Complete and balance the following reactions: Ag + HNO 3 ( dilute ) → _____+_____+_____.

When nitric acid reacts with silver, silver nitrate is formed along with water and oxides of nitrogen. Silver metal reacts with cold dilute nitric acid and produce silver nitrate ( AgNO 3 ) salt, nitric oxide ( NO ) gas and water as products. This reaction is a redox reaction (oxidation - reduction reaction) too. The balanced chemical reaction is given below, 3 Ag + 4 HNO 3 ( dilute ) → 3 AgNO 3 + NO + 2 H 2 O .

The correct order of increasing acidic strength of the oxoacids of chlorine is:

HClO < HClO 2 < HClO 3 < HClO 4

HCIO 3 < HClO 4 < HClO 2 < HClO

HClO 2 < HClO < HClO 4 < HClO 3

HClO 3 < HClO 4 < HClO < HClO 2

Explain why hydride of sulphur is a gas while hydride of oxygen is a liquid.

In hydrides of oxygen, due to the oxygen's high electronegativity, it has the ability to form hydrogen bonds. In water, there are numerous hydrogen bonds that increase its boiling point and at room temperature, it exists as liquid (water). In case of sulphur hydrides, sulphur is unable to form hydrogen bonds due to it's less electronegativity. So, the intermolecular forces are very weak and are existed in the form of Van der Waal’s forces, which does not increase the boiling point much. So, at room temperature, hydrogen sulphide exists as a gas.

Explain why halogens are coloured and the colour deepens on moving down in the group from fluorine to iodine.

When photons (light) of suitable energy hit the halogen atom, the unpaired valence electron gets excited and moves to higher energy states and return to the normal state by releasing the energy in the form of photons the frequency of these emitted photons, for halogens, usually lies in the visible range for human eye. And thus we see them coloured. As we move down in the groups atomic size increases and the energy gap between molecular orbitals decreases. With decrease of energy gap the probability of transition also increases. This is why the intensity of colour also increases from fluorine to iodine.

Explain why mercury loses its meniscus in contact with ozone.

When ozone is passed through mercury, it forms mercurous oxide, Hg 2 O , because of this mercury loses meniscus and lustre (due to dissolution of Hg 2 O in mercury) and Hg 2 O sticks on to the Walls of the glass appears like a tail due to the dissolution of Hg 2 O in mercury. This phenomenon is called as tailing of mercury. 2 Hg + O 3 → Hg 2 O + O 2

Draw the structure of H 3 PO 3 .

H 3 PO 3 is called orthophosphorous acid or phosphorous acid. It is one of the phosphorus oxygenic acids. Phosphorous acid ( H 3 PO 3 ) forms salts known as phosphites which are sometimes used as reduction agents. The structure of H 3 PO 3 is

Draw the structure of HClO 4 .

Perchloric acid ( HClO 4 ) is an oxoacid of chlorine, which contains one hydroxyl group attached to the central chlorine atom, and three chlorine to oxygen double bonds. Therefore, the structure of HClO 4 can be written as given below:

Explain why ICl is more reactive than I 2 .

ICl is a polar compound because of the difference in electronegativity. While I 2 is halogen molecule which is non polar in nature. The bond length of ICl is greater than I 2 so the bond of ICl breaks easily then I 2 , so ICl is more reactive than I 2 .

Explain why helium is used for filling weather balloons.

Helium is used for filling weather balloons because of two reasons: 1. It is lighter than air as its density is about one-eighth to that of air, therefore can go upward in air for weather forecasting. 2. It is inert and non-inflammable, therefore will have no risk of explosion unlike hydrogen.