NIOS Solved TMA Class 12: Chemistry 2023

Chemistry (3)
Tutor Marked Assignment

Max. Marks: 20

Note:

• All questions are compulsory. The marks allowed for each question are given at same place
• Write your name enrollment numbers, AI name, and subject on the top of the first page of the answer sheet.

1. Answer any one out of the following questions in about 40-50 words.

(b) Provide the formula for one compound that is positively charged and one that is negatively charged that is isoelectronic with \[Ne\].

\[ Ans:\] The formula of one species positively charged and negatively charged which is isoelectronic with Ne are respectively Na⁺ (Sodium-ion) and F⁻ (Floride ion). The term Isoelectronic means the ions have identical electrons in the same ground state configurations. Here, Neon (Ne) has a ground state configuration of \[1s^{2} 2s^{2} 2p^{6}\] and has 2,8 electrons.
On the other hand, Na has a configuration of\[ [Ne]3s^1\] So if Sodium loses one electron of 3s orbital it becomes sodium ion (Na⁺) which also has 6 electrons in 2p orbital which makes Na⁺ isoelectronic with Neon. As we know F has a configuration of \[1s^{2} 2s^{2} 2p^{5}\] and when F gains one electron it becomes Floride ion (F⁻) which again has identical numbers of Ne.
Hence, Na⁺ is the positively charged and F⁻ is the negatively charged ion which are isoelectronic with Neon.

2. Answer any one out of the following questions in about 40-50 words.

(b) Classify each of the following semiconductors as p-type or n-type:
(i) Ge mixed/doped with In.
(ii) B mixed/doped with Si.

\[ Ans:\] When Germanium is doped with Indium, P-type semiconductor is formed.
p-type semiconductor: It contains large number of positive charges i.e. holes, known as majority charges. Hence it is called P-type semiconductor (P for positive-holes).
• Ge is group 14 element and In is group 13 element. Hence an electron deficient hole is created and therefore, it is p-type.
• B is group 13 elements and Si is group 14 elements, there will be a free electron. Hence, it is n-type
n-type semiconductor: An extrinsic semiconductor which has been doped with electron donor atoms is called an n-type semiconductor, because the majority of charge carriers in the crystal are negative electrons.

3. Answer any one out of the following questions in about 40-50 words.

(b) Pure liquids and solids can be ignored while writing the value of equilibrium constant, Explain.

\[ Ans:\]• Pure solids and liquids are not written in the equilibrium constant expression. This is because they do not affect the concentration of reactant at equilibrium in the reaction.
• For pure solid or pure liquid- \[ M=\frac{n}{V} =\frac{m}{MV} =\frac{d}{M}\].
• Here d is the density and M is the molecular mass.
• Now the density and molecular mass of a pure substance is always constant and is included in the equilibrium constant.
• So the pure solids and pure solids can be ignored while writing the equilibrium constant expression.
As the density and molecular mass of a pure substance is always constant and is included in the equilibrium constant. So the pure solids and pure solids can be ignored while writing the equilibrium constant expression.

4. Answer any one out of the following questions in about 100-150 words.

(b) Carbon monoxide gas is more dangerous than carbon dioxide gas. Explain the reason.

\[ Ans:\] Human blood has hemoglobin responsible for transporting oxygen to all cells and taking back \[CO_2\] from them to the lungs. The haeme group thus forms reversible bonds with oxygen and carbon dioxide. Carbon monoxide forms a stronger bond than carbon dioxide with haeme’s iron; if it happens, that is if carbon monoxide bonds with haeme, oxygen can not bond as carbon monoxide bond is stronger. Thus, the supply of oxygen decreases in the body and may lead to individual death.
Both are deadly, in sufficient quantities, they can each kill you. Carbon monoxide kills at much lower concentrations because it readily and preferentially displaces oxygen at red blood sites basically depriving your brain of oxygen even when there’s plenty of oxygen around. Lethal concentrations are around 200 ppm and up. That's 0.02%.
Carbon dioxide will kill you when its concentration is the air is so high there is little oxygen left. Oxygen is normally ~20% of air or 200,000 ppm. Carbon dioxide lethal levels are around 150,000–250,000 ppm or 15–25% of air. That’s 1000 times higher than carbon monoxide lethal levels.
Both monoxide and dioxide are deadly in closed spaces with poor ventilation. Carbon Dioxide particularly accumulates in somewhat sealed spaces because being denser than normal air accumulates in low places so you literally drown in an invisible gas.


5. Answer any one out of the following questions in about 100-150 words.
(a) Froth flotation is used for the concentration of sulphide ores because it is a highly effective method. Explain.



\[ Ans:\] Froth flotation process:
i) The froth flotation process is based on the principle of difference in the wetting properties of the ore and gangue particles with water and oil.
ii) It is used for the extraction of those metals in which the ore particles are preferentially wetted by oil and gangue particles by water.
iii) This method has been used for removing gangue from sulphide ores. eg. Galena (PbS), zinc blende (ZnS), copper pyrites \[(CuFeS_2)\], etc.
iv) In this method, a suspension of the powdered ore is made with water. To this suspension small quantities of collectors and froth stabilizers are added. Collectors (eg. pine oil, eucalyptus oil, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilizers (eg. cresols, aniline) help in stabilization of the froth.
v) In the flotation tank, a current of compressed air is circulated through the water. A rotating paddle agitates the mixture and draws air into it. As a result, froth is formed which carries the mineral particles. The froth is light and is skimmed off. It is then dried for recovery of the ore particles. The gangue material is wetted by water and settles at the bottom.
vi) Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using 'depressants'. ego In case of an ore containing ZnS and PbS, the depressant used is NaCN. It selectively prevents ZnS from coming to the froth but allows PbS to come with the froth, which can be further removed off.


6. Prepare any one of the project out of two given below.



a) The students from Class XII visited a nearby village as part of a group excursion. Rural and urban environments differ significantly from one another. In urban area, there is a lot of pollution. Peoples are suffering from cough, typhoid, and dengue diseases but in rural area people are healthy. There are a large number of trees in rural area therefore. Environment is clean.
(i) Explain the main reasons of air pollution.
(ii) Identify primary and secondary pollutants.
(iii) Name two water borne diseases.
(iv) Illustrate the global warming.
(v) It is advisable to switch off engine of vehicle at red light, explain with reason.
(vi) Define photochemical smog.

\[ Ans:\] (i) Explain the main reasons of air pollution.
The main cause of air pollution is the burning of fossil fuels. Harmful gases like sulphur dioxide, carbon monoxide etc. are released into the atmosphere due to incomplete combustion of fossil fuels which pollutes the air.
(ii) Identify primary and secondary pollutants.
Primary pollutants are those that are emitted directly from a source, which can be natural (volcanic eruptions or fires, for example) or of anthropogenic origin (carbon monoxide from vehicles).
Secondary pollutants, on the other hand, are not emitted directly. Its origin lies in the interactions between the primary emissions in the atmosphere. One of the most known secondary pollutants is tropospheric ozone.
(iii) Name two water borne diseases.
Waterborne diseases are illnesses caused by microscopic organisms, like viruses and bacteria, that are ingested through contaminated water or by coming in contact with feces.
1. Diarrhea
2. Cholera
(iv) Illustrate the global warming.
Global warming is a gradual, long-term increase in the average temperature of Earth's atmosphere due to the greenhouse effect where gasses from various human activities, including the burning of fossil fuels, trap heat from solar radiation.
(v) It is advisable to switch off engine of vehicle at red light, explain with reason. Switching off the engine of the vehicles at the red light on the road will help to save fuel and cause less pollution.
(vi) Define photochemical smog.
Photochemical smog is a type of air pollution due to the reaction of solar radiation with airborne pollutant mixtures of nitrogen oxides and volatile organic compounds (hydrocarbons). Smog is a byproduct of modern industrialization. Due to industry and the number of motor vehicles, this is more of a problem in large cities that have a warm, sunny and dry climate.