Chemistry: CUET Mock Test - 8 - CUET MCQ

Hyponitric acid does not exist. The rest three mentioned are commonly occurring oxoacids of nitrogen. Hyponitrous acid, H₂N₂O₂ is an isomer tautomer of nitramide, with the structure of the former being HON = NOH. Nitrous acid, HNO₂ is usually formed in the atmosphere prior conversion to nitric acid. It is highly unstable.

The most appropriate lab scale preparation method of nitric acid, HNO₃ is using an alkali nitrate salt and react it with concentration nitric acid in a glass retort. Nitrous acid being highly unstable decomposes into nitric acid. The other two sets of reaction represent the industrial process of manufacturing nitric acid i.e. Ostwald’s process.

Pt-Rh gauze sheet is widely used as the catalyst in ammonic oxidation, the first step of Ostwald’s process. Fe₂O₃ is used in Haber’s process; V₂O₅ in contact process and Zn (Hg) is used in Clemmensen reduction of aldehydes.
 

The products released depend on the concentration of nitric acid. In case of zinc metal, diluted nitric acid treatment release nitrous oxide and concentrated nitric acid causes the release of nitrogen dioxide.

Pickling of stainless steel is the process of removal of a thin layer of the alloyed metal from the surface. The common reagent used is nitric acid along with calculated amounts of hydrofluoric acid.

1 mole of sulfur, S₈ requires 48 moles of concentrated nitric acid. The reaction is given by S₈ + 48HNO₃ → 8H₂SO₄ + 48NO₂ + 16H₂O. 10, 4 and 20 moles of concentrated nitric acid is required to produce iodic acid, carbon dioxide and phosphoric acid from 1 mole of iodine, carbon and phosphorus, respectively.
 

Aluminum does not dissolve in nitric acid. This is because treatment with nitric acid results in the formation of a tough oxide layer. This oxide layer prevents it from further reacting with the oxide. Hence, the compound formed is Al₂O₃ i.e. aluminum (III) oxide.

Experimentally, it is determined that nitric acid and water form a constant boiling azeotrope at 68% – 32% by mass composition, respectively. Here, it becomes impossible to separate water and nitric acid by distillation methods. Thus, concentrated sulfuric acid is used for dehydration and removal of water.

Ostwald’s process is the name of the industrial process to manufacture nitric acid in bulk. It involves the oxidation of ammonia which forms nitric oxide. This is then reacted with more oxygen to produce nitrogen dioxide. Subsequently, nitrogen dioxide is dissolved in water to produce adequate concentrations of nitric acid. Contact process is used to produce sulfuric acid. Solvay is used to obtain sodium carbonate and Haber-Bosch to obtain ammonia.

Nitric acid is a very weak reducing agent since it has a polar O – H bond. This breaks to donate the H⁺ ion which is why it is a strong oxidizing agent and a strong acid. Since there is only one cleavable O – H bond, the basicity of nitric acid is unity (one HNO₃ molecule can donate only 1 H⁺ ion). It exists as a planar molecule in vapor phase.

The size of the atoms of the elements decrease from left to right in the same period. Considering the row to be the same, the electrons are added to the same shell. However, the increase in atomic number reflects the increase in number of protons i.e. the positive charge. Hence, the overall effective nuclear charge increases. Consequently, the electron cloud is pulled even more closer to the nucleus of the atom. Therefore, the size decreases.

The N – N single bond is highly weak and unstable due to high magnitude of inter-electronic repulsions of non-bonding electrons which in turn is caused by the single bond’s small bond length. As a result the catenation tendency becomes weaker due to the mentioned factors leading to instability.

Treating copper chips with concentrated nitric acid releases toxic brown gas, NO2, nitrogen (IV) oxide. It is a reddish-brown gas with pungent odor.

The brown ring test is used to determine the presence of nitrate ions, NO₃^-. Dilute ferrous sulfate solution is added to solution containing nitrate ion. Following this, concentrated sulfuric acid is added along the sides of the test tube. A brown ring is formed at the junction concentrated sulfuric acid and solutions.

Di-nitrogen trioxide is formulated as N₂O₃
The oxidation state of oxygen atom is fixed at -2 since it is the more electronegative atom in this case.
If oxidation state of nitrogen is assumed to be ‘x’, then:
2x + (3x -2) = 0
2x – 6 = 0
x = +3
The oxidation state of nitrogen is +3.

Ammonia is oxidized to nitrogen (II) oxide in the presence of Pt/Rh gauze catalyst at a temperature of 500 K and a pressure of 9 bars. The nitrous oxide is then converted to nitrogen dioxide which is further reacted with water to produce nitric acid. The NO formed is recycled.

In the gas state, the nitric acid molecule has a triangular planar shape with a steric number of 3 no lone pairs of electron. There are two major resonance forms of nitric acid.

The primary product of Haber-Bosch process is ammonia, NH₃. In this process, N_2(g) and H_2(g) are reacted at a high temperature of 700 K and 200 atm pressure in presence of iron-bed catalysts. It is an exothermic process which takes place in accordance with Le Chatelier’s principle. Nitric acid is produced by Ostwald’s process. Nitrous acid is produced by reacting sodium nitrite with a mineral and pyridine by Chichibabin process.

Covalency of an atom refers to the number of electrons that atom can share to form chemical bonds. Usually it is the number of bonds formed by the atom. In case of nitrogen, its atom can share up to four electrons, one in the s-subshell and the other three in the p-subshell. In addition to this, absence of d-orbitals restricts its covalency to four only.

Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involves the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials.

The ore is subjected to leaching when both the ore and impurity are insoluble in water. Leaching process is commonly referred to as extraction. This is a process in which water soluble substances are washed out from soil or wastes.

Oxide ores are subjected to roasting to remove the volatile impurities in the form of their oxides. It is easier to obtain metals from their oxides (by reduction) than from carbonates or sulphides. So before reduction can be done, the ore is converted into metal oxide.

 In magnetic separators, the effect of magnetism is used to separate ferromagnetic materials from non-magnetic materials. In principle, this process is also suitable for the iron ores siderite and hematite, which become weakly magnetic when heated.

Actually the extraction of a metal from its ore depends upon the selection of a proper reducing agent. Iron is a moderately active metal and its oxides can be reduced using carbon and not by using electrolysis. Reactive metals, such as aluminium, are extracted by electrolysis, while a less reactive metal, such as iron, may be extracted by reduction with carbon.

The main reaction occurring in the blast furnace during extraction of iron from haematite is:
Fe₂O₃ + 3CO → 2Fe + 3CO₂
This reaction involves the reduction of iron (III) oxide to iron and oxidation of carbon monoxide to carbon dioxide.

The froth flotation method is widely used for the concentration of sulphide ores such as zinc blende (ZnS), copper pyrites (CuFeS₂), galena (PbS), etc. This method is based upon the fact that the surface of the sulphide ores is preferentially wetted by oils while that of gangue is preferentially wetted by water.

Smelting is the process of extraction of a metal from its oxide by reduction with carbon (coke). Alkali metals, alkaline earth metals, etc. cannot be prepared by reduction of their respective oxides with carbon. The slag formed during smelting has high melting point and is lighter than the metal.

Bauxite is the chief ore of aluminium. The composition of bauxite is Al₂O₃.2H₂O, it’s a mixture of hydrated iron oxide and hydrated aluminium oxide. Kaolinite is another ore of aluminium but its less availability is less compare to bauxite and the extraction of aluminium from kaolinite is a hard process and costs more.

Kaolinite is a soft clay type material with the chemical composition [Al₂(OH)₄Si₂O₄]. It’s basically made up of hydrous aluminium silicates, they comprise the principle ingredients of kaolin (china clay). It is usually white in appearance and sometimes red due to iron oxide.

The composition of iron pyrite is FeS₂. Iron pyrite is exothermic and can cause hazard in mines, it is more economical to extract iron from other ores such as magnetite and hematite. Pyrites are generally unstable and might turn into sulfurous minerals.