P Block Elements

7.19

One of the quantitative method for estimating O₃ gas is when ozone reacts with an excess of potassium iodide solution buffered with a borate buffer (pH 9.2), iodine is liberated. This iodine can be titrated against a standard solution of sodium thiosulphate.

2I^– (aq) + H₂O (l) + O₃ (g)? 2OH^– (aq) + I₂ (s) + O₂ (g)

7.18

Since ozone is not very stable at room temperature; it decomposes to give oxygen molecule and nascent oxygen on heating. The nascent oxygen, being a free radical is very reactive. Hence, it acts as a powerful oxidizing agent. The equation for the above reaction is given by,

7.17

(i) C₂H₄ + O₂→ 2CO₂ + 2H₂O

Ethane in reaction with oxygen gives carbon dioxide and water.

(ii) 4Al + 3 O₂→ 2Al₂O₃

Aluminium on reaction with oxygen gives alumina.

7.16

Pt is a noble metal (inert) and does not react with oxygen, whereas Zn, Ti, and Fe react with quickly with oxygen.

7.15

The oxygen atom has a smaller size and greater electronegativity than sulphur atom, hence intermolecular hydrogen bonding is possible in water (H₂O). But, only weak Van there Waal's force holds H₂S molecules, hence water is liquid and H₂S is a gas.

7.14

The enthalpy of dissociation of H-E bond (E= O, S, Se, Te, Po) in the hydrides decreases down the group. Hence, the thermal stability of the hydrides decreases down the group. The thermal stability is in the order H₂O > H₂S> H₂Se> H₂Te >H₂Po.

7.13

Sulphur generally exists in the combined form in the following sulphate minerals like gypsum (CaSO₄.2H₂O), Epsom salt (MgSO₄.7H₂O), barite (BaSO₄) and sulphide minerals such as galena (PbS), zinc blende (ZnS), copper pyrites (CuFeS₂).

Traces of sulphur are present in volcanoes as hydrogen sulphide. Sulphur is also present in organic materials such as eggs, proteins, garlic, onion, mustard, hair, and wool.

7.12

H₃PO₃ on heating dissociates into orthophosphoricacid (H₃PO₄) and phosphine (PH₃). Since, the oxidation states of orthophosphorous acid (H₃PO₃), orthophosphoric acid (H₃PO₄) and phosphine (PH₃) are +3, +5 and -3 respectively, this reaction is known as a disproportionate reaction (since the oxidation states of one of the product are positive and the other is negative). The reaction is as follows.

7.11

The basicity of a compound is defined as the number of acidic hydrogen atoms present in the compound. For a hydrogen atom to be acidic, it should be bonded to a strongly electronegative element like fluorine or oxygen atom.

As shown in the figure, 3 hydrogen atoms (green circled) are attached to an oxygen atom, which makes them acidic. Hence, the basicity of H₃PO₄ is 3.

7.10

 The balanced equation for the hydrolytic reaction of PCl₅ in heavy water (D₂O):

Therefore, on adding the above two equation we can say that the net reaction is: