1. Water is a colorless, odorless and tasteless liquid, which is clear and transparent when shallow and blue-green when deep.
2. At 1 atmospheric pressure, the freezing and boiling points of water are 100℃.
The heat of solidification of water at 0℃ is 5.99 kJ/mol (or 80 calories/g).
The heat of vaporization of water at 100℃ is 40.6 kJ/mol (or 540 calories/g).
Because there are hydrogen bonds between water molecules, the boiling point is high, the molar heat of vaporization is high, and the steam pressure is low.
(1) boiling point: the saturated vapor pressure of the liquid is equal to the atmospheric pressure on the surface of the liquid. At this time, all points of the liquid are violently vaporized, and the liquid-gas phase can exist. If the liquid level is 1 atm(76 mmHg), the boiling point is called "normal boiling point", and the normal boiling point of water is 100℃.
(2) If the air pressure on the liquid surface increases, the liquid needs a higher vapor pressure to boil; Higher temperature leads to higher vapor pressure, so the boiling point of liquid will rise.
The greater the vapor pressure on the liquid surface, the higher the boiling point of the liquid.
Example: pressure cooker, the water surface in the pressure cooker causes 6atm, and the boiling point of water rises above 105℃, so boiling water at such a high temperature will cook things faster than usual.
(3) On the contrary, if the air pressure on the liquid surface becomes smaller, the boiling point of the liquid surface will drop.
3. Water has the smallest volume and the largest density at 4℃ (the exact value is 3.98℃), and D = 1g/mL.
(1) triple point: In a vacuum container, the temperature and pressure when pure liquid phase, solid phase and gas phase coexist in an equilibrium state are called.
(2) The critical temperature is the critical temperature and the pressure is the critical pressure.
1. Critical temperature: The highest temperature of gas liquefaction under pressure is called critical temperature. For example, the critical temperature of water is 374℃. If the temperature is higher than 374℃, it is impossible for water vapor to liquefy under pressure.
2. Critical pressure: At critical temperature, the minimum pressure at which gas is liquefied by pressure is called critical pressure. The critical pressure is equal to the saturated vapor pressure of liquid at the critical temperature.
Second, the chemical properties of water.
1. Water is the most common solvent.
(1) Generally speaking, the solubility of metals and nonpolar molecular substances with low activity in water is very small. However, molecular substances with small molecular weight and high polarity, which can form hydrogen bonds with water molecules, such as ammonia (NH3), methanol (CH3OH) and sucrose (C12H2O11), are easily soluble in water.
Such as 2na+2h2o → 2nNaOH+H2.
(2) Water is an excellent solvent for electrolyte. Because water is a polar molecule, it can hydrate with anions and cations of electrolyte, which isolates the attraction between cations and anions and makes electrolyte soluble in water.
See textbook p.67, figure 4- 1.
2. Both hydrogen and oxygen in water molecules have isotopes.
(1) There are three isotopes of hydrogen.
Hydrogen (or H): 99.98% of natural hydrogen.
Deuterium: 0.04% natural hydrogen.
Tritium (or T): radioactive
(2) There are three isotopes of oxygen.
Oxygen-16 (): accounting for 99.76% of naturally occurring oxygen.
Oxygen-17 (): accounting for 0.04% of naturally occurring oxygen.
Oxygen-18 (): accounting for 0.20% of naturally occurring oxygen.
(3) Pure water can be regarded as 1H2 16O.
Natural water contains a very small amount of deuterium oxide (D2O), which can be obtained by fractionating the residual liquid after water electrolysis.
∵ When water is electrolyzed, H2O is lighter than D2O, and it is easier to move to the electrode for decomposition, so the proportion of D2O in the liquid left after electrolysis is higher than that before electrolysis.
Deuterium oxide, commonly known as heavy water, is widely used as neutron reductant in nuclear reactors.
3. Common chemical reactions related to water
(1) Water can react with all alkali metals, calcium, strontium and barium. Produce hydroxide and hydrogen.
Such as Ca(s)+2H2O(l)→Ca(OH)2(aq)+H2(g)
(2) Water reacts with many metal oxides to generate alkali.
K2O (south) +H2O (left) →2KOH (water)
Calcium oxide +H2O→ calcium hydroxide
(3) Water reacts with many nonmetallic oxides to generate acids.
SO3 (g) +H2O (L) → sulfuric acid (aqueous solution)
Carbon dioxide (gram) +H2O (liter) →H2CO3 (water)
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Basic physical and chemical properties of water
1, water form, freezing point, boiling point:
Pure water is a colorless and odorless transparent liquid. When water is at 1 atmospheric pressure (105Pa), the temperature is below 0℃, and 0℃ is the freezing point of water. The temperature from 0℃ to 100℃ is liquid (usually water is liquid), the temperature above 100℃ is gas (gaseous water), and 100℃ is the boiling point of water.
2, the specific heat of water:
The heat absorbed by unit mass of water when it rises 1℃ is called the specific heat capacity of water, which is 4.2x 103[ coke/g]. ℃].
3. Heat of vaporization of water:
The heat required for a unit mass of water to completely become gaseous water (steam) at the same temperature is called the heat of vaporization of water. The process of water changing from liquid to gas is called vaporization, and the vaporization phenomenon on the surface of water is called evaporation, which can be carried out at any temperature. Heat of solution of ice (solid water);
The heat required for a unit mass of ice to completely dissolve in water at the melting point (0℃) is called the heat of solution of ice.
5, the density of water:
At atmospheric pressure (105Pa) and temperature of 4℃, the density of water is the highest (1g/cm3), and when the temperature is lower or higher than 4℃, its density is less than 1g/cm3.
6, water pressure:
Water exerts pressure on the bottom and side walls of the container (the pressure per unit area is called pressure). There is pressure in all directions in the water; At the same depth, the pressure of water in all directions is equal; With the increase of depth, the water pressure increases; As the density of water increases, so does the water pressure.
7. Buoyancy of water:
The upward and downward pressure difference of water on an object is the buoyancy of water on the object. Buoyancy is always vertical. 8. Hardness of water:
The hardness of water refers to the number of calcium, magnesium and manganese ions contained in water (generally calculated by calcium carbonate).
Hardness unit: mg/L, mmol /L (mg equivalent/l), PPM (PCs/million) and GPG (grains/gallon).
9.pH value:
PH value refers to the pH value of water, indicating the content ratio of H+ and OH- in water (the range is 0- 14).
The human body is very sensitive to pH value. The pH value of most substances in the body is 6.8, and the pH value of blood and cell water is 7.2-7.3.
10，TDS:
TDS refers to the content of all solids dissolved in water in mg/L or PPM. The lower the TDS, the purer the water.
1 1, conductivity (CND):
The conductivity (CND) of water refers to the current passing through the water divided by the voltage difference between the two sides of the water, indicating the ability of the aqueous solution to conduct current, which indirectly reflects the total amount of soluble salts and minerals in the water.
12, van der Waals gravity:
For a water molecule, its positive charge center is on one side of two hydrogen atoms and its negative charge center is on the other side of oxygen atoms, thus forming a polar molecule. When water molecules are close to each other, the attraction between different poles is greater than the repulsion between distant poles. This intermolecular electrostatic force is called van der Waals attraction.
13, surface tension of water:
There is a force on the water surface, which makes the water surface tend to contract. This force acting on the water surface is called surface tension.
What are the characteristics of natural water?
Water exists as a liquid at room temperature and has the characteristics of ordinary liquid. Compared with other liquids, it has many unique properties.
(1) Water does not expand with heat and contract with cold in the range of 0~4℃, but expands with cold, that is, the temperature increases, the volume decreases and the density increases.
(2) Among all liquids, the specific heat capacity of water is the largest, which is 4. 18 Joule/g.. Therefore, water can be used as a high-quality heat transfer medium for cooling, heat storage and heat transfer.
(3) At normal temperature (0~ 100℃), water can be changed into solid, liquid and gas, so it is very convenient to use the phase change heat of water to convert energy.
(4) In liquid, except for mercury (Hg), the surface energy of water is the largest.
(5) Strong water solubility and reactivity. Many substances not only have high solubility in water, but also have the highest degree of ionization.
(6) The conductivity of water increases with the increase of salt content in water.