory to see the colours of these metals burning. Actually sometimes you don’t even have to get up from your easy chair to see these colours. When Christmas and New Year or even in Sinhalese new year celebrations time, people celebrate by lighting fireworks. Next time watch out for these colours in the fireworks. If you see yellow flames that is due to Sodium, lilac colour due to potassium, brick red due to calcium then nice blue colour is due to burning copper, any apple green flame is due to barium. Many years ago flash photography bulbs were used instead of present day electronic guns. Magnesium ribbons inside these bulbs burnt with an electric spark to give a brilliant white flame. Some street lights have yellow light and that is the colour of sodium when it burns.

A short cut to identify metals

When I did my Advanced level chemistry practical we had to do them at the University but now they do them at their schools and colleges. I used the metal burning principal to quick check for any coloured metals in the given mixture. Just take some of the given compound, carefully sprinkle some into the clear blue flame of the Bunsen flame and watch out for any colours. If there was any sodium, potassium, calcium, copper or barium in the mixture, try and identify by their colours. This is just a short cut only; actual procedure is to use a platinum wire.

What about polymers?

A polymer has repeated units just like a long train; it is nothing but repeated units of same carriages. To form a polymer, the starting compound must have a C=C bond then it opens up to combine more and more of the starting materials for example when ethene undergoes forming a polymer or polymerisation it forms polyethene or polythene. When one of the H atoms of ethene is replaced by a CH3 group you get propene. When it undergoes polymerisation it forms polypropene. In exams either they give the polymer or the particular alkene and ask to mark the repeated unit or to make a polymer. Then look out for this repeated unit. In ethene if one H atom is replaced by a benzene ring you get styrene then the polymerised product is called polystyrene which is the packing material for breakable items such as TV, phone and many more. If one H atom of ethene is now replaced by a chlorine atom then you get a compound called vinyl chloride. I am sure now you have guessed the polymerised product as poly vinyl chloride or popular name is PVC. I started with the basic unit alkene then showed how to make other alkenes and their polymerised products. This simple approach can build the confidence in students in understanding of complicated chemistry, am I correct?

 These alkenes undergo polymerisation in the presence of certain substances called catalysts which do not take part in the reaction but it must be there. This was discovered by a scientist called Ziegler and he was awarded a Nobel Prize as well, otherwise the supermarkets would be without polythene bags. Now they regard polythene bags are environmentally unfriendly material and treat as a pollutant.

 Imagine if there was a noisy bunch of students in a class and the teacher finds difficult to control and line up. Then comes the principal, as soon as they see him they behave. The students hold hands and form a large circle or form into a line. The individual students are the repeated units of the line or can I say a polymer of students? Here the principal is the catalyst, he didn’t take part but without his presence they wouldn’t have behaved.

Esters

This results when an organic acid is reacted with an alcohol for example ethanoic acid and ethanol. This is a familiar reaction to GCSE students and nothing special about it. At home even our servants do this reaction in a different way for example in making pickle. Usually coconut vinegar, mustard, red inions, green chillies and raw papaws are added. They are expert in making this pickle especially nearer the Sinhalese New Year. When the proper ingredients are added and left over in a tight container for few days, an unmistakable odour comes out due to the formation of an ester and this is a common day to day reaction.

There are plenty of other esters found at home for example the scents and colognes are nothing but esters. Even the nail varnish is dissolved in esters. Have you not noticed when ladies applied them on the nails, they blow on them to dry or shake the fingers. The important character of esters is sweet smell and easily volatile.

Fermentation reaction

At home we make use of this reaction to make the bread, pizza or hopper dough. When yeast is added to some sugar it undergoes a reaction called fermentation. In making bread, pizza or hoppers, some yeast is added with some sugar then yeast reacts or undergoes anaerobic respiration and give out carbon dioxide which raises the dough. When the bread dough is baked in making bread the gas escapes through the dough but it raises it as well. The gas escapes slowly as the temperature rises that gives softness to the bread due to the formation of tiny holes.

Making whisky and arrack

In distilleries they make use of this reaction in making alcohol for example in making whisky, brandy or even making arrack. Some people make use of the same reaction to make illicit liquors. In making alcohol, the fermented mixture is distilled at a temperature control to get a particular alcohol but in making illicit alcohol there is no temperature control. That is because those people are unaware of fractional distillation.  In that case all the possible alcohols in the fermented mixture are distilled. Have I got to say when the alcohols get mixed up and if that was consumed, it is possible to get alcohol poisoning. Even in parties one needs to be careful not drink too many different alcohols, wines and beers, unless they want to sick in the gutter and end up in the hospital.

Saponification, emulsification

Apart from these there are plenty of day to day chemical reactions taking place at home. Applying soap and shampooing the hair, washing clothes, brushing teeth or even washing mouth with salt water are chemical reactions. What about cleaning plates with washing up liquid or cleaning the oils on the cooker surface, they are all chemical reactions. To me kitchen is a kind of chemistry laboratory. All the food we eat is nothing but complicated chemicals and cooking is a kind of chemical reaction. This subject chemistry may sound mystery but actually that is not too complicated to follow if it was done systematically.

To me cooking is nothing but a series of chemical reactions. There are intermolecular, intramolecular reactions, adsorption, absorption, chemisorption, vaporisation, condensation and many more reactions taking place in cooking. When time permits I will explain in simple terms what these terms are all about. In order to save about 60% wasting cooking gas, one needs to follow the Thermodynamic equilibrium cooking.

The rms [root mean square] velocity is directly proportional to the square root of temperature and inversely proportional to the square root of molar mass. Thus quadrupling the temperature of a given gas doubles the rms velocity of the molecules. Doubling this average velocity doubles the number of collisions between gas molecules and the walls of a container. It also doubles the impulse of each collision. Thus the pressure quadruples. Pressure is thus directly proportional to temperature, as required by Gay-Lussac’s law. That why I intend to increase the pressure of the cooking vessel while cooking pasta, rice, spaghetti or even chicken curry or vegetable curries, the technique save time and energy.

Adaptation of technique

Suppose if I was to cook rice in a cooking pan, I need to make sure it has a close fitting lid without any dents because it cannot develop enough pressure, if there was a leak. In a steam engine when it reaches a certain pressure, the excess was released similarly in a pressure cooker the excess pressure get released. In ordinary cooking vessel there is no such devices but you need to adopt to develop the pressure but one must be able to keep it under control. In doing this technique one can cook faster and save energy and time. That is what I mentioned that I apply science in cooking and energy saving. If any energy saving experts need to know what this is all about, why not contact me

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