Water has the ability to dissolve substances because... All-Russian Biology Olympiad for Schoolchildren (3) - Document

However, the most amazing feature of water is its ability to dissolve other substances. The ability of substances to dissolve depends on their dielectric constant. The higher it is, the more capable the substance is of dissolving others. So, for water this value is 9 times higher than for air or vacuum. Therefore, fresh or clean waters are practically never found in nature. There is always something dissolved in earth's water. These can be gases, molecules or ions of chemical elements. It is believed that all elements of the table of the periodic table of elements can be dissolved in the waters of the World Ocean; at least, more than 80 of them have been discovered today.

Water hardness, its cause and solutions

Water hardness is understood as a property of natural water determined by the presence in it of mainly dissolved calcium and magnesium salts. Water hardness is divided into carbonate(presence of magnesium and calcium bicarbonates) And non-carbonate (presence of calcium and magnesium chlorides or sulfates). The sum of carbonate and non-carbonate hardness determines general hardness.

The need to eliminate water hardness is caused primarily by an undesirable effect due to its properties.

Thermal effects on hard water lead to the formation of scale on the walls of metal structures (steam boilers, pipes, etc.). This phenomenon is associated with additional energy costs, since scale is a poor conductor of heat. Corrosion processes occur much faster in hard water.

Water hardness is expressed in millimole equivalents of a substance per 1 liter of water - mmol-eq/l. 1 mmol-equiv of calcium or magnesium hardness corresponds to the content of 20.4 mg Ca 2+ and 12.11 mg Mg 2+ in 1 liter of water.

Water hardness is calculated using the formula:

where m is the mass of a substance that determines water hardness or is used to eliminate water hardness, mg;

Mae- molar mass of equivalents of this substance, g/mol;

V- volume of water, l.

Carbonate hardness is called temporal, because for a long time boiling water With such hardness, bicarbonate decomposes:

Ca(HCO 3) 2 →CaCO 3 ↓ + CO 2 + H 2 0

M g (HCO 3) 2 → M g (OH) 2 ↓ + 2CO 2

Water hardness caused by the presence of magnesium and calcium chlorides or sulfates is called constant. Permanent hardness can be eliminated chemically, for example by adding calcium carbonate or calcium hydroxide:

CaS0 4 (p) + Na 2 CO 3 (p) = CaCO e (t)↓ + Na 2 SO 4 (p)

Ca(HCO 3) 2 (p) + Ca(OH) 2 (p) = 2CaCO 3 (t) ↓ + 2H 2 O

M g SO 4 (p) + Ca (OH) 2 (p) = Mg (OH) 2 (t) ↓ + CaSO 4 (p)

To remove Ca 2+ and Mg 2+ ions, sodium phosphates, borax, potassium carbonate and other salts are also used.

Water. Water softening method

Natural water always dissolves the salts in it, which determine the hardness of the water. Divide the instantaneous hardness of water containing calcium and magnesium hydrocarbonates (Ca(HCO 3) 2, Mg(HCO 3) 2. It is called so that when boiling it can be put into drocarbonates, which are transformed into important decomposition of carbonate (CaCO 3, MgCO 3), as they fall into siege, scale settles.

The constant hardness of water is determined by chlorides and sulfates of calcium and magnesium (CaCl 2, CaSO 4, MgCl 2, MgSO 4). This hardness of water is not subject to boiling and it is necessary to use chemical reagents to reduce it.

Time-hour and constant hardness determine the final hardness of water, which is characterized or measured by the total concentration of calcium and magnesium ions in milligram equivalent per 1 kg of water (mg-eq/kg). Milligram-equivalent is a number of words that indicate its aqueous atomic mass. Thus, 1 mg-eq/kg is equivalent to 0.02 mg Ca and 0.012 mg magnesium per 1 kg of water. To ensure safe and trouble-free operation of modern ship steam power plants, it is necessary to freeze a number of inputs related to the solidification of various chemical reagents. Reagents are supplied to them to paint the water of boiler and living waters and regulate the internal physical and chemical processes of the boiler.

Increase the concentration of salts in the boiler water until scale builds up, which results in increased heat transfer and overheating of the boiler, which can lead to boiling. Under the action of water, steam and steam-water mixture, the metal surface of the boiler heating promotes intercrystalline corrosion, such metal retains its shape and dimensions, but collapses upon impact. This type of corrosion can be quickly detected only with the help of ultrasonic and magnetic flaw detectors.

09/18/2018 10th grade lesson No. 3

Subject: Inorganic substances of the cell

Goals: study the chemical composition of the cell, identify the role of inorganic substances in the cell.

Tasks:

educational: show the variety of chemical elements and compounds that make up living organisms, their significance in life processes;

developmental: continue the formation of skills and abilities of independent work with the textbook, the ability to highlight the main thing, formulate conclusions;

educational: development of communication skills.

Equipment: presentation, table of D.I. Mendeleev, textbook.

Lesson progress:

I .Organizational moment

II . Examination homework

Conversation on issues (slide 1)

Who first introduced the concept of “cell”?

Who is the creator of the cell theory?

What contributions did Rudolf Virchow and Karl Baer make to the creation of cell theory?

What methods of studying cells exist?

For which representatives? organic world Are the concepts of “cell” and “organism” the same?

III .Motivation (slide 2)

There is nothing else in nature, neither here nor there, in the depths of space:

everything - from small grains of sand to planets - consists of single elements.

Like a formula, like a schedule, the labor system of the Mendeleev system is strict.

A living world is happening around you, enter it, breathe it in, touch it with your hands.

(Shchipachev “Reading Mendeleev”)

Think about what this poem is about? How might this relate to today's lesson? Try to formulate the topic of the lesson and set goals for the lesson.

Recording the lesson topic (slide 3)

IV . Learning new material

Remember the chemical composition of a cell from the 8th grade biology course and reproduce this diagram (orally) (slide 4)

Does this diagram fully reflect the chemical composition of the cell?

What do substances consist of? (from chemical elements).

This means it would be more correct to depict the proposed scheme in a different way (slide 5)

What do we include in the first group? To the second group?

Independent work with the textbook (paragraph 2 by L.N. Sukhorukova, V.S. Kuchmenko “Biology grades 10-11”). Find answers to questions:

Which chemical elements are they found in the cells of living organisms?

How are they classified?

Give examples of each group.

The cell contains approximately 80 chemical elements of the periodic system. All these elements are also found in inanimate nature (slide 6).

What does the similarity between living and inanimate nature?

Substances in cells different quantities(slide 7).

They are classified into 3 groups (slide 8).

Their examples and meaning (slides 9-23).

What inorganic substances make up cells?

Let's work in groups. The first group will study and prepare a story for us about the mineral salts that make up the cells, and the second about water (about their role in the cell).

The story of a representative of the 2nd group.

Antoine de Saint-Exupéry (slide 28) said:

Water - you don't have
no taste, no color, no smell.
They enjoy you
not knowing what you are...
You are life itself!

What are your thoughts on this matter?

The properties of water are unusual (slides 29-31). What do they depend on? (depending on the structure of the water molecule). Let's remember their chemistry course on the structure of the water molecule (slide 32).

Properties of water (slide 32-34)

The meaning of water (slide 35 -39)

V . Reinforcing the material learned

Test “Inorganic substances of cells” (slide 40-49)

1. What chemical elements contained in the cell are classified as macroelements?

A ) S, Na, Ca, K; b) O, H, C, N; c) Ni, Cu, I, Br.

2.What are the functions of water in a cell?

a) Transfer of hereditary information;

b) environment for chemical reactions;

c) source of energy.

3. Hydrophobic substances include:

a) salt; b) sugar; c) fats.

4. What ions are part of hemoglobin?

a) Mg2+; b) Fe2+; c) Zn2+.

5. Water is the basis of life, because she:

a) can be in three states (liquid, solid and gaseous);

b) is a solvent that ensures both the influx of substances into the cell and the removal of metabolic products from it;

c) cools the surface during evaporation.

6. Substances that are highly soluble in water are called:

a) hydrophilic; b) hydrophobic; c) amphiphilic.

7. Water has the ability to dissolve substances because its molecules:

A) polar; B) have small molecules;

C) contain atoms connected by ionic bonds; D) form hydrogen bonds with each other

8.The main function of mineral salts in the cell is to maintain:

A) diffuseness; B) buffering; B) osmosis

9.What chemical bonds do water molecules form among themselves:

A) covalent; B) hydrophobic; B) hydrogen

10. A water molecule carrying a positive charge at one end and a negative charge at the other is called: A) dipole; B) dimole; B) dirol

VI . Homework(slide 50)

P. 2, answer questions.

All living organisms on planet Earth are made of water. This liquid is found everywhere and life is impossible without it. The great value of water is due to unique properties liquids and simple composition. To understand all the features, it is recommended to familiarize yourself in detail with the structure of the water molecule.

Water structure model

A water molecule contains two hydrogen atoms (H) and one oxygen atom (O). The elements that make up the liquid determine all the functionality and features. The model of a water molecule has the shape of a triangle. The top of this geometric figure is represented by the large element oxygen, and at the bottom there are small hydrogen atoms.

A water molecule has two positive and two negative charge poles. Negative charges are formed due to an excess of electron density in oxygen atoms, and positive charges are formed due to a lack of electron density in hydrogen.

The uneven distribution of electrical charges creates a dipole, where the dipolar moment is 1.87 debye. Water has the ability to dissolve substances because its molecules try to neutralize the electric field. Dipoles lead to the fact that on the surface of substances immersed in a liquid, interatomic and intermolecular bonds become weaker.

Water is highly resistant to dissolving other compounds. Under normal conditions, out of 1 billion molecules, only 2 disintegrate, and the proton goes into the structure of the hydronium ion (formed when acids dissolve).

Water does not change its composition when interacting with other substances and does not affect the structure of these compounds. Such a liquid is considered an inert solvent, which is especially important for living organisms. Beneficial substances reach various organs through aqueous solutions, so it is important that their composition and properties remain unchanged. Water retains the memory of the substances dissolved in it and can be used repeatedly.

What are the features of the spatial organization of a water molecule:

• The connection is made by opposite charges;
• Intermolecular hydrogen bonds appear, which correct the electron deficiency of hydrogen with the help of an additional molecule;
• The second molecule fixes hydrogen to oxygen;
• Thanks to this, four hydrogen bonds are formed that can contact 4 neighbors;
• This model resembles a butterfly and has angles equal to 109 degrees.

Hydrogen atoms combine with oxygen atoms to form a water molecule with a covalent bond. Hydrogen bonds are stronger, so when they break, the molecules attach to other substances, helping them dissolve.

Other chemical elements that contain hydrogen freeze at -90 degrees and boil at 70 degrees. But water becomes ice when the temperature reaches zero, and boils at 100 degrees. To explain such deviations from the norm, it is necessary to understand what is special about the structure of the water molecule. The fact is that water is an associated liquid.

This property is confirmed by the high heat of vaporization, which makes the liquid a good energy carrier. Water is an excellent temperature regulator and can normalize sudden changes in this indicator. The heat capacity of a liquid increases when its temperature is 37 degrees. The minimum values ​​correspond to the temperature of the human body.

The relative molecular weight of water is 18. This indicator is quite easy to calculate. You should familiarize yourself in advance with the atomic mass of oxygen and hydrogen, which is 16 and 1, respectively. In chemical problems, the mass fraction of water is often encountered. This indicator is measured as a percentage and depends on the formula that needs to be calculated.

The structure of the molecule in various states of aggregation of water

In the liquid state, a water molecule consists of a monohydrol, dihydrol and trihydrol. The amount of these elements depends on the state of aggregation of the liquid. Steam includes one H₂O – hydrol (monohydrol). Two H₂O indicate the liquid state - dihydrol. Three H₂O includes ice.

Aggregate states of water:

• Liquid. There are voids between single molecules that are connected by hydrogen bonds.
• Steam. Single H₂O do not connect with each other in any way.
• Ice. The solid state is characterized by strong hydrogen bonds.

In this case, there are transitional states of the liquid, for example, during evaporation or freezing. First you need to figure out whether water molecules are different from ice molecules. So the frozen liquid has a crystalline structure. The ice model can have the shape of a tetrahedron, trigonal and monoclinic system, or cube.

Regular and frozen water differ in density. The crystalline structure results in lower density and increased volume. The main difference between liquid and solid states is the number, strength and type of hydrogen bonds.

The composition does not change in any state of aggregation. The structure and movement are different components liquids, hydrogen bond strength. Typically, water molecules are weakly attracted to each other and are placed randomly, which is why the liquid is so fluid. Ice has a stronger attraction, as it creates a dense crystal lattice.

Many people are interested in whether the volumes and composition of the molecules of cold and hot water are the same. It is important to remember that the composition of the liquid does not change in any of the states of aggregation. When a liquid is heated or cooled, the molecules differ in their arrangement. Cold and hot water have different volumes, since in the first case the structure is ordered, and in the second it is chaotic.

When ice melts, its temperature does not change. Only after the liquid changes its physical state, the numbers are starting to rise. Melting requires a certain amount energy, which is called the specific heat of fusion or lambda of water. For ice, the figure is 25,000 J/kg.