Archive for March, 2015

Science Makes Sense-Week 29: Nitrogen, fertilizers, Haber Process.

March 29, 2015

I used to love growing a garden and in the early 80’s I would read lots of books on organic gardening. Words like ‘crop rotation’ ‘leguminous crops’ were phrases that would keep coming up. So I started growing peas and beans in one spot and the next year I would plant heavy feeders like tomatoes in that area. The books were telling me that I was enriching the soil with nitrogen salts with these leguminous plants (like peas and beans) and was creating a natural fertilizer for the subsequent year to plant tomato seedlings in that area.
Nitrogen is plentiful in the atmosphere as elemental nitrogen and is almost 80% of the air around us. As an element it is colorless and odorless and is not too reactive. It was discovered almost at the end of the 18th century by Daniel Rutherford (and independently by others such as Priestly and Cavendish). Rutherford was able to remove oxygen and carbon dioxide from a contained tube full of air and he demonstrated that the residual gas did not support combustion.(Ref.1)
Nitrogen is the 7th element in the Periodic Table and has three electrons in its 2p shell. This means that nitrogen has the ability to form triple bonds (six electrons sharing) with itself and with other elements. Consequently,nitrogen compounds have a lot of energy. A hundred years ago not much was known about nitrogen, but today it has several biochemical and industrial applications. It is used mainly to preserve food and in the production of fertilizers.(Ref.1) Nitrogen does not burn, nor support combustion and is slightly soluble in water. This gas is fairly un-reactive while its compounds are more reactive.(Ref.2)
There are basically three oxides of nitrogen, nitrous oxide N2O,which is used as an anaesthetic, NO,which is nitrogen oxide, used in the production of sulfuric acid and NO2 which is nitrogen dioxide found as an air pollutant.(Week28) The important compounds of nitrogen are ammonia, nitric acid and cyanides.(Ref.2)
One of the most important needs for nitrogen is in biological processes. All organisms need mineral nutrients for growth and nitrogen is essential here and is required in large amounts for proteins, nucleic acids and cellular components.(Ref.3) Amino acids are the smallest units of proteins and are organic acids with amine(a nitrogen atom with two hydrogen atoms) groups in them. Some of these amino acids are essential in the functioning of a lot of activities in our body. The Nitrogen Cycle explains how leguminous plants( beans, soybeans, peas) add fertilizer to the land. Some bacteria/microbes that reside in the nodules of the roots of these plants can convert atmospheric nitrogen to ammonium or nitrate ions. These are called ‘nitrogen-fixing’ bacteria that create fertilizers using atmospheric nitrogen. Then other bacteria and fungi convert the decaying organic matter to release atmospheric nitrogen once again to repeat the cycle.(Ref.3)
Nitrogen, a colorless odorless gas, has been shown to be invaluable in our very existence. Perhaps the fact that there is so much of it present in our air should have given us a clue about its importance!
Activities for Middle School Teachers
Study the Nitrogen Cycle and other cycles, what do they teach the students?
Let the teacher illustrate the uses of liquid nitrogen to study its effects on different objects. What are its uses in industry?
Study the essential and non-essential amino acids; what roles do they play?
Create their structures using model kits or marshmallows, toothpicks, raisins etc.
Nuggets of Information
The French chemist Lavoisier, named nitrogen “azote” meaning “without life”.(Ref.3)
About 2.5 % of the weight of living organisms comes from nitrogen in organic molecules.(Ref.4)
In the body, it is the 4th most abundant element.(Ref.4)
Nitrogen is the seventh most abundant element in the universe.(Ref.3)
Nitroglycerin is a nitrogen containing compound and can be used for relief of angina, a life threatening heart condition.(Ref.4)
In 1919, the world learned for the first time that atomic nuclei could be disintegrated. Ernest Rutherford reported that he had bombarded nitrogen gas with alpha-particles (helium nuclei) and found hydrogen was produced.(Ref.4)
The universe‚Äôs nitrogen was made, and is being made, by the CNO cycle in stars heavier than our sun. What exactly is the CNO cycle? When the universe was first formed following the ‘big-bang theory’, there was hydrogen, helium and a tiny amount of lithium. Helium ions bombarded the nucleus of these early elements to form carbon 12 which got bombarded to form the heavier nitrogen atom and the oxygen atom. These nuclear reactions leading to the formation of the different elements carbon, nitrogen and oxygen in the Periodic Table, is called the CNO Cycle. (Ref.4)
Sodium and potassium nitrates are formed during the decomposition of organic matter. They are called salt-peters and are found in dry areas of the world and are used as natural fertilizers.(Ref.3)
The Haber Process:Methane reacts with steam to get hydrogen; this hydrogen reacts with nitrogen in the Haber Process to form ammonia. Liquid ammonia/ ammonium ions are used as nitrogen fertilizers. Ammonia is the starting point for making many important nitrogen compounds and so the Haber Process is significant.(Ref.3)
Excess nitrogen in the atmosphere leads to eutrophication, toxic algae blooms, acid rain and also global warming.(Ref.3)
If nitrates get into groundwater that is used for drinking, it causes toxicity for newborns, a condition called anoxia, which leads to suffocation. This is also termed Blue Baby Syndrome.(Ref.3)