By definition, an indicator is a substance that changes colour in different pH environments. Universal indicator is a brown-coloured solution—containing a mixture of indicators—that can be added to any substance to determine its pH. Like all indicators, universal indicator changes colour in different pH environments. At low pH, it appears red, and at high pH, it appears blue or violet. At neutral pH, it appears green. Universal indicator can form a continuous spectrum of colours that give an approximate reading of the concentration of protons in a sample.
Water and propan-1-ol are used as solvents. They are both polar and dissolve all the other ingredients in the solution. Sodium hydroxide (NaOH) is an alkaline solution that adjusts the pH of the universal indicator to ensure that each colour is shown at the correct pH value. It is necessary to add NaOH to the universal indicator because some of the indicator compounds (e.g. methyl red) are acidic themselves, which would affect the colour of the other indicators present. NaOH is added to neutralise the solution.
Methyl red is red at pH <5 and yellow at pH >5. It provides orange and red hues to the universal indicator solution at low pH. The end point of an indicator compound is defined as the pH at which it changes colour. The end point of methyl red, therefore, is somewhere around pH 5.
Bromothymol blue is blue at pH >6 and yellow at pH <6. It gives blue and indigo hues at high pH. Its end point is therefore around pH 6.
Thymol blue has two end points: it is red below pH <2, blue at pH >8 and yellow in the middle. Thymol blue allows universal indicator to differentiate low and very low pH by providing another red hue below pH 2. Thymol blue is yellow at pH 7, which, when combined with bromothymol blue (which is blue at pH 7), give a green colour.
Finally, phenolphthalein gives universal indicator a deep violet colour at very high pH.
This 2-miunte BBC video is a great introduction to universal indicator:
Mid-Autumn Festival (中秋节) is a traditional Chinese festival celebrated on the 15th day of the 8th lunar month each year (a full moon night in September). It started as an agricultural tradition (like harvest festival in western cultures) around 1000 BC in the Zhou Dynasty, and was formally acknowledged as a festival during the Northern Song Dynasty (between 960 and 1279 AD).
Today, Mid-Autumn Festival is celebrated with moon cakes, family reunions and three days off work. Moon cakes are circular to represent the full moon that always occurs on the Mid-Autumn Festival. Watch the video below to learn about the story behind the festival:
Moon cakes consist of crust, filling and an egg wash. The crust is made from flour, the polysaccharides in which bind together at oven temperatures to form a strong, intricate network (also including proteins) that allows the moon cake to keep its all-important circular shape.
The crust also contains invert sugar syrup, which is chemically similar to both honey and golden syrup. Invert sugar syrup is made by hydrolysingsucrose into its constituent monomers, glucose and fructose. The result is a sweeter-tasting, gooey liquid that doesn’t crystallise during cooking. This gives the moon cake a smooth mouthfeel.
Peanut oil (a blend of mostly monounsaturated triglycerides) is added to the crust for two reasons. First, it is a non-volatile liquid at room temperature, which prevents the moon cake from drying out. Second, the peanut oil molecules disrupt the protein matrix in the crust and give it an even smoother texture (not a doughy texture).
Maillard reactions are caramelisation reactions involving the removal of two hydrogen atoms from a sugar aldehyde or ketone. The resulting compounds are yellow/brown in colour because they contain carbon-carbon double bonds (C=C), which absorb violet and UV light (λmax ≈ 190 nm). The moon cake is usually also given an egg wash, which provides extra protein necessary for Maillard reactions to occur. More egg wash will provide a deeper brown colour to the dough.
Alkaline water (枧水) is a common ingredient in Guangdong-style cuisine. Chemically, it’s a ~0.020 molar solution of potassium carbonate and can be considered as the ‘opposite of vinegar’. It raises the pH in the moon cake, which accelerates the Maillard reaction, which is favoured by alkaline conditions. Alkaline water thus makes the crust more brown!
Finally, the fillings can be very diverse. Lotus seed with salted duck egg yolks is a common filling, but “five kernels”, red bean and green tea (with beans) are also quite popular. Lotus seed filling, for example, is made by soaking dried lotus seeds in alkaline water, pulverising and adding sugar. The resulting paste is then cooked with more oil and sugar before being used to fill a moon cake. ●
From today, all 12 Ingredients of an All-Natural Banana (and other Fruits) posters are available for just $99 with free world shipping by clicking the image below.
They’ve been featured on dozens of news websites and magazines and received over 2 million views in total this year. They started as an educational ‘hook’ for the classroom (specifically to introduce organic chemistry), but went viral online and sparked articles from all sides of the “is natural always best?” debate.
From today, get the entire original 12-poster set on sturdy 300 gsm card stock for just $99 with free world shipping by clicking the button above. (Usual selling price is $10 each plus postage).
If you’ve ever tried Beats® headphones, you’ll have felt the rich, powerful baselines they give you without overwhelming the rest of the music. Beats® and its music streaming service, BeatsMusic, have become so popular so fast that they now recently acquired by Apple for a whopping $3 billion, making co-founder Dr Dre the most financially successful hip-hop artist of all time. By far.
Here’s how this best-selling product works. Each headphone contains a neodymium magnet (the strongest known permanent magnet). When an electrical signal from your iPod (or similar) passes through the gold-plated audio cable to the voice coil, electromagnetic induction gives the voice coil a variable magnetic field. The exact strength and timing of the variable magnetic field represent perfectly the music being played. The voice coil’s magnetic field then interacts with the magnetic field of the headphone’s neodymium magnet via magnetic attraction (or repulsion), which moves the diaphragm, which sits between the magnet and the ear. When the diaphragm moves, it creates differences in air pressure (sound waves) that are detected by the diaphragm in your ear.
Excellent sound quality requires an air-tight seal between the headphone’s diaphragm and the diaphragm in your ear. Overstuffed leather guarantees this air-tight fit. Leather requires over 20 treatment processes before it’s ready to use in manufacturing. One of those processes is dying using polyazo dyes. When used in lower concentrations, these dyes are brightly-coloured; when mixed together and used in very high concentrations, they give an overall ‘black’ appearance to the leather.
The Beats® headphone frame is made from strong anodised aluminium. Aluminium, a strong yet lightweight metal perfect for making wearable tech, is anodised to increase its ability to resist wear-and-tear. The aluminium headphone frame is dipped into an electrolytic solution with a ~20-volt direct current flowing through it. Bubbles of hydrogen form at the cathode, and bubbles of oxygen form on the surface of the headphone. This oxygen gas buildup quickly oxidises not only the surface of the headphone, but deep into pores in the surface, which give the frame very high resistance to corrosion. ●
Today’s graphic explores the chemistry of Levi’s® famous blue jeans. It’ll show you why they’re blue, and how the dye is made; why the blue colour survives so well in the wash; and what’s special about the denim cotton weave that makes your Levi’s® jeans so strong.
Indican is a colourless, water-soluble compound extracted from leaves of the Indigofera species. Indican is a dextrose molecule conjugated to an indoxyl group by a glycosidic ether (C–O–C) bond.
The indican is hydrolysed at high pH, which separates the dextrose from the indoxyl group. The resulting indoxyl compound is whisked to aerate it, which causes the indoxyl molecules to oxidise and dimerise into indigotin, which is the famous blue dye used in Levi’s® jeans.
However, the indigotin blue dye isn’t soluble in water, and must be changed chemically before the jeans are dyed. Indigotin is subjected to high pH again, which reduces the indigotin, forming leuco-indigotin (also known as indigo white dye), which is, despite the name, pale yellow in colour.
Jeans are steeped in this water-soluble “indigo white dye”, which is still pale yellow at this stage! However, as soon as the jeans are removed from the vat of dye, the leuco-indigotin oxidises back into indigotin, which is blue in colour. The oxidised form (indigo blue) is insoluble in water, which helps the colour stick to the jeans despite being washed hundreds of times.
Denim is a traditional way of weaving cotton into a thick, sturdy material. Cotton is predominantly cellulose, a strong polymer of beta-D-glucose monomer units. Several thousand glucose monomers are present in each polymer chain. Polar hydroxyl groups form hydrogen bonds with hydroxyl groups on adjacent chains to form strong microfibrils, which the cotton plant then meshes into a strong poly- saccharide matrix. This matrix, and the denim weave, give high strength and durability to your Levi’s® jeans. ●
Many people are openly addicted to coffee. In northern Europe, home of the world’s greatest coffee drinkers, annual coffee bean consumption hovers around 9 kg per capita, which equates to 400 mg of caffeine per person per day (this is a highly addictive, highly stimulating dose). In North America, coffee bean consumption is much lower at 4.2 kg per capita per year, which equates to 185 mg of caffeine per person per day. However, this is still a highly addictive dose.
Caffeine (around 225 mg in the beverage shown above) causes short, sharp increases in your blood pressure. It makes you feel alert, but jittery in large doses. Caffeine stimulates nerves by counteracting adenosine, which is a nerve activity suppressant. The brain develops a tolerance to caffeine intake after a few weeks, which can cause some people to take increasingly large doses—sometimes exceeding the ~300 mg per day limit recommended by many doctors. That said, smaller doses are believed to provide some protection against Parkinson’s Disease in the long term.
Milk, a butterfat emulsion, gives the coffee its light colour and pleasant mouthfeel. Vanilla syrup adds an interesting flavour and aroma, and consists of glucose syrup and vanillin, an artificial flavour compound modelled on the main aroma compound in real vanilla beans.
The most amazing aspect of the product shown is the polypropylene cup. Starbucks® sells these reusable cups for just $1 in its United States stores, which is part of an attempt to serve 5% of all its beverages in reusable containers by 2015. In addition to giving you a 10-cent discount for bringing your own cup, and selling these reusable cups ridiculously cheaply, Starbucks® makes these cups from a fully recyclable plastic that’s completely inert at boiling-hot temperatures (100°C). This ensures that absolutely nothing from the cup leeches into your piping hot drink before you drink it. ●
Cherries are extremely sweet, and are unusual in that they contain more glucose (52%) than fructose (42%). Their bright red colour comes from the carotenes and capsanthin (the E160 colourings) that are present in high quantities throughout the fruit.
Cherry flavour comes from a huge collection of aroma compounds produced naturally by the cherry. To make all of these compounds in the lab, then mix them together in the correct proportions would be ridiculously time-consuming and expensive.
When making artificial cherry flavourings, only the first two compounds are usually added: (Z)-3-hexenol and 2-heptanone. Artificial cherry flavouring thus tastes absolutely nothing like real cherries: it lacks most of the ingredients that give real cherries their delicious flavour.
It’s quite a different story with oranges and lemons, though. Most of the flavour of oranges and lemons comes from (+)-limonene and (-)-limonene, which, by themselves, smell like orange and lemon, respectively.
The video made me feel sorry for LEGO®. It also reminded me that LEGO® is made from oil-based products (even though they’re trying to find a sustainable alternative), and it inspired me to make this infographic: the Chemistry of everyone’s favourite building block.
LEGO® is made from ABS (acrylonitrile butadiene styrene), a thermoplastic polymer comprised of three monomers. The first monomer, acrylonitrile, gives the bricks strength. The second, 1,3-butadiene, gives them resilience (i.e. stops them from snapping so easily) and the third, styrene, gives them a shiny, hard surface. These three ingredients are mixed with colorants then polymerised (hardened) with the help of an initiator called potassium peroxydisulphate. LEGO® buys pre-made ABS granules and injects them into brick shapes on a massive scale.
LEGO® make 20 billion bricks each year (that’s 35,000 bricks a minute) and according to the Guinness Book of World Records, they produce more plastic tyres than anyone else. Personally, I think that’s a remarkable feat. It’s engineering genius.
In a statement, LEGO® said: “We firmly believe that this matter must be handled between Shell and Greenpeace. We are saddened when the LEGO brand is used as a tool in any dispute between organisations. We will continue to… deliver creative and inspiring LEGO play experiences to children all over the world.” •
Inspired by the recent Peach infographic, I set out to find the least natural fruit in existence, and decided it was probably the modern watermelon. Take a look below: which one would you rather eat?
The watermelon, delicious as it is, has increased from 50 mm to 660 mm in diameter, which represents a 1680-fold increase in volume. While ancient “wild watermelons” weighed no more than 80 grams, modern watermelons can range from 2 kg to 8 kg in the supermarket, while the Guiness World Record for the heaviest watermelon recorded exceeded 121 kilograms in the year 2000. Thousands of years of human-induced evolution have worked miracles on these fruits. Let’s not forget that they’re completely artificial.
The most famous example of artificial selection is of course the selective breeding of the feeble teosinte plant into juicy, delicious, North American sweetcorn.
In 9000 years, sweetcorn has become 1000 times larger, 3.5 times sweeter, much easier to peel and much easier to grow than its wild ancestor. It no longer resembles the original teosinte plant at all. Around half of this artificial selection happened since the fifteenth century, when European settlers placed new selection pressures on the crop to suit their exotic taste buds.
That’s all for now… More exciting infographics coming soon. Enjoy! 😉
Why is Gold yellow? Special relativity causes length contractions and time dilations in objects that travel at speeds approaching the speed of light. The valence electrons of large atoms such as gold have such high energies that their speeds actually approach the speed of light—and the relativistic effects on those electrons can become quite large.
Special relativity changes the energy levels of the 5d orbital in a gold atom so that the energy difference between 5d and 6s orbitals equals the energy of a ‘blue’ photon. Gold thus absorbs blue light when electrons are elevated from the 5d to the 6s orbitals, while other metals do not. These special relativistic changes to the energy levels of atomic orbitals are slightly different for each element.
Relativistic contractions on gold’s valence electrons (the 6s subshell) pull the 6s electron very close to the nucleus. Being closer to the nucleus makes the 6s electron less accessible to any potential reactants. Special relativity is not only the reason for gold’s yellow colour but also for its very low reactivity! ●