Interference with absorption
- Antinutrient
Antinutrients are natural or synthetic compounds that interfere with the absorption of nutrient s Nutrition studies focus on those …6 KB (864 words) – 13:42, 2 February 2011
- Malabsorption (redirect from D-Xylose absorption test)
Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract . …13 KB (1,530 words) – 17:54, 25 January 2011
- Magnesium hydroxide
Magnesium hydroxide is a common component of antacid s and laxative s; it interferes with the absorption of folic acid and iron …13 KB (1,805 words) – 01:25, 1 January 2011
- Levothyroxine
There are also foods and other substances that can interfere with absorption of thyroxine replacement. these can reduce absorption of the drug. …9 KB (1,213 words) – 14:08, 3 February 2011
- Zinc gluconate
Zinc gluconate may interfere with the absorption of antibiotic s, so combinations may be unsafe. Zinc and the common cold : Some studies have …9 KB (1,263 words) – 12:27, 27 December 2010
- Oxalis tetraphylla
However, since the oxalic acid in the plant can interfere with the absorption of certain nutrients in the body, especially calcium , too …2 KB (289 words) – 11:03, 6 September 2010
- Absorption spectroscopy
Absorption spectroscopy refers to spectroscopic techniques that measure the … The absorption of other materials could interfere with or …20 KB (2,691 words) – 16:37, 22 January 2011
- Abetalipoproteinemia
Abetalipoproteinemia, or Bassen-Kornzweig syndrome is a rare autosomal recessive disorder that interferes with the normal absorption of …7 KB (913 words) – 21:17, 13 January 2011
- Tannin
Tannins interfere with iron absorption through a complex formation with iron when it is in the gastrointestinal lumen which decreases the …35 KB (4,949 words) – 23:02, 2 February 2011
- Coeliac disease
This interferes with the absorption of nutrients, because the intestinal villi are responsible for absorption. The only known effective …81 KB (11,015 words) – 15:56, 26 January 2011
- Ionospheric absorption
scientific name for absorption occurring as a result of the … electrons in the ionosphere , which can interfere with radio transmissions. …3 KB (345 words) – 18:21, 6 October 2009
- Ultraviolet–visible spectroscopy (section Absorption flattening)
(UV-Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy … interfering substances can influence the absorption spectrum. …17 KB (2,485 words) – 11:28, 22 January 2011
- Freshman fifteen
date May 2010 Alcohol can interfere with nutrient absorption. alcohol and from food consumed with alcohol have a good chance of not being absorbed. …29 KB (4,439 words) – 04:27, 25 January 2011
- Common wood sorrel
contains oxalic acid which is considered slightly toxic because it interferes with food digestion and the absorption of some trace minerals. …5 KB (632 words) – 11:12, 18 November 2010
- Electromagnetically induced transparency
renders a medium transparent over a narrow spectral range within an absorption line . … can interfere destructively , preventing absorption. …9 KB (1,375 words) – 10:58, 26 December 2010
- Vitamin
prevents or limits the absorption or use of the vitamin, due to a “ … consumption, or the use of medications that interfere with the absorption or use of the …41 KB (5,256 words) – 22:07, 1 February 2011
- Iron deficiency (medicine)
Too little iron can interfere with these vital functions and lead to … substances (in diet or drugs) interfering with iron absorption …14 KB (2,014 words) – 12:34, 1 February 2011
- Molecular imaging
Above 900 nm, water absorption can interfere with signal-to-background ratio. Because the absorption coefficient of tissue is considerably …15 KB (2,174 words) – 05:21, 31 January 2011
- Sudden ionospheric disturbance
increase in radio-wave absorption that is most severe in the upper … and as a result often interrupts or interferes with telecommunication s systems. …3 KB (381 words) – 18:20, 9 November 2010
- Microbarom
(0.2 hertz Due to low atmospheric absorption at these low frequencies , … source that can potentially interfere with the detection of …24 KB (3,193 words) – 11:10, 18 September 2010
Amphoterism
Amphoterism
In chemistry, an amphoteric or amphiprotic substance is a compound that can react as an acid as well as a base.[1] The word is derived from the Greek word amphoteroi (ἀμφότεροι) meaning “both”. Many metals (such as zinc, tin, lead, aluminium, and beryllium) and most metalloids have amphoteric oxides or hydroxides. Amphoteric substances can either donate or accept a proton. Examples include amino acids and proteins, which have amine and carboxylic acid groups, and self-ionizable compounds such as water and ammonia.
Ampholytes are amphoteric molecules that contain both acidic and basic groups and will exist mostly as zwitterions in a certain range of pH. The pH at which the average charge is zero is known as the molecule’s isoelectric point. Ampholytes are used to establish a stable pH gradient for use in isoelectric focusing.
Contents[hide] |
[edit] Amphoteric oxides and hydroxides[2]
Zinc oxide (ZnO) reacts differently depending on the pH of the solution:
- In acids: ZnO + 2H+ → Zn2+ + H2O
- In bases: ZnO + H2O + 2OH– → [Zn(OH)4]2-
This effect can be used to separate different cations, such as zinc from manganese.
Aluminium hydroxide is as well:
- Base (neutralizing an acid): Al(OH)3 + 3HCl → AlCl3 + 3H2O
- Acid (neutralizing a base): Al(OH)3 + NaOH → Na[Al(OH)4]
Some other examples include:
- Beryllium hydroxide
- with Acid: Be(OH)2 + 2HCl → BeCl2 + 2H2O
- with Base: Be(OH)2 + 2NaOH → Na2Be(OH)4
- Aluminium oxide
- with acid: Al2O3 + 3 H2O + 6 H3O+(aq) → 2 [Al(H2O)6]3+(aq)
- with base: Al2O3 + 3 H2O + 2 OH–(aq) → 2 [Al(OH)4]–(aq)
- Lead oxide
- with acid: PbO + 2HCl → PbCl2 + H2O
- with base: PbO + Ca(OH)2 +H2O → Ca2+[Pb(OH)4]2-
Some other elements which form amphoteric oxides: Si, Ti, V, Fe, Co, Ge, Zr, Ag, Sn, Au[3]
[edit] Amphiprotic molecules
According to the Brønsted-Lowry theory of acids and bases: acids are proton donors and bases are proton acceptors.[4] An amphiprotic molecule (or ion) can either donate or accept a proton, thus acting either as an acid or a base. Water, amino acids, hydrogen carbonate ions and hydrogen sulfate ions are common examples of amphiprotic species. Since they can donate a proton, all amphiprotic substances contain a hydrogen atom. Also, since they can act like an acid or a base, they are amphoteric.
[edit] Examples
A common example of an amphiprotic substance is the hydrogen carbonate ion, which can act as a base:
HCO3– + H3O+ → H2CO3 + H2O
or as an acid:
HCO3– + OH– → CO32- + H2O
Thus, it can effectively accept or donate a proton.
Water is the most common example, acting as a base when reacting with an acid such as hydrogen chloride
H2O + HCl → H3O+ + Cl–,
and acting as an acid when reacting with a base such as ammonia:
H2O + NH3 → NH4+ + OH–
[edit] See also
[edit] References
 |
This June 2009 includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. P
lease improve this article by introducing more precise citations where appropriate. (June 2009) |
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”) (1997). Online corrected version: (2006-) “amphoteric“.
- ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. ISBN 978-0130399137.
- ^ CHEMIX School & Lab – Software for Chemistry Learning, by Arne Standnes (program download required)
- ^ R.H. Petrucci, W.S. Harwood, and F.G. Herring, “General Chemistry” (8th edn, Prentice-Hall 2002), p.669
Base (chemistry)
Base (chemistry)
 |
This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (September 2010) |
A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions (OH−) quantitatively. The Brønsted-Lowry theory defines bases as proton (hydrogen ion) acceptors, while the more general Lewis theory defines bases as electron pair donors, allowing other Lewis acids than protons to be included.[1] The oldest Arrhenius theory defines bases as hydroxide anions,[2] which is strictly applicable only to alkali. In water, by altering the autoionization equilibrium, bases give solutions with a hydrogen ion activity lower than that of pure water, i.e. a pH higher than 7.0 at standard conditions. Examples of common bases are sodium hydroxide and ammonia. Metal oxides, hydroxides and especially alkoxides are basic, and counteranions of weak acids are weak bases.
Bases can be thought of as the chemical opposite of acids. A reaction between an acid and base is called neutralization. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium ion (H3O+) concentration in water, whereas bases reduce this concentration. Bases and acids are typically found in aqueous solution forms. Aqueous solutions of bases react with aqueous solutions of acids to produce water and salts in aqueous solutions in which the salts separate into their component ions. If the aqueous solution is a saturated solution with respect to a given salt solute any additional such salt present in the solution will result in formation of a precipitate of the salt.
Contents[hide] |
[edit] Definitions
A strong base is a base which hydrolyzes completely, raising the pH of the solution toward 14. Concentrated bases, like concentrated acids, attack living tissue and cause serious burns. The reaction of bases upon contact with skin is different from that of acids. So while either may be quite destructive, strong acids are called corrosive, and strong bases are referred to as caustic. Superbases are a class of especially basic compounds and non-nucleophilic bases are a special class of strong bases with poor nucleophilicity. Bases may also be weak bases such as ammonia, which is used for cleaning. Arrhenius bases are water-soluble and these solutions always have a pH greater than 7 at standard conditions. An alkali is a special example of a base, where in an aqueous environment, hydroxide ions are donated. There are other more generalized and advanced definitions of acids and bases.
The notion of a base as a concept in chemistry was first introduced by the French chemist Guillaume François Rouelle in 1754. He noted that acids, which in those days were mostly volatile liquids (like acetic acid), turned into solid salts only when combined with specific substances. Rouelle considered that such a substance serves as a base for the salt, giving the salt a “concrete or solid form”.[3]
[edit] Properties
Some general properties of bases include:
- Slimy or soapy feel on fingers, due to saponification of the lipids in human skin
- Concentrated or strong bases are caustic on organic matter and react violently with acidic substances
- Aqueous solutions or molten bases dissociate in ions and conduct electricity.
- Reactions with indicators: bases turn red litmus paper blue, phenolphthalein pink, keep bromthymol blue in its natural colour of blue, and turn methyl orange yellow.
- the pH is above 7
- bitter tasting[4]
[edit] Bases and pH
The pH of an aqueous sample (water) is a measure of its acidity. In pure water, about one in ten million molecules dissociate into hydronium ions and hydroxide ions according to the following equation:
- 2H2O(l) → H3O+(aq) + OH−(aq)
The concentration, measured in molarity (M or moles per litre), of the ions is indicated as [H3O+] and [OH−]; their product is the dissociation constant of water with and has the value 10−7 M. The pH is defined as −log [H3O+]; thus, pure water has a pH of 7. (These numbers are correct at 23 °C and slightly different at other temperatures.)
A base accepts (removes) hydronium ions from the solution, or donates hydroxide ions to the solution. Both actions will lower the concentration of hydronium ions, and thus raise pH. By contrast, an acid donates H3O+ ions to the solution or accepts OH−, thus lowering pH.
For example, if 1 mole (40 g) of sodium hydroxide (NaOH) is dissolved in water to make 1 litre of solution, the concentration of hydroxide ions becomes [OH−] = 1 mol/L. Therefore [H+] = 1×10−14 mol/L, and pH = −log 10−14 = 14. Note that in this calculation, it is assumed that the activity is equivalent to the concentration, which is not realistic at concentrations over 0.1 mol/L.
The base dissociation constant, Kb, is a measure of basicity. It is related to the acid dissociation constant, Ka, by the simple relationship pKa + pKb = 14. Where pKb and pKa are the negative logarithms of Kb and Ka respectively.
Alkalinity is a measure of the ability of a solution to neutralize acids to the equivalence points of carbonates or bicarbonates.
[edit] Neutralization of acids
When dissolved in water, the strong base sodium hydroxide decomposes into hydroxide and sodium ions:
- NaOH → Na+ + OH−
and similarly, in water hydrogen chloride forms hydronium and chloride ions:
- HCl + H2O → H3O+ + Cl−
When the two solutions are mixed, the H3O+ and OH− ions combine to form water molecules:
- H3O+ + OH− → 2 H2O
If equal quantities of NaOH and HCl are dissolved, the base and the acid exactly neutralize, leaving only NaCl, effectively table salt, in solution.
Weak bases, such as soda or egg white, should be used to neutralize any acid spills. Neutralizing acid spills with strong bases, such as sodium hydroxide or potassium hydroxide can cause a violent exothermic reaction, and the base itself can cause just as much damage as the original acid spill.
[edit] Alkalinity of non-hydroxides
Bases are generally compounds that can neutralize an amount of acids. Both sodium carbonate and ammonia are bases, although neither of these substances contains OH− groups. Both compounds accept H+ when dissolved in water:
- Na2CO3 + H2O → 2 Na+ + HCO3– + OH–
- NH3 + H2O → NH4+ + OH–
From this, a pH, or acidity, can be calculated for aqueous solutions of bases. Bas
es also directly act as electron-pair donors themselves:
- CO32- + H+ → HCO3–
- NH3 + H+ → NH4+
Carbon can act as a base as well as nitrogen and oxygen. This occurs typically in compounds such as butyl lithium, alkoxides, and metal amides such as sodium amide. Bases of carbon, nitrogen and oxygen without resonance stabilization are usually very strong, or superbases, which cannot exist in a water solution due to the acidity of water. Resonance stabilization, however, enables weaker bases such as carboxylates; for example, sodium acetate is a weak base.
[edit] Strong bases
A strong base is a basic chemical compound that is able to deprotonate very weak acids in an acid-base reaction. Common examples of strong bases are the hydroxides of alkali metals and alkaline earth metals like NaOH and Ca(OH)2. Very strong bases are even able to deprotonate very weakly acidic C–H groups in the absence of water. Here is a list of several strong bases:
- Potassium hydroxide (KOH)
- Barium hydroxide (Ba(OH)2)
- Caesium hydroxide (CsOH)
- Sodium hydroxide (NaOH)
- Strontium hydroxide (Sr(OH)2)
- Calcium hydroxide (Ca(OH)2)
- Lithium hydroxide (LiOH)
- Rubidium hydroxide (RbOH)
The cations of these strong bases appear in the first and second groups of the periodic table (alkali and earth alkali metals).
Acids with a pKa of more than about 13 are considered very weak, and their conjugate bases are strong bases.
[edit] Superbases
Group 1 salts of carbanions, amides, and hydrides tend to be even stronger bases due the conjugate acids, which are stable hydrocarbons, amines, and dihydrogen. Usually these bases are created by adding pure alkali metals such as sodium into the conjugate acid. They are called superbases and it is not possible to keep them in water solution, due to the fact they are stronger bases than the hydroxide ion and as such they will deprotonate the conjugate acid water. For example, the ethoxide ion (conjugate base of ethanol) in the presence of water will undergo this reaction.
- CH3CH2O− + H2O → CH3CH2OH + OH−
Here are some superbases:
- Butyl lithium (n-BuLi)
- Lithium diisopropylamide (LDA) (C6H14LiN)
- Lithium diethylamide (LDEA)
- Sodium amide (NaNH2)
- Sodium hydride (NaH)
- Lithium bis(trimethylsilyl)amide (((CH3)3Si)2NLi)
[edit] Bases as catalysts
Basic substances can be used as insoluble heterogeneous catalysts for chemical reactions. Some examples are metal oxides such as magnesium oxide, calcium oxide, and barium oxide as well as potassium fluoride on alumina and some zeolites. Many transition metals make good catalysts, many of which form basic substances. Basic catalysts have been used for hydrogenations, the migration of double bonds, in the Meerwein-Ponndorf-Verley reduction, the Michael reaction, and many other reactions.
[edit] See also
- Conjugate base
- Acid-base reactions
- Acids
- Base-richness (used in ecology, referring to environments)
[edit] References
- ^ Chemistry, 9th Edition. Kenneth W. Whitten, Larry Peck, Raymond E. Davis, Lisa Lockwood, George G. Stanley. (2009) ISBN 0495391638. Page 363
- ^ Chemistry. Page 349
- ^ The Origin of the Term Base William B. Jensen Journal of Chemical Education • 1130 Vol. 83 No. 8 August 2006
- ^ http://www.merriam-webster.com/dictionary/base
Phillip Greaves [counter conspiracy /counter slander]
Phillip Greaves
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Phillip Greaves is an author from Colorado. He is known for a controversial book he wrote titled The Pedophile’s Guide to Love and Pleasure: A Child-lover’s Code of Conduct. The book, which was pulled by Amazon.com, resulted in his arrest by the Sheriff’s department of Polk County, Florida[1]. The state of Colorado, however, does not consider Greaves to be a sex offender[2].
Contents[show] |
[edit] Personal life
Greaves is a former nurse’s aide[3].
[edit] Book authored
In 2010, Greaves authored a book titled The Pedophile’s Guide to Love and Pleasure: A Child-lover’s Code of Conduct. The self-published book was not offered in print, but only as an e-book, sold on Amazon’s site for $4.79. Greaves himself stated that the purpose of the book was to change peoples’ perception of pedophiles[3].
[edit] Reaction
[edit] Pulling of book from Amazon
On November 11, 2010, Amazon pulled Greaves’s book from its site under threat of a boycott. Amazon stated that it does not believe in censorship of books over their content[4].
Readers threatened to boycott Amazon over its selling of the book, which was described by critics as a “pedophile guide”. Amazon initially defended the sale of the book, saying that the site “believes it is censorship not to sell certain books simply because we or others believe their message is objectionable”[5] and that the site “supported the right of every individual to make their own purchasing decisions”. However, the site later removed the book.[6] The San Francisco Chronicle wrote that Amazon “defended the book, then removed it, then reinstated it, and then removed it again“.[5]
Christopher Finan, the president of the American Booksellers Association for Free Expression, argued that Amazon has the right to sell the book as it is not child pornography or legally obscene since it does not have pictures. On the other hand, Enough is Enough, a child safety organization, issued a statement saying that the book should be removed and that it “lends the impression that child abuse is normal”.[7] People for the Ethical Treatment of Animals, citing the removal of The Pedophile’s Guide from Amazon, urged the website to also remove books on dog fighting from its catalogue.[8]
[edit] Arrest
On Monday, December 20, 2010, Greaves was arrested in Colorado on a warrant issued by the Polk County Sheriff’s office, violating a Florida law prohibiting the distribution of obscene materials. He was extradited from Colorado to Florida. The arrest occurred after the county’s undercover officers purchased a copy of his book for $50. Greaves signed the book himself[2]. According to Sheriff Grady Judd, upon receipt of the book, Greaves violated local laws prohibiting the distribution of “obscene material depicting minors engaged in harmful conduct,” a third degree felony.[9]
[edit] References
- ^ http://www.aolnews.com/2010/12/21/arrest-of-pedophile-guide-author-phillip-greaves-raises-legal-is/
- ^ a b http://articles.orlandosentinel.com/2010-12-20/news/os-obscenity-arrest-polk-county-20101220_1_obscenity-laws-obscenity-charge-obscene-material
- ^ a b http://www.aolnews.com/2010/11/11/amazon-yanks-pedophilia-e-book-amid-boycott-threats/
- ^ http://www.aolnews.com/2010/11/11/amazon-yanks-pedophilia-e-book-amid-boycott-threats/
- ^ a b Saint, Nick (2010-11-11). “Amazon Caves: Pedophile Guide Pulled From The Kindle Store (AMZN)”. San Francisco Gate. Retrieved November 11, 2010.
- ^ Beaumont, Claudine (November 11, 2010). “Amazon removes ‘paedophile guide’ from Kindle store”. London: The Telegraph. Retrieved November 11, 2010.
- ^ “Amazon no longer selling guide for pedophiles”. Associated Press. November 11, 2010. Retrieved November 11, 2010.
- ^ “PETA wants animal-fighting books removed”. United Press International. November 13, 2010. Retrieved November 13, 2010.
- ^ “Polk Sheriff: Pedophilia book author arrested”. Bay News 9. December 20, 2010. Retrieved December 20, 2010.
Powers and Principalities 