salt

Examples of salt in the following topics:

• Salts that Produce Basic Solutions

  • When dissolved in water, a basic salt yields a solution with pH greater than 7.0.
  • There are several varieties of salts, and in this section we will consider basic salts.
  • What makes a basic salt basic?
  • It is due to the fact that the anion in the salt is the conjugate base of a weak acid.
  • An example of a basic salt is sodium bicarbonate, NaHCO3.

• Salts that Produce Acidic Solutions

  • When dissolved in water, acidic salts form solutions with pH less than 7.0.
  • Salts with acidic protons in the cation are most commonly ammonium salts, or organic compounds that contain a protonated amine group.
  • Acid salts can also contain an acidic proton in the anion.
  • From the previous concept, we know that salts containing the bicarbonate ion (HCO3-) are basic, whereas salts containing bisulfate ion (HSO4-) are acidic.
  • Anilinium chloride is an example of an acid salt.

• Extremely Halophilic Archaea

  • One example is Chromohalobacter beijerinckii, found in salted beans preserved in brine and in salted herring.
  • Tetragenococcus halophilus is found in salted anchovies and soy sauce.
  • The extremely halophilic Haloarchaea require at least a 2 M salt concentration and are usually found in saturated solutions (about 36% w/v salts).
  • Halophiles are adapted to conditions of extreme salt concentration, such as the Great Salt Lake in Utah.
  • Salt builds up along the Dead Sea.

• Overview of the Acid-Base Properties of Salt

  • Acid salts are the converse of basic salts; they are formed in the neutralization reaction between a strong acid and a weak base.
  • The conjugate acid of the weak base makes the salt acidic.
  • The ammonium ion contains a hydrolyzable proton, which makes it an acid salt.
  • A good example of such a salt is ammonium bicarbonate, NH4HCO3; like all ammonium salts, it is highly soluble, and its dissociation reaction in water is as follows:
  • This video examines the hydrolysis of an acid salt, a basic salt, and a salt in which both ions hydrolyze.

• Salt Formation

  • Because of their enhanced acidity, carboxylic acids react with bases to form ionic salts, as shown in the following equations.
  • In the case of alkali metal hydroxides and simple amines (or ammonia) the resulting salts have pronounced ionic character and are usually soluble in water.
  • Heavy metals such as silver, mercury and lead form salts having more covalent character (3rd example), and the water solubility is reduced, especially for acids composed of four or more carbon atoms.
  • Carboxylic acids and salts having alkyl chains longer than six carbons exhibit unusual behavior in water due to the presence of both hydrophilic (CO2) and hydrophobic (alkyl) regions in the same molecule.

• Estuaries: Where the Ocean Meets Fresh Water

  • Estuaries, composed of a mix of fresh and salt water and their living communities, are influenced by salinity and the changing tides.
  • Therefore, both fresh water and salt water are found in the same vicinity.
  • Once or twice a day, high tides bring salt water into the estuary.
  • Low tides, occurring at the same frequency, reverse the current of salt water .
  • In some halophytes, filters in the roots remove the salt from the water that the plant absorbs.

• Precipitation Reactions

  • Precipitation reactions transform ions into an insoluble salt in aqueous solution.
  • Precipitation refers to a chemical reaction that occurs in aqueous solution when two ions bond together to form an insoluble salt, which is known as the precipitate.
  • A precipitation reaction can occur when two solutions containing different salts are mixed, and a cation/anion pair in the resulting combined solution forms an insoluble salt; this salt then precipitates out of solution.
  • For instance, if silver nitrate is added to a solution of an unknown salt and a precipitate is observed, the unknown solution might contain chloride (Cl-).
  • To determine the solubility of an given salt, find the cationic component along the left-hand side, match it to the anionic component along the top, then check to see if it is S - soluble, I - insoluble, or sS - slightly soluble.

• Bile

  • Bile is a composition of the following materials: water (85%), bile salts (10%), mucus and pigments (3%), fats (1%), inorganic salts (0.7%), and cholesterol (0.3%).
  • The bile salts are ionically charged, with a hydrophobic end and a hydrophillic end.
  • When exposed to water mixed with fat, like in the small intestine, the bile salts congregate around a fat droplet, with their hydrophobic side pointing towards the fat and their hydrophillic side pointing towards the water .
  • Bile salts also act as bactericides, destroying many of the microbes that may be present in the food.
  • Bile salts congregate around fat, separating them into small droplets called micelles.

• Nucleophilicity of Sulfur Compounds

  • Sulfides, for example, react with alkyl halides to give ternary sulfonium salts (equation # 1) in the same manner that 3º-amines are alkylated to quaternary ammonium salts.
  • Although equivalent oxonium salts of ethers are known, they are only prepared under extreme conditions, and are exceptionally reactive.
  • Remarkably, sulfoxides (equation # 2), sulfinate salts (# 3) and sulfite anion (# 4) also alkylate on sulfur, despite the partial negative formal charge on oxygen and partial positive charge on sulfur.

• Nucleophilicity of Phosphorus Compounds

  • The nucleophilicity of trivalent phosphorus results in rapid formation of phosphonium salts when such compounds are treated with reactive alkyl halides.
  • For example, although resonance delocalization of the nitrogen electron pair in triphenylamine, (C6H5)3N, renders it relatively unreactive in SN2 reactions, the corresponding phosphorus compound, triphenylphosphine, undergoes a rapid and exothermic reaction to give a phosphonium salt, as shown below in the first equation.
  • Phosphite esters react in the same manner, but the resulting phosphonium salts (shaded box) are often unstable, and on heating yield dialkyl phosphonate esters by way of a second SN2 reaction (equation 2 below).