Chemistry – Page 4 – Awesci

Mpemba Effect – Hot Water Freezes Faster Than Cold Water

By Anupum Pant

In the past, we have seen that when it comes to estimating temperature, we are not so smart. Once again seeing the Mpemba Effect defying all known logic, reminds me to be careful about applying logic to most of the natural phenomena which are seemingly simple but in reality are extremely complicated.

By applying simple logic, a 7-year-old could tell you that cold water should turn into ice quicker than hot water would. It should, because a hot liquid contains a lot more heat as compared to a colder liquid, which [the heat] has to be removed in order to freeze it. Yes, it is what anyone who is unaware of the Mpemba Effect would think. But, that isn’t the case with water. It turns out that a very common substance – water – is not as simple as it looks.

Mpemba Effect

Since the time of Aristotle and Descartes, scientists have noted that hot water can freeze faster than cold water (and yet the effect is not popularly known among us today). Although the effect was noted back then, the actual mechanism which caused it remained a mystery all along…until the year 2013.

All this time this effect must have been known by some other term because, it was not until the 1960s it was named “Mpemba effect”. It was named that after a Tanzanian cookery student Erasto Mpemba when he observed that hot ice cream mix froze faster than the cold mix.

Several theories have tried to explain the mechanisms that cause the Mpemba Effect. Not even one of them was convincing enough. Probably this is what propelled the geniuses from Singapore who could finally solve this mystery during the month of October this year.

What causes it?

In simple words, Hydrogen bonds cause this effect – faster freezing hot water. Normally, individual water molecules are connected by this bond called the Hydrogen bond. Think of the water molecule as a string with two bullies – hydrogen bonds – one on either side. These Hydrogen bonds pull this string from both sides. As a result, the string stretches. We’ve all fought with rubber bands and know that a stretched string has a butt load of energy stored inside it. The same thing happens with water. Energy is stored in stretched water molecules at normal temperature. This extra energy has to be removed to cool water.

At a higher temperature, the heat kind of weakens these bullies. So, the weak bullies aren’t able to pull the string as much. Now, individual molecules sit apart. They are no longer stretched. Thus, not much energy is stored in these strings anymore. They have given up energy. There is no longer any extra energy that needs to be removed. Hence, cooling is faster.

Sorry: Today I don’t have my buddy – the internet – with me. So, you won’t see any outgoing reference links today. I have a just a bit of internet (a slower 2G connection) which I’m using up to publish this.

Cellphones and Safety at Gas Stations

By Anupum Pant

I’ve been chided several times for taking a call while filling up my vehicle at a petrol pump. All these times I’ve felt bad for going against the clearly displayed signs which say “no cellphones”. Unfortunately, phones today have become our extended arms, we are not always aware when we click the green button on them (touch the green button these days). When I do, I usually run out of the gas station to save my life. Do you know why?

Widely circulated chain messages

Well, the displayed signs at the gas station have coded it in me to keep the cellphone away. They clearly tell you to keep your phones away. But, it is mostly because I’ve received about a 100 chain messages telling me this (please don’t pass it on):

*** PASS THIS ON TO ALL YOUR FAMILY AND FRIENDS ***

Mobile phones an explosive risk at gas stations. Switch off your mobile phone while filling your car. This is the latest advice for mobile phone users and gas station attendants alike from the Chinese Petroleum Corp. (CPC), which has recently informed all its affiliates to be on alert for people chatting on mobiles while pumping gas, a practice it asserts can cause explosions. “There have been several explosions in Southeast Asia and Europe and we hope similar tragedies can be avoided in Taiwan,” said David Tung from CPC’s main engineering division….

But is it really that dangerous to use a phone in the gas station? Even if TOI tell me it is, I decided to find out.

Most end up simply believing these messages, especially when they [the messages] are strengthened by videos like these: [Video 1] [Video 2]. The truck video doesn’t show where exactly the cellphone came from. Like a comment under the video points out, he could have been using a lighter to see the level of petrol (this couldn’t be true either).

But, let me tell you, not all videos on the internet are real. For example see these: [Video 1] [Video 2] [Video 3].
Cellphone ‘Radiation’: According to one of these videos, radiation from a couple of cellphones has enough energy to pop popcorn. This is pure BS. To counter that, I’ll tell you it takes my microwave 2 minute 45 seconds at full power to pop a bowl of popcorn. If cell phones could do that, well, great. We would need no microwave ovens anymore. Still, it is up to you, you could go ahead and believe that if you want to…

Still, what if a spark coming off from the battery of a cellphone could cause petrol to set on fire?
No, it won’t. A car’s ignition spark could do that as well. Moreover, sparks in cellphone batteries are extremely rare events as compared to Ignition sparks, that happen thousands of times at every gas station everyday.
Also, some sources say that it needs a naked flame to set petrol fumes on fire. Even a lit cigarette isn’t capable to set petrol on fire. [Source]. But, I can’t confirm that. And I do not want to try to, by shooting a video of me doing that. Nor should you.

There is no credible evidence of an event where a cellphone has caused a blast in a gas station. Not even one!

Best way to stay safe

As far as science is concerned, it is highly unlikely that a cellphone could kill you at gas stations (but something else certainly can, read on to find out). I won’t tell you to go around talking on your cellphone when you are at a gas station. Your family members will sue me if you die. But, there is no point in taking the trouble to switch it off before you enter a gas station.
So, better avoid talking, even if you know nothing will go wrong because science tells you so. Not everything can be explained or substantiated by science. Also, don’t try to explain it to the authorities at the gas station. No one will believe you. They’ll make fun of you and call you mad – Like the Roman Catholic Church back then KNEW Galileo was a mad person.
In short, no one knows for sure if phones cause these fires or not.

What is the point of this article then?

There you go! The point is to inform you and tell you that there are some things that can actually kill you at a gas station; like something as harmless as your Nylon windcheater! I’ve attached a credible evidence below:

So, the signs at a gas station should probably say, “No nylon” instead.
[Read more]

The Musty Old Book Scent

By Anupum Pant

Note: Since I’ve been getting quite a lot of visitors on this blog now, I think it would make sense to imbue a conversational tone in my posts. At least with enough readers, I won’t feel as if I’m talking to the air. So, instead of just creating a repository for archived trivia, I’ll take freedom to write my blogs in a more personal way from now on. You’ll have to wait for comments though (Tomorrow I’ll tell you why). Till then, you can get in touch through my about page.

The state of reading

No longer does a major chunk of human population has the drive or patience to go through a long chain of black letters. Instead, we prefer a stream of individual quick-visual-gags (memes). Others like to listen to audio books while they are slashing fruits on their smart-phones; some others like to ‘read’ info-graphics instead of blog posts.
A blog post without images is quickly discarded as an uninteresting one (like mine). Nevertheless, I believe, among those billions of people on the internet now, there is a tiny chunk of people who like to read. And a tinier part of that tiny chunk of people have come here to read this. I salute you. Salute me back on twitter.

That said, I’m not against info-graphics. I love them too. Also, it doesn’t mean I’m against audio books or memes.

So, if you’ve read past the two paragraphs above, I can safely assume, you are one of those who like to read. And I think we’ll connect well if I state – There is nothing like the smell of an old book; or a fresh book for some. Both ways, I think it makes sense to book lovers.

The smell according to experts

Unike Petrichor, the smell of old books does not have a specific name but you could call it “musty” in a good way. Experts need a much more detailed phrase to communicate the subjective experience. Back in 2009, the lead scientist who looked into what actually caused the smell described it as:

A combination of grassy notes with a tang of acids and a hint of vanilla over an underlying mustiness. [Source]

The pleasant aromatic smell is due to aromatic compounds emitted mainly from papers made from ground wood which are characterized by their yellowish-brown color. They emit vanilla-like, sweetly fragrant vanillin, aromatic anisol and benzaldehyde, with fruity almond-like odor. On the other hand, terpene compounds, deriving from rosin, which is used to make paper more impermeable to inks, contribute to the camphorous, oily and woody smell of books. A mushroom odour is caused by some other, intensely fragrant aliphatic alcohols. [Source]

What causes the book scent

A typical “old book” smell is a mixture of fragrant volatile substances and does not comprise of any single compound. So, all books do not smell the same, as materials and printing inks vary from book to book.

As a book ages, a compound called Lignin that makes up the cell walls of wood used to make paper, starts breaking down. It releases a smell that is a lot similar to Vanilla. In fact this is the same compound that makes Vanilla smell like Vanilla. This smell is a major contributor among several other scents that make up the characteristic book scent.
Other factors that may cause the scent to vary could be due to the kind of ink and chemicals used to process the paper.

Bring it home

It is a good thing for book worms who just can’t stop smelling their books. A creative enterprise, Lucky scent, sells it in a bottle – Paper Passion perfume – sold here.

If you prefer reading eBooks and at the same time also miss the sweet book scent, you’ll find this interesting – Classic Musty Scent and New Book scent.

Another company CafeScribe shipped “musty-smelling” scratch-and-sniff stickers with every eBook order. I’m not sure if they still do it. This was around 6 years back.

Disclaimer: I’m in no way related to the above products, they aren’t affiliate links.

Hot Ice

By Anupum Pant

For years we’ve been subconsciously conditioned to think of something cool when the word ‘ice’ is heard. But, does ice always has to be cool? How much more interesting, than water-ice, can ice be?

What is it?

The name: Hot ice isn’t solidified water, it isn’t anything even close to water. Neither is hot ice, hot. It is just a common name for Sodium Acetate Trihydrate. At room temperature, this substance looks like ice crystals and if heated, it starts turning into a transparent liquid. Since, the ice like crystals are formed at a relatively hotter temperature than water-ice, it is called hot ice.

Everything freezes. While metals ‘freeze’ at extremely high temperatures and carbon dioxide freezes at extremely low temperature, Sodium acetate freezes at 54 degrees centigrade. But, that is hardly anything interesting about it. There is more.

Touch water and turn it to ice

Think about water: Cooling water, beyond its freezing point without it getting solidified, can be done and it is called ‘super-cooling‘. This can be done by not letting water (distilled water) find any ‘nucleation points’ or simply by using an extremely clean tray to freeze it. Now, water remains in a liquid state despite being cooled under 0 degree centigrade. At such a state, if water is disturbed, say using your finger, a chain reaction starts and the water freezes almost instantly. But, doing it is tough.

Making hot ice at home – The same thing that happens with super-cooled water, can happen with sodium acetate. Touch the liquid sodium acetate and it magically turns to ice, it is indeed a fascinating process to watch (watch in the video below). And can be done fairly easily. Moreover, you are not at a danger of getting poisoned in any way. This is the reason it is used to make hot ice. It can be made at home using vinegar, baking soda and a steel vessel.

Gallium Metal Melts in Your Hands

By Anupum Pant

Atomic number: 31
Symbol: Ga

At first what seems like an uninteresting material, Gallium, in truth has, much more to it than meets the eye.

Gallium’s melting point

Like most other metals, Gallium is solid at room temperature (or liquid if it is too hot in your room). But, if it is held [in hands] for long enough, it melts in your hands, and doesn’t poison you like Mercury would. This is because of its unusually low melting point of (~29 degree Centigrade). It can melt by drawing heat from a human body which is normally at around 37 degrees.

Buy Gallium: This property, and the affordable price of $24 for 15 grams, probably makes it an appropriate gift for science geeks. They will love making mirrors at home by sticking it onto plain glass sheets.

Talking about a classic prank, it is advised to beware of the scientists who would offer spoons made out of Gallium to unsuspecting guests at a tea party. These spoons melt in hot tea and make it a potentially harmful concoction to ingest.

Since it isn’t poisonous like Mercury, Gallium is often mixed with Indium to further lower its melting point to -19 degrees. This makes it a safer option for us to use in thermometers instead of Mercury.

Interesting uses and compounds

Dilute sulphuric acid changes the surface properties of Gallium due to the formation of Gallium Sulfide on the surface. It no longer sticks that badly to glass, gets pulled up into a ball and starts beating like a heart when dichromate is added.
98% of the world’s Gallium metal is used as Gallium Arsenide and Gallium Nitride, used in the electronic industry for making semiconductors, LEDs and high-speed circuits. In fact the laser in your Blu-Ray player is also made using Gallium.
Probably the most amount of Gallium used in a single place is at a Neutrino observatory in Russia. It houses around 57 tons of liquid Gallium.
With Silicon, Graphite and Molybdenum, Gallium is also used in ski wax to make skis more slippery.
Finally, nothing beats a metal that melts in your hands.

That Sweet Scent of Rain

by Anupum Pant

When rain starts falling after a long dry spell, most of us notice a sweet-musky scent around us. Sometimes, it is as if you can smell the rain coming. Have you ever wondered what causes this peculiar smell?

Well, scientists have also wondered the same for a long time and now they have some concrete answers for us. According to them, this evocative scent is a mixture of several individual smells. In essence, there are three factors which combine to form the “petrichor” – The smell of rain.

Bacteria – The best (my favorite) of all the three is caused because of a specific type of bacteria in mud called Actinomycetes. The force, with which the rain water falls, disrupts the bacteria-produced-spores in dry mud, and the moisture present in the air carries them to our noses. Most people love this odor and associate it with rain.
So, spores of bacteria are responsible for the kind of smell you get, when rain falls on dry mud.
Plant Oils – A blend of oils produced by plants during the dry spell is another main source of this aroma. When it rains, volatile parts of these oils get released into the air. It is the kind of smell you get when you are getting wet in the woods.
Ozone – Another smell associated with the rain, is a minor part of petrichor and it smells like burning wires. This is produced by a reaction caused when lightning strikes, the Nitrogen and Oxygen present in air to form Ozone molecules.

Subjective senses

Besides that, smell is a subjective sensation. That means, you can’t explain a smell to someone, and you can never know what the other person smells. So, it becomes really hard for scientists to communicate to us, which scent is which.

Some of us like the bacteria smell, while others might like the third component of petrichor.

Some like the smell of rain, others don’t. But we’ll never know accurately, if the scent you adore is the same as the one your friend hates. One way to communicate some information about these scents is by comparing them with other popular smells (like I did above). This could probably give you a vague idea, but the exact sensation will remain elusive. It is like trying to explain the color red to a person who’s been blind all his/her life.