Effect of mercury on aluminum. Test in physics "Archimedean force and floating conditions of bodies" (7th grade) Aluminum 1 was placed in liquid mercury

Test compiled in three versions. Answers are attached. When completing the work, students need to be given a table of densities. When compiling the test, tasks from the book "Testing Students' Knowledge in Physics" were used under edited by V,G, Razumovsky and R.F. Krivoshapova.

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“Check in physics “Archimedean force and conditions of floating bodies” (7th grade)”

Physics test for 7th grade students

Archimedean force and floating conditions of bodies

Ioption

1. Determine the buoyant force acting on a stone with a volume of 0.5 m 3 located in water.

2. What force must be applied to hold a steel rail with a volume of 0.7 m 3 in water?

3. Three immiscible liquids are poured into a vessel: water, alcohol, mercury. In what order are they arranged? Justify your answer.

IIoption

1. A piece of granite with a volume of 10 dm2 is immersed in water. How much force must be applied to keep it in the water?

2. A block in the shape of a rectangular parallelepiped was dipped in gasoline. Its dimensions are 4x5x10 cm. Determine the buoyant force acting on the block.

3. Aluminum 1, steel 2 and platinum 3 balls of the same volume were placed in liquid mercury. How will the balls arrange themselves in the liquid?

IIIoption

1. A wooden block with a volume of 80 cm 3 floats on the surface of kerosene, half immersed in it. What is the Archimedean force acting on it?

2. A granite stone attached to a dynamometer spring is immersed in water. The volume of the cobblestone is 0.004 m3. What force does the dynamometer show?

3. Which water is easier to swim in: sea or river? Why?

Mercury was once considered a panacea for all diseases and the elixir of immortality, but it was also the cause of the “old hatter’s disease.” Mercury killed Ivan the Terrible and put airplanes out of service forever.

So heavy I can't lift it

Mercury is a substance with a high specific gravity and high density. If you try to even lift a 10-liter bucket filled with mercury, you will not succeed. For the first time, the weight of mercury was measured by Robert Boyle in 1627, but his figures are still correct: 1 liter of mercury corresponds to approximately 13.6 kilograms, by the same number the density of mercury is higher than the density of water. Our body is also “burdened” with mercury, but its amount is negligible - 13 milligrams.

Mascot

Just a couple of centuries ago, people believed that if purified mercury was turned into a solid, it could be turned into gold. But they relied even more on magical properties of this substance. For example, the priests of Ancient Egypt put several grams of mercury in a wooden or granite vessel and placed it in the throat of the pharaoh's mummy - they believed that after death this would protect their ruler. Ordinary Egyptians also counted on the help of mercury, carrying a bottle of it as an amulet. Many believed and still believe that mercury brings good luck, which is why mercury talismans are not uncommon these days. They are used by horse racing enthusiasts and card games. To ensure that the toxic properties of mercury do not adversely affect health, the substance is placed in a hole made in nutmeg and sealed with wax. And among modern magicians you can see glass rings in which mercury is sealed.

Medicine

Due to its high toxicity, mercury is now practically not used in medical preparations, with the exception of perhaps a thermometer, which contains about 2 grams of this metal. Mercury can also act as a preservative for vaccines. However, back in the 1970s, mercury was readily used in medicine. For example, mercusal, containing mercury ions, acted as a strong diuretic, mercuric chloride was used as a laxative, and mercuric cyanide was part of antiseptics and ointments. Silver amalgam, consisting of mercury, was recently used in dentistry as a filling material. The traveler Francois Bernier (1620-1688) during his visit to India noted that local yogis live surprisingly long - up to 200 years. Bernier wrote that yogis drink a drink that contains mercury and sulfur. Yogis have confirmed that a few drops a day of this drug help keep the body in good shape, but most importantly, it contributes to longevity. It is also known that in ancient times the Chinese made “immortality pills” based on mercury.

Victim of treatment

When exhuming the body of Ivan the Terrible, scientists determined that the mercury content in the king’s body was 5 times higher than the permissible standards. It is known that in Rus' mercury was used to treat syphilis back in the 15th-16th centuries. Some researchers have suggested that Ivan the Terrible, who suffered from this dangerous illness, was treated with “liquid silver.” N.M. Karamzin wrote that the tsar “changed so much that it was impossible to recognize him: gloomy ferocity was depicted on his face, all his features were distorted, his gaze faded, almost not a single hair remained on his head and beard.” Sudden hair loss is one of the obvious signs mercury poisoning, as well as epileptic seizures that tormented the king. Mercury intoxication is the cause of death of Ivan the Terrible, according to modern experts.

"Mercury" fish

It is known that mercury is contained in sea water. It was recently discovered that small fish are capable of accumulating this substance. At the same time, predators, both fish and birds that hunt small fish, can retain mercury in their bodies at even higher concentrations. For example, if a herring contains 0.01 ppm of mercury, then a shark has an indicator of more than 1 ppm. American scientists who examined fish for mercury content found this substance in every fish! At the same time, 25% of fish have mercury levels above the permissible level. Tuna and lobster are at risk. Environmentalists have already begun to sound the alarm, warning about the dangers of eating fish and other seafood, however, fishing companies, for obvious reasons, call this “horror stories.”

Poisonous, but not always dangerous

"The more we study mercury, the more toxic it becomes," says David Evers of the Biodiversity Institute. “The threat from trace amounts of mercury is greater than previously thought.” Indeed, people previously clearly underestimated the toxic properties of mercury. For example, it was part of the felt from which hats were made. Those who wore hats gradually undermined their health by accumulating toxic substances in their bodies. Even more were poisoned during the production of hats - the expression “old hatter’s disease” clearly demonstrates this. Today, people who primarily suffer from mercury poisoning are those who live by fishing and actively eat fish (heat treatment, as is known, does not remove mercury from food). A large number of such people live in Canada, Brazil, Colombia and China. According to statistics, an average of 8 children per thousand from a dangerous region have chronic disorders, manifested in weakened memory and mental retardation. But the danger of mercury vapor poisoning, according to some experts, is greatly exaggerated, since the density limit of mercury vapor is much lower than that of air, and therefore their concentration in dangerous indicators is possible only with a large amount of this substance. Liquid mercury is not so dangerous. If you swallow metal balls of mercury from a thermometer, they will pass through the entire intestine without causing harm. This is explained by the consistency of mercury, which the gastrointestinal tract is not able to absorb.

Prohibited for transportation!

Interestingly, mercury is prohibited from being carried on airplanes, but not because passengers and crew members can be poisoned by it. When mercury gets on aluminum alloys, it destroys the surface film of aluminum oxide, without which the metal becomes brittle and quickly breaks down in the air. This problem was relevant for aviation in the 1970s. Airplanes with a leak on board large quantity mercury were no longer subject to exploitation. Depending on the degree of damage, they were either sent for major repairs or completely written off.

There are many reasons why you should not deal with mercury under any circumstances. Not only is it toxic and can lead to emotional and mental disorders in a person, but it can also lead to the destruction of the aluminum structure of the aircraft and a plane crash! How can this be?

Aluminum oxide and iron rust

Aluminum is used everywhere these days, from beer cans to airplanes. The point is that aluminum is a good choice between other materials for many situations. It is lightweight, durable and has a coating that can only be matched in hardness by diamond. Iron – or rather steel – has great strength and is not yet replaceable, for example, in construction. However, if you force this iron-steel to fly on the sea every day, it will quickly rust. When iron rusts, it combines with oxygen. In this case, the iron turns into light, red flakes that are easily peeled off the surface of the iron. Unlike iron, aluminum reacts with oxygen to form aluminum oxide, an incredibly hard substance that is very difficult to scratch.

The sharp difference in the behavior of iron and aluminum when interacting with oxygen only confirms this idea that “chemistry is witchcraft.” Aluminum oxide does not flake off aluminum like rust does from iron. Instead, the aluminum oxide film seals the remaining aluminum and prevents further rusting. This is what is needed for an aluminum structure that flies in the air and, often, over seas and oceans.

Mercury and fresh aluminum

Mercury breaks all that beautiful perfection of aluminum. Or, at least, it can break if it hits an aluminum part with a fresh scratch. If this happens, the mercury actively combines with the aluminum, tearing it out of the aluminum structure. Of course, when aluminum and mercury amalgam are exposed to air, the aluminum immediately combines with oxygen to form the same ultra-strong aluminum oxide. It’s just that all this is happening in the wrong place in the form of growing feathers and pillars that rise from liquid mercury.

This release of aluminum oxide from the initial scratch allows the mercury to break through the aluminum until all the mercury has evaporated into the air. Therefore, even small amounts of mercury can cause great damage.

How mercury eats aluminum

Well, not really! What the mercury does do is penetrate the protective oxide layer of the aluminum, allowing the aluminum to oxidize at a very high rate. Mercury allows the surface of aluminum to be in constant contact with air and ensures the continuous process of formation of aluminum oxide. It looks like the mercury is actually eating the aluminum.

Of course, under normal conditions this does not happen, as a film of aluminum oxide instantly forms on the exposed surface of aluminum, which protects the aluminum from further oxidation. Mercury inhibits the formation of an oxide film and gives this creepy picture of aluminum being eaten by mercury, which is shown.

Reaction mechanism

The mechanism of the reaction of aluminum with mercury is very complex. A spontaneous reaction occurs between the mercury film, aluminum, moisture and oxygen from the air (figure). While mercury is insoluble in aluminum, aluminum is slightly soluble in mercury (0.002% at room temperature). When mercury wets the surface of aluminum, it maintains the surface in an activated state so that an oxide layer cannot form on it. Aluminum will dissolve in mercury and oxidize in contact with air.

There is no consumption of mercury during this reaction, so once it starts, it will, in principle, never stop.

Figure - Effect of mercury on aluminum

Chemistry of interaction between aluminum and mercury

If there is no oxide layer on aluminum, then mercury forms an amalgam with it - an alloy of aluminum with mercury. Fresh aluminum with amalgam on its surface reacts violently with moisture in the air - it reacts very actively, especially on days with high humidity:

Al(s) + 3H 2 O(l) => Al(OH 3) (s) + 3 / 2 H 2 (g)
H= -418 kJ/mol.