Sunday, December 9, 2007

Questions-Answers-Ch.13 Non-Metals

Boron (B) - Preparation and Properties

1. What is the atomic number of Boron and what is its electronic configuration

Z = 5, 1s²2s²2px¹

2. What are the main ores of Boron?

Borax, Kernite, Colemanite and Orthoboric acid.

3. What are the methods of obtaining Boron?

1. By the reduction of boric oxide y an electropositive metal like magnesium.
2. By the reductin of volatile boron compounds by dihydrogen at high temperatures (1270K).
3. By the electrolytic reduction of fused borates or other boron compounds (e.g., KBF-4, potasium tetrafluoroborate) in molten KCL/KF at 1073K.
4. By the thermal decomposition of boron tri-iodided over red hot tungsten.
5. By thermal decomposition of boron hydrides and boron halides at about 1173K.

4. what are physical properties of Boron?

1. Boron is an extremely hard solid next to diamond.
2. Its melting point is 2450K and boiling point is 3925K.
3. It is a poor conductor of heat electricity.
4. It has two isotopic forms - B-10 and B-11. Relative abundance 19% and 81% respectively.

5. what are chemical Properties of Boron?

1. Comination with nonmetals: At room temperature, it reacts with flourine. Superficial reaction with oxygen. At higher termperatures, it reacts directly with all nonmetals except H, Ge, Te and nobles gases.
2. With water: It does not react with water even in the form of steam.
3. Acids: HCL does not react with boron.
When heated with concentrated sulphuric acid or nitric acid, boron is oxidized to boric acid.
Boron does not react with nonoxidizing acids.
4. Boron react with fused caustic alkalies like NaOH and KOH forming borates.
It dissolves in fused Na-2CO-3 and NaNO-3 mixture at 1173K.
5. Boron comines directly with almost all metals (except heavy metals) at higher temperatures.
Heavy Metals not combining with boron include Ag, Au, Cd, Hg, Ga, In, Tl, Pb, Sn, Bi etc.
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silicon (Si) - Preparation and Properties

1. What is electronic configuration of Silicon?
Atomic Number is 14. 1s²2s²2p^63s²3p²

2. What are the methods of obtaining Silicon?

1. Heating finely divided silica with magnesium powder.
2. Heating potassium silicoflouride with potassium metal.
3. Heating potassium silicoflouride wtih Al or Zn in an iron crucible.
4. Passing a current of SiCl-4 over molten aluminium.

3. What are physical Properties of Silicon?

Silicon is available in two allotropic forms. the amorphous silicon and the crystalline or admantine silicon.

amorphous silicon is a dark brown powder which is insoluble in water.
Crystalline silicon forms pale yellow crystals.

4. What are chemical properties of silicon?

1. Silicon burns in air or oxygen forming silicon dioxide.
2. With halogens, it forms halides, SiX-4.
3. With fused acqueous caustic alkalies, silicon forms alkali silicates with liberation of hydrogen.
4. silicon decomposes on red heating liberating hydrogen.
5. Metals like Magnesium and nonmetal carbon form silicides with silicon.
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Nitrogen (N)

1. what is electronic configuration of Nitrogen?
Z = 7 ; 1s²2s²2p³
2. What are the methods of obtaining Nitrogen?

1. Heating an aqueous solution containing an equivalent amount of ammonium chloride and sodium nitrite.
2. Thermal decompostion of ammonium dichromate.
3. By the action of ammonia with cupric oxide or bleaching powder.
4. Very pure nitrogen can be obtained by the thermal decomposition of sodium or barium azide.
5. Commercially, nitrogen is prepared by the fractional distillation of liquid air.

3. What are physical Properties of Nitrogen?

1. It is colourless odourless and tasteless gas.
2. It has two stable isotopes N-14 and N-15.
3. It is a nontoxic gas.
4. It slightly lighter than air and the vapour density is 14.
5. It has very low solubility in water.
6. Its melting point is 63.2 K and boiling point is 77K.

4. What are chemical properties of Nitrogen?

1. It has no effect on red litmus or blue litmus.
2. It combines with active metals on strong heating to form their nitrides.
3. Reaction with Nonmetals:
---With hydrogen: at 750K under a pressure of 200 atm in the presence of iron as catalyst it forms ammonia.

---with oxygen: duirng lightning or at about 3300 K it forms nitric oxide. And then Nitrogen dioxide is formed.

4. Reaction with some compounds:
-------With calcium carbide at 1300 K calcium cyanamide is formed.
-------With aluminium oxide at 2100 K aluminium nitride is formed.

5. What is fixation of nitrogen?

The process of conversion of atmospheric nitrogen into useful compound is called nitrogen fixation.

1. Natural fixation: During the lightning, nitrogen and oxygen in atmopshere combine to form nitric oxide. Nitric oxide is very unstable and is immediately oxidized to nitrogen dioxide. This gets dissolved in rain water in combination with oxygen to form nitric acid. Nitric acid comes down along with rain and goes into soil. IN the soil it combines with salts like CaCO-3 and MgCO-3 to form their nitrites. These nitrites are used by plants.

2. The symbiotic bacteria prsent in the root modules of leguminous plants (e.g., beans, grams etc.) convert the nitrogen in atmosphere to useful compounds andsupply to the plant.

3. Non leguminous plants like Alnus and Ginkgo also fix nitrogen.

4. Certrain blue algae found in paddy fields also fix nitrogen.

5. Artificial or industrial fixation: Commercially as well as in laboratories, atmospheric nitrogen is made to react under suitable conditions with other chemicals to form useful compounds. Ex: Ammonia.

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Phosphorus (P)

1. what is electronic configuration of Phosphorus?
Z = 15; 1s²2s²2p^63s²3p³

2. What are the methods of obtaining Phosphorus?

1. heating bone ash or phosphate rock with silica and coke in an electric furnace.
2. by reduction of a mineral phosphate by carbon in the presence of silicaf in an electrical furnace.

3. What are physical Properties of Phosphorus?
Phosphorus is available in allotropic forms - white, red and black.
When freshly prepared, white phosphorus is nearly colourless but acquires lemon yellow colour on standing due to the formatin of a film of red variety on the surface. It has a garlic smell, poisonous in nature, insoluble in water and soluble in carbon disulphide. It glows in the dark.

The properties of other allotropes are discussed in allotrope section.


4. What are chemical properties of Phosphorus?

Phsophorus directly combines with halogens and a number of metals giving halides and phosphides.
It is a powerful reducing agent and concentrated nitric acid and sulphuric acid are reduced on heating with Phsophorus.
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Oxygen (O)

1. what is electronic configuration of Oxygen?
Z = 8

2. What are the methods of obtaining Oxygen?

1. compounds such as chlorates, nitrates, permanganates, etc. give oxygen on strong heating.
2. Certain oxides of metals give oxygen on heating.

3. Laboratory method: i) As mentioned in point 1, in the laboratory, oxygen is prepared by heating amixture of potassium permanganate(4 parts) and manganese dioxide (1 aprt) in a hard glass tuble to about 420 K. MnO-2 acts as catalyst.
ii) by the actin water on sodium peroxide.
4. Electrolysis of barium hydroxide.
5. Fractional distillationo of air
6. Electrolysis of water containing small amount of acid or alkali.

3. What are physical Properties of Oxygen?

1. Oxygen is colourless, tasteless and odourless gas.
2.It is slightly soluble in water.
3. it can be liquified under pressure.
4. Its melting point is 54.4K and boiling point is 90.2 K.

4. What are chemical properties of Oxygen?

1. Oxygen is a supporter of combustion but itself is not combustible.
2. reacts with active metals at room temperature to form their respective oxides.
3. At 575K with sodium it forms sodium peroxide Na-2O-2.
4. Metals like Fe, Al react with oxygen only on heating.
5. Less active methals like gold and platinum do not combine with oxygen.
6. Oxygen reacts with a number of non-metals to form their respective oxides.
7. It oxidizes number of compounds underspecific conditions.
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Sulphur (S)

1. what is electronic configuration of Sulphur?

Z = 16
2. What are the methods of obtaining Sulphur?

From deep below the surface of the earth, sulphur is extracted using a special technique known as Frasch process.

Hydrogen sulphide present as an impurity in natural gas, is absorbed in mono ethanol amine. Sulphur is then recovered from it by passing oxygen at low temperature.

3. What are chemical properties of sulphur

Sulphur combines with a large number of metals and nonmetals.
Sulphur is oxidized by concentrated nitric acid and sulphuric acid.
sulphur also reacts with hot concentrated solution of alkalies

Halogens
Halogens is a big topic by itself and hence it will be taken up in a separate post/unit

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