Solubility, symbol S, at a certain temperature, a solid substance is 100gsolventMedium ReachSaturation stateDissolved solutequalityIs called the solubility of this substance in this solvent.The solubility of the substance belongs tophysical property。[1]
1. The solubility of solid and a small amount of liquid substances refers to the degree of saturation of a solid substance in 100g solvent (usually water) at a certain temperatureSoluble mass (100 at a certain temperatureThe maximum amount of a substance dissolved in g solvent), expressed with the letter S, and its unit is "g/100g water (g)".In case of no indication, usually the solubility refers to the solubility of the substance in water.For example, when 0.165g of calcium hydroxide is dissolved in 100g of water at 20 ° C, the solution is saturated. The solubility of calcium hydroxide at 20 ° C is 0.165g, which can also be written as 0.165g/100g of water.For another example, at 20 ° C, 36 grams of salt or 203.9 grams of sucrose must be dissolved in 100 grams of water to be saturated. The solubility of salt and sucrose at 20 ° C is 36 grams and 203.9 grams, respectively. It can also be written as 36 grams/100 grams of water and 203.9 grams/100 grams of water.[2]
2. The solubility of gas usually refers to the volume of the gas (its pressure is 1 standard atmospheric pressure) dissolved in 1 volume of solvent at a certain temperature."G/100g solvent" is also commonly used as the unit (volume can also be used naturally).
3. Special attention: the unit of solubility is g (or g/100g solvent) instead of no unit.
At a certain temperature andpressureThe highest amount of substance dissolved in a certain amount of solvent.It is generally expressed in grams of soluble substances in 100 grams of solvent.The solubility of a substance in a solvent mainly depends on the properties of the solvent and solute, that is, the solubility equilibrium constant of the solute in the solvent.For example,waterIt is the most common solvent. Methanol and ethanol can be miscible with water in any proportion.majorityAlkali metal saltsAre soluble in water;benzeneAlmost insoluble in water.
Solubility meter
The solubility is obviously affected by temperature, and the solubility of most solid substances increases with the increase of temperature;Gaseous substanceOn the contrary, the solubility of is decreased with the increase of temperature.The dependence of solubility on temperature can be expressed by solubility curve.The solubility of sodium chloride NaCl slowly increases with the increase of temperature, and potassium nitrate KNOthreeThe solubility oftwoSOfourHowever, the solubility decreases with the increase of temperature.
The solubility of solid and liquid is basically not affected by pressure, while the solubility of gas in liquid is proportional to the partial pressure of gas.The solubility of substances is very important for chemistry and chemical industryRecrystallizationAnd fractional crystallization, preparation and separation of chemical substancesmixed gas The difference in solubility of substances should be used in the separation process.
At a certain temperature, a substance reaches saturation state in 100g solvent (orDissolution equilibrium）Dissolved atGramsIt is called the solubility of this substance in this solvent.The maximum amount of a substance dissolved in a certain amount of solvent at a certain temperature and pressure is called the solubility of this substance in this solvent.Solubility means that one substance in anotherSolubility, usually usedSoluble、soluble 、Slightly soluble、InsolubleOr insoluble.Solubility is a measure of the solubility of a substance in a solvent and a quantitative expression of solubility.
The solubility is usually represented by the symbol S.The unit of solubility is g/100gHtwoO means.For example, at 20 ℃, 36 g NaCl can be dissolved at most in 100 g water, thensodium chlorideThe solubility at 20 ℃ is 36g/100gHtwoO. It can be expressed as S (NaCl)=36g/100gHtwoO。In fact, the solubility is the relative ratio without unit, according toLegal measurement unit, which can be expressed by mass fraction.For example, at 20 ℃, S (NaCl)=0.36.Solubility can also be usedSaturated solutionThe concentration of.For example, the solubility of potassium chloride at 20 ℃ is 4.627mol/1000gHtwoO (This concentration isMolar mass concentration）It means that 4.627mol potassium chloride can be dissolved at most in 1000g water at 20 ℃.The solubility of insoluble substances can also be usedAmount and concentration of substance(molar concentration).For example, at 25 ℃,Ferric hydroxideThe concentration of the substance is 0.45μMol/L, which means that 1L saturated ferric hydroxide solution contains 0.45μMol ferric hydroxide.The solubility of most solid substances increases with temperature, such asammonium chloride、potassium nitrate。The solubility of a few substances is little affected by temperature changes, such as sodium chloride.containCrystal waterSodium sulfate（Na₂SO₄·10H₂O）The solubility oftwoSOfour·10HtwoO dehydration to NatwoSOfour）。Containing crystal watercalcium hydroxide[Ca(OH)two·2HtwoO] AndCalcium acetate[Ca(CHthreeCOO)two·2HtwoO] The solubility of such substances decreases with the increase of temperature.The gas solubility decreases with the increase of temperature and increases with the increase of pressure.The factor affecting the solubility is temperature.
Different status
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Solid solubility
The energy capacity solubility of a solid substance refers to the mass of a substance dissolved when it reaches saturation in 100g solvent at a certain temperature, expressed with the letter S, and its unit is "g/100g water".In case of no indication, usually the solubility refers to the solubility of the substance in water.For example: at 20 ℃, 36g can be dissolved in 100g water at mostsodium chloride(At this time, the solution is saturated). At 20 ℃, the solubility of sodium chloride in water is 36g.
Gas solubility
At a certain temperature andpressureThe highest amount of gas dissolved in a certain amount of solvent is called gas solubility.It is usually expressed by the maximum volume dissolved in one volume of solvent at constant temperature.If 1.82mL hydrogen can be dissolved in 100mL water at 20 ℃, it means 1.82mL/100mL water, etc.The solubility of gas is not only related to the nature of gas and solvent, but also related to temperature and pressure. Its solubility generally decreases with the increase of temperature. Because the volume of gas changes greatly when it dissolves, its solubility increases significantly with the increase of pressure.As for the solubility of gas dissolved in liquid, in 1803, British chemist W. Henry summarized a law calledHenry's law。
example
The solubility of most solids increases with temperature, such aspotassium nitrate。
The solubility of a few solids is not affected by temperature, such as salt（sodium chloride）。
The solubility of a few substances decreases with the increase of temperature, such ascalcium hydroxide。Because there are two kinds of calcium hydroxidehydrate[Ca (OH) ₂ · 2H ₂ O and Ca (OH) ₂ · 12H ₂ O].The solubility of these two hydrates is relatively high, while that of anhydrous calcium hydroxide is very low.As the temperature increases, theseCrystalline hydrateIt gradually becomes anhydrous calcium hydroxide, so the solubility of calcium hydroxide decreases with the increase of temperature.In addition to calcium hydroxide, the solubility of other substances also decreases with the increase of temperature, such asLithium sulfate。
influence factor
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The solubility of carbon dioxide varies with temperature
Whether a substance is dissolved or not depends on the nature of the substance (solvent and solute);On the other hand, it is also related to external conditions such as temperature, pressure, solvent type, etc.Under the same conditions, some substances are easy to dissolve, while others are difficult to dissolve, that is, different substances are in the same solventSolubilityDifferent.The ability to dissolve one substance in another is usually called solubility.For example, sugar is easily soluble in water, while oil is insoluble in water, which means that they have different solubility in water.Solubility is a quantitative expression of solubility.
In case of no indication, usually the solubility refers to the solubility of the substance in water.For example, at 20 ℃, the solubility of salt is 36g,potassium chlorideThe solubility of is 34 g.These data can show that at 20 ℃, the maximum amount of salt and potassium chloride dissolved in 100 grams of water is 36 grams and 34 grams respectively;It also indicates that at this temperature, salt in water is more than potassium chlorideSolubilityStrong.
Generally, substances with a solubility of more than 10g/100g water at room temperature (20 ° C) are called soluble substances, substances with a solubility of 1~10g/100g water are called soluble substances, and substances with a solubility of 0.01~1g/100g water are calledSlightly solubleSubstance, the substance whose solubility is less than 0.01g/100g water is called insoluble substance.It can be seen that dissolution is absolute, while non dissolution is relative.
The solubility of gas is also related to pressure.pressureThe higher the solubility, the smaller the solubility.
When other conditions are constant, the higher the temperature, the lower the gas solubility.
In addition, the solubility is different from the dissolution rate.MixingoscillationThe dissolving speed of crushed particles increases, but the solubility cannot be increased.The solubility is also different from the dissolved mass. As the mass of solvent increases, the mass of soluble solute also increases, but the solubility will not change.
Dissolution equilibrium
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Dissolution forming karst cave
The maximum amount of solute that can be dissolved in each (usually each mass) solvent (sometimes solution) is the solubility of solute in this solvent.If the solvent is not specified, it usually means that the solvent is water. For example, "solubility of sodium chloride" and "solubility of sodium chloride in water" can be considered to have the same meaning.Solubility is not a constant value.The solubility of a solute in solvent is determined by itsIntermolecular force, temperature, the change of entropy accompanying the dissolution process, the existence and quantity of other substances, and sometimesGaseous soluteIs related to the partial pressure of.Therefore, the solubility of a substance can best be expressed as: "At a certain temperature and pressure, the solubility of a substance in a substance is xxxx." If not specified, the temperature and pressure usually refer toStandard status(STP)。
In fact, the solubility often depends on thein the waterDissolution ofequilibrium constant。This is one of the equilibrium constants, which reflects the dissolution precipitation equilibrium relationship of solutes. Of course, it can also be used in the precipitation process (at that time, it was calledSolubility product）。Therefore, solubility has a great relationship with temperature, which is not difficult to explain.The solution that reaches chemical equilibrium cannot contain moresolute(Of course, other solutes can still be dissolved), we call it saturated solution.Under special conditions, there will be more solutes dissolved in the solution than normal, and then it will becomeSupersaturated solution。The maximum amount of substance dissolved in a certain amount of solvent under a certain temperature and pressure.
The solubility of solid or liquid solute is usually expressed by the grams of solute dissolved in 100 grams of solvent.For example, at 20 ℃ and normal pressure, the solubility of potassium nitrate in water is 31.5g/100g water, or 31.5g for short.The solubility of gas solute is usually expressed by the number of milliliters of gas dissolved in each milliliter of solvent.For example, at 20 ℃ and normal pressure, the solubility of ammonia is 700ml/1ml water.In addition to the properties of solute and solvent, the solubility of substances is also related to temperature, pressure and other conditions.With the increase of temperature, the solubility of most solids and liquids increases, while that of gases decreases.With the increase of pressure, the solubility of gas increases.
Change principle
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The solubility of a gas depends first on the nature of the gas, and also changes with the pressure of the gas and the temperature of the solvent.For example, at 20 ℃, the pressure of gas is 1.013 × 10fivePa, one liter of water candissolved gas The volume of is:ammonia702L, 0.01819L for hydrogen,oxygen0.03102L.Ammonia is easily soluble in water because ammonia isPolar moleculeWater is also a polar molecule, and ammonia and water molecules can formhydrogen bond, significantHydrationTherefore, its solubility is very high;Hydrogen and oxygen are non-polar molecules, so their solubility in water is very small.
When the pressure is constant, the gas solubility decreases with the increase of temperature.This is no exception for gas, because when the temperature rises, the movement speed of gas molecules will accelerate and it is easy to escape from the water surface.
When the temperature is constant, the gas solubility increases with the increase of gas pressure.This is because when the pressure increases, the concentration of gas on the liquid surface increases. Therefore, there are more gas molecules entering the liquid surface than those escaping from the liquid surface, which makes the solubility of gas larger.Moreover, the solubility of the gas and the pressure of the gas（partial pressure）It is proportional in a certain range (when gas does not occur with waterChemical change).For example, at 20 ℃, the pressure of hydrogen is 1.013 × 10fivePa, the solubility of hydrogen in one liter of water is 0.01819L;Also at 20 ℃, at 2 × 1.013 × 10fiveAt Pa, the solubility of hydrogen in one liter of water is 0.01819 × 2=0.03638L.
There are two ways to express the solubility of gaspressure(or the partial pressure of the gas, excluding the pressure of water vapor) is 1.013 × 10fivePa, it is dissolved in a volume of water to reach the volume of saturated gas (and needs to be converted to the volume number at 0 ℃), that is, the solubility of this gas in water.Another way to express the solubility of the gas is that at a certain temperature, the total pressure of the gas in 100g water is 1.013 × 10fivePa (partial pressure of gas plus pressure of water vapor at that time).
In summer, when the soda bottle cap is opened, the pressure decreases, the gas solubility decreases, and a large amount of gas will gush out.
After drinking soda, you will belch because the temperature of soda will rise and the solubility of gas will decrease after it reaches the stomach.
Solubility curve
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Solubility curveIts significance and application can be analyzed from four aspects: point, line, surface and intersection.
Solubility curve
onespot
Each point on the solubility curve represents the solubility of a substance at a certain temperature.That is, any point on the curve has corresponding temperature and solubility.Temperature atAbscissaIt can be found atOrdinateCan be found on the.The points on the solubility curve have three functions: (1) find out the solubility of related substances according to the known temperature;(2) Find out the corresponding temperature according to the solubility of the substance;(3) Compare the solubility of different substances or the mass fraction of solute in saturated solution at the same temperature.
twoLine
The solubility curve shows the solubility of a substance at different temperatures or the solubility changes with temperature.The greater the slope of the curve, the greater the influence of temperature on solubility;On the contrary, it indicates that the temperature is less affected.The solubility curve also has three applications: (1) According to the solubility curve, it can be seen that the solubility of substances changes with temperature.(2) According to the solubility curve, compare the solubility of substances within a certain temperature range.(3) According to the solubility curve, select the method of separating some soluble mixtures.
threenoodles
sodium chloride
For any point on the lower area of the curve, the solution prepared according to its data is the unsaturated solution at the corresponding temperature;At the point on the upper area of the curve, the solution prepared according to its data is the saturated solution at the corresponding temperature, and there is residual solute.If you want to makeUnsaturated solution(a point at the lower part of the curve) into a saturated solution at the corresponding temperature in two ways: the first way is to add solute to the solution to make it reach the curve;The second method is to evaporate a certain amount of solvent.
fourintersection
The intersection point of the two solubility curves indicates that the solubility of the two substances is the same at the temperature shown at this pointMass fraction of soluteSame.
(Extremely soluble in water) (Easily soluble in water) (Soluble in water) (Difficult) (Extremely difficult)
features
Dissolution curve
(1) The solubility curve of most solid substances is low on the left and high on the right, and the solubility increases with the increase of temperature;
(2) The solubility curve of a few solid substances is relatively flat, and the solubility is less affected by temperature, such as salt;
(3) The solubility curve of a few solid substances is high on the left and low on the right. The solubility decreases with the increase of temperature, such asHydrated lime；
It is qualitative and rough to use solubility to express the solubility of substances.
application
(1) Check the solubility of a substance according to the known temperature;
(2) Check the temperature of the substance according to its solubility;
(3) Compare the solubility of different substances at the same temperature;Compare the solubility of the same substance at different temperatures.
(4) Compare and determine the extent to which the solubility of the substance is affected by temperature, and design the method for separation or purification of the mixture according to it. For example, the evaporation solvent method can be used to purify NaCl, and the separation of NaCl and NaNO can be usedCooling crystallizationLaw.
(5) It can judge the mass ratio of solute, solvent and solution in the saturated solution of a substance at a certain temperature.
(6) Judge whether the solution formed by dissolving a certain amount of solute in a certain amount of solvent at a certain temperature is saturated solution.
(7) The solubility of the substance is determined according to its solubility at 20 ℃.
(8) Determine the state of the solution (saturated and unsaturated).
Mass fraction type
solubility
It generally includes the following four types:
(1) Given the amount of solute and solvent, calculate the mass fraction of solute;
(2) To prepare a solution with a certain amount of solute and a certain mass fraction, calculate the amount of solute and solvent required;
(3) Calculation of solution dilution and preparation problems;
(4) Apply the mass fraction of solute toChemical equationCalculation of.
Calculation method of solute mass fraction:
Mass fraction of solute=(solute mass/solution mass) * 100%=[solute mass/(solute mass+solvent mass)] * 100%
Example 10 g sodium chloride is dissolved in 90 g water, then the mass fraction of solute in the obtained sodium chloride solution=10/100=10%
Dilution of solution
Calculate according to the total amount of solute before and after dilution, whether it is diluted with water or dilute solutionConcentrated solution, can be calculated.
(1) Dilute the concentrated solution with water
Suppose the mass of the concentrated solution before dilution is m, the mass fraction of the solute is a%, the mass of the added water during dilution is n, and the mass fraction of the solute after dilution is b%.
Then m × a%=(m+n) × b%
(2) Dilute the concentrated solution with dilute solution
Assume that the mass fraction of the concentrated solution is A, the mass fraction of the solute is a%, the mass fraction of the dilute solution is B, the mass fraction of the solute is b%, and the mass fraction of the solute after the two solutions are mixed is c%.
Then A × a%+B × b%=(A+B) × c% (1)
Or A/B=(c% - b%)/(a% - c%) (2)
calculation
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Mass fraction of solute=solute mass/solution mass × 100%
One of solid solubility
At a certain temperature, the grams of a solid substance dissolved when it reaches saturation in 100g solvent are called the solubility of this substance in this solvent.Symbol: S
Solid solubility 2
potassium nitrate
The amount of solid solute contained in a certain amount of saturated solution at a certain temperature is called the solubility of the solid substance at a specified temperature.Generally, the solubility of a substance in 100g solvent is expressed by the grams dissolved when the substance reaches saturation in 100g solvent at a certain temperature. For example, at 20 ℃, 35.8g sodium chloride can be dissolved in 100g water at most, that is, the solubility of sodium chloride at this temperature is 35.8g/100g water.
The solubility of solid matter is related to the nature of solute and solvent. Generally, when the structure of solute is similar to that of solvent, it is easier to dissolve, which is calledPrinciple of similarity compatibility, which can explain some facts.The solubility of most solid substances increases with the increase of temperature. Temperature has different effects on different substances. The solubility curve can be made according to the relationship between the solubility of substances and temperature. The solubility of a substance at any temperature can be found by using the solubility curve, and some substances can also be purified and separated by using the solubility curve.The solubility of solid matter is less affected by pressure.
