‘ORGANIC CHEMISTRY AND MODERN LIFE’ At first glance, the term “organic chemistry” might sound like something Made from Crbon.. A NOTHER BYPRODUCT OF ORGANIC CHEMISTRY : PETROLEUM JELLY . (Laura Dwight/Corbis . Reproduced by permission.) everyday life, but this could not be further from the truth. The reality of the role played by organic chemistry in modern existence is summed up in a famous advertising slogan used by E. I. du Pont de Nemours and Company (usually referred to as “du Pont”): “Better Things for Better Living Through Chemistry.” Often rendered simply as “Better Living Through Chemistry,” the advertising campaign made its debut in 1938, just as du Pont introduced a revolutionary product of organic chemistry: nylon, the creation of a brilliant young chemist named Wallace Carothers (1896-1937). Nylon, an example of a polymer (discussed below), started a revolution in plastics that was still unfolding three decades later, in 1967. That was the year of the film The Graduate , which included a famous interchange between the character of Benjamin Braddock (Dustin Hoffman) and an adult named Mr. McGuire (Walter Brooke): Mr. McGuire: I just want to say one word to you… just one word. Benjamin Braddock: Yes, sir. Mr. McGuire: Are you listening? Benjamin Braddock: Yes, sir, I am. Mr. McGuire: Plastics. The meaning of this interchange was that plastics were the wave of the future, and that an intelligent young man such as Ben should invest his energies in this promising new field. Instead, Ben puts his attention into other things, quite removed from “plastics,” and much of the plot revolves around his revolt against what he perceives as the “plastic” (that is, artificial) character of modern life. In this way, The Graduate spoke for a whole generation that had become ambivalent concerning “better living through chemistry,” a phrase that eventually was perceived as ironic in view of concerns about the environment and the many artificial products that make up modern life. Responding to this ambivalence, du Pont dropped the slogan in the late 1970s; yet the reality is that people truly do enjoy “better living through chemistry”—particularly organic chemistry. APPLICATIONS OF ORGANIC CHEMISTRY. What would the world be like without the fruits of organic chemistry? First, it would be necessary to take away all the various forms of rubber, vitamins, cloth, and paper made from organically based compounds. Aspirins and all types of other drugs; preservatives that keep food from spoiling; perfumes and toiletries; dyes and flavorings—all these things would have to go as well. Synthetic fibers such as nylon—used in everything from toothbrushes to parachutes—would be out of the picture if it were not for the enormous progress made by organic chemistry. The same is true of plastics or polymers in general, which have literally hundreds upon hundreds of applications. Indeed, it is virtually impossible for a person in twenty-first century America to spend an entire day without coming into contact with at least one, and more likely dozens, of plastic products. Car parts, toys, computer housings, Velcro fasteners, PVC (polyvinyl chloride) plumbing pipes, and many more fixtures of modern life are all made possible by plastics and polymers. Then there is the vast array of petrochemicals that power modern civilization. Best-known among these is gasoline, but there is also coal, still one of the most significant fuels used in electrical power plants, as well as natural gas and various other forms of oil used either directly or indirectly in providing heat, light, and electric power to homes. But the influence of petrochemicals extends far beyond their applications for fuel. For instance, the roofing materials and tar that (quite literally) keep a roof over people’s heads, protecting them from sun and rain, are the product of petrochemicals—and ultimately, of organic chemistry. H YDROCARBONS Carbon, together with other elements, forms so many millions of organic compounds that even introductory textbooks on organic chemistry consist of many hundreds of pages. Fortunately, it is possible to classify broad groupings of organic compounds. The largest and most significant is that class of organic compounds known as hydrocarbons—chemical compounds whose molecules are made up of nothing but carbon and hydrogen atoms. Every molecule in a hydrocarbon is built upon a “skeleton” composed of carbon atoms, either in closed rings or in long chains. The chains may be straight or branched, but in each case—rings or chains, straight chains or branched ones— the carbon bonds not used in tying the carbon atoms together are taken up by hydrogen atoms. Theoretically, there is no limit to the number of possible hydrocarbons. Not only does carbon form itself into apparently limitless molecular shapes, but hydrogen is a particularly good partner. It has the smallest atom of any element on the periodic table, and therefore it can bond to one of carbon’s valence electrons without getting in the way of the other three. There are two basic varieties of hydrocarbon, distinguished by shape: aliphatic and aromatic. The first of these forms straight or branched chains, as well as rings, while the second forms only benzene rings, discussed below. Within the aliphatic hydrocarbons are three varieties: those that form single bonds (alkanes), double bonds (alkenes), and triple bonds (alkynes.) ALKANES. The alkanes are also known as saturated hydrocarbons, because all the bonds not used to make the skeleton itself are filled to their capacity (that is, saturated) with hydrogen atoms. The formula for any alkane is C n H 2n+2 , where n is the number of carbon atoms. In the case of a linear, unbranched alkane, every carbon atom has two hydrogen atoms attached, but the two end carbon atoms each have an extra hydrogen. What follows are the names and formulas for the first eight normal, or unbranched, alkanes. Note that the first four of these received common names before their structures were known; from C 5 onward, however, they were given names with Greek roots indicating the number of carbon atoms (e.g., octane, a reference to “eight.”) Methane (CH 4 ) Ethane (C 2 H 6 ) Propane (C 3 H 8 ) Butane (C 4 H 10 ) Pentane (C 5 H 12 ) Hexane (C 6 H 14 ) Heptane (C 7 H 16 ) Octane (C 8 H 18 ) The reader will undoubtedly notice a number of familiar names on this list. The first four, being the lowest in molecular mass, are gases at room temperature, while the heavier ones are oily liquids. Alkanes even heavier than those on this list tend to be waxy solids, an example being paraffin wax, for making candles. It should be noted that from butane on up, the alkanes have numerous structural isomers, depending on whether they are straight or branched, and these isomers have differing chemical properties. Branched alkanes are named by indicating the branch attached to the principal chain. Branches, known as substituents, are named by taking the name of an alkane and replacing the suffix with yl—for example, methyl, ethyl, and so on. The general term for an alkane which functions as a substituent is alkyl. Cycloalkanes are alkanes joined in a closed loop to form a ring-shaped molecule. They are named by using the names above, with cyclo-as a prefix. These start with propane, or rather cyclopropane, which has the minimum number of carbon atoms to form a closed shape: three atoms, forming a triangle. ALKENES AND ALKYNES. The names of the alkenes, hydrocarbons that contain one or more double bonds per molecule, are parallel to those of the alkanes, but the family ending is- ene. Likewise they have a common formula: C n H 2n . Both alkenes and alkynes, discussed below, are unsaturated—in other words, some of the carbon atoms in them are free to form other bonds. Alkenes with more than one double bond are referred to as being polyunsaturated. As with the alkenes, the names of alkynes (hydrocarbons containing one or more triple bonds per molecule) are parallel to those of the alkanes, only with the replacement of the suffix -yne in place of-ane. The formula for alkenes is C n H 2n-2 . Among the members of this group are acetylene, or C 2 H 2 , used for welding steel. Plastic polystyrene is another important product from this division of the hydrocarbon family. AROMATIC HYDROCARBONS. Aromatic hydrocarbons, despite their name, do not necessarily have distinctive smells. In fact the name is a traditional one, and today these compounds are defined by the fact that they have benzene rings in the middle. Benzene has a formula C 6 H 6 , and a benzene ring is usually represented as a hexagon (the six carbon atoms and their attached hydrogen atoms) surrounding a circle, which represents all the bonding electrons as though they were everywhere in the molecule at once. In this group are products such as naphthalene, toluene, and dimethyl benzene. These last two are used as solvents, as well as in the synthesis of drugs, dyes, and plastics. One of the more famous (or infamous) products in this part of the vast hydrocarbon network is trinitrotoluene, or TNT. Naphthalene is derived from coal tar, and used in the synthesis of other compounds. A crystalline solid with a powerful odor, it is found in mothballs and various deodorant-disinfectants. PETROCHEMICALS. As for petro-chemicals, these are simply derivatives of petroleum, itself a mixture of alkanes with some alkenes, as well as aromatic hydrocarbons. Through a process known as fractional distillation, the petrochemicals of the lowest molecular mass boil off first, and those having higher mass separate at higher temperatures. Among the products derived from the fractional distillation of petroleum are the following, listed from the lowest temperature range (that is, the first material to be separated) to the highest: natural gas; petroleum ether, a solvent; naphtha, a solvent (used for example in paint thinner); gasoline; kerosene; fuel for heating and diesel fuel; lubricating oils; petroleum jelly; paraffin wax; and pitch, or tar. A host of other organic chemicals, including various drugs, plastics, paints, adhesives, fibers, detergents, synthetic rubber, and agricultural chemicals, owe their existence to petrochemicals. Obviously, petroleum is not just for making gasoline, though of course this is the first product people think of when they hear the word “petroleum.” Not all hydrocarbons in gasoline are desirable. Straight-chain or normal heptane, for instance, does not fire smoothly in an internal-combustion engine, and therefore disrupts the engine’s rhythm. For this reason, it is given a rating of zero on a scale of desirability, while octane has a rating of 100. This is why gas stations list octane ratings at the pump: the higher the presence of octane, the better the gas is for one’s automobile. H YDROCARBON D ERIVATIVES With carbon and hydrogen as the backbone, the hydrocarbons are capable of forming a vast array of hydrocarbon derivatives by combining with other elements. These other elements are arranged in functional groups—an atom or group of atoms whose presence identifies a specific family of compounds. Below we will briefly discuss some of the principal hydrocarbon derivatives, which are basically hydrocarbons with the addition of other molecules or single atoms. Alcohols are oxygen-hydrogen molecules wedded to hydrocarbons. The two most important commercial types of alcohol are methanol, or wood alcohol; and ethanol, which is found in alcoholic beverages, such as beer, wine, and liquor. Though methanol is still known as “wood alcohol,” it is no longer obtained by heating wood, but rather by the industrial hydrogenation of carbon monoxide. Used in adhesives, fibers, and plastics, it can also be applied as a fuel. Ethanol, too, can be burned in an internal-combustion engine, when combined with gasoline to make gasohol. Another significant alcohol is cholesterol, found in most living organisms. Though biochemically important, cholesterol can pose a risk to human health. Aldehydes and ketones both involve a double-bonded carbon-oxygen molecule, known as a carbonyl group. In a ketone, the carbonyl group bonds to two hydrocarbons, while in an aldehyde, the carbonyl group is always at the end of a hydrocarbon chain. Therefore, instead of two hydrocarbons, there is always a hydrocarbon and at least one other hydrogen bonded to the carbon atom in the carbonyl. One prominent example of a ketone is acetone, used in nail polish remover. Aldehydes often appear in nature—for instance, as vanillin, which gives vanilla beans their pleasing aroma. The ketones carvone and camphor impart the characteristic flavors of spearmint leaves and caraway seeds. CARBOXYLIC ACIDS AND ESTERS. Carboxylic acids all have in common what is known as a carboxyl group, designated by the symbol -COOH. This consists of a carbon atom with a double bond to an oxygen atom, and a single bond to another oxygen atom that is, in turn, wedded to a hydrogen. All carboxylic acids can be generally symbolized by RCOOH, with R as the standard designation of any hydrocarbon. Lactic acid, generated by the human body, is a carboxylic acid: when a person overexerts, the muscles generate lactic acid, resulting in a feeling of fatigue until the body converts the acid to water and carbon dioxide. Another example of a carboxylic acid is butyric acid, responsible in part for the smells of rancid butter and human sweat. When a carboxylic acid reacts with an alcohol, it forms an ester. An ester has a structure similar to that described for a carboxylic acid, with a few key differences. In addition to its bonds (one double, one single) with the oxygen atoms, the carbon atom is also attached to a hydrocarbon, which comes from the carboxylic acid. Furthermore, the single-bonded oxygen atom is attached not to a hydrogen, but to a second hydrocarbon, this one from the alcohol. One well- known ester is acetylsalicylic acid—better known as aspirin. Esters, which are a key factor in the aroma of various types of fruit, are often noted for their pleasant smell. P OLYMERS Polymers are long, stringy molecules made of smaller molecules called monomers. They appear in nature, but thanks to Carothers—a tragic figure, who committed suicide a year before Nylon made its public debut—as well as other scientists and inventors, synthetic polymers are a fundamental part of daily life. The structure of even the simplest polymer, polyethylene, is far too complicated to discuss in ordinary language, but must be represented by chemical symbolism. Indeed, polymers are a subject unto themselves, but it is worth noting here just how many products used today involve polymers in some form or another. Polyethylene, for instance, is the plastic used in garbage bags, electrical insulation, bottles, and a host of other applications. A variation on polyethylene is Teflon, used not only in nonstick cookware, but also in a number of other devices, such as bearings for low-temperature use. Polymers of various kinds are found in siding for houses, tire tread, toys, carpets and fabrics, and a variety of other products far too lengthy to enumerate.
Time: 3 to 3 ½ hours Max. Marks: 80
Term 1 – Summative Assessment
Question Paper Set – 1
1. The question paper consists of two sections, A and B. You are to attempt both the sections.
2. All questions are compulsory.
3. There is no overall choice. However, internal choice has been provided in all the three questions
of five marks each. You have to attempt only one option in each question.
4. All questions in Section A and all questions in Section B are to be attempted separately.
5. Question numbers 1 to 4 in Section A carry 1 mark each. These are to be answered in one word
or one sentence each.
6. Question numbers 5 to 13 carry 2 marks each. These are to be answered in about 30 words
7. Question numbers 14 to 22 carry 3 marks each. These are to be answered in about 50 words
8. Question numbers 23 to 25 carry 5 marks each. These are to be answered in about 70 words
9. Question numbers 26 to 41 in Section B are multiple-choice questions based on practical skills.
Each question carries one mark. You are to choose the most appropriate answer from among the
1. Write the valence shell configuration of an element “X” with the atomic number 13.
2. What gas is evolved when lead nitrate is heated?
3. State and define the unit of electrical resistance.
4. By what process is biogas produced in the digester of a biogas plant?
5. State the chemical property on which the following uses of baking soda are based: a) As a
constituent of baking powder
b) As an antacid
6. Differentiate between calcination and roasting. Which of the two is employed for the extraction of
7. Write a balanced equation for the reaction between aluminium sulphate and sodium hydroxide.
Also indicate that one of the products Al(OH)3 is an insoluble product.
8. In the laboratory, most reagents are stored in transparent glass bottles, while some are stored in
brown bottles. A solution of silver nitrate is stored in a brown bottle. Why?
9. There are three resistors, each having a resistance of 2 Ω
(a) How can these be connected to get the maximum resistance? What is the maximum
(b) What is the least possible resistance that can be obtained by combining these resistors?
What type of combination is required for obtaining it? (1, 1)
10. An electric iron is rated at 1500 W. If the iron is used for 3 hours every day, find the number of
units it consumes in the month of February 2008.
11. (a) Why don’t two magnetic field lines intersect?
(b) What is the nature of the magnetic field lines formed due to a straight current – carrying
12. Why is the rate of breathing in aquatic organisms faster than in terrestrial organisms?
13. On certain plain areas on land, the speed of wind is of the order of 15 km/h. Discuss how this
wind can be harnessed to generate electricity.
14. Balance the following equations:
15. i. An aqueous solution has a pH equal to 2. What do you infer about its acidic or basic
ii. What is the role of pH in tooth decay?
iii. What is the colour of methyl orange in a) an acidic medium b) a basic medium?
16. i. What gas is usually liberated when an acid reacts with a metal?
ii. What is a neutralisation reaction? Give a practical application of it.
17. a. What are the fourth and fifth states of matter? (1 mark)
b. What symbols are used to represent following units? (i) kelvin (ii) pascal (1)
c. Define sublimation. (1)
18. Find the equivalent resistances in the following cases:
A) A series combination of four resistors of resistances 0.5 Ω, 2.5 Ω, 3 Ω and 4 Ω.
B) A parallel combination of three resistors of resistances 3 Ω, 4 Ω and 6 Ω.
C) Two resistors of resistance 3 Ω and 6 Ω are first connected in series, and the combination is
then connected in parallel with a resistor of resistance 9 Ω. (1, 1, 1)
19. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet
is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil? (1,
20. Define each of the following in a sentence each:
a. Positive tropism
e. Thigmo tropism
21. Draw a diagram of a reflex arc and label the following parts:
a. The nerve that carries impulses from receptors
b. Interneuron or association neuron
c. The nerve that carries information to a muscle
22. How are nuclear reactions different from chemical reactions?
23. Railway tracks can be welded using a displacement reaction
a. Name the process.
b. Write a balanced equation for the process.
c. Is the reaction exothermic or endothermic?
d. From the equation you wrote in (b), identify:
a. The element getting oxidised
b. The element getting reduced
c. The substance behaving as an oxidising agent
d. The substance behaving as a reducing agent
a. Metals are good conductors of electricity.
b. Sodium is kept under kerosene.
c. Metals are not found in their native state in nature.
d. Silver does not displace hydrogen from acid solutions.
e. An iron rod dipped in copper sulphate solution turns the blue solution light green.
24. Draw the pattern of magnetic field lines around a circular current-carrying conductor. How does
the pattern change if the number of loops is increased to form a helical shape? How can we
increase the magnetic field due to the current in the spiral coil?
(Draw a schematic diagram of an electric motor and label it. Explain its principle and working.
What is the function of a split ring in an electric motor?
25. Draw a diagram of the digestive system and label the following parts:
a. The part that helps in deglutition
b. The part where no digestion occurs and which connects the mouth with the stomach
c. The organ that has both pyloric and cardiac sphincters
d. The part where disaccharides get converted into monosaccharides
e. The part where water is absorbed from unabsorbed food
Draw a diagram of the respiratory system and label the following parts:
a. The part that humidifies air
b. The part where exchange of gases takes place
c. The part that protects the trachea from closing and collapsing
d. The muscular partition that separates the thoracic cavity from the abdominal cavity
e. The voice box
f. The skeletal structure that protects the lungs from either side
26. A student dropped some pieces of marble in dilute HCl in a test tube. The gas evolved was
passed through limewater. What change would be observed in limewater? (a) Becomes
colourless (b) Changes to milky white (c) Changes to black (d) No significant change
27. What change takes place when zinc is treated with dilute nitric sulphuric acid? (a) Hydrogen is
evolved (b) Nitrogen is evolved (c) Nitrogen dioxide is evolved (d) No Ammonia gas is released
28. What change takes place when sulphuric acid is added to a test tube containing water? (a) Test
tube becomes cold (b) Test tube becomes hot (c) No significant change in temperature (d) A
pungent gas is released
29. An aqueous solution of a salt turns red litmus blue. What would be the pH of that salt? (a) 4 (b) 2
(c) 7 (d) 13
30. Blue copper sulphate solution is added to a test tube containing zinc granules. What will be the
colour of the resulting solution? (a) White (b) Blue (c) Green (d) Black
32. Which of the following is a non-ohmic conductor? (a) Copper (b) Aluminium (c) Silicon (d) Iron
33. Which of the following physical quantities of a conductor should be maintained in order to satisfy
Ohm’s law? (a) Length (b) Area of cross-section (c) Temperature (d) Colour
34. The commercial unit of electrical energy is: (a) Volt (b) Watt (c) Watt-hour (d) Kilowatt-hour
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35. In an experiment related to electricity, which of the following is false? (a) An ammeter is always
connected in series (b) A voltmeter is always connected in parallel (c) The positive terminal of a
battery is always connected to the positive terminal of the ammeter in the circuit
(d) The negative terminal of a battery can be connected to the positive terminal of a voltmeter
36. In which of the following groups of organisms is food material broken down outside the body and
then absorbed? (a) Euglena, Hibiscus, Drosera (b) Yeast, Mucor, Aspergillus (c) Man, Dog,
Elephant (d) Lice, Mosquito, Bed bug
37. The reserve cellular energies in autotrophs and heterotrophs respectively are: (a) Starch and
glycogen (b) Glycogen and starch (c) Proteins and fats (d) Carbohydrates and proteins
38. In which of the following groups is single circuit circulation seen? (a) Dog, Cat, Buffalo (b)
Monkey, Apes, Lion (c) Catla catla, Exocoetus, Scoliodon (d) Crocodile, Najanaja, Gallus gallus
39. Which of the following is not produced in the respiration of yeast? (a) Adenosine Tri Phosphate
(b) Ethyl alcohol (c) Carbon dioxide (d) Water
40. Oxygenated blood is sent to the heart muscles through the: (a) Brachial artery (b) Pulmonary
artery (c) Coronary artery (d) Femoral artery
41. The phloem in plants is responsible for the transport of: (a) Sugars (b) Water and mineral salts
(c) Sugars, water and mineral salts (d) Chitin