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From Wikipedia

Solubility equilibrium

Solubility equilibrium is a type of dynamic equilibrium. It exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound. The solid may dissolve unchanged, with dissociation or with chemical reaction with another constituent of the solvent, such as acid or alkali. Each type of equilibrium is characterized by a temperature-dependent equilibrium constant. Solubility equilibria are important in pharmaceutical, environmental and many other scenarios.


A solubility equilibrium exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound. The equilibrium is an example of dynamic equilibrium in that some individual molecules migrate between the solid and solution phases such that the rates of dissolution and precipitation are equal to one another. When equilibrium is established, the solution is said to be saturated. The concentration of the solute in a saturated solution is known as the solubility. Units of solubility may be molar (mol dm−3) or expressed as mass per unit volume, such as μg ml−1. Solubility is temperature dependent. A solution containing a higher concentration of solute than the solubility is said to be supersaturated. A supersaturated solution may be induced to come to equilibrium by the addition of a "seed" which may be a tiny crystal of the solute, or a tiny solid particle, which initiates precipitation.

There are three main types of solubility equilibria.

  1. Simple dissolution.
  2. Dissolution with dissociation. This is characteristic of salts. The equilibrium constant is known in this case as a solubility product.
  3. Dissolution with reaction. This is characteristic of the dissolution of weak acids or weak bases in aqueous media of varying pH.

In each case an equilibrium constant can be specified as a quotient of activities. This equilibrium constant is dimensionless as activity is a dimensionless quantity. However, use of activities is very inconvenient, so the equilibrium constant is usually divided by the quotient of activity coefficients, to become a quotient of concentrations. See equilibrium chemistry#Equilibrium constant for details. Moreover, the concentration of solvent is usually taken to be constant and so is also subsumed into the equilibrium constant. For these reasons, the constant for a solubility equilibrium has dimensions related to the scale on which concentrations are measured. Solubility constants defined in terms of concentrations are not only temperature dependent, but also may depend on solvent composition when the solvent contains also species other than those derived from the solute.

Phase effect

Equilibria are defined for specific crystal phases. Therefore, the solubility product is expected to be different depending on the phase of the solid. For example, aragonite and calcite will have different solubility products even though they have both the same chemical identity (calcium carbonate). Nevertheless, under given conditions, most likely only one phase is thermodynamically stable and therefore this phase enters a true equilibrium.

Particle size effect

The thermodynamic solubility constant is defined for large monocrystals. Solubility will increase with decreasing size of solute particle (or droplet) because of the additional surface energy. This effect is generally small unless particles become very small, typically smaller than 1 μm. The effect of the particle size on solubility constant can be quantified as follows:

\log(^*K_{A}) = \log(^*K_{A \to 0}) + \frac{\gamma A_m} {3.454RT}

where ^*K_{A} is the solubility constant for the solute particles with the molar surface area A, ^*K_{A \to 0} is the solubility constant for substance with molar surface area tending to zero (i.e., when the particles are large), γ is the surface tension of the solute particle in the solvent, Am is the molar surface area of the solute (in m2/mol), R is the universal gas constant, and T is the absolute temperature.

Salt effect

The salt effect refers to the fact that the presence of a salt which has no ion in common with the solute, has an effect on the ionic strength of the solution and hence on activity coefficients, so that the equilibrium constant, expressed as a concentration quotient, changes.

Temperature effect

Solubility is sensitive to changes in temperature. For example, sugar is more soluble in hot water than cool water. It occurs because solubility constants, like other types of equilibrium constant, are functions of temperature. In accordance with Le Chatelier's Principle, when the dissolution process is endothermic (heat is absorbed), solubility increases with rising temperature, but when the process is exothermic (heat is released) solubility decreases with rising temperature. The temperature effect is the basis for the process of recrystallization, which can be used to purify a chemical compound.

From Yahoo Answers

Question:I want to know the solubility of the following organic substances, with comparing. Alkane, alkene, alkanol, alkanoic acid, ester, alkanal I heard that the solubility decrease when their carbon chain lengthen. How many C is maximum to be soluble in water? Also, is ester soluble in organic solvent? thanks for answering this long question xd

Answers:carboxylic (alkanoic) acid > aldehyde (alkanal) > alcohol (alkanol) >> Ester >> alkene > alkane butanoic acid is fully miscible in water, while n-butanol is soluble to the extent of 9 mL/100 mL water. Esters are soluble in organic solvents.

Question:solubility in water/ solubility in oil /solubility in alcohol Magnesium Sulfate Naphthalene Salicylic Acid Sugar Can you please answer this question by saying yes or no ?

Answers:Can you please answer this question by saying yes or no ? No, because it is not a yes or no question. Magnesium Sulfate is soluble in water. Like are inorganic ionic compounds, it is not very soluble in alcohol, and in just about insoluble in oil. Naphthalene. Is very soluble in oil, not very soluble in alcohol, and insoluble in water. Salicylic Acid is soluble in alcohol, sparingly soluble in water, and somewhat soluble in oil. Sugar, is most soluble in alcohol, somewhat soluble in water, and slightly soluble in oil.

Question:Which of the following substances is a nonpolar molecule that is not soluble in water? A. Starch B. Lipid C. DNA D. Glucose E. Protein

Answers:Lipids, such as oil, are non polar and as we know they don't mix with water. Proteins may or may not dissolve in water depending on their nature, globular dissolve but fibrous do not.

Question:1. Is nitric acid (HNO3) soluble in water? 2. Is nitric acid (HNO3) soluble in ethanol? 3. Is nitric acid (HNO3) soluble in oil? 4. Is methane (CH4) soluble in water? 5. Is methane (CH4) soluble in ethanol? 6. Is methane (CH4) soluble in oil? 7. Is Sodium hydrogen carbonate (NaHCO3) soluble in water? 8. Is Sodium hydrogen carbonate (NaHCO3) soluble in ethanol? 9. Is Sodium hydrogen carbonate (NaHCO3) soluble in oil? 10. Is ammonia gas (NH3) soluble in water? 11. Is ammonia gas (NH3) soluble in ethanol? 12. Is ammonia gas (NH3) soluble in oil?

Answers:Everything is soluble in everything, the question is, how soluble is it? But that's probably next semester. For now... I don't know what exactly they're defining soluble as, but I generally go by the rule "like dissolves like." If the substance is polar, it will dissolve in polar substances, and wont dissolve in non polar substances. (Think oil and water.) Water, which contains an extremely electronegative Oxygen, and hydrogen atoms with a relatively low electronegativity, is polar. Oil, which contains mostly C-H bonds, is non polar. Ethanol, is also polar. Now just figure out the polarity of the other molecules. Do they contain a very electronegative atom next to one with a relatively low electronegativity? It is polar. Does it contain atoms that aren't extremely electronegative? It is non polar. If you have two non polar or two polar substances, they will be soluble. Remember that Florine is the most electronegative element, and the elements right next to it on the periodic table are very electronegative. (Except for the noble gasses!!)

From Youtube

Solubility RULES!!! | Learn the Rules of Solubility with MC Hammer :We did this as a fun way to learn the rules of solubility. Sing the rules with us, you'll regret having us stuck in your head, but you'll be thanking us when you remember Solubility RULES!!! Lyrics: Dissolve this Dissolve this Dissolve this Ni ni ni ni nitrate and acetate Perchlorate and even chlorate Always are soluble No exceptions to that rule What else? theres ammonium Plus the el-ments in group 1 plus charge. And such There are salts that water cant touch Carbonate, chromate Oxalate and phosphate Remember sulfides Dont forget hydroxides. (while its rollin) Hold on! But some salts are soluble Like that: Like that: But with metals, its too much These are salts and metals, uh, you cant touch Dissolve this Dissolve this Dissolve this Learn the Rules of Solubility with MC Hammer or you can do it the fun way and read Wikipedia... en.wikipedia.org - Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution. The solubility of a substance strongly depends on the used solvent as well as on temperature and pressure. The pressure also affects the solution whether it is gas or liquid, like temperature. So, in definition of solubility we always mention the pressure and temperature "fixed". The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration where adding more solute does not increase the concentration of the solution ...