During the sultry and sunny summer days, what is that one drink you would crave while travelling?
Something that is healthy, refreshing, uncontaminated and easily available, right. What could be a better choice than coconut water for this? Now, do you know what this refreshing drink is actually composed of?
Well, it is 94% water and the rest are some vital minerals and sugar (sucrose, glucose, fructose).
The most significant mineral present in coconut water is potassium!
One cup of coconut water consists of 600 mg of potassium. In multiple ways, It is indispensable for both plant and animal life and is thus necessary for us to study it.
TABLE OF CONTENTS
Potassium (K) with an atomic number of 19, is an element of Group - I of the periodic table, an alkali metal as well as an integral member of the s-block of the modern periodic table. Its symbol (K) originates from its Latin name ‘Kalium’. Atomic weight of Potassium is 39.0983 u. It's a silver, lustrous shiny white metal. At room temperature, it exists as a soft solid which can be easily cut by a knife.
Other members of its group include Sodium, Lithium, Cesium, Francium, and Rubidium as alkali metals. Potassium is a metal that is extremely reactive and hence does not occur freely in nature. It exists in the form of a compound.
Sir Humphrey Davy, in 1807, was the first scientist to isolate Potassium from the compound caustic potash (KOH) in its molten state by the process of electrolysis. Potassium was seen to be accumulated at the cathode side. Potassium is the first metal that was successfully isolated by electrolysis. Earlier, it was extremely difficult to distinguish Sodium and Potassium from each other.
Potassium is not found in its free state in nature. It is found in shale, igneous rocks, and sediment in some minerals such as orthoclase feldspar and muscovite.
Apart from this, the minerals orthoclase feldspar and muscovite are highly insoluble in water which makes it extremely difficult to obtain the element by refining.
Hence, we use the compounds of Potassium like langbeinite, sylvite, carnallite, and polyhalite that are soluble in water to procure the commercial compounds of Potassium.
We can also use KCI for the production of Potassium. This reaction is termed the sodium reduction of molten potassium chloride (KCI) at a temperature of 870oC Molten potassium chloride is fed into a packed distilled column along with sodium vapours that are passed through the column. The volatile Potassium will be formed on the top of the distillation tower after condensation.
Potassium has three isotopes that occur naturally, K - 39, K - 40 and K - 41.
Isotopes of Potassium
K - 39
K - 40
K - 41
K - 40 is highly radioactive in nature and can be found in rocks, plants, and animals. This isotope after beta decay breaks down into a stable isotope of calcium and by electron or positron capture it forms an isotope of argon.
Reaction of Potassium with Air:
The alkali metals tarnish in dry air due to the formation of their oxides which in turn react with
moisture to form hydroxides.
When Potassium is burned with air, its shiny lustre is lost, and an orange-yellow colour of potassium superoxide (KO2) is formed as the product. The superoxide O2 ions are stable only in the presence of large cations such as K, Rb, Cs. KO2 is yellowish-orange in colour and paramagnetic in nature.
K(s) + 02(g) --> KO2(s)
In fact three species of oxides are possible as potassium oxidises in the presence of air.
Potassium oxide hydrolysis produces potassium hydroxide only. Potassium peroxide and potassium superoxide hydrolysis give potassium hydroxide and hydrogen peroxide. Oxides, peroxides and superoxides hydrolyse in the following manner respectively:
K2O(s) + H2O(i) + 2KPH(aq)
K2O2(s) + 2H2O(i) + 2KOH(aq) + H2O2(aq)
2KO2(s) + 2H2O(i) + 2KOH(aq) + H2O2(aq) + O2(i)
Reaction of potassium with water:
Potassium being highly reactive, reacts vigorously with water and gives off hydrogen gas. The product formed is a solution of potassium hydroxide which is also basic in nature. This reaction is highly exothermic and explosive in nature. The rate of this reaction is higher than that of sodium reacting with water but lesser than that of rubidium reacting with water. In the group - I, the reactivity of alkali metals with water increases down the group.
K(s) + 2H2O(i) + 2KOH(aq) + 2H2(g): ΔH = -ve
Reaction of potassium with dihydrogen:
Potassium reacts with dihydrogen at about 673 K to form potassium hydride. All the alkali metal hydrides are ionic solids with high melting points.
2K(s) + H2(g) + 2KH(s)
Reaction of potassium with halogens:
Potassium reacts with halogens to form solid potassium halide salts. The reaction is highly robust. The reactions are as follows:
2K(s) + F2(g) --> 2KF(s)
2K(s) + Ci2(g) --> 2KFi(s)
2K(s) + FN2g) --> 2KBr(s)
2K(s) + I2(g) --> 2KI(s)
Reaction of potassium with sulphuric acid:
Potassium readily dissolves in dilute sulphuric acid, which produces a solution of potassium ions along with hydrogen gas. The reaction is as follows:
2K(s) + H2SO4(aq) --> 2K2SO4(aq) + H2(g)
Reaction of potassium with potassium peroxide:
Potassium oxide is highly reactive, hence it forms potassium peroxide and potassium superoxide when oxidised. Now, the treatment of potassium peroxide with potassium results in the formation of potassium oxide.
K2O2(s) + 2K(s) --> 2K2O(s)
Q1. What is the oxidation state of potassium in potassium superoxide?
Solution: The formula of potassium superoxide is KO2 Here the oxidation state of potassium (K) is + 1 and of oxygen (O) is - ½.
Q2. Choose the correct option.
Solution: The electronic configuration of potassium is 1s2 2s2 2p6 3s2 3p6 4s1. Ionisation energy is the amount of energy required to remove the outermost electron of an atom in its gaseous state. Now, if you see the configuration, it is rather easy to remove electrons from 4s orbital, as the potassium atom will attain a noble gas configuration (But now it is difficult to remove an electron from K+, as it already attained a noble gas configuration. So, the amount of energy required to remove the first electron will always be lesser than removing the second electron from the potassium atom. Hence, the second ionisation energy is greater than the first ionisation energy of potassium.
Three types of oxides are possible when potassium oxidises in the presence of air which is potassium oxide K2O, potassium peroxide K2O2 and potassium superoxide KO2.
8K(s) + 4O2(g) --> 2K2O(s) + 2KO2(s) + K2O2(s)
The reaction of potassium with water is highly exothermic and explosive in nature.
K(s) + 2H2O(i) --> 2KOH(aq) + 2KH2(g); ΔH = -ve
Question 1. Where is potassium metal used?
Answer. It is used in fertilizers, as a salt substitute and to produce other chemicals. Potassium hydroxide (KOH) is used to make soaps, detergents and drain cleaners.
Question 2. Why is potassium stored in kerosene?
Answer. Being highly reactive potassium is stored in kerosene to avoid contact with air. Otherwise, it would react vigorously with air and produce explosion and form oxides, peroxides, superoxides and respective hydroxides too.
Question 3. What are the natural sources of potassium?
Answer. Some natural sources of potassium are green beans, raw onion, coconut water, cucumber, radish, grapes, pineapple, lettuce leaves, eggplant, mushrooms etc.
Question 4. What are the industrial uses of potassium?
Answer. Industrially potassium finds its application in the making of many things like soaps, detergents, gold mining, gunpowder, batteries, dyes and glass production.
Question 5. What is the role of potassium in our body?
Answer. Potassium is an essential electrolyte responsible for the adequate functioning of our cells and tissues. Besides this, potassium helps maintain blood pHlevels, regulates water content in the body, and helps in reducing high blood pressure levels caused by excess sodium intake. It also assists in skeletal and muscular functioning and healthy heartbeat patterns in our body.
Water of Crystallisation