no longer an exclusively vicarious one.

Wednesday, February 23, 2005

Chemistry: acidic: 5

5. Esterification is a naturally occurring process which can be performed in the laboratory.

Describe the difference between the alkanol and alkanoic acid functional groups in carbon compounds
A functional group is an atom or group of atoms that reacts in a characteristic way in different carbon compounds. The hydroxy functional group, -OH, in alkanols provides their characteristic properties, such as high melting points and boiling points. This is because of the hydrogen bonding between the hydroxy groups
The carboxylic acid functional group, -COOH, in alkanoic acids can lose a hydrogen ion and behave as a weak acid.

Identify the IUPAC nomenclature for describing the esters produced by reactions of straight-chained alkanoic acids from C1 to C8 and straight-chained primary alkanols from C1 to C8

Alkanoic acid
methyl methanoate
methyl ethanoate
methyl propanoate
methyl butanoate
methyl pentanoate
methyl hexanoate
methyl heptanoate
methyl octanoate
ethyl methanoate
ethyl ethanoate
ethyl propanoate
ethyl butanoate
ethyl pentanoate
ethyl hexanoate
ethyl heptanoate
ethyl octanoate
propyl methanoate
propyl ethanoate
propyl propanoate
propyl butanoate
propyl pentanoate
propyl hexanoate
propyl heptanoate
propyl octanoate
butyl methanoate
butyl ethanoate
butyl propanoate
butyl butanoate
butyl pentanoate
butyl hexanoate
butyl heptanoate
butyl octanoate
pentyl methanoate
pentyl ethanoate
pentyl propanoate
pentyl butanoate
pentyl pentanoate
pentyl hexanoate
pentyl heptanoate
pentyl octanoate
hexyl methanoate
hexyl ethanoate
hexyl propanoate
hexyl butanoate
hexyl pentanoate
hexyl hexanoate
hexyl heptanoate
hexyl octanoate
heptyl methanoate
heptyl ethanoate
heptyl propanoate
heptyl butanoate
heptyl pentanoate
heptyl hexanoate
heptyl heptanoate
heptyl octanoate
octyl methanoate
octyl ethanoate
octyl propanoate
octyl butanoate
octyl pentanoate
octyl hexanoate
octyl heptanoate
octyl octanoate

Explain the difference in melting point and boiling point caused by straight-chained alkanoic and straight-chained primary alkanol structures
Straight-chained structures do not have any branches on the hydrocarbon chain.A primary alkanol has the -OH group at the end of the hydrocarbon chain.The high melting points and boiling points in alkanols is due to hydrogen bonding between the O in one molecule and the H of an -OH in a nearby molecule.

The ability of the -COOH group to be involved in two hydrogen bonds gives an alkanoic acid an even higher boiling point than that of a similar sized alkanol. Two hydrogen bonds can occur between a pair of alkanoic acid molecules because the electrons in the bond between the H and its attached O in COOH is weak.

Identify esterification as the reaction between and acid and an alkanol and describe, using equations, examples of esterification
An acid, containing the -COOH functional group, can react with an alkanol, containing the -OH functional group, to produce an ester and water. R-OH + HOOC-R! R-OOC-R! + H2Oalkanol acid ester water
If an oxygen-18 isotope, O, is used in the alkanol only, it is found in the ester, but not in the water product. Use of this tracer shows that the O in water comes from the acid. R-OH + HOOC-R! R-OOC-R! + H2Oalkanol acid ester water
The reaction is reversible and comparable quantities of alkanol, acid, ester and water are present at equilibrium.
Common names, rather than systematic names, are often used to obtain the ester name: CH3OH + HOOCCH3 CH3OOCCH3 + H2OCommon: methyl alcohol acetic acid methyl acetate waterSystematic: methanol ethanoic acid methyl ethanoate CH3CH2OH + HOOCH CH3CH2OOCH + H2OCommon: ethyl alcohol formic acid ethyl formate waterSystematic: ethanol methanoic acid ethyl methanoate

Describe the purpose of using acid in esterification for catalysts
Esterification is catalysed by the addition of a small amount of acid. Esterification is called a condensation reaction because a water molecule condenses out.
Only a few drops of concentrated acid needs to be added to a mixture of alkanol and alkanoic acid to catalyse the reaction.
If concentrated sulfuric acid is added in large amounts, say 5% to 10% of the reaction volume, it can have a significant effect on the position of equilibrium. Concentrated sulfuric acid is a dehydrating agent, that is, it has a strong affinity for water. If a significant amount of sulfuric acid is present, it will shift the equilibrium position to the right by absorbing water. This increases the yield of ester (5-10% of the reactant volume). However using large amounts of sulfuric acid is wasteful, uneconomic and complicates the separation of ester from the reaction mixture.

Explain the need for refluxing during esterification
Esterification requires heat for the reaction to reach equilibrium within an hour, rather than after many days. When the reaction mixture is heated, volatile components, such as the reactant alcohol and the product ester, could escape. This problem is overcome by refluxing the reaction mixture.
A condenser is placed on top of the reaction vessel so that any volatile components pass into the condenser. The condenser can be water or air-cooled and causes the volatile components to condense back to liquid and fall back into the reaction mixture, thereby also increasing the yield of ester collected.
Refluxing also improves the safety of the operation, as the volatile components are flammable.

Outline some examples of the occurrence, production and uses of esters
A number of compounds with characteristic fragrances have similar chemical composition and are called esters. Many flowers and fruits produce volatile esters. Many of the essential oils of plants contain them, and animal fats and fish and plant oils are also esters. Foods, sweets and other products like perfumes contain artificial flavourings and fragrances, many of which are esters.
Aspirin: salicylic acid (2-hydroxybenzoic acid) condenses with ethanoic acid to produce the ester acetylsalicylic acid.
Solvent in nail polish remover and paints: Ethyl acetate (ethanoate)
Toothpaste: propyl hydroxybenzoate
Esters are used :
- as artificial perfumes or scents as they emit a sweet smell.
- in making artificial food flavours that are added in many edible items like ice creams, soft drinks, sweets, etc
- as industrial solvents for making cellulose, fats, paints and varnishes
- as solvents in pharmaceutical industries
- as softeners in plastic industries and molding industries
Essences (flavourings):
- methyl butanoate (apple)
- ethyl methanoate (rum essence)
- ethyl butanoate (pineapple)
- pentyl ethanoate (banana)
- octyl butanoate (orange)
- methyl ethanoate and ethyl ethanoate (solvent)
Identify data, plan, select equipment and perform a first-hand investigation to prepare and ester using reflux
Place 12mL of 1-butanol, 9mL of concentrated ethanoic acid (glacial acetic acid) and 1mL of concentrated sulfuric acid in a 50mL pear shaped flask.
Add a few boiling chips followed by condenser as shown in diagram 1.
Heat the mixture under reflux in a hot water bath for about 30 minutes and then allow to cool for 5 minutes.


Pour the mixture into a separating funnel containing about 10-15mL water. Shake and allow to separate. The aqueous layer, which contains most of the sulfuric acid, is the lower layer and is discarded.
Pour the top layer into a small beaker. Add a few r.g. of solid Na2CO3(s) until effervescence ceases. Pour back into the separating funnel. Separate the mixture and discard the lower aqueous layer.
Pour the organic layer into a small beaker and add fused CaCl2 to dry the organic layer.
Decant into a 50mL pear-shaped flask. Distil the product as below. The boiling point of the ester is 126.5°C.
An ester was produced from the reaction mixture, of a purple colour. This ester was butyl ethanoate. It was then purified. The separating funnel was used to remove most of the sulfuric acid, which was in the lower, (denser) aqueous layer of the mixture. The remaining ester was then yellow. NaCO3 was added to completely react with the remaining acid, then it was put through the separating funnel again. CaCl2 was added to use up the remaining water, then the ester was distilled. This final product was clear in colour. The boiling point of the ester was 162°C.
1-butanol + ethanoic acid water + butyl ethanoate
Na2CO3 was added to react with any remaining acid.
Na2CO3(s) + H2SO4(aq) + CH3COOH(aq)
Then CaCl2(s) was added to remove any remaining water.
CaCl2(s) + H2O(l) CaO + 2HCl(aq)
Distilling the ester was the final step and this was done by evaporating the ester (at about 126°C), then condensing the vapour. The condensed vapour fell through the condenser to drip out into the beaker at the other end.

Process information from secondary sources to identify and describe the uses of esters as flavours and perfumes in processed foods and cosmetics
Esters are used :
- as artificial perfumes or scents as they emit a sweet smell.
- in making artificial food flavours that are added in many edible items like ice creams, soft drinks, sweets, etc
- as industrial solvents for making cellulose, fats, paints and varnishes
- as solvents in pharmaceutical industries
- as softeners in plastic industries and molding industries
Essences (flavourings in food):
- methyl butanoate (apple)
- ethyl methanoate (rum essence)
- ethyl butanoate (pineapple)
- pentyl ethanoate (banana)
- octyl butanoate (orange)
- methyl ethanoate and ethyl ethanoate (solvent)
In cosmetics, esters can help improve the feel of a product that they are blended into since their physical and chemical properties, including viscosity, fluidity and melting point, can be altered by varying the combination of fatty acid and alcohol employed. Esters are used in nail products and skincare products, as well as in sunscreen (octyl methoxycinnamate) and lipstick (2-propyl myristate).

sorry no pics

Sunday, February 20, 2005

production of transuranic elements

Production of Transuranic Elements

Transuranic elements are elements with an atomic number above that of uranium with atomic number Z= 92.

Only three of the transuranic elements, those with atomic numbers 93, 94 and 95, have been produced in nuclear reactors. Nuclear reactors produce lots of neutrons from fission reactions. Some of these neutrons are captured by heavy nuclei, such as uranium-238. This makes a new nucleus with the same atomic number but a higher atomic mass.Some of these new heavier nuclei can then convert to nuclei of other elements by beta decay, in which one neutron converts to a proton, an electron (beta particle), and an electron anti-neutrino (usually undetectable). So the mass of the nucleus stays about the same, but the number of neutrons goes down by one and the number of protons goes up by one. Plutonium-239, for instance, is produced by on electron capture by uranium-238 followed by two beta decays:
U-238 + n --> U-239 --> Np-239 + beta --> Pu-239 + beta

Pu-239 is changed to americium by neutron bombardment.
Pu-239 + n --> Pu-240 ; Pu-240 + n --> Pu-241 ; Pu-241 --> Am-241 + beta

Transuranic elements from atomic number 96 and up are all made by accelerating a small nucleus (such as He, B or C) in a charged particle accelerator to collide with a heavy nucleus (often of a previously made transuranic element) target.
Californium, with atomic number of 98, is a man-made element that was originally made in 1950 by bombarding an element called curium, a previously discovered synthetic element, with high-energy helium ions produced in a cyclotron, which is a type of charged-particle accelerator that can cause charged particles to develop high kinetic energies; these high-energy particles can then be used to bombard the nuclei of target atoms with the possibility of changing the nuclear configuration. Thus, curium, with 96 protons in its nucleus, can be bombarded by high-energy helium ions, each containing two protons along with two neutrons, to yield californium with 98 protons in its nucleus. Californium, symbolized Cf, particularly an isotope (isotopes of an element are species with the same numbers of protons in their nuclei but with different numbers of neutrons) referred to as californium-252 (252 is the combined number of neutrons plus protons in the nucleus), can also be made by bombarding selected target nuclei in an intense field of neutron radiation, most often in a nuclear reactor; such reactors are our most prolific sources of neutrons.

Saturday, February 19, 2005

Chemistry radioisotopes assignment

take whatever you want: biblio is at the end
have fun!

Radioisotopes assignment

Chemical symbol
1. Use
In medicine: gamma rays released are used in radiotherapy to treat cancer.
2. Production
Produced as a by-product of nuclear reactor operations, when structural materials, such as steel, are exposed to neutron radiation
3. How used
Co-60 releases gamma rays because it has an unstable nucleus. Unstable nuclei spontaneously emit radiation as they are transformed back to a stable state (ie. As Co-60 decays to Ni-60). High intensity gamma radiation will kill cells. It is used in a technique called radiotherapy to treat cancer by targeting the cancer cells with a beam of radiation and then rotating the source of the beam. The normal cells receive a lower dose of gamma radiation than the cancer cells, where all the rays meet. Radiotherapy aims to kill the cancer cells while doing as little damage as possible to healthy normal cells.
4. a) Benefits
The half-life of cobalt-60 is 5.27 years. This is short enough to make isolation a useful treatment strategy for contaminated areas. In some cases, simply waiting 10 to 20 years allows for sufficient decay to make the site acceptable for use again.
4. b) Problems
All ionising radiation, including that of cobalt-60, is known to cause cancer. Therefore, exposures to gamma radiation from cobalt-60 result in an increased risk of cancer. The magnitude of the health risk depends on the quantity of cobalt-60 involved and on exposure conditions (length of exposure, distance from the source, whether the cobalt-60 was ingested or inhaled). Because of their metallic housings, sources of Co-60 can get mixed in with scrap metal and pass undetected into scrap metal recycling facilities. If melted in a mill, they can contaminate the entire batch of metal and the larger facility, costing millions of dollars in lost productivity and cleanup costs.

Use: In industry: in levelling gauges.
Produced: Produced when uranium and plutonium absorb neutrons and undergo fission, eg. in nuclear reactors and nuclear weapons. The splitting of uranium and plutonium in fission creates numerous fission products, including Cs-137
How used: Cs-137 releases gamma rays because it has an unstable nucleus. Unstable nuclei spontaneously emit radiation as they are transformed back to a stable state. Radiation emitted from Cs-137 will be reduced in intensity by matter between the radioisotope and a detector. The amount of this reduction can be used to gauge the presence or absence of the material, or even to measure the quantity of material between the source and the detector.
Benefits: In gauging, there is no contact with the material being measured, therefore no radioactive contamination. Because it has a half-life of 30 years, Cs-137 can be used many times without needing to be replaced, thus reducing costs in industry.
Problems: Caesium-137 can be mistaken for potassium by living organisms and taken up as part of the fluid electrolytes. This means that it is passed on up the food chain and reconcentrated from the environment by that process. This makes the cleanup of caesium-137 difficult, as it moves easily through the environment. The half-life of caesium-137 is 30.17 years, which is relatively long, especially if it enters a living organism, because like all radionuclides, exposure to radiation from caesium-137 results in increased risk of cancer. Caesium-137 is an inorganic salt, and is highly soluble in water. If a leak were to develop in a storage facility, the radioactive material could easily contaminate surrounding water.

(a by-product from nuclear fission in nuclear reactors)

For a number of medical procedures, including to monitor and trace the flow of thyroxin from the thyroid.

With its short half-life of 8 days, it is essentially gone from a body in less than three months.

It emits fairly high-energy beta particles and a number of gamma rays. The gamma rays are of sufficient energy to be measured outside the body if deposited in tissue such as the thyroid. Because iodine selectively deposits in the thyroid, the primary health hazard for iodine is thyroid tumours resulting from ionising radiation emitted.

(a by-product from nuclear fission in nuclear reactors)

In thickness gauges (for paper, cardboard) because of its release of beta particles – the penetration of these particles indicates the thickness of a material.

Has a half-life long enough for repeated use (28 years).

Strontium is radioactive, and decays very slowly, so if exposed, it will take 28 years to decay. Strontium-90 mimics the properties of calcium and is taken up by living organisms and made a part of their electrolytes as well as deposited in bones. As a part of the bones, it is not subsequently excreted like caesium-137 would be. It has the potential for causing cancer or damaging the rapidly reproducing bone marrow cells.

6. Use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine.

Radioactive isotopes of various elements can be used for a range of purposes, and have the potential to be very efficient and useful, but their use must be balanced against the dangers that are inherent in handling any sort of radioactive material.
In medicine the isotope cobalt-60 is used to treat cancer. Its high intensity gamma radiation is directed at the malignant cells and is used to kill these cells, while trying to minimise damage to healthy cells. As with any radioisotope, exposure to gamma radiation may also damage healthy tissue, and this is one of the risks to be considered when undergoing radiotherapy for cancer. Another medical isotope is iodine-131, used to monitor the efficiency of the human thyroid. It is used to trace the flow of thyroxine to the gland, and is of great help when trying to diagnose thyroid-related problems. It has a short half-life (8 days) and this means that any exposure to radiation from this source will only be minimal and over a short period of time. However, the gamma rays emitted from iodine-131 are strong enough to be measured outside the body once in the thyroid, and this means that the radiation is still strong enough to cause damage to cells. Because iodine-131 is still used in diagnosing thyroid problems, it can be seen that the usefulness and efficiency of this method of testing outweighs the potential dangers in the eyes of the medical industry.
In industry, the gamma radiation produced by the radioisotope caesium-137 is used in levelling gauges to ensure that materials are level. The amount of gamma radiation that penetrates the material depends on the amount of material there is between the source of the radiation (in this case caesium-137) and the detector. In much the same way, strontium-90 is used as a thickness gauge for other, thinner materials. Here, instead of measuring the amount of gamma rays penetrating the material, beta particles are measured. Both of these industrial isotopes are created as by-products from the nuclear fission of elements such as uranium or plutonium, in nuclear reactors or from nuclear weapons. These types of nuclear reactions can be quite risky in themselves, and although many safety measures are in place at nuclear reactors around the world, it only takes one bad accident to have far-reaching and long-lasting effects (eg. Chernobyl 1986). In particular, both strontium-90 and caesium-137 can be mistaken by the body as calcium and potassium respectively, and are taken into the body as part of fluid electrolytes. In this manner, the radiation from the isotopes directly enters the body and can begin to harm living tissue. The half-lives of these two radioisotopes are about 30 years, which is a dangerously long time for a living organism to be exposed to radiation. However, for use in industry, the lengths of these half-lives is cost effective, because the isotopes only need to be replaced about every 30 years.
Besides the risks involved in producing all of these radioactive isotopes, and the health hazards from direct contact with the isotopes, there is also an environmental issue. Co-60, I-131 and Cs-137 are all soluble in water, one of the reasons for their use in medicine. Because of this, any leaks in storage facilities could result in the contamination of surrounding water, and thus the surrounding environment. Excessive radiation exposure is harmful to all living organisms, and if radioactive sources are ingested or absorbed, radiation build-up could occur within food chains and webs.
These examples of radioisotopes used in medicine and industry are a small cross section of the all the radioactive isotopes used. Each has its merits and makes the process of diagnosis and treatment more efficient in medicine, and the process of mass production more efficient in industry. However, the benefits from using these isotopes must be balanced with careful and strict safety precautions, due to the danger involved in handling radioactive substances.


“Cesium”, “Cobalt”, “Iodine”, “Strontium”, (2004)

“Electromagnetic Waves – Gamma Rays” (2005)

“Fission Fragments”, “Beta Decay Examples” (2005)

“Medical and Industrial Radioisotopes” (2004)

“Nuclear Data Section” (2004)

“Radioisotope Brief – Cesium-127” (2004)