Chemistry – Page 39 – David Bradley

Salt and the Boiling Point of Water

TL:DR – If you dissolve salt in water, you raise its boiling point. Similarly, you also lower its freezing point. These effects occur with any solute dissolved in any solvent and depend on how many solute particles are dissolved in the solvent. The key phrase is colligative properties.

Colligative properties include: Relative lowering of vapour pressure (Raoult’s law), elevation of boiling point, freezing point depression, osmotic pressure.

Colligative properties determine how a solvent will behave once a solute is added to make a solution. The degree of change depends on the amount of solute dissolved in the bulk liquid, not the type of solute. So, without my doing your homework for you…how does adding salt to water affect its boiling point? You will find several clues and several keywords above and below.

The fact that dissolving a salt in a liquid, such as water, affects its boiling point comes under the general heading of colligative properties in chemistry. In fact, it’s a generic phenomenon dissolve one substance (the solute) in another (the solvent) and you will raise its boiling point.

So, here’s a rough explanation of what’s going on. If a substance has a lower vapour pressure than the liquid (it’s relatively non-volatile in other words) then dissolving that substance in the liquid, common salt (NaCl) in water (H₂O), for instance, will lower the overall vapour pressure of the resulting solution compared with the pure liquid. A lower vapour pressure means that the solution has to be heated more than the pure liquid to make its molecules vaporise. It is an effect of the dilution of the solvent in the presence of a solute. If you want to know about tungsten and why it is used in incandescent light bulbs please check out the Wikipedia entry.

Put another way, if a solute is dissolved in a solvent, then the number of solvent molecules at the surface of the solution is less than for pure solvent. The surface molecules can thus be considered “diluted” by the less volatile particles of solute. The rate of exchange between solvent in the solution and in the air above the solution is lower (vapour pressure of the solvent is reduced). A lower vapour pressure means that a higher temperature is necessary to boil the water in the solution, hence boiling-point elevation.

Conversely, adding common salt to water will lower its freezing point. This effect is exploited in cold weather when adding grit (rock salt) to the roads. The salt dissolves in the water condensing on the road surface and lowers its freezing point so that the temperature has to fall that bit more before ice will form on the roads.

A much more fun use for freezing point depression is to add salt to ice to make ice cream. The About site has some instructions on how to do this, although it’s probably not too tasty.

Curiously, at least one Sciencebase reader was searching for the phrase “how does sugar affect the boiling point of water?” and landed on this page. This is essentially the same question as, “does salt affect the boiling point of water?” The nature of the solute, the material being dissolved in the solvent, is pretty much irrelevant at a first estimate. Rather, it is the amount of material that is dissolved (which depends on the materials solubility) that influences the boiling and freezing points as described above.

Drugs and addiction

Fly agaric Many people in the modern Western world delude themselves that their culture is generally free from the effects of intoxicating substances except in the criminal underworld, and that ‘nice people don’t take drugs’. But Richard Rudgley of the University of Oxford, a researcher of the oasis communities of Chinese Central Asia, shows that our culture and other cultures across the world have a rich tradition of using chemicals, mainly from plants, to produce altered states of consciousness. These range from the ritualistic use of the fly-agaric in Palaeolithic Europe to betel-nut chewing in Papua New Guinea, and from pretentious bone-china tea sets in Surbiton to the tragic inhaling of petrol fumes by Aboriginal Australians.

Although each intoxicant has its own effects on the mind – there is some overlap – but researchers have classed them as belonging to four types. Hallucinogens – compounds such as mescaline – are often found in ‘poisonous’ varieties of mushroom or South American weeds. Inebriants consist of generally simpler organic compounds such as alcohol, and the constituents of organic solvents and other volatile chemicals. Hypnotics are compounds that induce states of sleep, stupor or calm and include tranquilizers and narcotics. Stimulants increase mental activity and include caffeine, tobacco and the more potent cocaine and amphetamines.

Rudgley has scoured the scientific literature for examples and evidence from the European Stone Age to modern day Australia to improve our understanding of how these broad classes of intoxicants have affected society and religion. Beginning with evidence from the earliest days of hallucinogen use in Palaeolithic cave art, Rudgley describes in fascinating detail intoxicants and their cultural effects over the past few thousand years.

For example, peyote, the mescaline-containing cactus of Texas and Northern Mexico, apparently played an important role in the cultural development of indigenous peoples of that area, although the plant is now threatened with extinction because of increasing use by modern hedonists. On the Steppes biochemical evidence shows that Cannabis sativa and ethanol have been commonly used for many thousands of years.

Rudgley even has an explanation for the supposed flight of witches and the symbolism of the witch’s broom. A witch wanting to ‘fly’ to a witches’ sabbat, or orgiastic ceremony, would anoint a staff with specially prepared oils containing psychoactive plant matter, as well as rather gruesome ingredients such as baby fat and human blood. The potion could then be administered to areas of the body that could absorb the active components most rapidly. Rudgley quotes one researcher: ‘The use of a staff or broom was undoubtedly more than a symbolic Freudian act, serving as an application for the atropine-containing plant to the sensitive vaginal membranes. . .’ So now you know.

There is little spiritualism attached to the modern Western use of intoxicants such as caffeine and nicotine, and society more than frowns on the use of mind-altering drugs. The modern view is perhaps distorted to some extent by the development of highly addictive stimulants such as ‘crack’, with its potentially devastating effects.

Rudgley hopes that a deeper knowledge of intoxicants’ use in other cultures will result in a better understanding of our own culture of cafes and bars, and this in turn might help us understand the ‘importance of altered states of consciousness in both our collective and our personal lives’.

I wrote the original version of this item as a book review that was published in New Scientist magazine (The Alchemy of Culture by Richard Rudgley, British Museum Press, reviewed issue 1909, p43).

The professional staff at an addiction treatment facility knows how to help a drug addict, so you can rest assured your loved one is in good hands.

Christmas rose and hellebrigenin

Members of the plant family Ranunculaceae are ever-popular at this time of year, especially in Europe, where the Christmas rose, Helleborus niger, is wheeled out as a natural decoration for countless households. Interesting then, that extracts of this plant have been used as a heart tonic in herbal medicine alongside the likes of digitalin (from foxglove) and strophanthin from the West African plant Strophanthus gratus.

H. niger contains various potent toxins in addition to cardiac glycosides helleborin, hellebrin and helleborein and saponosides and the ranunculoside derivative, protoanemonine. It was searching for information on the compound hellebrigenin (3-acetate) that brought one Sciencebase reader to this site, so here’s the structure of the molecule. This biologically active compound, which also goes by the name (3beta,5beta,14beta)-3,5,14-trihydroxy-19-oxobufa-20,22-dienolide, is a cardioactive steroid compound as well as having been demonstrated (in the 1960s) to have activity against tumour growth.

Latest chemical discoveries

The latest bumper Xmas issue of Reactive Reports, actually the 61st issue I’ve produced for the site is now online. In this issue we cover:

Molecular Light Switch – According to Nobel laureate Roald Hoffmann, “Nanotechnology is the result of the marriage of the synthetic talent of Chemists with a device-driven ingenuity.”

Blood, Light, and Water – Two molecules that occur naturally in blood have been engineered by scientists from the UK and Japan to use sunlight to split water into hydrogen and oxygen.

Plastic Shape Shifter – Temperature-controlled “triple-shaped plastics” that can change shape from one form to another, then another, have been developed by researchers in Germany and the US.

Top Chemical Discoveries of 2006

My good friend Stu Borman and his colleagues at Chemical & Engineering News (C&EN) have come up with a fascinating mash up of the most important chemical discoveries of 2006.

First up, is the total synthesis of UCS1025A, this esoteric-sounding compound is actually a potential inhibitor of the enzyme telomerase, and the incredibly compact synthesis was achieved by Tristan Lambert and Samuel Danishefsky of the Sloan-Kettering Institute for Cancer Research and Columbia University (J. Am. Chem. Soc. 2006, 128, 426). Inhibiting this enzyme could retard the growth of tumours.

Another synthesis published in JACS is second in Stu’s list. The scheme comes from Elias J. Corey’s group at Harvard University and represents a cheaper and faster way to construct the flu drug oseltamivir phosphate, better known as Roche’s antiviral Tamiflu (J. Am. Chem. Soc. 2006, 128, 6310).

Another synthetic achievement this year is the construction of the compound 2-quinuclidone by Brian Stoltz and Kousuke Tani at California Institute of Technology (Nature 2006, 441, 731). A quick glance at this simple-seeming structure might have you reaching for your Merck Index thinking that surely it must have been synthesised decades ago. But, no, this is the first synthesis of this bicyclic. Their synthetic scheme may provide new insights into biological amide hydrolysis as well as representing a rather aesthetically pleasing synthesis.

You can read about the other syntheses picked out by Borman and his colleagues in C&EN.

Also on their list is research at the frontiers of carbohydrate chemistry, where researchers have developed a high-throughput technique for screening mutant glycosyltransferases (GTs) for biomedical activity. The work could lead to a new generation of designer sugars for a range of medical conditions. Advances in structural biology (chemistry by any other name) achieved Nobel status this year, and crystallography also produced some amazing results in revealing the structure of Dicer, an enzyme that initiates RNA interference (RNAi). Also in this field a new NMR technique, SAIL, on which I reported for SpectroscopyNOW earlier in the year, could revolutionize solution structure determination of proteins.

Molecular biology (also chemistry by another name) features in Borman’s round-up with researchers gaining important insights into the molecular mechanisms of cellular protein production, Alzheimer’s disease, and RNA interference.

In the field of analytical chemistry, a new approach to nanoscale secondary ion mass spectrometry (nanoSIMS) was developed for imaging lipid bilayers at below 100 nm resolution and computational chemistry produced a 3000-member family of artificial cytochrome P450 enzymes for studying how these enzymes metabolize drugs and toxins.

In inorganic chemistry, says Borman, researchers produced previously elusive molecules and atoms, such as P₂. Nuclear, polymer, and space chemistry also feature in this year’s round-up as does nanotechnology, not surprisingly.

But, one highlight of the chemical year not mentioned in C&EN, but certainly on my list was the culmination of work at a small laboratory in Northern Ireland that has led to the maturation of work I first wrote about for New Scientist back in the early 1990s and that has now, in its teens, reached a level of application its detractors said could never be – AP de Silva’s research on molecular logic.

Marrying up lost chemistry and chemists

British-born Dick Lewin Wife followed a traditional educational path, receiving his chemistry first degree from the University of Leeds in 1969 and staying on to do an organic PhD with David W. Jones. Research fellowships then took him to London, New York, and finally California, after which he returned to a job in the UK with Shell in 1976, moving to The Netherlands with the company in 1979. He stayed with Shell until 1987 at which point he founded SPECS and BioSPECS BV, in The Netherlands. In 2005, he co-founded a new company, SORD, which aims to find “lost chemistry” and make it accessible to the scientific world.

Read the full story in the latest issue of Reactive Reports online now.

Sniffing out our sense of smell

How we smell Our sense of smell is much better than we give it credit for. A report in Nature Neuroscience puts paid to the notion that the human reputation for having a poor sense of smell compared to other animals.

Noam Sobel and colleagues laid down scent trails in a grassy field, and asked human subjects to find the trail and track it to the end. Subjects were blindfolded and wore thick gloves and earplugs to force them to rely exclusively on smell. Contrary to expectations, the volunteers exhibited some of the same tracking strategies used by dogs and were certainly capable of following the trail.

In follow-up experiments, the authors also demonstrated that this ability partially depends on comparisons of odour information in each nostril, it’s almost like smelling in stereo.

When subjects had one nostril plugged their tracking performance was much worse.

Admittedly, the volunteers were much slower than dogs at following the scent trail, but with practice they got quicker.

the findings raise the intriguing possibility that our sense of smell is far better than we think and that using it more effectively is simply a skill we don’t teach our children so it gives us the impression that we don’t have it.

For more on a provocative theory of how we smell check out this page from the Sciencebase archives.

Influenza’s long tail

A long protein tail found in all influenza A virus raises the possibility of novel drugs that can grab on to it and stop the virus in its tracks. The protein tail is present in common human influenza A which kills thousands of people every year as well as rare forms such as bird flu.

US scientists used crystallography to study the long flexible tail of the influenza virus’ nucleoprotein. They found that even seemingly insignificant changes to the structure of this protein tail prevent it from fulfilling a key role in viral replication. That is, they prevent them from linking together to form structural columns used by the virus to transmit copies of itself.

More…

Flu mechanics

With the holiday season almost upon us, that means only one thing, flu is also on its way and if the scaremongers are to be believed the long-forewarned bird flu epidemic might follow in its wake any time soon.

Now, US researchers have put to work the 15-ton 900 MHz NMR machine at Florida State U to help them figure out the mechanics of infection by influenza A virus. The common human form of the disease already kills several hundred thousand people every year, and forecasters predict the emergence of a human transmissible form of avian influenza could kill millions more.

“Using NMR helps us build a blueprint for a virus’s mechanics of survival,” explains FSU’s Tim Cross, “The more detailed the blueprint, the better our chances of developing drugs capable of destroying it.” The researchers have found that the virus’ protein coat contains channels that control various biochemical reactions crucial to viral infection and replication.

Read on…

Emerging environmental contaminants

Lake Contamination More than forty research papers highlight the effects of emerging contaminants on human health and the environment in the December 2006 issue of the journal Environmental Science & Technology, among their number are reports on nanoparticles, pharmaceuticals, disinfectant by-products, and fluorochemicals.

“It might be tempting to define emerging contaminants as one thing or following certain criteria but it’s not that simple,” says the journal’s guest editor Jennifer Field of Oregon State University. The following Spotlight editorial reveals some of the issues and diversity of materials studied as well as highlighting a significant technology that might allow decontamination for certain materials to be carried out. An audio summary from the journal’s editors is available as an mp3 download courtesy of ES&T.

Read the full article under Intute’s Spotlight