Solvent molecules can surround solute molecules, to make one phase {solution, chemistry}|. Liquid solutions are transparent, because they are one phase with no surfaces for light reflection. To find solution substance concentration, divide substance moles by volume in liters of solution, not just solvent.
Membrane allows solvent molecules to pass but not solute molecules. If membrane separates solution from another solution, solvent passes into solution with higher solute concentration, because more solvent molecules hit membrane on side with less solute and pass through to other side {osmosis}|.
For example, solvent can be water, with many solute molecules inside membrane bag. See Figure 1.
pressure
Osmosis increases solvent amount on membrane side with higher solute concentration, causing extra pressure on that membrane side. The osmotic pressure resists further osmosis, because number of solvent molecules hitting both membrane sides becomes equal.
For example, water passes into bag, making bag bigger and stretching it. Membrane is under pressure. The extra water inside causes higher pressure inside, meaning more water molecules hit membrane inside. See Figure 2.
chemical potential
Mixtures have higher chemical potential than pure liquids, so pure liquid goes from pure-liquid membrane side to mixture membrane side, raises liquid level on mixture side, and lowers chemical potential. Chemical-potential decrease generates osmotic pressure, which tries to bring system into equilibrium.
small solutes
Membrane can allow small solute molecules and ions to pass through, but not large solute molecules. Small molecules diffuse through membrane, tending to make small-solute molecule concentrations equal on both membrane sides.
Osmosis increases solvent amount on membrane side with higher concentration, causing extra pressure {osmotic pressure}| on membrane from that side. The extra pressure resists further osmosis, as number of solvent molecules hitting both sides becomes same.
Solvents can have electronegative atoms {polarity}|.
types
Polar solvents include water, ethyl alcohol, and methyl alcohol. Acetone is slightly polar. Benzene is non-polar.
solution
Like dissolves like. Polar solvents can dissolve in each other. Non-polar solvents can dissolve in each other. Sticky non-polar solids are harder to dissolve in non-polar solvents, because they do not break up. Acetone, methyl alcohol, ethyl ether, and ethyl alcohol are soluble in water. Benzene, carbon tetrachloride, chloroform, hexane, cyclohexane, methylene chloride, toluene, and xylene are insoluble in water.
Solid can dissolve in water to make ion solutes {electrolyte}|.
Two liquids {immiscible liquids}| can be unable to dissolve in each other, like benzene and water.
Two liquids {miscible liquids}| can dissolve in each other, like alcohol and water.
Material true concentration or partial pressure {partial molar quantity} depends on other-substance concentrations or partial pressures, because having different substances contributes more disorder to system. Substances interact, because system has total pressure, temperature, and concentration.
Material true concentration or partial pressure {chemical potential, solution}| {free energy per mole} depends on partial molar quantity, because having different substances contributes more disorder to system. Substances interact, because system has total pressure, temperature, and concentration that distribute among substances. Substance partial molar Gibbs free energy is partial derivative of free energy with substance moles, if temperature, pressure, and other-substance amounts are constant.
Gas solubility in liquid is proportional to partial pressure of gas in contact with liquid {Henry's law} {Henry law}.
Gases in mixtures independently contribute pressure {partial pressure} to total gas pressure {law of partial pressures}.
Solute-vapor partial pressure above solution equals solute mole fraction times pure-solute vapor pressure {Raoult's law} {Raoult law}.
Pure substances have molar quantities, but mixtures have partial molar quantities, which depend on material moles divided by total moles, the mole fraction. Solution properties {colligative property}|, such as partial pressures, boiling point elevation, freezing point depression, osmotic pressure, solubility, volatility, and surface tension, can depend on solute mole fraction. Partial molar quantities are interdependent, because mole fraction total must be one.
Solutions have higher boiling point than pure solvent {boiling point elevation}|, because solute molecules are heavier than solvent molecules and have lower volatility. If liquid includes impurities that are less volatile than liquid, liquid boils only at higher temperature. Salt in water raises boiling temperature. Mixture boiling point is higher, because mixtures are more random, so difference between liquid and gas is less. Immiscible substances lower boiling point, because both vapor pressures add to increase pressure. In boiling-point elevation, temperature change dT equals constant k times molality M: dT = K*M. People know constants for solutes and solvents.
Solutions have lower freezing point than pure solvent {freezing point depression}|, because solute molecules are impurities in solvent crystals and so make crystals harder to form. In freezing-point depression, temperature change dT equals constant k times molality M: dT = K*M. People know constants for solutes and solvents.
Solid solute molecules can crystallize and separate from liquid solvent molecules {precipitation from solution}|.
causes
Decreasing solubility causes precipitation. Solubility decreases by cooling. Solubility decreases by adding organic non-polar solvents, such as acetone and ethanol, to water solution.
polarity
Solubility decreases by neutralizing solution to reduce acidity and polarity. Adding concentrated ammonium sulfate usually causes precipitation from aqueous solution. Molecules precipitate best at isoelectric points, because they have least polarization there.
types
Precipitates {lyophobic}, like sulfur and metal salts, can be small pellet-like precipitates, with molecules that reject water and adsorb ions. Precipitates {lyophilic}, like starch and gelatin, can be large curd-like precipitates, with molecules that adsorb water.
Crystals can precipitate from solution {fractional crystallization}, by evaporating solvent, by cooling solution, or by adding another solvent to solution.
At temperature, a number of solute grams can dissolve in 100 milliliters of solvent {solubility}|. If solubility is greater than one percent, solute can dissolve well in solvent {soluble}.
water solubility
Compounds have solubility in water {aqueous solubility}. Nitrates, acetates, chlorides, bromides, most iodides, most sulfates, sodium salts, potassium salts, and ammonium salts are soluble in water.
Hydroxides except sodium hydroxide and potassium hydroxide; sulfides except sodium sulfide, magnesium sulfide, and aluminum sulfide; arsenates except sodium arsenate and potassium arsenate; carbonates except sodium carbonate and potassium carbonate; and phosphates except sodium phosphate and potassium phosphate are insoluble in water.
precipitation
Solubility is maximum concentration before precipitation from solvent. For precipitation, concentration product {solubility product} must be greater than equilibrium constant.
factors
Solute solubility in solvent depends on solute polarity, size, and surroundableness and solvent polarity, size, and surroundability.
factors: temperature
Higher temperature increases solubility, because increased random motion breaks up and mixes solute and solvent more.
factors: concentration
Low concentration increases solubility, because solvent molecules can better surround solute molecules, with less solute molecules near other solute molecules.
factors: stirring
Stirring increases solubility, because more motion mixes solute and solvent more.
factors: ions
More hydrogen ion increases solubility in polar solvent, by increasing polarity. More ions increase solubility in polar solvent, by increasing polarity.
Ionic solutes with large ions and large charges are harder to dissolve. Ionic solutes with small ions and charges of +1 or -1 are easier to dissolve. Large ions with charge +1 or -1 dissolve better than small ions with charge +2, -2, +3, -3, or greater. Salts with small volume, especially hydrogen ions and acids, increase solubility by allowing more shielding. Higher-charge salts increase solubility more, because they shield better. Salts that form metal-ion complexes increase solubility, by more shielding.
factors: common ion
Low concentration of ion common to two solutes increases solubility, because solvent molecules can better surround solute molecules, with less solute molecules near other solute molecules. Common ion provides more molecules for collision. Solubility decreases if common ion is present in large amounts, because the other ion must then be at low concentration to equal solubility product.
factors: diverse ion
Solubility increases if diverse ion is present, because charges have more shielding and polarity increases.
factors: polarity
Similar-polarity molecules dissolve each other best, because electrical attractions for similar molecules are stronger.
factors: size
Small molecules dissolve better, because solvent molecules can better surround solute molecules.
factors: shape
Spherical molecules dissolve better than elongated ones, because solvent molecules can better surround spherical molecules.
When water molecules surround ions, energy {energy of hydration} {hydration energy}| releases. Small atoms have more hydration than large ones, because water surrounds them better.
Solvent molecules can surround other-substance {solute} molecules.
Solubility can decrease by adding salt with common ion and higher solubility, to make higher concentration and force solute out of solution {common ion effect}.
Ions in solution increase polarity and increase solubility {Debye-Hückel law}.
Substance {solvent, chemistry}| molecules can surround solute molecules.
Solvent is usually water {aqueous solution}.
Solvent can be alcohol {tincture}|.
Solid can dissolve in another solid {alloy}|, as in steel, bronze, and brass. Steel is carbon in iron. Bronze is tin in copper. Brass is zinc in copper.
Liquid can dissolve solid {amalgam}|, as metals can dissolve in mercury.
Solutions have ratio {concentration}| of solute mass or volume to total solution or solvent mass or volume.
Concentration {molal} can measure number of solute moles dissolved in one solution kilogram.
Concentration {molar, concentration} (M) can measure number of solute moles dissolved in one solution liter.
Concentration {mole fraction} can measure number of solute moles dissolved in one solution mole.
Concentration {normal, concentration} (N) can measure number of solute-ion equivalents dissolved in one solution liter.
Concentration {parts per million} (ppm) can measure number of solute milligrams dissolved in one solution liter.
Concentration {percent solution} can measure number of solute grams or milliliters dissolved in 100 solution grams or milliliters.
Solutions {dilute solution}| can have low concentration.
Solutions {concentrated solution} can have high concentration.
Solutions {saturated solution}| can have maximum concentration, at temperature, if dissolved solute is in contact with solid solute.
At a temperature, if no solid is present and solution has no crystallization, solution can have concentration higher than saturated concentration {supersaturated}|.
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Date Modified: 2022.0225