Does hot water freeze faster than cold?

Hi,
what is wrong with this title? Well it should sound like a nonsense, NO, of course not! Hot water freezes slower than the cold water simply because it takes some time for the water temperature to drop to the same value as the first water.


Actually you could find out that this is entirely not true and it has been a big mystery for a long time.

Of course I must add that such a water, in glass bottle for example is put into the freezer on the same place as the second bottle because if you put the hot one next to the side of the freezer, then of course it will freeze sooner.

While I did not try this experiment yet, it seems that there were already thousands of people who have done so before me and they have many hypothesis about what really happens there.

It has been actually known for years, even Aristotle pointed this out. This effect is called Mpemba effect, after the guy who wrote about it in 20th century, he discovered it when he was just a kid, with ice cream.

The graph below shows the temperatures of two water samples.

We of course must assume that this was very well conducted experiment but it works for illustration.

Now something had to happen when the water was hot. That is for sure because after about 4,000 seconds the water is same right?

Well it does not need to be, first we must know the factors that change for example how much the water holds its temperature.

Those are: its volume and its inside.

Its volume? Well 10 milliliters of water will lose their temperature almost “immediately” so this is important factor. How could it change (of course we assume that on start the volume is the same with the same water from tap)? Well water evaporates and it evaporates more quickly when it is hot. This is true the water will relly lose significant amount of its volume to have some effect. We can actually test if this is the only factor. We can close the container so it wont happen. This has been tested and even that it looked as a great hypothesis it was falsificated from what I read.

Another thing could be that when you have water and you heat it, its inside will change causing it to have different “hold” of temperature so it drops more quickly, gases dissolve better in cold liquids so there are less in the hot water.

What other factor could play here? One guy on physics stack exchange said that without the ice around the bottles everything worked perfectly fine but it seems that this is not actually the case while it could change it.

The problem here is that even if you have some process which will get it extra fast down, at one point it will be same anyway.

Another one could be convection. The top will be always hotter since the way water works. Since it loses heat primarily through surface it could lose its heat faster than we would expect because the top would be always warmer while the cold water would not be able to make such a great convection.

I came up with another solution. Even if you close the glass bottle so there is the same amount of water, the water will still evaporate and the side of the bottle will get wet with the condensated water. There will be bigger surface which will get cold while the water which condensated fell down again, cooling it by little bit. Also of course that when you put it freezer which has ice on bottom, it will melt through it and since water has higher thermal conductivity, it will get colder from the bottom.

What else? Maybe you can come up with something but I did not find the complete answer yet!

Dragallur

Is water extremely poisonous?

Hi,
the title could be misleading but that is actually what I will write about. What happened to me this week in the school was pretty interesting. We were in chemistry class and it was nothing too unusual. Then at one point the teacher said something what sounded to me very illogical, this would not be for the first time, last time the teacher said that plasma has to do a lot with absolute zero -_-.


What happened this day was very suprising to me, it was this reaction below:Autoprotolyse eau.svg

Two molecules of water will change into hydroxide and hydronium. This process will go back because of chemical equlibrium.

Why? When I saw this on the chalkboard I thought that this is some kind of crap, but actually it is very interesting. At first I thought that she just forgot to write some kind of catalyzator but no, this is equation.. it seemed to me that she wants me to believe that water just alone changes to base and acid.

Now this actually really happens. The problem is that the concetration of such ions is

1.00×10−7 mol∙dm−3

This is not much since one mol is the number of carbon-12 atoms in 12 grams while this is much more space in decimeter and there is not many moles in there (10−7).

How this happens? Well you may ask, why should water do this? Is it not stable? Well this is because of random fluctuations inside the molecules which may cause such thing. For every ten hours this happens approximitely once per molecule of water. The process takes only few femto seconds which is quite cool and after sometime I guess that it will just return while other molecules will do this again (because there are both acidic and basic ions they will cancel out so water is neutral).

This is important since this is why water is conductive, because there are ions even in pure water. This process is called self-ionization or autoprotolysis.

Dragallur

 

Elements of Periodic table: 4) Selenium

Hi,
why Selenium? Well I was not sure what element to choose, I did not want to write about some precious metal since last two time I have covered gold and palladium. I used random generator and I got 34, which is proton number of Se.


History

Selenium is one of those elements which were find in last centuries. This usually happens because the element is not enough common for some alchemists to find it or it is always well bonded with other element (here it is sulfur) and it took some time before we were able to extract it.

Jöns Jakob Berzelius and Johan Gottlieb Gahn were chemists in Sweden and they were working close to Falun mine [1], which you can see on the next pictureThe Copper Mine in Falun, the Great Pit

Guys there wanted to know what was it what they mined so they gave sample to those two chemists. It seemed to be some kind of arsenic compound but it was smelling strange and soon they found out that it is similar to sulfur and tellurium. Tellurium was named after Earth so they named Selenium (in Greece) after Moon, this happened in 1817.

Occurrence

  • Universe: 3.0×10-6 %
  • Earth’s crust: 5.0×10-6 %
  • Ocean: 4.5×10-8 %
  • Human: 5.0×10-6 %

You see it is not very common, at least it does not seem to be. But if I compare it’s occurrence in Universe with other elements it is not so bad. Most metals have one or two magnitudes less occurrence, from what I found selenium is not produced in solar fusion which means that it is created from supernovas, which would explain it’s  relative rarity.

On the picture above you can see some Se in piece of sandstone from uranium mines.

Usually you will find it with sulfur so you need to extract it using methods as SX/EW [2].

Properties

Se is non metal element which can exist in several allotropes [3]. SeBlackRed.jpg

It is usually red powder as you can see above but if you melt it rapidly you will get this kind of grey form which is usually sold. Se makes big and complex structures.

There are five Se stable isotopes and the couple of others with half life ranging to thousands of years, than there is Se 82 which has half life of 10^20 years which is considered relatively stable.

It has extremely important property of photo-conductivity, its conductivity depends on the amount of light hitting its surface.

Selenium is toxic element.

Usage

Selenium dioxide has a great usage during manganese electrolysis because it decreases the energy needed to get manganese (it works as catalyst). China is largest consumer of this compound for such use. For ton of manganese there are two kilograms of Se used. There are 31,200,000 tonnes of manganese produced each year.

Glass gets often kind of yellow or green color because of iron or other things accidentally mixed into it so Se is used to color it into red, this is the most common usage.

Also since lead is so toxic Se is used in brass with bismuth. At low concentrations it also improves machinability of lead, which is similar usage as of vanadium which improves the strength of steel.

Because of its photo voltaic property, it is used in photo voltaic cells called CIGS (copper indium gallium selenide solar cell).

There are other trace uses like radiography.

On the pie graph you can see the production of Se. While I did not find the graph of biggest consumers of Se, on the top is clearly China, as always.

Selenium in organisms

Organisms need selenium as we found out. It is important in some cellular processes but only really small amount like tens of micro grams.

At one time people thought that it is going to be good if they get more Se through some pills. Soon it was found out that more than 200 micro grams can cause cancer and so on. More accurately in one test, doctors got their patients 17% higher chance of prostate cancer which is number two of cancers killing male humans.

There are some illnesses with the lack of selenium but they are not very common even in places where is small amount of Se in the soil like New Zealand.

The price for Se is about 60$ for pound while at some times it lowered to about 30$.

Dragallur


[1] Falun mine was extremely important mine producing 2/3 of Europe’s needs of copper. It was working for almost 1,000 years and it is now cultural heritage with museum.

[2] SX/EW (Solvent extraction and electrowinning) is method used to get some metals like nickel, cobalt, zinc and uranium.

[3] Allotrope of carbon is for example graphite and diamond, both made up of only carbon but with different shape of molecules.

Chemical bonds

Hi,
this post is just a systematic list and explanation of chemical bonds because I needed to learn them for chemistry class and at the same time, why not make a post from it?


 

Chemical bonds are bonds between two atoms. There are various ways in which they can “connect”, and that is what this post is about:

Covalent bond

Covalent bond is bond between two atoms which causes sharing of electron pairs. The difference between electronegativity is less than 1.67. If it would be bigger than the bond would be called ionic bond. Covalent bond is always going to be between two same atoms, for example H-H or   C-C and so on.

EDIT (18.2.2016): Also if the difference is less than 0.4 the bond is nonpolar while if it is between 0.4 and 1.67 it is polar bond. This is important when you want to dissolve some stuff because only polar things with polar dissolve and nonpolar and nonpolar while not polar and nonpolar. For example water has polar covalent bond because the difference is roughly 1.2 or so.

Ionic bond

Ionic bond is extreme case of covalent bond since the difference between electronegativity of two atoms is greater than 1.67. This means that one atom is going to attract the other electron so much that the first atom wont even hold it anymore. Examples of such cases are: Na+ and Cl or Li+ and F .. this “plus” means that the electron was moved a lot towards the other atom while “minus” means that the atom has a lot greater electronegativity and is able to catch this electron causing the atom to be negatively charged.

Above you can see how atom of fluorine takes one electron from lithium under his control (red arrow). Such molecules are easily dissolved in water and they are called non-polar molecules.

Dipolar bond

Dipolar bond is very similar to covalent bond and it can create when one of the atoms do not have any free electrons while the other one has two in one orbital. One of them then may move to the first atom and create bond with the other electron which is alone now.

Because bond can always create from electrons of opposite spin, with dipolar bond you can be sure that it will create because both the electrons came from one orbital so they have to have opposite spin.

An example of such a bond is NH4. Nitrogen has three orbitals ready to be connected with hydrogen which happens. Then the last hydrogen is actually H+ so he does not have any electron but nitrogen can share both his electrons from 2s2 orbital as you can see on the next picture. Here nitrogen is called “donor” and hydrogen “acceptor“.

Metallic bond

Metallic bond is very often seen on metals and it is the reason for their thermal and electric conductivity. As you can see below atoms are all positively charged, which means they are cations while their electrons keep flying around making what is called “electron gas” (as you can see on the next picture), that is why the current so easily “flows” through metals.

Dragallur

Elements of Periodic table: 3) Gold

Hi,
it is probably one of the best known metals in the world and even throughout the history. Humankind knows it for a long time. It is precious metal with amazing properties from conductivity to ductility. It does not react so much which means you can actually eat it pretty easily!


Right, we are talking about gold, or aurum.
There is really lot about this element so I will start with its chemical properties and where you can find it.

Attributes

Gold (Au) is amazing because it does not react much. It does not react with oxygen so you can easily have it in open place (while silver does react with oxygen), not only that but gold does not react with the strongest an-organic acids like hydrochloric acid (HCl) so only thing in which you can dissolve it is in aqua regia. 
On the left you can see aqua regia with piece of platinum which is very resistant too.

Once in Denmark during WW2 one chemist had two Nobel medals for some people. Those medals are made of gold and since Denmark was going to be captured by Nazis he did not want them to get those medals. He took them and placed them in aqua regia.
After the world he returned and the solution was still there so he extracted it and made new medals.

On the next picture you can see thin plate of gold. Gold is so ductile that one gram can be spread on 1 square meter. This picture is from Japan Toi museum.

This is very useful since gold is not very cheap but when you use only one gram for such a large area it gets to whole new level!

There is only one stable isotope of gold which is the one we are mining and using. There were found many others but all of them decay in matter of weeks, days or even couple of microseconds (actually some radioactive isotopes are used for curing cancer).

While gold does not react and so on, it is very soft so if you want to use it in jewelry it is always mixed up with palladium (white gold) or copper.

Gold is conductive. This is great but how does that happen?
Well gold and silver and copper are in the same column which means that they have similar properties. All of them are very conductive because they have one free valence electron.
So gold for example has configuration: 4f14, 5d10,6s1
“d” and “f” orbitals are both full since “d” has limit of 10 electrons and “f” 14.
You could ask why other elements with one valence electron are not so conductive and it is because the farther away from the core of the atom the easier it is to break the electron free. Also different atoms have different ionizing energy which means that it takes different amount of energy to free their electron.

Mining

Before I get to mining of gold I will mention the places where you can find it.

In the Earth’s crust there are about 0,0075-0,01 ppm of Palladium about which I wrote earlier. There is about 190 ppm of Vanadium but for gold it is: 0.0031 ppm. Which means that there is not much of it.

Unlike Palladium, gold was detected in the ocean to be 0.011 μg Au/l.
In whole Universe the estimated value of Au is one atom per 300 billions of hydrogen atoms, which is ten times less than palladium.

This is only guess but I think that this could be caused because in supernovas it is surely much easier to create element with 33 less protons.

Lets see how it looks like for different countries. The list of the countries is taken from Wikipedia and it is measured in tons (it is for mining in the year of 2013).

  • 1. Čína China 420
  • 2. Austrálie Australia 255
  • 3. USA USA 227
  • 4. Rusko Russia 220
  • 5. Peru Peru 150
  • 6. Jihoafrická republika South Africa 145
  • 7. Kanada Canada 120
  • 8. Mexiko Mexico 100
  • 9. Uzbekistán Uzbekistan 93
  • 10. Ghana Ghana 85

It is assumed that there were altogether mined 175,000 tons of gold. If you would pile it, it would use the volume of 21 cubic meters. While you may say that this is not much, imagine it standing next to your house + gold is very heavy. If you would make the same pile from hydrogen it would be about 200 times as large.

On the map below you can see the approximate storage of country’s gold (you could easily criticize it, look at South Africa.. but I did not find better, just don’t take it to be a good source).

There are few ways to mine gold. The older one, which you may have seen in movies and it is not used anymore, is the method of panning. This is based on the effect of gravity which pulls heavier gold down to the bottom of the bowl while the rest of the sand is slowly floating away (this was used often in rivers).

The modern way is to crush the material to small pieces and then leach it in some acid, rich in chlorine ions. It is then excluded in electric current on the cathode. There was also way to get it using mercury but only in specific situations and the soil was polluted with mercury.

Now there are ecological problems all the same because of hydrometalurgy which is the process of getting metals from their ores. There are huge amounts of cyanides used which in history already happened to cause some disasters, polluting large rivers and letting them toxic for years.

Usage

For the last chapter lets get to usage of this amazing metal.

In history the first usage was only jewelry. This is obvious since people back then did not even know what electricity is and they did not have enough gold to make isolation from it but it has such a nice color so they made lot of jewelry.

You can surely find lot of rings and various necklaces, this one is ring of Egyptian pharaoh. Like I said at the start, now gold is mixed with some other metal so it is not so soft.
You can see that metal gets different colors depending on the percentage of all the various metals.

Most often the objects are not whole made up of gold but rather only the top layer which can be extremely thin, even transparent.

Even in food you can find gold like a decoration, it is tagged as E175 and it is not dangerous at all since anything in human body is, won’t react with gold.

In industry, the property of high conductivity is used in computers in processors.

In dentistry gold is used as dental alloy, because again it does not react. There is not only gold but other metals too, mercury for example (because of Hg it is important for the alloy to not react and survive the environment in mouth).
I still remember when I went with my grandmother to guy who was collecting gold with her old golden dental alloys.

Gold was used as backup for money, this was called gold standard and I am going to write a whole separate post about it. This system fell and it is not used anymore.

Gold is even used by NASA. I read that for some flight there was 43 kg of gold used. To give specific example, there is gold used in astronauts helmet. This is because of radiation in space where you are not protected by atmosphere.
Gold foil will reflect most of the ultraviolet and infrared radiation which could otherwise cause serious damage to astronauts eyes. Full explanation.

This is all from me for today, already this has been the longest post ever so I hope someone will read it.

Dragallur

Cube of gold
Map of world gold storage
Other images from wiki articles about gold and gold mining and aqua regia

 

 

 

Elements of Periodic table: 2) Palladium

Hi,
this time comes the post about another element of periodic table. Last time it was Vanad and I will continue with Palladium!
Palladium is extremely important in car industry, it is also beautiful in jewelry and has surprising history.


 

What I found most interesting about Palladium (Pd for the rest of the post) is that it is related to astronomy.
In the beginning of 19th century guy named William Hyde Wollaston was PallasHST2007.jpgable to separate Pd and then he published it in a scientific journal. Some people thought that it was fake, that what he called Pd was just some kind of alloy of Nickel and Silver. Wollaston named it after dwarf planet found two months earlier called Pallas, you can see the planet on the right (Pallas is second largest dwarf planet in the belt between Mars and Jupiter).

Palladium (46 Pd).jpgPalladium is white and grey metal right above Platinum in the table of elements. There are many isotopes and lot of them naturally occur and few of them are radioactive decaying into Ruthenium, for example.

It is used on various things. In cars it is used as part of catalytic converter which is next to motor and takes CO and other toxic and poisonous molecules out. For the converter to be fully functional we had to stop using leaded petrol. (Wikipedia says that there are still companies in China that produce tetraethylead which is the source of the lead in petrol, it is making the car more efficient).
Pb (lead) was destroying these catalytic converters in very short time while now it is assumed that it should be working for over 120,000 km. On the left you can see the three way catalytic converter.

Palladium is used a lot in jewelry like “white gold”, also in dentistry because it is cheaper than gold, but some people may be allergic. Smartphones and lot of various electronic devices contain Pd.
Pd is also used as storage for hydrogen.

Now for mining. Most of Pd is mined in Russia,
South Africa is right behind then for a long time nothing and rest is produced by USA and Canada mostly.

Some sources say that Russia is running low with their storage, which would be big problem if true (it is the state secret so no one can be sure). In 2001 there was a Pd crisis when Russia had some problems with mining (the problem was linked to politics). Prices of Pd rose to over 1000$ per troy ounce (OZ=27 grams). It seemed that it would rise even more so Ford Motor Company bought a big amount and then the prices dropped rapidly, leaving Ford with loss about 1 billion $! On the picture below you can nullsee the peak of the price and then the drop to about 200$. For now the price is about 560$/OZ for the last years the price seems to drop. On the next picture you can see the graph of prices for 18th December which of course do not 1 Day Spot Palladium Prices - Palladium Price Chartchange very much. In whole Earth there is about 0,0075-0,01 ppm (mg/kg) of Palladium. PPM is parts per million which is the same as miligram per kilogram. In sea water the amount is unmeasurable, because even the most precise technology is not able to detect it. In space there is about 1 atom of Pd per 30 billions of atoms of hydrogen.

Pd is also created in nuclear reactors but this source is not used.

Usually you will find pure (100%) palladium with gold or ruthenium around. Also oxygen is not reacting with Pd, which is extremely good attribute (this is not true above 800°C, then PdO is created on the top layers). For some time Pd was used as cure for tuberculosis but there were many side effects so it was banned. Pd is not very toxic since our body is not able to absorb it, but there is some evidence that it may be carcinogenic.

Dragallur

Pallas picture
Palladium picture
Catalytic converter
Palladium demand
Pie graph of production
Kitco 2001 graph
World map of Pd production

 

Elements of Periodic table: 1) Vanadium

Hi,
ok wow, yes it gets even more complicated when I create another series, lets see how it will work.
Anyway I will talk about Vanadium today. Have you ever wondered what is this element? How is it used? Where is it mined? What are its properties? Here we go, I will try to answer what I can.


Vanadium (V for the rest of the post) is metal.
V has the atomic number 23 and it stands right next to Titanium and Chromium. So yes, V is pretty light metal and has lot of uses there.

V is mined mostly in China. Actually as you can see on the picture below the supply by china is

increasing in very high rate while other state`s production remains about the same. China is kind of able to move whole market with V.

V is mined not as clear metal but rather in some minerals like vanadinite or patronite. Also V can be found in fossil fuels but it is such a low amounts that it is not very usable.
For its usage.. as many other metals V is used in steel as ferrovanadium to increase the strange of steel. Then it can be used on various tools, for
the shell of nuclear reactor and with gallium like a tape for superconductive magnets. Also some very good batteries may be made with it.

For us humans, for survival Vanadium is not very useful but some fungi, algae and other organisms may contain it and also use it.

It is proved that lot of chemicals with V are toxic but with insufficient data one can only guess how much would kill him (or try it).

For consumption you can see that China has the largest demand. When they realized that vanadium can make steel twice as strong they become to use it in great mass (first boom was around 2004).

For various isotopes, the most common is V51 which is the one we are mining and also the only one which is not radioactive. The others have half-life mostly under couple of seconds with longest 330 days.

Dragallur

1st picture
2nd picture
3rd picture
4th picture

Some elements of periodic table

Hi,
today I am writing from Brazil which is why I had this few day pause from writing. I have got and idea to write about some elements of periodic table so this post will rather be mess of some stuff I found over time, probably a bit related to astronomy.

First of all I will start with one thing that comes to my mind and that is Hydrogen and Helium. Only those two elements in astronomy count as something different than metal.

PeriodicTable.gifThe reason for this is that astronomers wanted to make some difference between the most important elements in universe and the rest and the rest was almost all metal.

Iron will be the next stop for me. Iron is very special because it is the last element which can be created through thermonuclear fusion. Actually star can fuse iron but only to isotope 55 and then the reaction would take energy to fuse any higher so it is the ending point of stars life. Higher elements can be created in supernovas.

Now let me jump right on the end of periodic table. The last known element is Ununoctium. It has proton number 118. He is also the last known noble gas right after Radon but this element with many others is synthetic which means that you can not find him in the nature and is only made in lab.
Once I asked my chemistry teacher where will be next element since Ununoctium marks the end of another period.
Sadly I had to find out by myself. The next one of course will be right under Francium.
But what is more interesting is that element with 121 proton number will have another shell filled, now it will be G shell. This element would also be the first superactinide.

To read more on this topic check out:
Island of stability
Interactive periodic table

Dragallur