Category Chemistry

WHAT IS A PLASTIC?

Plastics are everywhere! You are sitting on a plastic chair, leaning on a plastic-coated table or wearing plastic shoes. There are many different types of plastics. So what makes something a plastic? The first plastics were made more than 100 years ago from cellulose which is naturally found in plants.

Today plastics are made mostly from crude oil, a raw material that is fast running out. In the future, new raw materials must be found to make plastics, and there must be greater recycling of plastic waste.

Plastics is the term commonly used to describe a wide range of synthetic or semi synthetic materials that are used in a huge and growing range of applications. Everywhere you look, you will find plastics. We use plastic products to help make our lives cleaner, easier, safer and more enjoyable. We find plastics in the clothes we wear, the houses we live in, and the cars we travel in. The toys we play with, the televisions we watch, the computers we use and the DVDs we watch all contain plastics.

Plastics are organic materials, just like wood, paper or wool. The raw materials used to produce plastics are natural products such as cellulose, coal, natural gas, and salt. Plastics have become the modern material of choice because they make it possible to balance today’s needs with environmental concerns.

  • The word plastic comes from the Greek Plastikos – meaning able to be shaped.
  • They can be shaped into almost anything.
  • Plastics are light and relatively cheap.
  • They can be produced in different colours.
  • Heat and electricity do not travel through plastics easily; they are good ‘insulators’.
  • Unlike metals and wood, they do not rust or rot.

But plastics do have some disadvantages too.

  • They are made from resources which will eventually run out, and they are difficult to recycle.
  • Because they do not naturally rot (biodegrade) like wood, they are an eyesore and a hazard in the environment.
  • They are not as strong as many metals and they melt at high temperatures, sometimes giving off poisonous fumes.

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How do it rainmakers make it rain?

The Hopi Indians of south west America still trying to make rain by sacrificing Golden Eagles and dancing with live rattlesnakes in their teeth. But while they perform their traditional rain dances to please their gods and get rain for their crops, others have adopted a more scientific approach.

In 1946 Vincent Schaefer and Irving Langmuir started their work at the general electric research laboratories in Schenectady, New York, which proved that rain clouds could be artificially encouraged to produce showers.

Clouds are made up of billions of particles of water too small to fall as rain. Only when the droplets grow to a quarter of a millimetre or more will they fall as a fine drizzle. Smaller droplets evaporate before reaching the ground.

One way the droplets grow is by freezing to form particles of ice. In the cloud containing some ice particles and some water droplets, the ice particles grow rapidly as the droplets evaporate and the valour is transferred to the ice. Since the temperature of clouds is often below freezing it might be expected that the droplets would freeze easily. But the water can be 10 or 20° below freezing (supercooled) without actually freezing.

The reason for this is that the water in clouds is absolutely pure, without any dust or other contaminates which can from the centre of an ice crystal. If tiny particles are provided, the droplets freeze, grow quickly until they are large enough to fall, and then melt as the temperature rises, reaching the ground as rain.

Schaefer and Langmuir proved that small particles, usually of silver iodide, added to supercooled clouds could create rapidly growing ice crystals. These particles have been dropped from aircraft, carried by rockets or even released at ground level for air currents to carry them aloft.

In the Soviet union, 70 mm artillery guns have been used to fire silver iodide particles into clouds, exploding at the right height to disperse the chemical.

As long as the clouds are supercooled the technique may work increasing rainfall by up to a fifth. But since it is impossible to know how much rain could have fallen and anyway there are still question marks over the methods economic effectiveness.

 

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How acidity is measured?

Acids can gradually wear away and destroy almost everything they touch. All are soluble in water, and their strength is measured by their potential of Hydrogen.

The potential of Hydrogen scale runs from 1 to 14. One is extremely acid, 7 is neutral, and 14 is very alkaline (the opposite of acid).

The potential of hydrogen content of a liquid is measured with a potential of Hydrogen metre or with Universal Indicator paper, such as litmus. A strong acid turns the indicator paper red, while a neutral liquid turns it green. Strong alkaline liquids turn the indicator purple.

 

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Who is known for liquefaction of oxygen?

French chemist Antoine Lavoisier (1743-1794) is a celebrated scientist and nobleman who was central to the chemical revolution in the 18th Century. A meticulous experimenter who changed the way chemistry was done and perceived, he had a large influence on how both chemistry and biology developed. While it is impossible to cover everything that Lavoisier achieved in a short article, we will be looking at how one of his predictions came true nearly 100 years later.

A prophetic idea

Lavoisier had a prophetic idea that “[t]he air, or at least some of its constituents, would cease to remain an invisible gas and would turn into the liquid stage. A transformation of this kind would thus produce new liquids of which we as yet have no idea.” Given that until 1877, the dominant thought was that the permanent gases – oxygen, hydrogen, nitrogen and carbon monoxide – were not capable of existing in liquid form, such a statement was indeed beyond his time.

And yet, it did come true. For within days of each other, French physicist Louis Paul Cailletet and Swiss physicist Raoul Pictet arrived independently at methods for the liquefaction of oxygen in December 1877. A whole new field of research and science then opened up.

Born in 1832 into an industrial family, Cailletet was privileged to attend Lycee Henri IV in Paris, and the Ecole des Mines as an unregistered student. He returned to work on his father’s ironworks after his studies, and even though his exact nature of work remains unknown, it is evident that he applied the knowledge he had acquired while studying.

Observations in ironworks

Starting 1856, Cailletet published his studies based on observations in the ironworks and techniques to improve the quality of products. Most of these were presented by French chemist Henri Etienne Sainte-Claire Deville, a person with whom Cailletet shared a friendship that when beyond the typical Parisian scientific environment.

So when Deville became director of the chemistry laboratory at the Ecole Normale Superieure in 1868, it was no surprise that Cailletet also switched to a new series of experiments a year later – experiments that were no longer directly related to observations from ironworks. In 1869, Cailletet started experiments on high-pressure chemistry and most of his publications thereon dealt with compressibility of gases.

In 1877, Cailletet successfully attempted liquefaction of gases with an experimental arrangement based on a compression apparatus. Cailletet paced oxygen and carbon monoxide into his liquefaction apparatus on separate occasions, cooled and compressed them to a specific temperature and pressure and let the gases expand. He observed a thick mist at the end of the expansion and was able to identify that these were the condensed form of both gases.

 Deville is in the detail

Cailletet shot a letter to Deville on December 2, 1877, announcing the liquefaction of oxygen and carbon monoxide. Deville had the presence of mind to seal the letter in an envelope and deposit it with the Academie des Sciences. As a result, even when the Academie received a telegram from Pictet on December 22 stating that he had liquefied oxygen, there was no confusion over who got there first.

Pictet denied any priority claim and there was no dispute between the two parties. Pictet and Cailletet arrived at their results using different techniques and both of them were awarded the Davy Medal by the Royal Society of London in 1878.

Pictet proved to be an exception as a number of others jumped in and disputes ensued, Parallel priority claims were a constant theme between 1877 and 1908, during which time all the so-called permanent gases were liquefied. Cailletet’s liquefaction of oxygen had thus heralded cryogenics – a new field of research that concerned itself with the produced and behaviour of materials at very low temperatures.

 

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Are there schools that accept plastic as fees?

           Does your school accept plastic as fees? There is a unique school in the outskirts of Guwahati, Assam which does. If a student brings 25 pieces of plastic, it is accepted as fees in Akshar School. The plastic waste that they bring is recycled to make eco-friendly bricks that can be used for construction.

          When Parmita Sarma and Mazin Mukhtar started this school in June 2016, their aim was to provide free education to poor kids. Their plan took a slight twist when they saw the villagers making bonfires of plastic to beat the cold.

           They wanted to educate the villagers about the harmful effects of plastic and hence modified the fee structure from having no fees to plastic waste as fees. A practical lesson in recycling! The school provides socially and environmentally relevant education.

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Which is the first Indian state to ban disposable plastic bags?

           Sikkim, a tiny state in the foothills of the Himalayas is famous not only for its natural beauty and biodiversity, but also for its eco-friendly stands.

           In 1998, Sikkim became the first Indian state to ban disposable plastic bags. They were eliminated from both rural and urban areas and labelled as hazardous. 2016 is an environmentally important year for Sikkim as the state took two landmark decisions. The first was to ban packaged drinking water in government offices and at government events.

           The state has also banned the use of disposable styro-foam and thermocol plates and cutlery.

           It now targets single-use plastic bottles.

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