Sunday, May 8, 2011

IB Chemistry on Acids and Bases

IB Chemistry on Acids and Bases
  • Arrhenius Theory (First Theory) states acid is a substance which produces hydrogen ions and base produces hydroxide ion in presence of water.
picture taken from
http://www.barransclass.com/phys1090/hw/hwk_13_acid.html

  • Bronstead Lowry Theory ( 1923 )

Acid is a proton donor/ base is proton acceptor.
Conjugate pair means a pair of species differing by a single proton.
Protonated member of a pair is called conjugate acid.
Deprotonated member is called conjugate base.


Strong acid will form weak conjugate base, weak acids will form strong conjugate base
picture taken from
http://www.flatworldknowledge.com/pub/basics-general-organic-and-bio/421660#web-421660
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Weak Acids/Bases have Ka/Kb ( acid/base dissociation constant)






Keywords 
  • Reversible, most acid exist in molecules (HA) form.( partial dissociation of HA )
  • High Ka value, ( pKa small ) stronger the acid
  • High Kb value, (pKb small) stronger the base
  • Strong acid/base completely dissociate in water ( 100% ionisation ), fully ionised
  • Weak acid/base partially dissociate in  water ( most acid exist in molecules , not ions )
  • Strong Acid HCI, H2SO4, HNO3 don't have Ka ( high) because they will dissociate fully.
Table showing Ka  and Kb values
picture taken from

Keywords for Strong, Weak, Concentrated, Diluted
Strong acid ------------------- completely dissociate into ions
Weak acid---------------------slightly/partially dissociate ( exist as molecules )
Concentrated ----------------high number of moles per unit volume
Diluted-------------------------low number of moles per unit volume
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Properties of Strong, Weak, World's Strongest Acid, World's Corrosive acid, World's Super Acids
  • HF (Weak Acid) but more Corrosive than HCl, H2SO4 and HNO3. Check Ka value for HF
  • Fluorosulfuric acid (HFSO3) is a super acid and considered the World's Strongest Acid before the discovery of Carborane Acid.
  • Carborane acid is considered the World's Strongest Acid
  • Magic acid (FSO3H-SbF5), is a superacid consisting of a mixture of fluorosulfonic acid (HSO3F) and antimony pentafluoride (SbF5), considered as World Strongest Isolable Acid
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Properties of Nitric Acid.
Strong oxidising agent due to nitrate ion
Dissolves metal Copper to form Copper sulphate
Strong oxidising agent (NO3)- ion which oxidises copper and itself is reduced to form NO2 gas 
HCI, (CI) and H2SO4, (SO4) ion are not strong oxiding agent compared to nitric
Nitric must be avoided if you are given a choice to choose which acids to use for your expt


Video on the oxiding power of nitric acid


Nitric and Sulphuric acid are used to make nitrating reagent, addition of nitro groups ( NO2) to make explosives.
Nitrating solution uses nitric acid and sulphuric acid to produce the nitronium ion (NO2+), which is the active species.

H2SO4 is stronger acid than HNO3. 
H2SO4 (Acid) is a proton donor, HNO3(Base ) is a proton acceptor
Video on Nitric/Sulphuric produce NO2 groups for Guncotton.

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Special Properties of Sulphuric acid
Video on Sulphuric acid and its uses.

Keywords are
  • Sulphuric Acid is strong dehydrating agent
  • hydration reaction of sulfuric acid is highly exothermic. Always add the acid to the water  rather than the water to the acid because the hydration of sulfuric acid is favorable and produces a lot of heat. 
  • Affinity of sulfuric acid for water is sufficiently strong that it will remove hydrogen and oxygen atoms from other compounds; for example, mixing sugar (C6H12O6)n and concentrated sulfuric acid will give elemental carbon
  • Potassium Chlorate is an oxidising agent ( KCIO3), produces oxygen  while sulphuric acid dehydrates the salt and heat produced (exothermic ) triggers combustion reaction.
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Properties of Hydrochloric acid
Hydrochloric Acid with Nitric Acid makes Aqua Regia ( Royal water )
Video on Royal Water able to dissolve Gold and Precious metals

Keywords
Royal water  used to dissolve gold, platinum and precious metals.( Inert Metals )
How it works



NO3- ion( HNO3) is a strong oxidising agent oxidises gold Au to Au3+.
CI- ion from HCI  will react with gold ions Au3+  to produce chloroaurate anions AuCl4
Au (s) + 3 NO3- (aq) + 6 H+ (aq) → Au3+ (aq) + 3 NO2 (g) + 3 H2
Au3+ (aq) + 4 Cl- (aq) → AuCl4- (aq).
End product will be NO2 gas and gold solution.
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World's Strongest and Most Corrosive Acids at Present.
Click HERE for more info
  • World's Strongest Acid used to be fluorosulfuric acid (HFSO3), but Carborane superacids (discovered recently) are hundreds of times stronger than fluorosulfuric acid and over a million times stronger than concentrated sulfuric acid.
  • The superacids readily release protons and form a stable anion 
  • Acid strength is measured by its ability to release proton or ability to form a stable anion after releasing H+ ion.
  • World's Strongest Isolable Acid, Magic acid (FSO3H-SbF), is a superacid consisting of a mixture of fluorosulfonic acid (HSO3F) and antimony pentafluoride SbF5
  • World's Most Corrosive Acid ,  Hydrofluoric acid, HF 

World's Most Corrosive Acid , Hydrofluoric acid, 
HF ( weak acid )
picture taken from
How a Weak acid be the Most corrosive acid in the world?
Corrosive property depends on the anion part of acid and not the amount of H+ ions.
HF dissolves to release H+ and F-. It is the strong fluoride ion ( most electronegative element ) which penetrates the skin, oxidises our cells and etches glass too.

Video on the Most Corrosive Acid ( Weak Acid, HF )
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World's Strongest Isolable Acid called Fluorosulfuric acid (HFSO3) and Magic Acid
Why it is so strong?
Oxygen and Fluorine atoms are electronegative and will attracted electrons from OH group causing polarisation of O-H group. Weakens the O-H bond and H+ will be easily released .
Predict which acid is the strongest, arrange them in order based on Ka value
Trichloroethanoic acid, Dichloroethanoic acid, Chloroethanoic acid, Trifluroethanoic acid, Ethanoic acid.


Click HERE for more info
  • Magic acid (FSO3H-SbF5), a superacid consist of a mixture of fluorosulfonic acid (HSO3F) and antimony pentafluoride (SbF5), considered as World Strongest Isolable Acid.   HSFO3·SbF5 + H2O → H2SO4 + HSbF6








picture taken from
http://www.chem.uoa.gr/chemicals/chem_magicacid.htm
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World's Strongest and Least Corrosive Acid Discovered called Carborane Acid


World's Strongest, Yet Gentle, Acid Uncovered


Riverside CA (SPX) Nov 17, 2004
Researchers at the University of California, Riverside have discovered the world’s strongest acid. It is also the gentlest acid. This non-toxic and non-corrosive acid may have a role in processes such as improving the quality of gasoline, developing polymers and synthesizing pharmaceuticals.


According to UC Riverside Distinguished Professor of Chemistry, Christopher Reed one of the authors of the findings.
Icosahedral arrangement of eleven boron atoms plus one carbon atom, which is probably the most chemically stable cluster of atoms in all of chemistry, according to Reed. This means that the carborane part of the acid cannot participate in the chemistry of corrosion and decomposition that fluoride and nitrate show in hydrofluoric acid and nitric acid. Makes the anion part of acid very stable and non corrosive.
Click HERE for more info and Nobel Prize awarded in 1994 for Superacids (Magic acid)

How strong are Carborane acids? 
At least a million times stronger than concentrated sulfuric acid (H2SO4) and hundreds of times stronger than the previous record holder, Fluorosulfuric acid (HFSO3)
The 1994 Nobel Prize in Chemistry was awarded to George Olah at USC for his pioneering studies in carbocations stablised by superacids.



Special thanks to all videos and pictures contributors for the above post

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