Assign the possible reason for the following: H 3 PO 2 acts as a good reducing agent while H 3 PO 4 does not.

The reducing character of the acid is due to H atoms bonded directly to P atom. H 3 PO 2 is a monobasic acid which has one P = O , one P - OH (ionizable H ) and two P - H (non-ionizable) bonds. So, due to presence of two P - H bonds, H 3 PO 2 is an acid as well as its salt behave as strong reducing agents. It is used in organic chemistry to reduce arene diazonium salts to arenes. The oxidation state of phosphorus, in H 3 PO 2 is + 1 which can further be oxidized to a higher oxidation state and hence can act as reducing agent. Whereas in H 3 PO 4 , the oxidation state of phosphorus is + 5 which is highest oxidation state for phosphorus. Hence, H 3 PO 2 acts as a reducing agent whereas H 3 PO 4 does not.

Assign the possible reason for the following: H 2 O is less acidic than H 2 S

H 2 O is less acidic than H 2 S because the decreasing acidic strength has the following trend- H 2 O < H 2 S < H 2 Se < H 2 Te . Acidic strength depends upon the size of the central atom and the distance between the central atom and hydrogen also increases. As a result of increase in bond length, the bond dissociation enthalpy decreases and bond cleavage becomes more and more easy. Therefore, the acidic strength of the hydrides increases down the group.

Account for the following: H 3 PO 3 is dibasic.

The molecular structure of H 3 P O 3 is shown below. The P - H bond in the above structure is not ionisable and thus, do not participate in the acidic reactions of H 3 P O 3 . Only O - H bonds are ionisable and are responsible for the acidity of H 3 P O 3 . Therefore, due to the presence of two ionisable hydrogen atoms, H 3 P O 3 is a dibasic acid.

Account for the following: Cl 2 is a powerful bleaching agent.

Chlorine is a good bleaching agent, due to its oxidising properties. It produces nascent oxygen in the presence of moisture. Cl 2 + H 2 O → 2 HCl + O coloured substance + O → colourless substance

Account for the following: PCl 3 fumes in moisture.

Phosphorous trichloride ( PCl 3 ) gets hydrolysed in the presence of moisture to form orthophosphorous acid and gives fumes of HCl . The following chemical reaction will take place: PCl 3 + 3 H 2 O → H 3 PO 3 + 3 HCl

Account for the following : N 2 , is less reactive at room temperature.

Dinitrogen is chemically inert at room temperature. It is neither combustible nor it supports combustion. The N - N bond in nitrogen molecule is a triple bond with a bond distance of 109 . 8 pm and bond dissociation enthalpy of 941 . 4 kJ mol - 1 . The low reactivity of nitrogen is due to very small size of the molecule and high bond dissociation enthalpy of the molecule. However, reactivity increases rapidly with the rise in temperature.

What are interhalogen compounds? Which interhalogen compound is used to fluorinate uranium ? How is it prepared ?

An interhalogen compound is a molecule that contains two or more separate halogen atoms (fluorine, chlorine, bromine, iodine, or astatine) and no atoms of any other group of elements. Most known interhalogen compounds are binary. The inter halogen compound that is used to fluoridate uranium is iodine pentafluoride. Iodine pentafluoride ( IF 5 ) is a colourless liquid, made by reacting iodine pentoxide with fluorine, or iodine with silver(II) fluoride. It is highly reactive, even slowly with glass. It reacts with water to form hydrofluoric acid and with fluorine gas to form iodine heptafluoride.

Draw the structure of H 3 PO 2 and account for its reducing character.

The acids which contain P – H bond have strong reducing properties. Thus, hypo phosphorous acid is a good reducing agent as it contains two P – H bonds and reduces, for example, conversion of AgNO 3 to metallic silver. 4 AgNO 3 + 2 H 2 O + H 3 PO 2 → 4 Ag + 4 HNO 3 + H 3 PO 4 These P – H bonds are not ionisable to give hydrogen ion, hence these are not responsible for basicity. Only those hydrogen atoms which are attached with oxygen in P – OH form are ionisable and cause the basicity.

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The product obtained by the reaction of calcium phosphide with water is

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