Water Solubility Effect
If we examine the solubility effects of water, the polarity of the water molecule plays an important role in the dissolution of ionic compounds during the formation of aqueous solutions. The world's oceans contain a large amount of dissolved salts, which provides a large natural resource. In addition, all of the hundreds of chemical reactions that occur every moment to keep living things alive occur in aqueous liquids. Although the solubility of substances in water is an extremely complex process, the interaction between the polar water molecules and the solute (i.e. the solute) plays an important role. When an ionic solid dissolves in water, the positive ends of the water molecules are attracted to anions and the negative ends to cations. This process is called hydration. The hydration of its ions tends to cause a salt to disintegrate (dissolve) in water. During the dissolution process, the strong forces that exist between the positive and negative ions of the solid are replaced by strong water-ion interactions. When ionic substances dissolve in water, they separate into separate cations and anions. For example, when sodium chloride (NaCl) dissolves in water, the resulting solution contains separated Na+ and Cl− ions. The formula representing sodium chloride (NaCl) dissolved in water, the resulting solution contains separated positive Na and Cl ions. Generally speaking, the greater the charge density (charge to surface area ratio) of an ion, the greater its hydration number will be. As a rule, negative ions have smaller hydration numbers than positive ions due to the greater crowding that occurs when the hydrogen atoms of the water molecules are oriented toward the anion. Of course, this does not mean that only ionic substances are soluble in water. For example, ethyl alcohol is also highly soluble in water. The reason for this is not ionicity, but the fact that ethanol contains a polar O―H bond similar to the structure in water, which allows it to interact effectively with water.
We can summarize the part about solubility with the principle that every chemist knows: “like dissolves like.”
The ability of water to act as a polar solvent (dissolving medium) changes when water is exposed to high temperatures and pressures. As water gets hotter, the molecules seem to be much more likely to interact with nonpolar molecules. For example, at 300 °C (572 °F) and high pressure, water has very similar solvating properties to acetone (CH3COCH3), a common organic solvent. Water exhibits particularly unusual behavior beyond its critical temperature and pressure (374 °C [705.2 °F], 218 atmospheres). Above its critical temperature, the distinction between the liquid and gas phases of water disappears—it becomes a supercritical fluid whose density can be changed from liquid-like to gaseous by changing its temperature and pressure. If the density of supercritical water is high enough, ionic solutes dissolve readily, as is true for "normal" water; however, surprisingly, this supercritical fluid can also dissolve nonpolar substances—something ordinary water cannot.
One of the most important chemical properties of water is its ability to act as both an acid (proton donor) and a base (proton acceptor), a characteristic feature of amphoteric substances. This behavior is most clearly seen in the autoionization of water.
The concentration of hydrated H+ in water at 25 °C (77 °F), i.e., the hydronium ion
is 1.0 × 10−7 M, where M represents moles per liter. Since one hydroxide ion is produced for every hydronium ion, the hydroxide concentration at 25 °C is also
It is 1.0 × 10−7 M.
The H3O+ (Hydronium) concentration and the OH− (hydroxide) concentration in water at 25 °C must always be in the following equation.
[H+][OH−] = 1.0 × 10−14
Here [H+] represents the concentration of hydrated H+ ions in moles per liter and [OH-] represents the concentration of OH- ions in moles per liter.
When an acid (a substance that can produce H+ ions) is dissolved in water, both the acid and the water add H+ ions to the solution. This results in a situation where the H+ concentration is greater than 1.0 × 10−7 M. Since the above equation must be satisfied at 25 °C;
[OH−] = 1.0 × 10−7
It should be lowered.
Therefore, when an acid is added to water, the resulting solution contains more H+ than OH-, i.e. [H+] > [OH-]. Such a solution is said to be acidic.
The most common method of determining the acidity of a solution is the pH value, which is defined in terms of hydrogen ion concentration:
pH = -log [H+]
In pure water, where [H+] = 1.0 × 10−7 M, pH = 7.0.
For an acidic solution the pH is less than 7.
When a base (a substance that acts as a proton acceptor) is dissolved in water, the H+ concentration decreases such that [OH−] > [H+].
A basic solution is characterized by having a pH > 7.
In aqueous solutions at 25 °C:
Neutral solution
[H+] = [OH−]
pH = 7
Acidic solution
[H+] > [OH−]
pH < 7
Basic solution
[OH−] > [H+]
pH>7
It is summarized as follows.
Although the subject is complicated by non-chemists, the new generation of coffee makers and coffee lovers who try to fully get into the business will catch the subject somewhere. We think that we have talked enough about the chemistry of water for coffee, but we have also started by conveying the chemical equations of the pH part, which is a vital parameter for the quality and suitability of water. Although these equations seem complicated, they are important in order to convey the basis of the subject. Here, we have examined the chemical definition of the pH subject, but all the parameters used to achieve the desired quality in coffee brewing water will be the subject of the third level title of water quality in coffee 😊
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