Shayona Academy: Chemestry

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ANSWER IN BRIEF

Mention physical properties of nonmetals.
ANS :
- Nonmetals occur in all three states : solid, liquid and gas.
- They are neither malleable nor ductile.
- They do not conduct heat and electricity (graphite is an exception).
- They are lustreless.
- They are generally soft (diamond is an exception).
- They are brittle.
- They generally have low melting points and boiling points.
- They are light in weight.
- Solid nonmetals do not produce ringing sound.

Explain chemical properties of nonmetals.
ANS : Nonmetals are electronegative elements because they accept electrons and form negatively charged ions. For example, oxygen forms negative oxide ion O^-2 by accepting two electrons.
1/2 O₂ + 2 e^- → O^-2

REACTION WITH OXYGEN : Nonmetals form either acidic oxide or neutral oxide with oxygen.
- When carbon burns in air, it forms carbon dioxide which is an acidic oxide.
  C_(s) + O_2(g) → CO_2(g)
  
  Carbon dioxide dissolves in water to form carbonic acid [H₂CO₃].
  CO_2(g) + H₂O_(l) → H₂CO_3(aq)
- When sulphur burns in air, it reacts with oxygen to form sulphur dioxide which is an acidic oxide.
  S_(s) + O_2(g) → SO_2(g)
  
  Sulphur dioxide dissolves in water to form sulphurous acid [H₂SO₃]
  SO_2(g) + H₂O_(l) → H₂SO_3(aq)
- Phosphorus forms phosphurus pentoxide (2P₂O₅) with oxygen which dissolves in water to form phosphoric acid [H₃PO_4(aq)].
  P_4(s) + 5O_2(g) → 2P₂O_5(g)
  
  2P₂O_5(g) + 6H₂O → 4H₃PO_4(aq)
- Oxides like CO, N₂O, H₂O are neutral oxides as their aqueous solutions are neither acidic nor basic or they do not have any effect on any litmus paper.
REACTION WITH ACIDS : Nonmetals do not react with dilute acids as they are not able to displace hydrogen from acids.

REACTION WITH CHLORINE : Nonmetals form chlorides with chlorine. These chlorides are either liquid or gas.

REACTION WITH HYDROGEN : Nonmetals form covalent hydrides with hydrogen.

Methane (CH₄), hydrochloric acid (HCl), etc. are hydrides of nonmetals.

Describe the Importance of nonmetals.
ANS :
- Carbon is the main constituent of all nutrients needed for the growth and development of living organisms.
- Carbon is also used in the preparation of gunpowder, sugar, cold drinks, dry ice, urea, etc.
- Oxygen supports life on earth.
- Oxygen also supports combustion process.
- Nitrogen is the major constituent of the atmosphere.
- Nitrogen reduces the rate of combustion.
- Nitrogen is used in the preparation of nitric acid, nitroglycerin and fertilisers.
- Hair, onion, garlic, etc. contain sulphur.
- Sulphur is used in the preparation of paper pulp, fungicides, etc.
- Phosphorus is used in making matchsticks, insecticides, etc.

Write a few sentences on Hydrogen.
ANS :
- Hydrogen was discovered in 1766 AD by English chemist Cavendish.
- Its chemical symbol is H.
- It is the lightest of all elements.
- It is the first element of the periodic table.
- Hydrogen does not occur in free state in the atmosphere.
- It is a diatomic molecule.
- it is a colourless, odourless gas.
- It is present in outer space.
- It is the main element present in sun.
- Sun's energy is produced due to the conversion of hydrogen into helium.
- Hydrogen is manufactured on large scale from natural gas by Steam Reforming.

Describe preparation of hydrogen in laboratory.
ANS :

AIM : To prepare hydrogen gas in laboratory.

APPARATUS & MATERIAL : Conical flask, Thistle funnel, glass container, bee-hive shelf, glass jar, glass tube, zinc granules, hydrochloric acid, water, etc.

PROCEDURE :
- Zinc granules are taken in conical flask and the equipment is set up as shown in figure.
- Dilute hydrochloric acid is added slowly to the flask through thistle funnel.
OBSERVATION : The reaction between zinc granules and dilute hydrochloric acid produces hydrogen gas which is collected by downward displacement of water in an inverted jar.

CHEMICAL REACTION :

Zn_(s) + 2HCl_(aq) → ZnCl_2(aq) + H_2(g)

NOTE : In place of dilute HCl we can also use dilute H₂SO₄.

Zn_(s) + H₂SO_4(aq) → ZnSO_4(aq) + H_2(g)

Describe manufacture of hydrogen from natural gas.
ANS :
- Hydrogen gas is manufactured on large scale from natural gas by steam reforming process.
- Methane (the main constituent of natural gas) is mixed with steam and passed over nickel catalyst at 800°C and 30 atm pressure.
- The reaction produces carbon dioxide and hydrogen.
- Hydrogen gas can also be obtained by the electrolysis of acidified water.

Describe chemical properties of hydrogen.
ANS :
1. Hydrogen gas burns in air (oxygen) with a blue flame forming watervapour.
  
  2H_2(g) + O_2(g) → 2H₂O_(g)
2. It burns in chlorine to form white fumes of hydrogen chloride gas.
  
  H_2(g) + Cl_2(g) → 2HCl_(g)
  
  Similarly it forms hydrogen fluoride gas with fluorine.
  
  H_2(g) + F_2(g) → 2HF_(g)
3. It forms hydrides with metals like lithium, sodium and calcium.
  
  H_2(g) + 2Li_(s) → 2LiH_(s)
  
  H_2(g) + 2Na_(s) → 2NaH_(s)
  
  H_2(g) + Ca_(s) → CaH_2(s)
4. Hydrogen reduces oxides of those metals, which are less reactive, to free metals. Thus, when hydrogen is passed over hot copper oxide copper metal and water are produced.
  
  CuO_(s) + H_2(g) → Cu_(s) + H₂O_(l)

Write a detailed note on ammonia, its manufacture, properties and uses.
ANS :
AMMONIA : Ammonia is a very important industrial chemical as it is used for the manufacture of a wide range of chemicals. It is manufactured commercially by Haber's process.

MANUFACTURE : A mixture of nitrogen and hydrogen in the ratio of 1 : 3 is heated under 200 - 300 atm pressure in presence of catalyst (finely divided iron + molybdenum) at about 450 °C. The reaction is reversible.

PHYSICAL PROPERTIES :
- It is a colourless gas.
- It has characteristic pungent smell.
- It is poisonous.
- It is lighter than air.
- It is highly soluble in water.
- It can be liquefied easily at room temperature by applying about 9 atm pressure.
- Liquid ammonia boils at 239.7 K and freezes at 198.4 K.
- Liquid ammonia has very high heat of vaporization.
- In liquid state, the ammonia molecules are present as associated molecules.
CHEMICAL PROPERTIES :
- Ammonia reacts with hydrochloric acid to form ammonium chloride.
  
  NH_3(g) + HCl_(l) → NH₄Cl_(s)
- Ammonia decomposes in presence of electric discharge.
- Ammonia reacts with oxygen in presence of catalyst platinum at 1073 K to form nitric oxide.
- Ammonia reacts with carbon dioxide to form urea (NH₂CONH₂)
- Aqueous solution of ammonia acts as a base.
USES :
- In the manufacture of fertilisers such as urea, ammonium nitrate and ammonium sulphate.
- In the manufacture of nitric acid by Ostwald process.
- In the manufacture of baking soda and washing soda.
- In the manufacture of some medicines such as para-aminobenzoic acid (PABA), folic acid, etc.
- As a nonaqueous solvent.
- As a coolant in ice factories and in refrigerators.

Describe Extraction of Sulphur.
ANS : Pure sulphur is obtained by (i)Frasch Process or (ii) from natural gas and oil by chemical process.

FRASCH PROCESS : The process is used to obtain pure sulphur from the sulphur bed in the ground. It is based on the fact that sulphur has relatively low melting point (388 K).
- A hole of about 30 cm diameter is bored upto the sulphur bed.
- Three concentric pipes A, B and C of different diameters are descended upto sulphur deposits as shown in the figure.
- Pressurised superheated water at about 170°C is forced down through the outermost pipe A. The heat of water melts the underground sulphur.
- Hot compressed air is passed through the innermost pipe C.
- A mixture of molten sulphur and water comes out through central pipe B.
- The sulphur-water emulsion is allowed to settle in settling tanks. Yellow solid sulphur separates from water after cooling. This sulphur is 99.5% pure.
FROM NATURAL GAS AND OIL :
- Sulphur compounds in natural gas and oil are first converted into hydrogen sulphide. (H₂S).
- Hydrogen sulphide is heated in presence of oxygen to obtain sulphur dioxide.
- This sulphur dioxide is then heated with additional hydrogen sulphide in the presence of catalyst Fe₂O₃ to obtain sulphur in free state.

Write a note on Allotropes of sulphur.
ANS :
- Different arrangement of molecules in the crystals give rise to allotropes of sulphur.
- There are two allotropes of crystalline sulphur. (i)Rhombic sulphur and (ii) Monoclinic sulphur.
- Rhombic sulphur is stable below 96°C and its crystals have octahedral shape.
- Monoclinic sulphur is stable above 96°C and its crystals are needle-shaped.
- As one allotrope changes into another at 96°C, it is called TRANSITION TEMPERATURE for sulphur.
- Both allotropes have similar chemical properties but their physical properties differ due to their different physical structures.
- When solid sulphur is heated its molecular chain breaks which on further heating yields viscous liquid sulphur. This on heating starts boiling.

Mention Chemical properties of sulphur.
ANS :
- Sulphur burns with blue flame and produces sulphur dioxide.
  
  S_(s) + O_2(g) → SO_2(g)
- REACTION WITH ACIDS : Sulphur is oxidised to sulphur dioxide when it reacts with hot and concentrated sulphuric acid.
  
  S_(s) + 2 H₂SO_4(aq) → 2H₂O_(l) 3SO_2(g)
  
  Sulphur is oxidised to sulphuric acid when it reacts with hot and concentrated nitric acid.
  
  S_(s) + 6HNO_3(aq) → H₂SO_4(aq) + 6NO_2(g) + 2H₂O_(g)
- REACTION WITH CARBON : Sulphur reacts with carbon at high temperature to give carbon disulphide.
  C_(s) + 2S_(s) → CS_2(l)
- REACTION WITH HYDROGEN : When hydrogen gas is passed through boiling sulphur, foul smelling hydrogen sulphide gas is formed.
  S_(s) + H_2(g) → H₂S_(g)

Mention uses of sulphur.
ANS :
- In the manufacture of sulphuric acid.
- As an antiseptic in skin ointments.
- For skin treatment in beauty parlours.
- For making dyes, matches, gunpowder, pulp of paper and fireworks.
- In vulcanisation of rubber.
- For manufacturing carbon disulphide which is a solvent.
- As a disinfectant, fungicide, germicide, etc. for destroying bacteria, fungi, insects, etc.
- In printing of clothes.

Write a detailed note on sulphur dioxide.
ANS : The reaction of sulphur with oxygen gives sulphur dioxide.

S_(s) + O_2(g) → SO_2(g)

PHYSICAL PROPERTIES :
- It is a colourless gas.
- It has a pungent smell.
- It is a pollutant gas.
CHEMICAL PROPERTIES :
- Sulphur dioxide dissolves in water to form sulphurous acid (H₂SO₃).
  
  SO_2(g) + H₂O_(l) ↔ H₂SO_3(aq)
- Sulphur dioxide reacts with aqueous sodium hydroxide to form sodium sulphite (Na₂SO₃).
  SO_2(g) + 2NaOH_(aq) → Na₂SO_3(aq) + H₂O_(l)
- When sulphur dioxide gas is passed through lime-water, the solution turns cloudy due to the formation of insoluble calcium sulphite (CaSO₃).
  
  SO_2(g) + Ca(OH)_2(aq) → CaSO_3(s) + H₂O_(l)
- When sulphur dioxide gas is passed through an aqueous solution of hydrogen sulphide, it turns milky (turbid) due to formation of colloidal sulphur.
  
  SO_2(g) + 2H₂S_(aq) → 3S_(s) + 2H₂O_(l)
- Sulphur dioxide combines with oxygen in presence of catalyst vanadium pentoxide [V₂O₅] at 450°C to form sulphur trioxide.
USES :
- For the manufacture of sulphuric acid.
- As a preservative in orange and lemon squashes and jams.
- For bleaching of wood pulp in paper industry.
- As a disinfectant.

Describe manufacture of sulphuric acid by Contact Process.
ANS : The contact process is divided into different stages and uses various units such as sulphur burner, precipitator, steam scrubber, drying tower, arsenic purifier, contact chamber and absorption unit.

PREPARATION OF SO₂ : SO₂ is obtained by burning sulphur or pyrites.

PURIFICATION OF SO₂ :
- The sulphur dioxide obtained during above process contains impurities like sulphur dust, acid fog, moisture, As₂O₃, etc.
- All these impurities are removed one by one by passing the gases through precipitator (to remove dust particles), steam scrubber (to remove acid fog), dry tower (to remove moisture) and arsenic purifier (to remove arsenious oxide).
CONVERSION OF SO₂ into SO₃ IN CONTACT CHAMBER : The mixture of purified SO₂ and air is passed over catalyst vanadium pentoxide [V₂O₅] or platinum in contact chamber to produce SO₃.

ABSORPTION OF SO₃ IN CONC. H₂SO₄ : SO₃ obtained from the contact chamber is dissolved in 98% H₂SO₄ acid in absorption tower giving oleum, H₂S₂O₇. [Oleum is also known as 'fuming sulphuric acid' or 'pyrosulphuric acid.]

The dissolution of SO₃ in water produces a large amount of heat resulting in the formation of dense fog. This fog does not condense easily. On the other hand, SO₃ dissolves in 98% sulphuric acid without complication.

Sulphuric acid of any concentration can be obtained by diluting oleum with water.

H₂S₂O_7(l) + H₂O_(l) → 2H₂SO_4(aq)

Contact process yields sulphuric acid which is pure and of about 100% strength.

Write physical properties and uses of sulphuric acid.
ANS :

PHYSICAL PROPERTIES :
- There are two forms of sulphuric acid : (i)concentrated sulphuric acid (ii) dilute sulphuric acid.
- Concentrated sulphuric acid contains about 98% sulphuric acid and 2% water.
- Concentrated sulphuric acid is a colourless, viscous, heavy liquid.
- It has high boiling point.
- It has high affinity for water.
- Dilute sulphuric acid contains about 10% sulphuric acid and 90% water.
- Dilution of concentrated sulphuric acid by addition of water is a highly exothermic reaction.
USES :
- In the manufacture of fertilisers, ammonium sulphate and calcium super phosphate (superphosphate of lime).
- In the manufacture of paints, dyes and pigments.
- In the manufacture of soap and detergent.
- In lead storage battery.
- In paper and textile industry.
- In the manufacture of alums, drugs, insecticides, etc.
- In the manufacture of hydrochloric acid and nitric acid.

Write chemical properties of sulphuric acid.
ANS :
- Concentrated sulphuric acid dehydrates sugar to carbon. The black mass of carbon is called sugar charcoal and the reaction is called charring of sugar.
- Dilute sulphuric acid reacts with metals like zinc and iron to form metal sulphates and hydrogen gas.
  
  Zn_(s) + H₂SO_4(aq) → ZnSO_4(aq) + H_2(g)
  
  Fe_(s) + H₂SO_4(aq) → FeSO_4(aq) + H_2(g)
- Sulphuric acid is strong dibasic acid from which two hydrogen atoms can be displaced in solution.
  
  H₂SO_4(l) + 2H₂O_(l) → 2H₃O⁺_(aq) + SO_4(aq)^-2

ANSWER IN BRIEF

Explain : Functional group.
ANS:
- An atom or a group of atoms responsible for the chemical reactions of an organic compound is known as 'Functional Group'.
- Functional groups are responsible for the properties of an organic compound.
- Functional group is a characteristic of an organic compound.
- Examples :
  1. Alcohol (-OH)
  2. Aldehyde (-CHO)
  3. Ketone (>C=O)
  4. Organic acid (-COOH)
  5. Ester (-COOR, R is alkyl part)
- Thus, CH₃CH₂OH (ethanol) is an alcohol and -OH group decides its properties.
- All compounds having similar functional group have similar properties.

Write physical properties of ethyl alcohol.
ANS:
- Pure ethanol is colourless.
- Its boiling point is 78°C.
- It is miscible with water.
- It is neutral.

Mention uses of ethyl alcohol.
ANS:
- As an antiseptic to clean wounds.
- To sterilise syringes, gauze, etc.
- In alcoholic drinks.
- In preparation of rectified spirit (alcohol containing 5% water).
- As an antifreezing agent in the radiators of vehicles in cold countries as the mixture of water with alcohol lowers the freezing point of water.

Write about the harmful effects of ethyl alcohol.
ANS:
- Person consuming alcohol becomes addict to it.
- Eyesight weakens and the person may lose eyesight in the long run.
- Ethyl alcohol damages liver and may cause death of the person.
- To restrict consumption of ethyl alcohol, some poisonous substance like methanol or CuSO₄ is added to ethanol. This is called 'Denatured Ethyl Alcohol'.

Show that the H atom in the -COOH group has acidic nature.
ANS:The H atom in the -COOH group has acidic nature. The following two reactions are the proof of this.

When acetic acid reacts with a metal like sodium or potassium, hydrogen gas is evolved.

Acetic acid reacts with an alkali to form the respective salt of acetic acid and water.

What is an enzyme ? Write three reactions involving different enzymes.
ANS: An enzyme is a biochemical catalyst which breaks down complex organic molecules into simpler ones. Some reactions involving enzymes are :

[NOTE : There is no mention in the text book (GSEB) of what an enzyme is.]

Mention the difference between 'Denatured Alcohol' and 'Rectified Spirit'.
ANS:
- Ethyl alcohol containing 5% water is called 'rectified spirit'.
- Ethyl alcohol containing some poisonous substance like methanol or copper sulphate in small amount is called 'denatured alcohol'.
- The purpose of adding poisonous substance is to prevent people from consuming alcohol as its addiction is harmful in the long run.

Write the names of the products of oxidation reaction of ethanol in presence of KMnO₄ and chromium oxide.
ANS: Oxidation of ethanol in presence of KMnO₄ yields ethanoic acid and water whereas its oxidation in presence of chromium oxide yields ethanal and water.

Explain : Tollen's test.
ANS:
[NOTE : Though this question appears in the list of questions given at the end of the chapter in the text book (GSEB), the description regarding it is given under the title 'ONLY FOR INFORMATION'. Refer to 'Activity 4' in the text book.]
- Add sufficient NaOH to a solution of silver nitrate to obtain permanent precipitates.
- Dissolve the precipitates in NH₄OH to prepare Tollen's reagent.
- Add some aldehyde in the test tube containing Tollen's reagent and place it in a beaker containing water.
- Heat the water in the beaker.
- The aldehyde will be oxidised and silver (Ag) metal will be liberated. This silver will appear as a mirror on the inner wall of the test tube.

Write addition reactions of formaldehyde and propanone.
ANS: Formaldehyde and propanone show following addition reactions with HCN forming corresponding cyanohydrins.

What is a polymer ? Give its classification.
ANS: A polymer is a long-chain compound with many smaller units called monomers.

Based on their reactions, polymers are classified into (i) Addition polymer and (ii) Condensation polymer.

Mention the types of artificial polymers giving examples.
ANS: Following are the types of artificial polymers :
1. Synthetic fibre : rayon, nylon, polyester.
2. Plastic : polythene, PVC, bakelite, melamine.
3. Synthetic Rubber : butadiene, neoprene.

What is the difference between 'thermoplastic' and 'thermosetting plastic' ?
ANS:
- Polymers which become soft on heating and regain original shape on cooling are called 'thermoplastics'. for example : polythene, polyvinyl chloride (PVC), and polystyrene.
- Polymers which do not soften on heating at high temperature are called 'thermosetting plastics'. If at all they soften then they do not regain their shape. for example : bakelite, melamine.

What are addition polymers ? Give examples.
ANS: Addition polymers are formed by addition of one or more than one (same or different) unsaturated monomer having double or triple bond.

Polythene, PVC, TEFLON, polypropene, natural rubber, polubutadiene and neoprene are addition polymers.

What are condensation polymers ? Give examples.
ANS: A polymer formed by the condensation of two or more than two monomers with the elimination of a simple molecule like water or ammonia is called a condensation polymer.

Polyester, polyamides and phenol-formaldehyde are condensation polymers.

Write a brief note on soap.
ANS: Soaps are sodium or potassium salts of higher fatty acids like stearic or palmitic acid, etc. In soaps, -COONa is the functional group attached to the hydrocarbon part.

PREPARATION : On heating vegetable oil or animal fat (esters of higher fatty acids) with sodium hydroxide, sodium salt of fatty acid (soap) and glycerol are formed.

This process is known as Saponification.

Write a note on 'Production of Soap'.
ANS:
[NOTE : this is described as preparation of soap as Activity 5 in the text book (GSEB) under the title 'For information of students'. The process described there is actually laboratory preparation of soap and is far from (large scale) production of soap.
However, since the question appears in the list of questions given at the end of the chapter, we write the following answer.].
- Take 20 ml of vegetable oil in a beaker and add 20% aqueous solution of NaOH to it.
- Heat the mixture and shake it constantly till the mixture becomes dense.
- Add 5 to 10 g NaCl to it.
- On cooling the mixture, insoluble soap comes to the upper part of the beaker.
- It is taken out in a separate plate and allowed to dry.
- We can add fragrant materials, antiseptic drugs, fillers or any other additive as per the requirement.
- Soap is generally used in the form of a cake in daily life.
  
  [NOTE : While preparing the text book, the so-called experts have forgotten to realise that by taking 20 ml vegetable oil it is difficult to prepare even single cake of soap. I am referring to the sentence given on page 217 which reads : 'Take this in other vessel and prepare cakes'.]

Write a note on Detergents.
ANS:
- Detergents are sodium salts of long-chain sulphonates.
- In detergents, -SO₃Na is the functional group attached to hydrocarbon part.
- Detergents are superior to soaps as soaps cannot be used with hard water. Soaps form insoluble salts of calcium and magnesium in hard water and cleansing becomes difficult.

Distinguish between soap and detergent.
ANS:

........................................................................................................

Explain with example : Reaction of nonmetals with chlorine.
ANS: Nonmetals form chlorides with chlorine. These chlorides are either liquid or gas.

Explain with example : Reaction of nonmetals with hydrogen.
ANS: Nonmetals form covalent hydrides with hydrogen.

Methane (CH₄), hydrochloric acid (HCl), etc. are hydrides of nonmetals.

Mention physical properties of hydrogen.
ANS:
- Hydrogen is the lightest gas.
- It is twenty times lighter than air.
- It is a colourless and odourless gas.
- It is insoluble in water.
- It is inflammable
- It is nonpoisonous.

Mention uses of hydrogen.
ANS:
- Hydrogen Welding : When an electric arc is passed through hydrogen, it splits into atoms which release large amount of heat when they recombine to form molecules. This heat is used to melt and join (weld) the metals.
- In the manufacture of ammonia by Haber's process.
- In the manufacture of methanol and hydrochloric acid.
- Liquid hydrogen is used as a fuel in space shuttles.
- In the manufacture of vegetable ghee.

Mention physical properties of sulphur.
ANS:
- It is pale greenish-yellow or greyish-yellow powder.
- It is odourless and tasteless.
- It is insoluble in water.
- It is soluble in organic solvents like carbon disulphide, toluene (methyl
  benzene), etc.

GIVE ANSWER IN DETAIL

_{_{Describe Solvay's Ammonia-soda process (manufacture of sodium carbonate or washing soda).}}
_{_{ANS : AMMONIA-SODA PROCESS}}
- _{_{A cold and concentrated solution of sodium chloride (brine) is saturated with ammonia to obtain ammoniacal brine.}}
- _{_{Ammoniacal brine is allowed to drop from the top of the reactor called carbonating tower.}}
- _{_{Simultaneously, carbon dioxide gas is introduced into the tower from the bottom.}}
- _{_{Following reaction takes place :}}
- _{_{Sodium hydrogen carbonate is separated from ammonium chloride.}}
- _{_{When sodium hydrogen carbonate is heated, it decomposes to give sodium carbonate.}}
- _{_{The sodium carbonate obtained in this process is anhydrous and is called 'Soda Ash'.}}
- _{_{Soda ash is dissolved in water and crystallized to get washing soda.}}
- _{_{RE-USE OF BY-PRODUCTS:}}
  - _{_{The chief attraction of Solvay's process is that the by-products can be re-used.}}
  - _{_{The carbon dioxide used in the process is obtained by decomposition of CaCO₃ in a lime-kiln (furnace).}}
  - _{_{Lime is heated with water to obtain slaked lime.}}
  - _{_{When this slaked lime is heated with ammonium chloride (also a by-product), it yields ammonia, which is recycled to the process.}}

_{_{Mention the properties of washing soda.}}
_{_ANS:}
- _{_{It is a colourless, crystalline solid.}}
- _{_{When exposed to air, the crystals of washing soda lose 9 molecules of water of crystallization to give sodium carbonate monohydrate. This process is called 'EFFLORESCENCE'.}}
- _{_{On strong heating it loses all the water of crystallization and forms anhydrous sodium carbonate (soda ash).}}
- _{_{As it is a salt of weak acid and strong base, the aqueous solution of washing soda is alkaline. It turns red litmus to blue.}}
- _{_{Its reaction with acid solution produces carbon dioxide gas.}}

_{_{Mention the properties of baking soda.}}
_{_ANS:}
- _{_{It is a white crystalline solid.}}
- _{_{It is soluble in water.}}
- _{_{It is a salt of weak acid and strong base. Therfore, its aqueous solution is slightly alkaline.}}
- _{_{On heating it decomposes to give sodium carbonate.}}
- _{_{It reacts with acid to form carbon dioxide.}}

_{_{Write a note on bleaching powder.}}
_{_{ANS:
MANUFACTURE : Bleaching powder is manufactured by Hesenclever process. In this process, chlorine gas is passed over slaked lime, Ca(OH)₂, to obtain bleaching powder.

PROPERTIES OF BLEACHING POWDER :}}
- _{_{It is yellowish white powder with strong smell of chlorine.}}
- _{_{In moist air it liberates chlorine gas.}}
- _{_{When it reacts with carbon dioxide or dilute sulphuric acid or dilute hydrochloric acid, it produces chlorine gas.}}
_{_{USES OF BLEACHING POWDER :}}
- _{_{For making drinking water germ-free.}}
- _{_{As an oxidising agent in industry.}}
- _{_{For bleaching of cotton, linen and wood-pulp.}}
- _{_{For bleaching (removing stains from ) washed clothes in laundry.}}
- _{_{For the manufacture of chloroform.}}

_{_{Write a note on Plaster of Paris.}}
_{_ANS:}
- _{_{The chemical formula of Plaster of Paris is CaSO₄.1/2 H₂O.
  
  [ONLY FOR INFORMATION: The formula of Plaster of Paris should be written as (CaSO₄)₂.H₂O because a molecule never exists in fraction. Here 1/2 molecule is written only for convenience.]}}
- _{_{Its chemical name is calcium sulphate hemihydrate.}}
- _{_{Plaster of Paris derived its name from the fact that it was made from gypsum which was found mainly in Paris.}}
- _{_{PREPARATION : Plaster of Paris is prepared by heating gypsum[CaSO₄.2H₂O] in a kiln to 100°C.}}
- _{_{PROPERTIES :}}
  - _{_{It is a white powder.}}
  - _{_{On addition of water, it forms crystals of gypsum and sets into a hard mass.}}
  - _{_{Its setting time increases if NaCl is added to it.}}
  - _{_{If gypsum is heated above 200°C, it forms dead burnt plaster which does not set like Plaster of Paris on adding water.[NOTE : This point is given in the text book as a property of Plaster of Paris. Actually, it is not the property of Plaster of Paris].}}
- _{_{USES :}}
  - _{_{In making toys, idols and casts for statues.}}
  - _{_{In preparation of denture castings.}}
  - _{_{In bone-setting, i.e. fixing fractured limbs, bone joints, etc.}}
  - _{_{For sealing air-gaps in laboratory apparatus during experiments.}}
  - _{_{For making black-board chalks,decorative materials,POP false ceilings, cosmetics, etc.}}

_{_{Write a note on lime.}}
_{_ANS:}
- _{_{Lime is calcium oxide ( also called slaked lime).}}
- _{_{MANUFACTURE :}}
  - _{_{Lime is manufactured by heating lime stone (CaCO₃) to 1000°C in a lime kiln.}}
  - _{_{Limestone decomposes to form lime and carbon dioxide gas.}}
  - _{_{The above reaction is reversible. Therefore to convert all the limestone into lime, carbon dioxide is allowed to escape from the kiln.}}
  - _{_{The process is known as CALCINATION (calcining) of limestone.}}
- _{_{PROPERTIES :}}
  - _{_{It is a colourless amorphous solid.}}
  - _{_{Its melting point is 2000°C.}}
  - _{_{When lime is heated in an oxy-hydrogen flame, it produces bright white light called "limelight".}}
  - _{_{Lime reacts with water vigourously releasing a lot of heat. Slaked lime is produced.}}
  - _{_{Lime forms calcium chloride with wet (moist) hydrogen chloride gas but it does not react with dry HCl gas.}}
  - _{_{When lime is heated at 2000°C in an electric arc furnace with carbon, it forms calcium carbide.}}
- _{_{USES :}}
  - _{_{As a drying agent for drying of gases like ammonia and alcohols.}}
  - _{_{In the manufacture of glass and cement.}}
  - _{_{In the manufacture of dyes.}}
  - _{_{For white washing of walls.}}

_{_{Write a note on cement.}}
_{_ANS:}
- _{_{Cement is an important building material.}}
- _{_{Cement was discovered by Joseph Aspdin of England in 1824.}}
- _{_{It is called 'Portland Cement' as the hardness obtained by mixing cement with water resembles Portland rock of England.}}
- _{_{MANUFACTURE :}}
  - _{_{A finely powdered mixture of limestone and clay is heated at 1500°C in a rotary kiln to form clinker (cement).}}
  - _{_{After cooling, the clinker is mixed with 2 to 5 % gypsum.}}
  - _{_{The mixture is then ground to obtain finely powdered cement (Portland Cement).}}
  - _{_{Dicalcium silicate, tricalcium silicate and tricalcium aluminate are the major constituents of Portland cement.}}
- _{_{PROPERTIES :}}
  - _{_{Cement is fine grey powder.}}
  - _{_{If water is mixed to it , it sets to a very hard mass.}}
  - _{_{If kepy open in moist air, it becomes hard like a rock.}}
- _{_{USES :}}
  - _{_{For making roads, bridges, dams and other building materials.}}
  - _{_{For the manufacture of concrete/R.C.C.[Reinforced Concrete Cement].}}
- _{_{R.C.C. : The concrete having an iron framework inside it is called Reinforced Concrete Cement or Reinforced Cement Concrete (R.C.C.). RCC is used for making structures like pillars, roofs (floors), bridges, tunnels, dams, etc.}}

_{_{Write the chemical formula of ordinary glass and describe its manufacture.}}
_{_{ANS: The approximate composition of ordinary glass is Na₂O.CaO.6SiO₂.

MANUFACTURE :}}
- _{_{A mixture of sodium carbonate, calcium carbonate and silica (sand) is heated at 1400°C in a furnace.}}
- _{_{The silica decomposes carbonate compounds into silicates and releases carbon dioxide.}}
- _{_{A mixture of sodium silicate and calcium silicate along with silica is obtained in molten state.}}
- _{_{This mixture is molten glass which on cooling forms solid glass.}}
- _{_{The hot molten glass is cooled carefully, i.e. neither very quickly nor very slowly.}}
- _{_{If it is cooled very quickly it becomes very brittle and cracks easily.}}
- _{_{If it is cooled very slowly it becomes opaque.}}

_{_{Describe different types of glass briefly.}}
_{_ANS:}
1. _{_{Soda Glass (Soft Glass) :}}
  - _{_{Soda glass is the ordinary glass also called soft glass.}}
  - _{_{It is made by melting sodium carbonate, calcium carbonate and silica.}}
  - _{_{It is used for making glass tumblers, dishes, bottles, mirrors, window panes, light bulbs, etc.}}
2. _{_{Potash Glass (Hard Glass) :}}
  - _{_{Hard glass is prepared by melting a mixture of potassium carbonate, calcium carbonate and silica.}}
  - _{_{It is more resistant to acids.}}
  - _{_{It is used for making hard glass laboratory apparatus.}}
3. _{_{Lead Crystal Glass :}}
  - _{_{Lead crystal glass is made by melting potassium carbonate, lead oxide and silica.}}
  - _{_{It is used for making expensive glassware and decorative patterns which reflect more light.}}
4. _{_{Pyrex Glass (Heat Resistant Glass) :}}
  - _{_{Pyrex glass is made by melting a mixture of sodium carbonate, potassium carbonate, calcium carbonate, silica, borax and aluminium oxide.}}
  - _{_{It is also known as Borosilicate glass.}}
  - _{_{It is used for making ampoules and laboratory apparatus.[An ampoule is used to store liquid medicines, usually for injections.]}}
5. _{_{Optical Glass :}}
  - _{_{It is made by fusing potassium carbonate, red lead and silica.}}
  - _{_{It is used for making lenses for spectacles, cameras, microscopes, telescopes and similar optical instruments.}}
6. _{_{Photochromatic Glass :}}
  - _{_{Photochromatic glass is the one which darkens temporarily when exposed to bright light.}}
  - _{_{Silver bromide in the glass gives it its property of automatic darkening.}}
  - _{_{It is used for making spectacles, goggles and cameras.}}
7. _{_{Safety Glass :}}
  - _{_{It is prepared by placing a thin sheet of transparent plastic between two layers of glass.}}
  - _{_{It is safe as it does not break easily.}}
  - _{_{It is used for making the windscreens of automobiles, trains and aeroplanes.}}
  - _{_{It is also used in making bullet-proof glass.}}
8. _{_{Glass Fibre :}}
  - _{_{There are two forms of glass fibre.(i) Glass wool (ii) Optical Fibre.}}
  - _{_{Uses of Glass wool : (i)As an insulating material in refrigerators, electric ovens, etc.
    (ii)For making fireproof clothing.}}
  - _{_{Uses of Optical fibre : (i)In endoscopy to examine the internal organs of human body.
    (ii)In telecommunication (e.g.,telephone)}}
9. _{_{Coloured Glass :}}
  - _{_{Coloured glass is obtained by adding small amounts of colouring material like certain metal oxides in molten state during preparation of glass.}}
  - _{_{For example, Ferric oxide for brown glass, chromium oxide for green glass, manganese dioxide for purple glass and cobalt oxide for blue glass.}}
  - _{_{Coloured glass is used for making fancy articles, artificial gems and window panes.}}

_{_{What is steel ? Describe its manufacture using Bessemer convertor.}}
_{_{ANS: Steel is an alloy of iron and carbon containing 0.1 to 1.5 % carbon. Different elements like nickel,manganese and silicon are added to it in different proportion to obtain steel of desired characteristics.

MANUFACTURE :}}
- _{_{Bessemer convertor is used to produce steel from pig iron.}}
- _{_{Bessemer convertor is lined with heat-resistant bricks from inside.}}
- _{_{First, the Bessemer convertor is turned sideways and molten pig iron is poured in to it.}}
- _{_{It is then brought back to vertical position.}}
- _{_{A blast of hot air with pressure is passed into the convertor from the bottom.}}
- _{_{This removes oxides of manganese, silicon, phosphorus, etc present as impurities in pig iron in the form of slag or gases.}}
- _{_{After the rem,oval of impurities, required amount of carbon is added to pure molten iron to obtain desired steel.}}

_{_ANS:}

_{_ANS:}

_{_{Thursday, March 15, 2007}}

_{_{SOME IMPORTANT CHEMICAL COMPOUNDS-II : BRIEF ANSWERS}}

_{_{ANSWER IN BRIEF}}

_{_{*INDEX-TOPIC SEARCH

Mention uses of washing soda (sodium carbonate).
ANS: The uses of washing soda are :

In the manufacture of glass, soap and paper.

For softening of hard water.

For the manufacture of caustic soda, borax, etc.

For the removal of dirt and grease from clothes.

As a laboratory reagent.

Write the uses of baking soda (sodium hydrogen carbonate).
ANS: The uses of baking soda are :

As an antacid in medicine to remove acidity of stomach.

In the preparation of baking powder (used in preparing cakes, breads, etc.)

As a fire-extinguisher.

As a laboratory reagent.

Describe the manufacture of bleaching powder.
ANS: Bleaching powder is manufactured by Hesenclever process. In this process, chlorine gas is passed over slaked lime, Ca(OH)₂, to obtain bleaching powder.

[figure and chemical reaction to be posted later on]

Mention the uses of bleaching powder.
ANS: The uses of bleaching powder are :

For making drinking water germ-free.

As an oxidising agent in industry.

For bleaching of cotton, linen and wood-pulp.

For bleaching (removing stains from ) washed clothes in laundry.

For the manufacture of chloroform.

Write the uses of Plaster of Paris.
ANS: The uses of Plaster of Paris are :

In making toys, idols and casts for statues.

In preparation of denture castings.

In bone-setting, i.e. fixing fractured limbs, bone joints, etc.

For sealing air-gaps in laboratory apparatus during experiments.

For making black-board chalks,decorative materials,POP false ceilings, cosmetics, etc.

Mention the uses of lime.
ANS: The uses of lime are :

As a drying agent for drying of gases like ammonia and alcohols.

In the manufacture of glass and cement.

In the manufacture of dyes.

For preparing basic lining in furnaces.
For white washing of walls.}}

ANSWER IN BRIEF

Explain : Alcohol group giving common name, IUPAC name and chemical formula of first five compounds.
ANS :
- The functional group of an alcohol is -OH.
- The general formula of alcohols is C_nH_{2n + 1}OH where C_nH_{2n + 1} is alkyl group (also written as R) and n=1,2,3,...
- The suffix "-ane" of an alkane is replaced by "-anol" to give name to the corresponding alcohol. For exampl : CH₄ is methane and CH₃OH is methanol.
- The first five alcohol compounds and their formulas are as follows :

Describe preparation of ethyl alcohol.
ANS : Ethyl alcohol can be prepared by two methods.
1. Fermentation of carbohydrates
2. Hydration of ethene
FERMENTATION OF CARBOHYDRATES :

Slow breaking down of carbon compounds in presence of enzymes and in absence of oxygen into simpler compounds is called fermentation.

The sugar (carbohydrates) present in sugarcane, juices of fruits, etc. is first broken down to simple sugars like glucose and fructose by enzyme invertase.

Glucose (and fructose) is converted to ethanol by the enzyme zymase.[Yeast contains both invertase and zymase].

HYDRATION OF ETHENE : Ethene reacts with water in presence of concentrated sulphuric acid to form ethyl alcohol.

Describe chemical properties of ethyl alcohol.
ANS :

Explain : Aldehyde group giving common name, IUPAC name and chemical formula of first four compounds.
ANS : Aldehydes are compounds with -CHO as their functional group.

The IUPAC name of an aldehyde is given by replacing "-ane" of the parent hydrocarbon to "-anal". Thus methane (CH₄) becomes methanal (HCHO) and ethane (C₂H₆) becomes ethanal (CH₃CHO).

The common name, IUPAC name and chemical formula of first four aldehyde compounds are as follows :

Describe preparation, properties and uses of formaldehyde.
ANS :

PREPARATION : Formaldehyde can be prepared by heating methanol to 600 - 700°C in presence of silver oxide as a catalyst. Methanol is oxidised to methanal (formaldehyde).

PHYSICAL PROPERTIES :
- Formaldehyde is a colourless gas.
- Its boiling point is 20°C.
- It is miscible with water.
CHEMICAL PROPERTIES :

Oxidation : Methanal is oxidised to methanoic acid (formic acid) in presence of oxidising agents like Tollen's reagent, Fehling's reagent, potassium permanganate solution or potassium dichromate solution.

{Note : Tollen's reagent contains silver ammonium ion [Ag(NH₃)₂]⁺ }

Reduction : In presence of catalyst palladium [Pd], hydrogen reduces methanal to methanol.

Addition of HCN : Addition of hydrogen cyanide to methanal gives methanal cyanohydrin.

USES :
- Formalin (40% solution of formaldehyde) is used to preserve biological specimens because it makes proteins insoluble in water.
- For the manufacture of polymers like phenol-formaldehyde.

Write an introductory note on carbonyl compounds.
ANS :
- The functional group >C=O is known as carbonyl group.
- Aldehydes and ketones are carbonyl compounds.
- When carbonyl group is attached to at least one hydrogen [i.e.it is attached to either two hydrogen atoms or one hydrogen atom and one alkyl group], an aldehyde compound is obtained.
- When carbonyl group is attached to two alkyl groups, a ketone is obtained.
- The name of an aldehyde is given by replacing "-ane" from the parent hydrocarbon by "-anal". Example : methane → methanal.
- The name of a ketone is given by replacing "-ane" from the parent hydrocarbon by "-anone". Example : propane → propanone.

Describe preparation, properties and uses of propanone (acetone).
ANS :

PREPARATION : Acetone is prepared by 'Fischer and Tropsch' process. When ethene, obtained from the cracking of petroleum, and water gas are mixed and passed over cobalt oxide catalyst at 180°C and 150 atm pressure, propanone is obtained.

PHYSICAL PROPERTIES :
- Acetone is a colourless, volatile liquid.
- It has a pleasant odour.
- It is miscible with water.
- Its boiling point is 56°C.
CHEMICAL PROPERTIES :

Reduction : Propanone reacts with hydrogen in presence of catalysts like sodium boron hydride (NaBH₄) or lithium aluminium hydride (LiAlH₄) to yield 2-propanol.

Oxidation : Propanone is oxidised to ethanoic acid by alkaline potassium permanganate.

Addition Reaction With HCN : Acetone reacts with hydrogen cyanide to give acetone cyanohydrin.

USES :
- As a nail-polish remover.
- In making models, air-plane glue, lacquers, paints, etc.
- In leather industry and in artificial fibres.
- As a solvent in laboratory.

What are organic acids ? Explain giving example.
ANS :
- Organic compounds having -COOH (carboxylic acid) as funcional group are called organic (carboxylic) acids.
- Their general formula is C_nH_{2n + 1}COOH where n = 0, 1, 2, 3,...
- The suffix "-ane" of parent alkane is replaced by "-anoic" to give the name to an organic acid.
- Following table gives common name, chemical name and formula of some organic acids. [Table : 12.4 to be posted- LA-15].

Describe preparation, properties and uses of acetic acid (ethanoic acid).
ANS :

PREPARATION :

Fermentation : Acetic acid is manufactured by the fermentation of ethyl alcohol with the help of bacteria (acetobacter). Acetic acid obtained by this process is very less and is called 'Vinegar'.

Chemical Synthesis : The reaction of methanol with carbon monoxide in the presence of catalyst iodine-rhodium (I₂-Rh) gives acetic acid.

PHYSICAL PROPERTIES :
- Acetic acid is a colourless liquid.
- It has pungent smell.
- It is miscible with water.
- Its boiling point is 118°C.
CHEMICAL PROPERTIES :

Reaction With Metals : Acetic acid reacts with metals such as sodium(Na), potassium(K) or magnesium(Mg) and liberates hydrogen.

Neutralisation : Acetic acid reacts with an alkali (NaOH or KOH) to form respective salt of acetic acid and water.

Esterification : Acetic acid reacts with alcohols in presence of concentrated sulphuric acid to form ester.

Decarboxylation : When acetic acid is heated with soda lime (CaO + NaOH) it loses (-COO) part forming methane.

USES :
- As vinegar, acetic acid is used as a preservative and taste-enhancer in food (like pickle).
- As a laboratory reagent.
- As a solvent.
- For the preparation of white lead and lead acetate.

Write a note on 'rubber'.
ANS :
- Rubber is an addition polymer.
- Natural rubber is obtained from the latex of rubber trees.
- Natural rubber consists of a long chain of isoprene (monomer) units.
- Elasticity of natural rubber is low and is less strong.
- Synthetic rubber (neoprene) is obtained by addition polymerization of chloroprene (monomer).
- Vulcanisation of Rubber :
  - Natural rubber becomes brittle below 10°C and melts above 60°C.
  - Thus, natural rubber is less elastic and less strong.
  - To make natural rubber more elastic and tough, it is mixed with sulphur powder and heated to 100 to 140°C.
  - This forms strong links of sulphur between isoprene units.
  - This process is called vulcanisation of rubber.
  - Vulcanised rubber is used for making rubber bends, tubes and tyres of vehicles.

Describe preparation of polyester and mention its uses.
ANS : Polyester is prepared by reacting two compounds, one having two carboxylic groups and the other having two hydroxyl groups. This forms a long chain of esters called polyester.

Uses : Polyester fibres are used in textiles industry along with cotton fibres.

Describe preparation of polyamides (nylon) and mention its uses.
ANS : Polyamides are prepared by reacting two compounds, one having two carboxylic groups and the other having two amide groups. This forms a long chain of amides called polyamides.

Uses :
1. As these fibres are strong and waterproof, they are used in making clothes and raincoats.
2. In making fishing nets and in tyres.

Describe the cleansing action of soaps and detergents.
ANS :
- The long-chain molecules of both the soaps and detergents have two parts :
  1. Long-chain hydrocarbon which is water repelling and nonpolar.
  2. -COONa (in soap) or -SO₃Na (in detergent) which is water attracting (polar).
- When soap and dirt particles come into contact with each other, the long hydrocarbon chain of soap begins to dissolve grease and dirt in it while the other polar part remains directed towards water.
- This arrangement of soap in water is called micelle formation.[LA-26].