30 мин
9 октября 2018 г.

Chemistry Lab-2019. Analysis.

Feedback: Chemistry Editor Andrey Bychkov, andrewbychkov@gmail.com Laba Science Editor Vladimir Gubaylovskiy, telega1@yandex.ru
Автор: Laba.Media

“Renyxa”

Chemical elements are everywhere. They are the bricks of the Universe. They are both in our body and distant stars. Check your knowledge, would you be able to distinguish solid facts about chemical elements from made-up skimble-skamble?

 

1. The element “oganesson” is named after a currently living scientist.

True

The 118th element of the Periodic Table is named after Yuri Oganessian, a famous Russian scientist who lives and works in Dubna, continuing to synthesize new elements.

 

2. There is water on the Sun.

True

Water molecules were discovered on the Sun relatively recently: due to developments of new spectroscopy techniques, characteristic water signals were detected in late 1999s. This was sensational, since, prior to that, the existence of water molecules on the Sun seemed to be very unlikely. Even though there’s both hydrogen and oxygen on the Sun, the temperature should not exceed 3000 degrees Celsius in order for the yielded water molecules not to dissociate immediately. However, it turned out that, in dark spots on the Sun, the temperature never gets as high as 3000 degrees, and that’s where water is formed.

Since water on the Sun can be consistently detected spectroscopically, it is likely that there’s more water on the Sun than in the whole Solar system.

Most likely, the amount of water molecules does not exceed hundredths of 1 percent of the total solar mass. Sun accounts for 98,6% of the total mass for the Solar system, with Jupiter accounting for almost everything left (and there’s very little water on Jupiter). The largest deposits of water can be found on Uranus and Neptune, the so-called ice planets. They account for hundredths of 1 percent for the total mass of the Solar system.

References: Chief paper in Science (1997): Polyansky, O. L. (1997). Water on the Sun: Line Assignments Based on Variational Calculations. Science, 277(5324), 346–348.doi:10.1126/science.277.5324.346, Tennyson, J., & Polyansky, O. L. (1998). Water on the Sun: The Sun yields more secrets to spectroscopy. Contemporary Physics, 39(4), 283–294.doi:10.1080/001075198181955, A down-to-earth explanation: https://postnauka.ru/faq/38351

 

3. Ozone-rich air is beneficial to human health.

False

Ozone is toxic at any concentration which is why it is so efficient against mold and bacteria.

High toxicity of ozone is determined by its extreme oxidizing ability and its propensity to form free oxygen radicals in many of its reactions. The toxic action of ozone upon a human organism is systemic in nature, irritant, cancerogenic and mutagenic. It can lead to premature death. In Russia, ozone is classified as a Class 1 dangerous substance (the most dangerous kind). The regulations on concentration are the following:

maximum one-time threshold limit value (TLV) in the atmospheric air of inhabited localities is 0,16 mg/m³;

daily TLV in the atmospheric air of inhabited localities is 0,03 mg/m³;

threshold limit value (TLV) in the air around a workplace is 0,1 mg/m³.

Lethal concentration, 50% (LC50) is 4,8 ppm

Notably, the threshold for the human sense of smell is approximately 0,01 mg/m³.

 

4. The melting point of mixtures composed of de-icing agents and ice is lower than 0°С at normal atmospheric pressure.

True

As this is exactly the process employed to get rid of ice on the roads in winter: cover the roads with so-called de-icing agents. Sodium chloride (regular table salt) or, for example, calcium chloride can be employed as de-icing agents. When mixed with ice, the resulting mixture freezes at temperatures lower than zero degrees Celsius, which is how roads are de-iced.

 

5. Touching hogweed leads to chemical burns on human skin.

False

Hogweed causes phytophotodermatitis.

The leaves and the fruit of hogweed are rich with volatile oils. Touching some of the species of plants in this genus can cause skin irritation and even burns due to all parts of the plant containing furanocoumarins (these substances greatly increase UV sensitivity in humans). The most intense skin burns caused by hogweed occur on bright sunny days. However, even short and non-intensive exposure to sun is enough for skin affected by plant liquids to get burned. Typically, affected skin areas get burns of the second degree (liquid-filled blisters). The timeline of the burn revealing itself stretches from a few hours to a few days. Notably and dangerously, initial tactile contact with the plant does not lead to unpleasant sensations.

Source: https://ru.wikipedia.org/wiki/Борщевик#Фототоксичность

 

6. Iron is the most abundant element in the Earth’s crust.

False.

The most abundant element in the Earth’s crust is oxygen. According to the Encyclopedia of Chemistry, the composition of Earth’s crust is this: 46% oxygen, 28% silicon, 8.2% aluminium, 5.6% iron. Iron and aluminium are kind of self-explanatory, but what about this much oxygen (and silicon)? Turns out, most ores are metal oxides -- meaning they are compounds containing metals and oxygen. There are many metals and only one oxygen. Also, as everyone knows, the upper layers of crust contain a lot of sand and clay which are SiO2 + other oxides (aluminium oxide, for one).

 

7. Helium was discovered on the Sun.

True.

Helium was discovered when observing the spectral lines of the Sun. There’s very little of it on Earth; however, it is the second most abundant element in the universe (its share is 23%). Most helium was formed in the first few minutes directly after the Big Bang.

 

8. Noble gases do not form any compounds.

False.

Inert gases are known to be chemically non-reactive (which is how they get their name and also their other name, “noble gases”). Nevertheless, in 1962 Neil Bartlett demonstrated that, at certain conditions, they can form compounds (fluorine-based compounds are the most likely). The most “inert” gases are neon and helium: to get them to react, strong measures have to been taken, like ionizing every atom artificially. On the other hand, xenon is sometimes even too reactive for a noble gas, already reacting at normal conditions and exhibiting most of the available oxidation states (+1, +2, +4, +6, +8).

 

9. Mercury can be turned into gold.

True.

In 1940, American physicists Sherr and Bainbridge reported that successful bombardment of mercury atoms with quick neutrons yielded gold. However, the resulting isotopes had mass numbers of 198, 199 and 200. Consequently, the yielded gold only existed for a very short amount of time. This couldn’t make modern fans of alchemy happy and led to further experiments. Later, it was shown that mercury atoms with mass numbers of 196 and 199 had the highest chances of turning into gold. Eventually, that was achieved: 100 g of mercury were turned into 35 µg of gold.

 

10. Iodine deficiency can be treated by sea salt.

False.

This is a popular misconception. Sea water may contain no iodine at all. When producing salt by evaporation, iodine can be removed. But if you use simple iodized rock salt (or, alternatively, sea salt, but it also should be iodized), then your problem is solved. Most of the countries around the world managed to overcome iodine deficiency problems by iodizing salt en masse. By the way, note that excess iodine can also be harmful, which is why extremely iodine-rich seaweed isn’t recommended for regular consumption.

 

11. There are amino acids in deep space (amino acids are building blocks of proteins).

True.

We can quite confidently say that there’s glycine in interstellar clouds. Therefore, amino acids are formed in space.

For example, in 2018, glycine was found on the surface of the 67P/Churyumov-Gerasimenko comet. https://habr.com/ru/post/411857/

 

12. Curium is the only element named after a female scientist.

False.

Since the element curium was named after the spouses Pierre and Marie Curie. The only element named after a woman is meitnerium (its namesake is Lise Meitner, an Austrian physicist).

 

“Dmitry Ivanovich and the Periodic Law”

150 ago a Russian chemist Dmitry Ivanovich Mendeleev had a flash of genius: chemical properties of elements depend on their atomic weights and change periodically. This is how the Periodic Table was born. Do you know it well enough?

 

13. As of now, there are 118 elements in the Periodic table. How many were there in the first published version of Mendeleev’s Periodic table?

A. 21

B. 42

C. 63

D. 84

Not nearly all of the elements in the modern Periodic table were known in Mendeleev’s time, let alone in earlier times. By the 1860s, around 60 elements were known along with their atomic weights. The first variant of the Periodic table included 63 elements.

 

14. Mendeleev is famous for formulating the Periodic Law. What else did he passionately want to discover?

A. A perfect vodka recipe

B. Aether

C. A cheap way of producing aluminium

D. A reliable type of glue for suitcases

Naturally, Mendeleev wasn’t searching for a perfect recipe for vodka, it’s just a famous tall tale (in fact, he studied different proportions in water-alcohol solutions only for science; by his own admission, he never even tasted vodka). Mendeleev was an intriguing and accomplished person, so people kept saying many things about him. For example, he was known to glue his own bookshelves, crates and even suitcases. There is a reported episode of Mendeleev being considered “a master suitcase maker”. It is not known whether he was trying to invent a perfect type of glue for suitcases, but no contemporary accounts of this work exist. That’s why we can exclude the suitcase option as well. In Mendeleev’s time, aluminium was very expensive, more so than platinum. He was even presented with a laboratory balance with one of its weighing pans made of aluminium, while the other one was made of gold. Nevertheless, Mendeleev wasn’t searching for a cheap way to produce aluminium. On the other hand, he was indeed searching for aether (it was a popular hypothesis in the 19th century). https://ru.wikipedia.org/wiki/%D0%9D%D1%8C%D1%8E%D1%82%D0%BE%D0%BD%D0%B8%D0%B9

 

15. One time, Mendeleev was presented with a laboratory balance with one of its weighing pans made of this metal (at the time, it was more expensive than gold):

A. titanium

B. aluminium

C. nickel

D. chromium

Nowadays, aluminium is produced by electrolysis from molten clay (this approach requires a significant amount of cheap electricity). This is the reason why producing aluminium in industrial quantities only became viable with the introduction of large power plants. In the 19th century, this metal was more expensive than gold. In 1889, some representatives of Great Britain, wanting to honor Mendeleev, the great Russian chemist, with an expensive gift, presented him with a laboratory balance with its weighing pans made of gold and aluminium, respectfully.

 

16. In “To a Tyrant”, Joseph Brodsky mentioned several elements and compounds.

He used to come here till he donned gold braid,
a good topcoat on, self-controlled, stoop-shouldered.
Arresting these cafe habitues –
he started snuffing out world culture somewhat later –
seemed sweet revenge (on Time, that is, not them)
for all the lack of cash, the sneers and insults,
the lousy coffee, boredom, and the battles
at vingt-et-un he lost time and again.

And Time has had to stomach that revenge.
The place is now quite crowded; bursts of laughter,
records boom out. But just before you sit
you seem to feel an urge to turn your head around.
Plastic and chrome are everywhere – not right;
the pastries have an aftertaste of bromide.
Sometimes before the place shuts down he’ll enter
straight from a theater, anonymous, no fuss.

(translated by Alan Myers)

Why do “the pastries have an aftertaste of bromide”? What was the reason for adding it to food?

A. as a “truth serum”

B. as a mood-enhancing stimulant

C. as a sedative

D. this compound is not bioactive in humans

Bromine compounds act as sedatives. This effect was used to treat mental illnesses in the mid-20th century.

Also, there’s a widespread urban legend about the staff in army barracks, correctional facilities and psychiatric wards adding bromine compounds to food to control sexual urges. The origin of this urban myth is mysterious..

 

17. Which of the elements listed has a common household use?

A. Americium

B. Europium

C. Plutonium

D. Moscovium

Notably, americium is used in some types of smoke detectors. Around 0,3 g of americium oxide is put into the indicator chamber of the detector, wherein the stream of alpha particles released by americium ionizes the air, allowing for electric current to flow between the electrodes of the detector. If the aerosol smoke particles appear in the air, they absorb the alpha particles, ionization in the chamber ceases, the electrical circuit in the detector breaks and the alarm sounds.. Source - Arkady Kuramshin, «Chemical elements».

 

18. Ruby, sapphire, corundum and emery are all forms of one oxide. The oxide of which element is that?

A. Manganese

B. Iron

C. Aluminium

D. Silicon

Aluminium is the most abundant metal in the Earth’s crust. It forms clay and many minerals.. It is aluminium oxide that presents itself in such different forms as ruby (transpare nt red, gemstone), sapphire (transparent blue), regular corundum (opaque, used as an abrasive material) and emery (grainy grey-black corundum with admixtures of hematite, magnetite, etc.; it is put on paper and used for polishing).

 

19. If a nucleus were blown up to the size of a cherry, what would be the corresponding size of an atom?

A. A football

B. A room

C. A football stadium

D. Planet Earth

Let’s estimate. Approximately, a nucleus is 10 thousand times smaller than the atom itself. Therefore, if we blow up the nucleus to the size of a cherry (around 1 cm), then the size of an atom would be around 100 m which is close to the FIFA-recommended length of a football field..

 

“Chemical Compounds”

Chemical elements form chemical compounds that are larger building blocks of the visible world. The real number of chemical compounds is so giant that no one knows it, but you still can excise your knowledge about the most common of them.

 

20. What is “hard water”?

A. Water that contains iron oxides and hydroxides

B. Plain untreated water

C. Water with solid impurities (grains of sand, microscopic particles, etc.)

D. Water that contains calcium and magnesium salts

The so-called “hard” water contains calcium and magnesium hydrocarbonates . These salts are soluble, but at higher temperatures they degrade to form carbonates which are insoluble, making them the culprits behind the formation of limescale in our kettles.

 

21. In humans, the ability to decipher the taste of protein-containing food is vital. There are special receptors devoted to that. They are sensitive to

A. Lysergic acid

B. Stearic acid

C. Benzoic acid

D. Glutamic acid

We should immediately point out that proteins consist of amino acids, with glutamic acid being one of the most common among these. In order to determine the taste of protein-containing food, humans have dedicated receptors, reacting to glutamic acid (or to the glutamate ion). This is among the reasons why “taste enhancers” are added to many dishes nowadays (the enhancer being sodium glutamate). In fact, this compound does not enhance taste but acts as a representative for the taste of proteins. Dedicated receptors in our mouth react to the glutamate ion, and this kind of food seems more enjoyable to us, since our organism receives a signal that this food contains protein. There is nothing scary about sodium glutamate, a salt of glutamic acid: it is widely represented in a variety of foods (cheese, meat, fish and even some vegetables).

A few words about the other acids on the list. Benzoic acid is not an amino acid: most people are familiar with its role as a preservative. Curiously, according to some sources, it is present in Nordic berries (cloudberry, cranberry) which is the reason why they don’t spoil easily. Stearic acid is a fatty acid. Interestingly, the latest data shows that there are receptors reacting to fatty food as well (detecting the “fatty taste”, that is).

Lysergic acid is among the alkaloids produced by ergot (also known as “ergot alkaloids”), but is mostly famous for its diethylamide, widely known by its abbreviated name, LSD.

 

22. Traditional (“black”) gunpowder is composed of sulphur, coal and saltpeter (potassium nitrate). What is the purpose of including saltpeter?

A. It burns quite intensively

B. It is required as an oxidizer for combustion

C. It is a destructive agent

D. It is an inert packaging filler

Saltpeter (potassium nitrate) is required as an oxidizer, since gunpowder is ignited in oxygen-less conditions (for example, in the breechblock of a gun).The mixtures of oxygen-containing compounds with something flammable (or should we say, “gunpowder”) do not require oxygen in the air to burn, and that is why they can burn underwater, underground or even in space.

 

23. Titan, a moon of Saturn, has lakes and rivers. Besides Earth, it is the only celestial body in the Solar system where the presence of surface liquids has been confirmed. What are the rivers on Titan composed of?

A. water

B. liquid nitrogen

C. liquid hydrocarbons

D. liquid helium

To answer this question, we have to consider the melting points and boiling points for the listed compounds.

Titan has its own atmosphere. Its pressure is only a little higher than the atmospheric pressure on Earth.

Water is not a viable option. It freezes at zero degrees Celsius, with temperatures on Titan being obviously lower than zero. Nitrogen liquefies at -196 degrees Celsius.

Helium liquefies at -269 degrees Celsius; this is significantly lower than the temperature on Titan (even though it’s far from the Sun, but no as far to have liquid helium).

Nitrogen and methane remain as the only two options.

The rivers and lakes on Titan are made of methane and ethane. These are alkanes (saturated aliphatic hydrocarbons).

The boiling point for methane lies around -190 degrees Celsius. This is approximately the temperature on the surface of Titan. Methane remains in the liquid state, but it can evaporate due to seasonal temperature fluctuations -- just like water on Earth.

The atmosphere on Titan is mostly composed of gaseous nitrogen. Titan has methane rains and methane clouds. If you look upon the sky from the surface of Titan, you’ll see that it’s dark brown. On the surface of this moon, erosion and weathering occur. Originally, liquid lakes on Titan were discovered by the sheen of large spots with regular and almost constant shapes. Only later it became evident that those were methane lakes.

You can think of Titan as an astronomically sized oil barrel: its hydrocarbon reserves would last for the earthlings’ whole lifespan. Too bad it’s really far away!

 

24. A deficiency of this compound can be connected to the development of Parkinson’s disease

A. Insulin

B. Adrenaline

C. Serotonin

D. Dopamine

The reason behind Parkinson’s disease is the death of neurons producing dopamine, primarily in the substantia nigra (a part of the brain). There are medicines known to increase the internal level of dopamine: e.g., levodopa, a famous medicine and a chemical precursor of dopamine.

 

25. Fractional distillation cannot yield an ethanol solution with a concentration higher than 96% by weight. How do you get absolute (100%) ethanol?

A. Multiple distillation

B. Repeated freezing

C. Removing water with a desiccant

D. It is impossible to obtain 100% pure ethanol

Due to the existence of azeotropic mixtures, it’s impossible to yield 100% ethanol by distillation. When distilling alcohol-containing liquids (this process is employed in the production of strong alcoholic drinks), one can never obtain a solution with a concentration higher than 96%, no matter how many times the mixture is distilled. It is possible to get 100% ethanol by using a special desiccant (e.g., dehydrated calcium chloride).

 

Identification.

Connect each element to its use. The use of elements

Tungsten is used to make filaments for incandescent light bulbs (1C). However, these lamps are being phased out due to their inefficiency. Use energy saving lamps!

Germanium is a prominent semiconductor material (2E). Without semiconductors, we’d have no electronics: watches, TV sets, computers, mobile phones.

Yttrium and other rare earth metals are used to make superconductive cables (3G).

Xenon is used in car headlamps (4A).

Lithium is prominently used to produce Li-ion or Li-polymer batteries in mobile phones, tablets, earphones (5B)

Neodymium is used to produce very strong neodymium magnets (6D). For example, those are used in headphone speakers.

Carbon is added to various iron alloys to produce steel. Alloys with the highest percentage of carbon are called cast iron. (7F)

Palladium and other metals of the platinum group are used as catalysts (8H)

 

Trivial and systematic names

slaked lime - calcium hydroxide (Ca(OH)2)

gypsum - calcium sulfate dihydrate (CaSO4 · 2H2О)

quartz, as with most types of sand - silicon dioxide (SiO2)

chalk - calcium carbonate (CaCO3) 

baking soda - sodium hydrocarbonate (NaHCO3)

table salt - sodium chloride (NaCl)

dry ice - carbon dioxide (CO2)