Category: Education

Education, learning, teaching, study. Not actively updated

Save a balloon with water

Balloon in a candle flameWhat connects cooling computer chips, melting car engines, and a balloon that will not pop? This week’s science video sees Robert Krampf explaining the principles behind heat sinks, car radiators, water cooling, and how to hold a balloon above a burning candle without it ever popping.

Krampf points out that, “Because we’re using fire, always be sure you keep safety in mind, and be sure you’ve got an adult around, so that you’ll have somebody to blame if something goes wrong!”

So, what is it about water that makes it absorb the heat from the candle flame so fast and so protect the rubber of the balloon from melting or burning? Water has the second highest specific heat capacity of any known chemical compound, after ammonia. This is due to the extensive but transient network of temporary hydrogen bonds that form between the oxygen atom at the centre of each water molecule and a hydrogen atom from a neighbouring water molecule. This fluxional network of loose bonds allows liquid water to rapidly absorb heat and also allows the heat to quickly be dispersed through the bulk liquid.

WARNING: Please don’t attempt this experiment with anything but water in the balloon. Water is about the only fluid that is safe to use but more to the point, it won’t work properly with any other fluid.

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.

Phase diagram of water simplified

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.

Are all snowflakes different?

Snowflake shapeThe short answer is no. Despite what you may have heard some snowflakes are exactly the same shape and size as other snowflakes, at least to the naked eye.

The long answer follows: Jon Nelson, a researcher with Ritsumeikan University in Japan, has studied snowflakes for fifteen years, and has some interesting insights into their delicate structures. He points out that the old adage that ‘no two snowflakes are alike’ might be true for larger snowflakes, but it does not hold true for smaller, simpler crystals that fall before they’ve had a chance to fully develop into the familiarly evocative hexagonal flakes. Regardless, the shape of snow crystals are incredibly diverse, this is partly due to their sensitivity to even the smallest temperature change as they fall through the clouds.

So, how do snowflakes form in the first place?

Put simply, at the heart of every snowflake is a minute grain of dust that was once floating in a cloud. Water vapor from the atmosphere condenses on this dust grain forming a droplet that freezes instantly (it’s a nucleation process to put it technically).

The ice crystals grow with hexagonal symmetry. The shape originates from the chemistry of the water molecule, which consists of two hydrogen atoms bonded to an oxygen atom, H-O-H. These atoms are not in a straight line though, they’re at an angle and this angle means that when several water molecules get hitched together through hydrogen-bonding in the frozen state the simplest way to do that (i.e. the lowest-energy arrangement) results in six-sided symmetry, hence six-sided snowflakes. By the way, you never get octagonal or pentagonal snowflakes, please report anyone who draws or makes snowy decorations with flakes showing that symmetry.

The growing flake eventually sprouts six tiny branches. Each of these branches grows to form side branches in a direction and shape that are influenced by the clustering of water molecules on the ice crystal surfaces.

The American Chemical Society has produced an excellent poster illustrating all this. You can download it as a PDF file here.

You may be wondering why scientists are so interested in snowflakes, after all in many parts of the world, you’re never going to get a chance to test your theories.

Well, snowflakes and ice crystals have an effect on the global climate because of the reflectivity, they are thought to help catalyze the break down of ozone in the upper atmosphere depletion, and they also play a critical role in the build up electric charges in clouds that leads to lightning.

The Scout Report recently highlighted another researcher with an interest in ice crystal growth and pattern formation in ice. Kenneth Libbrecht at Caltech University, the Report says, is “so interested in fact, he went
ahead and created this lovely website that documents the very wide, and very
interesting world, of ‘snowflakes, snow crystals, and other ice phenomena.’

But, that’s probably enough science for today. So, wherever you are let it snow, let it snow, let it snow…and compliments of the season from Sciencebase.com

Synthesizing a new breed of chemist

Mark LeachFrom the age of 13, Mark Leach has had a subscription to the popular-science magazine Scientific American, and more recently the journal Nature. His scientific interests include cosmology, high energy and nuclear physics, materials science (particularly carbon nanotubes), geophysics, molecular biology, evolution, information technology, the brain, defense technology, and scientific ethics. Professionally, Mark is a chemist interested in ‘chemistry, the-whole-thing’. I interviewed for my Reactive Profile column this month, find out about the origins of meta-synthesis.com, Dr Leach’s aspirations for his various sites, and how he believes chemistry education could be radically improved through a re-think of some fundamental principles.

The latest Reactive Profile is in Issue 60 of our chemistry magazine.

Science fair projects and experiments

With a new school year almost upon us, there is a pressing need for parents everywhere to get advance warning of the kind of science conundrums (conundra?) they will face when their little darlings return with that first batch of science homework.

As ever, sciencebase is here to help with a bench covered in science fair projects, a labful of science experiments and all the science books for home study you can bear.

A word of warning, please DO NOT try to light your last barbecue of the summer with liquid oxygen…

Owl pellet dissection

owl pellet dissection

A friend of mine is into nature conservation in a big way and one of the tools of the trade, which to the outsider may seem rather odd, is owl pellet dissection. I had a go at dissecting an owl pellet myself, here you can see the results

Owl pellets are the regurgitated remains (bones, feathers and other indigestibles) that accumulate in this bird of prey’s gizzard after it dines on small rodents and other critters. The dessicated pellets are to be found lying where they are discarded by the owl and can provide important information about what critters are being preyed on in owl territory.

The only way to get at that information, however, is to tease apart the pellet with tweezers and other implements to extract the bones from the tangle of hair and other detritus. It needs a steady hand, a keen eye, and a lot of patience. What you will find within is quite amazing though, tiny jaw bones and skulls, femurs, tibias pelvic bones and more.

Identifying which bone belongs to which creature takes even more patience, but it is possible and provides useful insights into the prevalence or otherwise of particular small mammals in a given area where owls prey.

For more on owl pellet dissection, check out this site http://www.kidwings.com/owlpellets/.

The reason I bring it up (pardon the pun) today, is that owl pellet dissection was the hot new search phrase on the sciencebase site this last month, with dozens of visitors all flapping for information on the subject. It’s not a topic that’s been searched for here before, so I thought I’d provide some background in case we have another flutter of en-raptor-ed activity.

Science Projects Demonstrations Guides Ideas

mad-professor

We’ve got a stack of information available to science students including science homework and chemistry assignment help, science fair projects and science class demonstration guides. The free stuff is fine, but we also offer science project resources in partnership with 24 Hour Science Projects, which you or your parent will have to pay for. We recommend these project packs very highly though as they’re almost guaranteed to help you make the grade in science class as well as improve your understanding of some important scientific principles.

The following pages in the Sciencebase archives will help you find the science project inspiration you need:

Apologies for those typos in some of the file names, they can’t be corrected now, but rest assured we do know how to spell science

Science Fair Project Guides – Bonus

Although I run sections of the Sciencebase site with science experiments and lesson plans, these aren’t necessarily aimed at the busy parents of a homeschooler with an assignment to complete. For that Sciencebase offers access to some independent science fair resources. These great projects (which I’ve tried with my own young children) are perfect for completing a science fair assignment in a given time, providing a complete list of equipment needed, full instructions, and sample spreadsheets to help young investigators make the most of their own results.

You can download individual project packs (24-hour or weekend) right now, but I’ve negotiated a limited time offer for Sciencebase visitors that isn’t mentioned on the company’s site so that you can get all ten project guides at a discount. Click here to start downloading your science fair project guides.

Science Lesson Plan on Magnetism

With news that after 400 years of stability, the Earth’s magnetic North Pole could soon reach Siberia. If that happens, you can kiss Alaska Borealis goodbye as the Northern Lights go with the flow.

The pole has moved hundreds of kilometres in the last couple of centuries and could reach Siberia within another fifty years according to Oregon State University paleomagnetist Joseph Stoner speaking at the annual meeting of the American Geophysical Union in San Francisco, California, this week. The remarkably rapid (for geological change) movement of the magnetic pole doesn’t necessarily mean that our planet is going through a large-scale change that would result in the reversal of the Earth’s magnetic field as some people fear. Instead, this may be part of a normal oscillation, says Stoner, and could swing back towards Canada again.

Whichever way it goes, check out the sciencebase magnetic science lesson plan courtesy of Oregon’s Columbia Education Center.

Science Fair Projects – Egg in a Bottle

The University of Illinois provides visitors to its website with various science fair projects, including the perennial favourite – “Can air pressure alone cause an egg to be pushed into a bottle?”. Of course, it can. To make it work you’ll need an egg, a bottle, and a couple of matches. It’s all to do with air pressure differences.

But, the procedure Illinois suggests students to follow begins with “Step 1 – Peel the shells off the eggs”.

Not until further down the page (below the fold in fact) does it mention a crucial preparatory step. Can you guess what it is? Or, would you end up with egg on your face, and all over your hands?

You can watch a video of this kind of egg in a bottle experiment here.