The elements of the group 13 – 18 come under the p – block elements. In these elements the last electron enters in the outermost p – orbital. They have ns2np1-6 electronic configuration in valence shell, helium being an exception. These elements show the maximum oxidation state equal to the sum of electrons in the outermost shell or valence shell. Most of the elements of the p – block form covalent compounds although some elements form ionic compounds (such as halogens) and coordination compounds as well. p-block contains elements which are either metals, non – metals or metalloids. p-block elements include the group of halogens and inert gases. First member of each family of the p-block elements is given below in the table with their general electronic configuration and oxidation states. p-block has the most electronegative element which is fluorine. Elements of p-block generally form acidic oxides. Many elements such as C, Si, Ge, O, N etc. also show phenomena of allotropy. Property of catenation is also shown by many elements.
We have covered the Boron Family (Group -13 elements) and the Carbon Family (Group – 14 elements) in another article of p-block elements (Class XI, Chemistry). In this article, we will cover the Nitrogen Family or Group 15 Elements of p-block elements (Class XII, Chemistry).
Group 15 is the third group of p-block elements. The first element of the group is nitrogen, that’s why it is also known as the Nitrogen Family.
Nitrogen differ from other elements of the group – 15 due to its high electronegative character, small size and high ionization enthalpy.
Nitrogen can form multiple bonds with itself and other elements. it forms p – p multiple bonds. Other heavier elements of the group 15 do not form p – p multiple bonds
d- orbitals are not found in the valence shell of the nitrogen element. It cannot form d – p bond while other heavier elements can. For example, phosphorous forms R3P=CH2.
Aim- To detect nitrate in the given sample.
Requirements- Test tubes, freshly prepared iron sulphate solution, concentrated sulphuric acid.
Principle- The test is based on the fact that nitrate ion acts as an oxidizing agent. In the reaction mixture reduction of nitrate ion takes place by iron (II) and iron(II) gets oxidized to iron (III) Nitric oxide is reduced to NO- and forms nitrosonium complex which forms a brown ring at the junction of two layers.
Brown ring test experiment for nitrate ions can be performed by using following steps-
Take a sample in which you suspect nitrate is present in a test tube.
Prepare fresh iron sulphate solution.
Now mix freshly prepared iron sulphate solution in the sample.
Add concentrated sulphuric acid solution along the side to the bottom of the test tube with the test tube tilted which containing the mixture of sample and freshly prepared iron sulphate solution. Concentrated sulphuric acid is added in such a way that it forms a layer below the aqueous solution.
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A brown ring is formed at the junction of two layers (one layer of mixture of iron sulphate solution + sample solution and second layer of concentrated sulphuric acid solution).
Brown ring confirms the presence of nitrate in the sample.
Following reactions take place during brown ring test –
2HNO3 + 3H2SO4 + 6FeSO4 🡪 3Fe2(SO4)3 + 2NO + 4H2O
[Fe(H2O)6]SO4 + NO 🡪 [Fe(H2O)6]SO4 + H2O
Brown ring test is mainly used for the detection of nitrate. It is used to detect the presence of nitrate in many food samples, soil and water. As high quantity of nitrate in food causes food poisoning and high quantity of nitrate in soil makes it very acidic which is harmful for plants and farming. If nitrate compounds are present in water more than 10miligrams per liter then it’s not drinkable.
Allotropes of Phosphorus – Important allotropic forms of phosphorus are red, white and black.
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