“We have already encountered some interesting properties of water that allow us to live in particular, and living beings in general. Let’s continue the topic and bring to your attention another interesting property (though it is not clear whether it is true or fictitious).
Interesting about water - the Mpemba effect: did you know that there are rumors on the Internet that hot water freezes faster than cold? You may not know, but these rumors are circulating. And very persistent. So what are we talking about - an experimental error or a new, interesting property of water that has not yet been studied?
Let's figure it out. The legend, repeated from site to site, is this: take two containers of water: pour hot water into one, and cold water into the other, and place them in the freezer. Hot water will freeze faster than cold water. Why is this happening?
In 1963, a Tanzanian student named Erasto B. Mpemba was freezing an ice cream mixture when he noticed that the hot mixture was solidifying into freezer faster than cold. When the young man shared his discovery with his physics teacher, he only laughed at him. Fortunately, the student was persistent and convinced the teacher to conduct an experiment, which confirmed his discovery: certain conditions Hot water actually freezes faster than cold water.
The second version of the legend - Mpemba turned to the great scientist, who, fortunately, was located next to Mpemba’s African school. And the scientist believed the boy and double-checked what was happening. Well, here we go... Now this phenomenon of hot water freezing faster than cold water is called the “Mpemba effect”. True, long before it unique property water was noted by Aristotle, Francis Bacon and René Descartes.
Scientists still do not fully understand the nature of this phenomenon, explaining it either by the difference in supercooling, evaporation, ice formation, convection, or by the effect of liquefied gases on hot and cold water.
So, we have the Mpemba effect (Mpemba Paradox) - a paradox that states that hot water (under certain conditions) can freeze faster than cold water. Although at the same time it must pass the temperature of cold water during the freezing process.
Accordingly, in order to deal with the paradox, there are two ways. The first is to start explaining this phenomenon, come up with theories and rejoice that water is a mysterious liquid. Or you can take a different route - conduct this experiment yourself. And draw the appropriate conclusions.
Let's turn to the people who actually conducted this experiment, trying to reproduce the Mpemba effect. And at the same time, let’s look at a small study that determines “where legs grow from.”
In Russian, a message about the Mpemba effect first appeared 42 years ago, as reported in the journal “Chemistry and Life” (1970, No. 1, p. 89). Being conscientious, the employees of “Chemistry and Life” decided to conduct experiments themselves and were convinced: “hot milk stubbornly refused to freeze first.” A natural explanation was given for this result: “A hot liquid should not freeze first. After all, its temperature must first be equal to the temperature of the cold liquid."
One of the readers of “Chemistry and Life” reported the following about his experiments (1970, No. 9, p. 81). He brought the milk to a boil, cooled it until room temperature and put it in the refrigerator at the same time as unboiled milk, which was also at room temperature. Boiled milk froze faster. The same effect, but weaker, was achieved when milk was heated to 60°C, rather than to a boil. Boiling could be of fundamental importance: this will evaporate some of the water and evaporate the lighter part of the fat. As a result, the freezing point may change. In addition, when heated, and especially when boiled, some chemical transformations of the organic part of milk are possible.
But the “damaged phone” had already started working, and more than 25 years later this story was described as follows: “A portion of ice cream becomes cold faster if you put it in the refrigerator, after warming it up thoroughly, than if you first leave it at a cold temperature” (“Knowledge is power” “, 1997, No. 10, p. 100). They gradually began to forget about milk, and the conversation turned mainly to water.
Thirteen years later, in the same “Chemistry and Life” the following dialogue appeared: “If you take two cups out into the cold - one with cold and one with hot water, “then which water will freeze faster?.. Wait until winter and check: hot water will freeze faster” (1993, no. 9, p. 79). A year later, there was a letter from one conscientious reader, who in winter diligently took cups of cold and hot water out into the cold and became convinced that cold water freezes faster (1994, no. 11, p. 62).
A similar experiment was carried out using a refrigerator in which the freezer was covered with a thick layer of frost. When I put hot and cold cups on this freezer cold water, then the frost under the cups of hot water melted, they sank and the water in them froze faster. When I placed glasses on the frost, the effect was not observed, since the frost under the glasses did not melt. There was no effect when, after defrosting the refrigerator, I placed the cups on a freezer that was not covered with frost. This proves that the cause of the effect is the thawing of frost under cups of hot water ("Chemistry and Life" 2000, No. 2, p. 55).
The story about the paradox noticed by the Tanzanian boy was repeatedly accompanied by a meaningful remark - they say that no information, even very strange, should be neglected. The wish is good, but unrealizable. If we don't filter out unreliable information first, we will drown in it. And implausible information is most often incorrect. In addition, it often happens (as in the case of the Mpemba effect) that implausibility is a consequence of distortion of information in the transmission process.
Thus, it’s interesting about water in general, and the Mpemba effect in particular - not always true :)
More details on the page http://wsyachina.narod.ru/physics/mpemba.html
In 1963, a Tanzanian schoolboy named Erasto Mpemba asked his teacher a stupid question - why did the warm ice cream in his freezer freeze faster than the cold one?
Being a student of Magambinskaya high school in Tanzania Erasto Mpemba did practical work in cooking. He needed to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature, and then put it in the refrigerator to freeze. Apparently, Mpemba was not a particularly diligent student and delayed completing the first part of the task. Fearing that he would not make it by the end of the lesson, he put still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to the given technology.
He turned to the physics teacher for clarification, but he only laughed at the student, saying the following: “This is not universal physics, but Mpemba physics.” After this, Mpemba experimented not only with milk, but also with ordinary water.
In any case, already as a student at Mkwava Secondary School, he asked Professor Dennis Osborne from the University College in Dar Es Salaam (invited by the school director to give a lecture on physics to the students) specifically about water: “If you take two identical containers with equal volumes of water so that in one of them the water has a temperature of 35°C, and in the other - 100°C, and put them in the freezer, then in the second the water will freeze faster. Why?" Osborne became interested in this issue and soon, in 1969, he and Mpemba published the results of their experiments in the journal Physics Education. Since then, the effect they discovered has been called the Mpemba effect.
Are you interested in knowing why this happens? Just a few years ago, scientists managed to explain this phenomenon...
The Mpemba Effect (Mpemba Paradox) is a paradox that states that hot water under some conditions freezes faster than cold water, although it must pass the temperature of cold water during the freezing process. This paradox is an experimental fact that contradicts the usual ideas, according to which, under the same conditions, a more heated body takes more time to cool to a certain temperature than a less heated body to cool to the same temperature.
This phenomenon was noticed in their time by Aristotle, Francis Bacon and Rene Descartes. Until now, no one knows exactly how to explain this strange effect. Scientists do not have a single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection or the effect of liquefied gases on water when different temperatures. The paradox of the Mpemba effect is that the time during which a body cools down to the ambient temperature should be proportional to the temperature difference between this body and the environment. This law was established by Newton and has since been confirmed many times in practice. In this effect, water with a temperature of 100°C cools to a temperature of 0°C faster than the same amount of water with a temperature of 35°C.
Since then, different versions have been expressed, one of which was as follows: part of the hot water first simply evaporates, and then, when less of it remains, the water freezes faster. This version, due to its simplicity, became the most popular, but did not completely satisfy scientists.
Now a team of researchers from Nanyang Technological University in Singapore, led by chemist Xi Zhang, says they have solved the age-old mystery of why warm water freezes faster than cold water. As Chinese experts have found out, the secret lies in the amount of energy stored in hydrogen bonds between water molecules.
As you know, water molecules consist of one oxygen atom and two hydrogen atoms held together by covalent bonds, which at the particle level looks like an exchange of electrons. Another known fact lies in the fact that hydrogen atoms are attracted to oxygen atoms from neighboring molecules - and hydrogen bonds are formed.
At the same time, water molecules generally repel each other. Scientists from Singapore noticed: the warmer the water, the greater the distance between the molecules of the liquid due to an increase in repulsive forces. As a result, hydrogen bonds are stretched and therefore store more energy. This energy is released when the water cools - the molecules move closer to each other. And the release of energy, as is known, means cooling.
Here are the assumptions put forward by scientists:
Evaporation
Hot water evaporates faster from the container, thereby reducing its volume, and a smaller volume of water at the same temperature freezes faster. Water heated to 100°C loses 16% of its mass when cooled to 0°C. The evaporation effect is a double effect. Firstly, the mass of water required for cooling decreases. And secondly, due to evaporation, its temperature decreases.
Temperature difference
Due to the fact that the temperature difference between hot water and cold air is greater, therefore, the heat exchange in this case is more intense and the hot water cools faster.
Hypothermia
When water cools below 0°C it does not always freeze. Under some conditions, it can undergo supercooling, continuing to remain liquid at temperatures below freezing. In some cases, water can remain liquid even at a temperature of -20°C. The reason for this effect is that in order for the first ice crystals to begin to form, crystal formation centers are needed. If they are not present in liquid water, then supercooling will continue until the temperature drops enough for crystals to form spontaneously. When they begin to form in the supercooled liquid, they will begin to grow faster, forming slush ice, which will freeze to form ice. Hot water is most susceptible to hypothermia because heating it removes dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals. Why does hypothermia cause hot water to freeze faster? In the case of cold water that is not supercooled, the following happens: on its surface a thin layer ice, which acts as an insulator between water and cold air, thereby preventing further evaporation. The rate of formation of ice crystals in this case will be lower. In the case of hot water subjected to supercooling, the supercooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through the open top. When the supercooling process ends and the water freezes, much more heat is lost and therefore formed more ice. Many researchers of this effect consider hypothermia to be the main factor in the case of the Mpemba effect.
Convection
Cold water begins to freeze from above, thereby worsening the processes of heat radiation and convection, and hence heat loss, while hot water begins to freeze from below. This effect is explained by an anomaly in water density. Water has its maximum density at 4°C. If you cool water to 4°C and place it in an environment with a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at 4°C, it will remain on the surface, forming a thin cold layer. Under these conditions, a thin layer of ice will form on the surface of the water within a short time, but this layer of ice will act as an insulator, protecting the lower layers of water, which will remain at a temperature of 4°C. Therefore, the further cooling process will be slower. In the case of hot water, the situation is completely different. The surface layer of water will cool more quickly due to evaporation and a greater temperature difference. Also, cold water layers are denser than hot water layers, so the cold water layer will sink down, raising the layer warm water to the surface. This circulation of water ensures a rapid drop in temperature. But why does this process not reach an equilibrium point? To explain the Mpemba effect from the point of view of convection, it would be necessary to assume that cold and hot layers of water are separated and the convection process itself continues after average temperature water will drop below 4°C. However, there is no experimental evidence to support this hypothesis that cold and hot layers of water are separated by the process of convection.
Gases dissolved in water
Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to reduce the freezing point of water. When water is heated, these gases are released from the water because their solubility in water is high temperature below. Therefore, when hot water is cooled, it always contains less dissolved gases than in unheated water. cold water. Therefore, the freezing point of heated water is higher and it freezes faster. This factor is sometimes considered as the main one in explaining the Mpemba effect, although there is no experimental data confirming this fact.
Thermal conductivity
This mechanism can play a significant role when water is placed in the freezer refrigeration chamber in small containers. Under these conditions, it has been observed that a container of hot water melts the ice in the freezer underneath, thereby improving thermal contact with the freezer wall and thermal conductivity. As a result, heat is removed from a hot water container faster than from a cold one. In turn, a container with cold water does not melt the snow underneath. All these (as well as other) conditions were studied in many experiments, but an unambiguous answer to the question - which of them ensure 100% reproduction of the Mpemba effect - was never obtained. For example, in 1995, German physicist David Auerbach studied the effect of supercooling water on this effect. He discovered that hot water, reaching a supercooled state, freezes at a higher temperature than cold water, and therefore faster than the latter. But cold water reaches a supercooled state faster than hot water, thereby compensating for the previous lag. In addition, Auerbach's results contradicted previous data that hot water was able to achieve greater supercooling due to fewer crystallization centers. When water is heated, gases dissolved in it are removed from it, and when it is boiled, some salts dissolved in it precipitate. For now, only one thing can be stated: the reproduction of this effect significantly depends on the conditions under which the experiment is carried out. Precisely because it is not always reproduced.
But as they say, the most likely reason.
As the chemists write in their article, which can be found on the preprint website arXiv.org, hydrogen bonds are stronger in hot water than in cold water. Thus, it turns out that more energy is stored in the hydrogen bonds of hot water, which means that more of it is released when cooled to subzero temperatures. For this reason, hardening occurs faster.
To date, scientists have solved this mystery only theoretically. When they present convincing evidence of their version, the question of why hot water freezes faster than cold water can be considered closed.
Water is one of the most amazing liquids in the world, which has unusual properties. For example, ice is a solid state of liquid, has specific gravity lower than the water itself, which did a lot possible occurrence and the development of life on Earth. In addition, in the pseudo-scientific and scientific world there are discussions about which water freezes faster - hot or cold. Anyone who can prove that hot liquid freezes faster under certain conditions and scientifically substantiates their solution will receive a £1,000 reward from the British Royal Society of Chemists.
Background
The fact that under a number of conditions, hot water freezes faster than cold water was noticed back in the Middle Ages. Francis Bacon and René Descartes spent a lot of effort explaining this phenomenon. However, from the point of view of classical heat engineering, this paradox cannot be explained, and they tried to bashfully hush up about it. The impetus for the continuation of the debate was a somewhat curious story that happened to Tanzanian schoolboy Erasto Mpemba in 1963. One day, during a lesson on making desserts at a chef school, the boy, distracted by other things, did not have time to cool the ice cream mixture in time and put a hot solution of sugar in milk into the freezer. To his surprise, the product cooled somewhat faster than that of his fellow practitioners who observed temperature regime making ice cream.
Trying to understand the essence of the phenomenon, the boy turned to a physics teacher, who, without going into details, ridiculed his culinary experiments. However, Erasto was distinguished by enviable tenacity and continued his experiments not on milk, but on water. He became convinced that in some cases hot water freezes faster than cold water.
Having entered the University of Dar es Salaam, Erasto Mpembe attended a lecture by Professor Dennis G. Osborne. After its completion, the student puzzled the scientist with a problem about the rate of freezing of water depending on its temperature. D.G. Osborne ridiculed the very posing of the question, declaring with aplomb that any poor student knows that cold water will freeze faster. However, the young man’s natural tenacity made itself felt. He made a bet with the professor, proposing to conduct an experimental test right here in the laboratory. Erasto placed two containers of water in the freezer, one at 95°F (35°C) and the other at 212°F (100°C). Imagine the surprise of the professor and the surrounding “fans” when the water in the second container froze faster. Since then, this phenomenon has been called the “Mpemba Paradox”.
However, to date there is no coherent theoretical hypothesis explaining the “Mpemba Paradox”. It is not clear what external factors chemical composition water, the presence of dissolved gases in it and minerals influence the rate of freezing of liquids at different temperatures. The paradox of the “Mpemba Effect” is that it contradicts one of the laws discovered by I. Newton, which states that the cooling time of water is directly proportional to the temperature difference between the liquid and the environment. And if all other liquids completely obey this law, then water in some cases is an exception.
Why does hot water freeze faster?T
There are several versions of why hot water freezes faster than cold water. The main ones are:
- hot water evaporates faster, while its volume decreases, and a smaller volume of liquid cools faster - when cooling water from + 100°C to 0°C, volumetric losses atmospheric pressure reach 15%;
- The greater the temperature difference, the higher the intensity of heat exchange between the liquid and the environment, therefore heat losses boiling water passes faster;
- when hot water cools, a crust of ice forms on its surface, preventing the liquid from completely freezing and evaporating;
- at high water temperatures, convection mixing occurs, reducing the freezing time;
- Gases dissolved in water lower the freezing point, removing energy for crystal formation - there are no dissolved gases in hot water.
All these conditions have been repeatedly tested experimentally. In particular, the German scientist David Auerbach discovered that the crystallization temperature of hot water is slightly higher than that of cold water, which makes it possible for the former to freeze more quickly. However, later his experiments were criticized and many scientists are convinced that the “Mpemba Effect”, which determines which water freezes faster - hot or cold, can only be reproduced under certain conditions, which no one has been searching for and specifying until now.
One of my favorite subjects at school was chemistry. Once a chemistry teacher gave us a very strange and difficult task. He gave us a list of questions that we had to answer in terms of chemistry. We were given several days for this task and were allowed to use libraries and other available sources of information. One of these questions concerned the freezing point of water. I don’t remember exactly how the question sounded, but it was about what if you take two wooden buckets same size, one with hot water, the other with cold (at exactly the specified temperature), and place them in an environment with a certain temperature, which one will freeze faster? Of course, the answer immediately suggested itself - a bucket of cold water, but we thought it was too simple. But this was not enough to give a complete answer; we needed to prove it from a chemical point of view. Despite all my thinking and research, I could not come to a logical conclusion. I even decided to skip this lesson that day, so I never learned the solution to this riddle.
Years passed, and I learned many everyday myths about the boiling point and freezing point of water, and one myth said: “hot water freezes faster.” I looked at many websites, but the information was too conflicting. And these were just opinions, unfounded from a scientific point of view. And I decided to conduct my own experiment. Since I couldn't find wooden buckets, I used the freezer, stove, some water and a digital thermometer. I will tell you about the results of my experience a little later. First, I will share with you some interesting arguments about water:
Hot water freezes faster than cold water. Most experts say that cold water will freeze faster than hot water. But one funny phenomenon (the so-called Memba effect), for unknown reasons, proves the opposite: Hot water freezes faster than cold water. One of several explanations is the process of evaporation: if very hot water is placed in a cold environment, the water will begin to evaporate (the remaining amount of water will freeze faster). And according to the laws of chemistry, this is not a myth at all, and most likely this is what the teacher wanted to hear from us.
Boiled water freezes faster tap water. Despite the previous explanation, some experts argue that boiled water When cooled to room temperature, it should freeze faster because boiling reduces the amount of oxygen.
Cold water boils faster than hot water. If hot water freezes faster, then maybe cold water boils faster! This is contrary to common sense and scientists say that this simply cannot be. Hot tap water should actually boil faster than cold water. But using hot water to boil does not save energy. You may use less gas or light, but the water heater will use the same amount of energy needed to heat cold water. (WITH solar energy things are a little different). As a result of heating the water by the water heater, sediment may appear, so the water will take longer to heat up.
If you add salt to water, it will boil faster. Salt increases the boiling point (and accordingly lowers the freezing point - which is why some housewives add a little rock salt to their ice cream). But we are in in this case I’m interested in another question: how long will water take to boil and whether the boiling point in this case can rise above 100°C). Despite what cookbooks say, scientists say that the amount of salt we add to boiling water is not enough to affect the boiling time or temperature.
But here's what I got:
Cold water: I used three 100 ml glass glasses of purified water: one glass with room temperature (72°F/22°C), one with hot water (115°F/46°C), and one with boiled water (212 °F/100°C). I placed all three glasses in the freezer at -18°C. And since I knew that water would not immediately turn into ice, I determined the degree of freezing using a “wooden float”. When the stick placed in the center of the glass no longer touched the base, I considered the water to be frozen. I checked the glasses every five minutes. And what are my results? The water in the first glass froze after 50 minutes. Hot water froze after 80 minutes. Boiled - after 95 minutes. My findings: Given the conditions in the freezer and the water I used, I was unable to reproduce the Memba effect.
I also tried this experiment with previously boiled water that had cooled to room temperature. It froze within 60 minutes - still took longer than cold water to freeze.
Boiled water: I took a liter of water at room temperature and put it on the fire. It boiled in 6 minutes. I then cooled it back down to room temperature and added it to it while it was hot. With the same fire, hot water boiled in 4 hours and 30 minutes. Conclusion: As expected, hot water boils much faster.
Boiled water (with salt): I added 2 large tablespoons of table salt per 1 liter of water. It boiled in 6 minutes 33 seconds, and as the thermometer showed, it reached a temperature of 102°C. Undoubtedly, salt affects the boiling point, but not much. Conclusion: salt in water does not greatly affect the temperature and boiling time. I honestly admit that my kitchen can hardly be called a laboratory, and perhaps my conclusions contradict reality. My freezer may not freeze food evenly. My glass glasses could be irregular shape, Etc. But no matter what happens in the laboratory, when it comes to freezing or boiling water in the kitchen, the most important thing is common sense.
link with interesting facts about waterall about water
as suggested on the forum forum.ixbt.com, this effect (the effect of hot water freezing faster than cold water) is called the “Aristotle-Mpemba effect”
Those. Boiled water (chilled) freezes faster than “raw” water
Water- a fairly simple substance from a chemical point of view, however, it has a number of unusual properties, which never cease to amaze scientists. Below are a few facts that few people know about.
1. Which water freezes faster - cold or hot?
Let's take two containers with water: pour hot water into one and cold water into the other, and place them in the freezer. Hot water will freeze faster than cold water, although logically, cold water should have turned into ice first: after all, hot water must first cool to the cold temperature, and then turn into ice, while cold water does not need to cool. Why is this happening?
In 1963, a Tanzanian student named Erasto B. Mpemba, while freezing an ice cream mixture, noticed that the hot mixture solidified faster in the freezer than the cold one. When the young man shared his discovery with his physics teacher, he only laughed at him. Fortunately, the student was persistent and convinced the teacher to conduct an experiment, which confirmed his discovery: under certain conditions, hot water actually freezes faster than cold water.
Now this phenomenon of hot water freezing faster than cold water is called “ Mpemba effect" True, long before him this unique property of water was noted by Aristotle, Francis Bacon and Rene Descartes.
Scientists still do not fully understand the nature of this phenomenon, explaining it either by the difference in supercooling, evaporation, ice formation, convection, or by the effect of liquefied gases on hot and cold water.
2. It can freeze instantly
Everyone knows that water always turns to ice when cooled to 0°C... with some exceptions! Such a case, for example, is supercooling, which is a property of very clean water remain liquid even when cooled to below freezing. This phenomenon becomes possible due to the fact that environment does not contain centers or nuclei of crystallization that could trigger the formation of ice crystals. And so the water remains in liquid form, even when cooled to temperatures below zero degrees Celsius.
Crystallization process can be caused, for example, by gas bubbles, impurities (contaminants), or an uneven surface of the container. Without them, water will remain in a liquid state. When the crystallization process starts, you can watch the super-cooled water instantly turn into ice.
Note that “superheated” water also remains liquid even when heated above its boiling point.
3. 19 states of water
Without hesitation, name how many different states does water have? If you answered three: solid, liquid, gas, then you were wrong. Scientists distinguish at least 5 different states of water in liquid form and 14 states in frozen form.
Remember the conversation about super-chilled water? So, no matter what you do, at -38 °C even the purest super-chilled water will suddenly turn into ice. What will happen as the temperature drops further? At -120 °C something strange begins to happen to the water: it becomes super viscous or viscous, like molasses, and at temperatures below -135 °C it turns into “glassy” or “vitreous” water - solid, in which there is no crystal structure.
4. Water surprises physicists
On molecular level water is even more surprising. In 1995, a neutron scattering experiment conducted by scientists yielded an unexpected result: physicists discovered that neutrons aimed at water molecules “see” 25% fewer hydrogen protons than expected.
It turned out that at a speed of one attosecond (10 -18 seconds) an unusual quantum effect takes place, and chemical formula water instead H2O, becomes H1.5O!
5. Water memory
Alternative official medicine homeopathy states that a dilute solution medicinal product can provide healing effect on the body, even if the dilution factor is so high that there is nothing left in the solution except water molecules. Proponents of homeopathy explain this paradox with a concept called " water memory“, according to which water at the molecular level has a “memory” of the substance that was once dissolved in it and retains the properties of the solution of the original concentration after not a single molecule of the ingredient remains in it.
An international team of scientists led by Professor Madeleine Ennis of Queen's University of Belfast, who had criticized the principles of homeopathy, conducted an experiment in 2002 to disprove the concept once and for all. The result was the opposite. After which, scientists stated that they were able to prove the reality of the effect “ water memory" However, experiments carried out under the supervision of independent experts did not bring results. Disputes about the existence of the phenomenon " water memory"continue.
Water has many other unusual properties that we did not talk about in this article. For example, the density of water changes depending on temperature (the density of ice is less than the density of water); water has a fairly high surface tension; in the liquid state, water is a complex and dynamically changing network of water clusters, and it is the behavior of the clusters that affects the structure of water, etc.
About these and many other unexpected features water can be read in the article “ Anomalous properties of water", authored by Martin Chaplin, professor at the University of London.