Ncert Solutions Chemistry Class 12th
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New answer posted
10 months agoContributor-Level 10
The steps involved in the extraction of zinc from zinc blende (ZnS) are as followed:-
- Concentration: the ore is crushed and then concentrated by froth floatation
- Roasting: the concentrated ore is heated in the presence of an excess of air at about 1200K to form zinc
- ZnS + 3 O2 → 2 ZnO + 2 SO2
- Reduction: ZnO obtained above is mixed with powdered coke and heated to 1673K in a fireclay
- ZnO + C → Zn + CO
- Electrolytic Refining: Zinc is refined by the process of electrolytic refining. In this process, impure zinc is made the anode and a pure copper strip is made the cathode. The electrode used in an acidified solution of zinc sulphate (ZnSO4).
New answer posted
10 months agoContributor-Level 10
7.49
Disproportionation is a chemical reaction typically a redox reaction where a molecule is transformed into two or more dissimilar products.
On heating, orthophosphorus acid (H3PO3) disproportionate to give orthophosphoric acid (H3PO4)
and phosphine (PH3). The oxidation states of Phosphorous in various species involved in the reaction are mentioned below.
New answer posted
10 months agoContributor-Level 10
During the extraction of iron, the reduction of iron oxides takes place in the blast furnace. In the process, hot air is blown from the bottom of the furnace and coke is burnt to raise the temperature up to 2200K in the lower portion itself. The temperature is lower in the upper part. Thus, it is the lower part where the reduction of iron oxides (Fe2O3 and Fe3O4) takes place.
The reactions taking place in the lower temperature range (500K – 800K ) in the blast furnace are:-
3 Fe2O3 + CO → 2 Fe3O4 + CO2
Fe3O4 + 4 CO → 3 Fe + 4 CO2
Fe2O3 + CO → 2 Fe3 + CO2
The reactions taking place in the higher temperature range ( 900 – 1500K ) in
New answer posted
10 months agoContributor-Level 10
The common elements present in anode mud in electrolytic refining are antimony, selenium, tellurium, silver, gold, and platinum. These elements being less reactive, are not affected by CuSO4 + H2SO4 solution and hence settle down under anode as anode mud.
New answer posted
10 months agoContributor-Level 10
7.48
Catenation is the bonding of atoms of the same element into a series to form a chain. Catenation is much more common in phosphorous compounds than in nitrogen compounds.
This is because of the relative weakness of the NN single bond as compared to the PP single bond. Since nitrogen atom is smaller, there is greater repulsion of electron density of two nitrogen atoms, thereby weakening the NN single bond. T
his is the reason why Nitrogen shows catenation properties less than phosphorous.
Phosphorous has larger atomic size because of which it has less repulsion of electron density of two phosphorous atoms and hence P-P single bond is st
New answer posted
10 months agoContributor-Level 10
At 673K, the value of G (CO, Co2) is less than that of G (C, Co). Therefore, CO can be reduced more easily to CO2 than C to CO. hence; CO is a better reducing agent than C at 673K.
New answer posted
10 months agoContributor-Level 10
Zone refining method is based on the principle that impurities are more soluble in the molten state of metal (the melt) than in the solid state. The impure metal is heated with the help of a circular mobile heater at one end. This results in the formation of the molten zone or melt. As the heater is removed along with the length of the rod, the pure metal crystallizes out of the melt and impurities pass into the adjacent molten zone. This process is repeated several times till the impurities are completely driven to the end of the rod which is then cut off and discarded. The method is very useful for semiconductor and other metals of v
New answer posted
10 months agoContributor-Level 10
7.13
Red Phosphorus |
White Phosphorus |
1. It is soft solid and almost colourless but acquires pale yellow colour on standing. | 1. It is a red solid. |
2. It melts at 317 K and boils at 563 K. | 2. It burns at 533K to give phosphorous pentaoxide. |
3. With air contact it undergoes slow combustion and glows in dark. This property is called chemiluminescence. | 3. It does not glow in dark. |
4. It is insoluble in water but readily soluble in carbon disulphide and oils. | 4. It is insoluble in water as well as in carbon disulphide. |
5. It is very reactive and catches fire when heated in air. On burning it gives dense white fumes of phosphorus pentoxide. | 5. It is more stable and chemically less reactive as compared to white phosphorus. |
New answer posted
10 months agoContributor-Level 10
The Gibbs free energy formation ( ΔfG) of Cu2S is less than that of H2S and CS2. Therefore, H2 and C cannot reduce Cu2S to Cu.
On the other hand, the Gibbs free energy formation of Cu2O is greater than that of CO. hence, C can reduce Cu2O to Cu.
C (s) + Cu2O (s) → 2Cu (s) + CO (g)
Hence, the extraction of copper from its pyrite ore is difficult than from its oxide ore through reduction.
New answer posted
10 months agoContributor-Level 10
In the froth floatation method, the role of depressants is to prevent certain types of particles from forming the froth with the air bubbles. For example, NaCN is used as a depressant to separate lead sulfide ore (PbS) from zinc Sulphide ore (ZnS).NaCN forms a zinc complex Na2 [Zn (CN)4] on the surface of ZnS thereby preventing it from the formation of froth.
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