difference between alkali and base

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From Wikipedia

Alkali soils

Alkali, or alkaline, soils are claysoils with high pH (> 9), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 meter depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate which causes the soil to swell. They derive their name from the alkali metal group of elements to which the sodium belongs and that can induce basicity. Sometimes these soils are also referred to as (alkaline) sodic soils.
Alkaline soils are basic, but not all basic soils are alkaline, see: "difference between alkali and base"

Causes

The causes of soil alkalinity are natural or they can be man-made.

  1. The natural cause is the presence of soil minerals producing sodium carbonate (Na2CO3) upon weathering.
  2. The man-made cause is the application of irrigation water (surface or ground water) containing a relatively high proportion of sodium bicarbonates.

Occurrence

The extent of alkaline soils is not precisely known.

Agricultural problems

Alkaline soils are difficult to take into agricultural production. Due to the low infiltration capacity, rain water stagnates on the soil easily and, in dry periods, irrigation is hardly possible. Agriculture is limited to crops tolerant to surface waterlogging (e.g. rice, grasses) and the productivity is low.

Chemistry

Soil alkalinity is associated with the presence of sodium carbonates or (soda) (Na2CO3) in the soil , either as a result of natural weathering of the soil particles or brought in by irrigation and/or flood water.

The sodium carbonate, when dissolved in water, dissociates into 2Na+ (two sodium cations, i.e. ions with a positive electric charge) and CO3= (a carbonate anion, i.e. an ion with a double negative electric charge).

The sodium carbonate can react with water to produce carbon dioxide (CO2), escaping as a gas, and sodium hydroxide (Na+OH–), which is alkaline (or rather basic) and gives high pH values (pH>9) .

Notes:
* Water (H2O) is partly dissociated into H+ (hydrogen) and OH– (hydroxyl) ions. The ion H+ has a positive electric charge (+) and the hydroxyl group OH– has a negative charge (–). In pure, neutral water, the concentration of H+ and OH– ions equals 10–7 eq/l each (respectively 10–7 g/l and 17x10–7 g/l), a very small concentration.
* 1 eq = 1 equivalent weight corresponds to as many grams of the substance as its molecular weight divided by its valence. It is also known as gram-molecule or mole per unit of valence. For the hydrogen ion (H+ ) the molecular weight equals 1, and for the hydroxyl group (OH–) it equals 17. As they are both monovalent (or univalent) their equivalent weights are the same. Substances with the same equivalent weight have equal positive or negative electric charge.
*In neutral water, the pH, being the negative log value of the H+ concentration in eq/l, is 7. Similarly, the pOH is also 7. Each unit decrease in pH indicates a tenfold increase of the H+ concentration. Similarly, each unit increase in pH indicates a tenfold increase of the OH– concentration.
* In water with dissolvedsalts, the concentrations of the H+ y OH– ions may change, but their sum remains constant, namely 7 + 7 = 14. A pH of 7 therefore corresponds to a pOH of 7, and a pH of 9 with a pOH of 5.
* Formally it deserves preference to express the ion concentrations in terms of chemical activity, but this does hardly affect the value of pH.
*Water with excess H+ ions is called acid (pH < 6), and water with excess OH&ndash; ions is called alkaline or rather basic (pH > 8). Soil moisture with pH&nbsp;<&nbsp;4 is called very acid and with pH&nbsp;>&nbsp;10 very alkaline (basic).

The reaction between Na2CO3 and H2O can be represented as follows:

  • 2Na+ + CO3= + 2H+ + 2OH&ndash; => 2Na+ + 2OH&ndash; + H2CO3

The acid H2CO3 is unstable and produces H2O (water) and CO2 (carbon dioxide gas, escaping into the atmosphere). This explains the remaining alkalinity (or rather basicity) in the form of soluble ionic compounds with simple chemical formula X+Y- or XY, where X is an alkali metal and Y is a halogen. One of the most well known of these is sodium chloride or common table salt.

In standard room conditions dry alkali halides tend to exist as white or translucent crystalline solids. The internal crystalline structure is centered cubic, usually face centered cubic.

The numbers beside the compounds show the electronegativity difference between the elements based on the Pauling scale. The higher the number is, the more ionic the bond is.

The table below provides links to each of the individual articles for these compounds:



From Yahoo Answers

Question:

Answers:Confusion between base and alkali The terms "base" and "alkali" are often used interchangeably, since most common bases are alkalis. It is common to speak of "measuring the alkalinity of soil" when what is actually meant is the measurement of the pH (base property). Similarly, bases which are not alkalis, such as ammonia, are sometimes erroneously referred to as alkaline. Note that not all or even most salts formed by alkali metals are alkaline; this designation applies only to those salts which are basic. While most electropositive metal oxides are basic, only the soluble alkali metal and alkali earth metal oxides can be correctly called alkalis. This definition of an alkali as a basic salt of an alkali metal or alkali earth metal does appear to be the most common, based on dictionary definitions

Question:

Answers:"Alkali" is an old term used to describe the hydroxides of alkaline earth metals. "Earth" is another old term meaning "Oxide". When alchemists burned substances, the ashes were often the oxides of things such as Potassium or Sodium. The "earth" combined with water to make an alkaline solution which made the skin slippery if exposed to it and eventually burned the skin if not washed off. When mixed with suet or lard, soap could be made. "Base" is a term which began being used when chemistry began being practiced as a science, replacing alchemy. It was given this name to distinguish it from another sort of substance called an acid. The two canceled one another's properties and produced a neutral solution. Beside alkaline earths, many other things gave the same reaction with acids. Ammonia is an example of a base which will neutralize an acid. However, all bases have hydroxyl groups. Sodium, potassium and ammonium hydroxides are all bases.

Question:In chemistry I never know what the difference is, or even if there is a difference!

Answers:a base that is soluble is known as an alkaline. alkaline mostly applies to bases of alkali metal or alkali earth metal elements.

Question:In higher level GCSE terms please 8>)

Answers:Generally, PH 7 is neutral. anything 0-7 is acid. 7-14 is alkali. Hope this helps.