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SALT

                                 SALT                                

In chemistry, salts are ionic compounds that can result from the neutralization reaction of an acid and a base. They are composed of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge). These component ions can be inorganic such as chloride (Cl^−), as well as organic such as acetate (CH₃COO^−) and monatomic ions such as fluoride (F^−), as well as polyatomic ions such as sulfate (SO₄^2−).
There are several varieties of salts. Salts that hydrolyze to produce hydroxide ions when dissolved in water are basic saltsand salts that hydrolyze to producehydronium ions in water are acid salts. Neutral salts are those that are neither acid nor basic salts.Zwitterions contain an anionic center and a cationic center in the same molecule but are not considered to be salts. Examples include amino acids, many metabolites, peptides and proteins.
Molten salts and solutions containing dissolved salts (e.g. sodium chloride in water) are called electrolytes, as they are able to conduct electricity. As observed in the cytoplasm of cells, in blood, urine, plant saps and mineral waters, mixtures of many different ions in solution usually do not form defined salts after evaporation of the water. Therefore, their salt content is given for the respective ions.

Properties                                                                

Color

Potassium dichromate, a bright orange salt used as a pigment

Salts can appear to be clear and transparent (sodium chloride), opaque, and even metallic and lustrous (iron disulfide). In many cases the apparent opacity or transparency are only related to the difference in size of the individual monocrystals. Since light reflects from the grain boundaries (boundaries between crystallites), larger crystals tend to be transparent, while polycrystalline aggregates look like white powders.
Salts exist in many different colors, for example:

• yellow (sodium chromate)
• orange (potassium dichromate)
• red (potassium ferricyanide)
• mauve (cobalt chloride hexahydrate)
• blue (copper sulfate pentahydrate, ferric hexacyanoferrate)
• purple (potassium permanganate)
• green (nickel chloride hexahydrate)
• colorless (sodium chloride, magnesium sulfate heptahydrate)—may appear white when powdered or in small pieces

Most minerals and inorganic pigments as well as many synthetic organic dyes are salts. The color of the specific salt is due to the presence of unpaired electrons in the d-orbital of transition elements.

Taste

Different salts can elicit all five basic tastes, e.g., salty (sodium chloride), sweet (lead diacetate, which will cause lead poisoning if ingested), sour (potassium bitartrate), bitter (magnesium sulfate), and umami or savory (monosodium glutamate).

Odor

Salts of strong acids and strong bases ("strong salts") are non-volatile and odorless, whereas salts of either weak acids or weak bases ("weak salts") may smell after the conjugate acid (e.g., acetates like acetic acid (vinegar) and cyanides like hydrogen cyanide (almonds)) or the conjugate base (e.g., ammonium salts like ammonia) of the component ions. That slow, partial decomposition is usually accelerated by the presence of water, since hydrolysis is the other half of the reversible reaction equation of formation of weak salts.

Solubility

See also: Solubility#Solubility of ionic compounds in water

Many ionic compounds can be dissolved in water or other similar solvents. The exact combination of ions involved makes each compound have a unique solubility in any solvent. The solubility is dependent upon how well each ion interacts with the solvent, so there are certain patterns. For example, all salts of sodium, potassium and ammonium are soluble in water, as are all nitrates and many sulfate salts except barium sulfate, calcium sulfate (sparingly soluble) and Lead(2)sulfate However, ions that bind tightly to each other and form highly stable lattices would be less soluble, because it would be harder for these structures to break apart for the compounds to dissolve. For example, most carbonate salts are not soluble in water, such as lead carbonate and Barium carbonate Soluble carbonate salts are: Sodium carbonate, Potassium carbonate and Ammonium carbonate

Degenerationism

The name of a salt starts with the name of the cation (e.g., sodium or ammonium) followed by the name of the anion (e.g., chloride or acetate). Salts are often referred to only by the name of the cation (e.g., sodium salt or ammonium salt) or by the name of the anion (e.g., chloride salt or acetate salt).
Common salt-forming cations include:

• Ammonium NH₄⁺
• Calcium Ca²⁺
• Iron Fe²⁺ and Fe³⁺
• Magnesium Mg²⁺
• Potassium K⁺
• Pyridinium C₅H₅NH⁺
• Quaternary ammonium NR₄⁺
• Sodium Na⁺

Common salt-forming anions (parent acids in parentheses where available) include:

• Acetate CH₃COO⁻ (acetic acid)
• Carbonate CO₃²⁻ (carbonic acid)
• Chloride Cl⁻ (hydrochloric acid)
• Citrate HOC(COO⁻)(CH₂COO⁻)₂ (citric acid)
• Cyanide C≡N⁻ (N/A)
• Nitrate NO₃⁻ (nitric acid)
• Nitrite NO₂⁻ (nitrous acid)
• Phosphate PO₄³⁻ (phosphoric acid)
• Sulfate SO₄²⁻ (sulfuric acid)

Formation

Solid lead(II) sulfate (PbSO₄)

Salts are formed by a chemical reaction between:

• A base and an acid, e.g., NH₃ + HCl → NH₄Cl
• A metal and an acid, e.g., Mg + H₂SO₄ → MgSO₄ + H₂
• A metal and a non-metal, e.g., Ca + Cl₂ → CaCl₂
• A base and an acid anhydride, e.g., 2 NaOH + Cl₂O → 2 NaClO + H₂O
• An acid and a basic anhydride, e.g., 2 HNO₃ + Na₂O → 2 NaNO₃ + H₂O
• Salts can also form if solutions of different salts are mixed, their ions recombine, and the new salt is insoluble and precipitates (see: solubility equilibrium), for example:

  Pb(NO₃)₂(aq) + Na₂SO₄(aq) → PbSO₄(s) + 2 NaNO₃(aq)

   

   

Salts Article from wikipedia.org
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Muneeb Qazi                                                                           

Acid Base Theories: Svante Arrhenius

Acid Base Theories: Svante Arrhenius

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I. Introduction
Svante Arrhenius was one of the towering giants of chemistry in the years surrounding the turn of the century. His most important contribution to chemistry was also his first - the idea of electrolytic dissociation. This idea, first published in 1883 and in refined form in 1887, was the mainstay of his doctoral dissertation. It was the source of much hurt in his life.
The basic idea is that certain substances remain ionized in solution all the time. Today, everyone accepts this without question, but it was the subject of much dissention and disagreement in 1884, when a twenty-five year old Arrhenius presented and defended his dissertation.
He was bitterly disappointed when the dissertation was awarded a fourth class (non since laude approbatur - approved not without praise) and his defense a third class (cum laude approbatur - approved with praise). Essentially, he got a grade of D for the dissertation and a C for his defense.
He could not obtain a job within his native Sweden, but he did get a travel grant and worked outside the country for several years. He did return in 1891, but even in 1895, his elevation to Professor of Physics was bitterly opposed as was his overdue election to the Swedish Academy of Sciences in 1901.
However, he received the 1903 Nobel Prize in Chemistry for his electrolytic dissociation theory and that effectively ended public criticism.

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II. The Acid Base Theory
Arrhenius published two articles on acids and bases, one in 1894 and the other in 1899.

Acid - any substance which delivers hydrogen ion (H⁺) to the solution.
Base - any substance which delivers hydroxide ion (OH¯) to the solution.

Here is a generic acid dissociating, according to Arrhenius:

HA H⁺ + A¯

This would be a generic base:

XOH X⁺ + OH¯

When acids and bases react according to this theory, they neutralize each other, forming water and a salt:

HA + XOH H₂O + XA

Keeping in mind that the acid, the base and the salt all ionize, we can write this:

H⁺ + A¯ + X⁺ + OH¯ H₂O + X⁺ + A¯

Fianlly, we can drop all spectator ions, to get this:

H⁺ + OH¯ H₂O

These ideas covered all of the known acids at the time (the usual suspects like hydrochloric acid, acetic acid, and so on) and most of the bases (sodium hydroxide, potassium hydroxide, calcium hydroxide and so on). HOWEVER, and it is a big however, the theory did not explain why ammonia (NH₃) was a base. There are other problems with the theory also.
III. Problems with Arrhenius' Theory
1) The solvent has no role to play in Arrhenius' theory. An acid is expected to be an acid in any solvent. This was found not to be the case. For example, HCl is an acid in water, behaving in the manner Arrhenius expected. However, if HCl is dissolved in benzene, there is no dissociation, the HCl remaining as undissociated molecules. The nature of the solvent plays a critical role in acid-base properties of substances.
2) All salts in Arrhenius' theory should produce solutions that are neither acidic or basic. This is not the case. If equal amounts of HCl and ammonia react, the solution is slightly acidic. If equal amounts of acetic acid and sodium hydroxide are reacted, the resulting solution is basic. Arrhenius had no explanation for this.
3) The need for hydroxide as the base led Arrhenius to propose the formula NH₄OH as the formula for ammonia in water. This led to the misconception that NH₄OH is the actual base, not NH₃.
In fact, by 1896, several years before Arrhenius announced his theory, it had been recognized that characteristic base properties where just as evident in such solvents as aniline, where no hydroxide ions were possible.
4) H⁺, a bare proton, does not exist for very long in water. The proton affinity of H₂O is about 799 kJ/mol. Consequently, this reaction:

H₂O + H⁺ H₃O⁺

happens to a very great degree. The "concentration" of free protons in water has been estimated to be 10¯¹³⁰ M. A rather preposterous value, indeed.
The Arrhenius theory of acids and bases will be fully supplanted by the theory proposed independently by Johannes Brønsted and Thomas Lowry in 1923.

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                      ALKANES                                  

Alkanes (also known as paraffins or saturated hydrocarbons) are chemical compoundsthat consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds(i.e., they are saturated compounds) without any cycles (or loops; i.e., cyclic structure). With the formula C_nH_2n+2, Alkanes belong to a homologous series of organic compounds in which the members differ by a constant relative molecular mass of 14. They have two main commercial sources: crude oil and natural gas.

Each carbon atom has 4 bonds (either C-H or C-C bonds), and each hydrogen atom is joined to a carbon atom (H-C bonds). A series of linked carbon atoms is known as the carbon skeleton or carbon backbone. The number of carbon atoms is used to define the size of the alkane (e.g., C₂-alkane).

An alkyl group, generally abbreviated with the symbol R, is a functional group or side-chain that, like an alkane, consists solely of single-bonded carbon and hydrogen atoms, for example a methyl or ethyl group.

The simplest possible alkane (the parent molecule) is methane, CH₄. There is no limit to the number of carbon atoms that can be linked together, the only limitation being that the molecule is acyclic, is saturated, and is a hydrocarbon. Saturated oils and waxes are examples of larger alkanes where the number of carbons in the carbon backbone is greater than 10.

Alkanes are not very reactive and have little biological activity. Alkanes can be viewed as a molecular tree upon which can be hung the more biologically active/reactive portions (functional groups) of the molecule.

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