Strong bases

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In chemistry, strong bases are a subgroup of bases . They are completely ionized in aqueous solutions . So they are strong electrolytes . The base strength always refers to the aqueous solutions of the base, not to the pure substances.

Reactivity

When a pure base is added to water, an alkaline solution is formed. This reaction, in which the base picks up a proton from the acid, is called protolysis . Strong bases are always completely protolyzed / ionized in aqueous solution. The reaction equilibrium is on the side of the products . The following is a general example of a base B that protolyzes in water:

In the case of a strong base, as already mentioned above, this equilibrium is on the right-hand side, the product side. A negatively charged hydroxide ion and a positively charged cation are formed . The cation is the corresponding acid to the base. These pairs are called corresponding acid-base pairs .
The reactivity of the strong bases depends essentially on the concentration of the hydroxide ions formed. In addition, the reactivity also depends on the acid of the acid-base pair.

pK s and pK b values

One way to find out how strong a base is is to use the protochemical voltage series in which the pK b and pK s values ​​of some acid-base pairs are listed. The pK b values ​​denote the base strength and the pK s values ​​denote the acid strength. The pK s and pK b values ​​indicate the extent to which a base is ionized in the equilibrium reaction with water. The following applies: the smaller the value, the stronger the acid / base. Very strong bases have a pK b value of less than −0.35. Strong bases have a pK b value of up to 3.75. Strong bases are always weak acids. The following table lists the pK s and pK b values ​​of some very strong to very weak bases and their corresponding acids under standard conditions. Medium-strength acids and bases are highlighted in light gray, while weak to very weak acids and bases are highlighted in dark gray. They are only listed for comparison:

Acid starch pK s Acid + H 2 O H 3 O + + base pK b Base strength
very weak 48 CH 4 CH 3 - very strong
23 NH 3 NH 2 - −9
15.90 CH 3 CH 2 -OH CH 3 -CH 2 -O - −1.90
weak 14.00 H 2 O OH - 0.00 strong
13.00 HS - S 2− 1.00
12.36 HPO 4 2− PO 4 3− 1.64
10.40 HCO 3 - CO 3 2− 3.60
9.40 HCN CN - 4.60
9.25 NH 4 + NH 3 4.75
medium strength 7.20 H 2 PO 4 - HPO 4 2− 6.80 medium strength
6.92 H 2 S HS - 7.08
6.52 H 2 CO 3 HCO 3 - 7.48
4.85 [Al (H 2 O) 6 ] 3+ [Al (OH) (H 2 O) 5 ] 2+ 9.15
4.75 CH 3 COOH CH 3 COO - 9.25
strong 3.75 HCOOH HCOO - 10.25 weak
3.14 HF F - 10.86
2.22 [Fe (H 2 O) 6 ] 3+ [Fe (OH) (H 2 O) 5 ] 2+ 11.78
2.13 H 3 PO 4 H 2 PO 4 - 11.87
1.92 HSO 4 - SO 4 2− 12.08
0.00 H 3 O + H 2 O 14.00
very strong −1.32 ENT 3 NO 3 - 15.32 very weak
−3 H 2 SO 4 HSO 4 - 17th
−6 HCl Cl - 20th
−10 HI I - 24
−10 HClO 4 ClO 4 - 24

Strong inorganic bases

The list of strong bases is relatively short compared to the list of weak bases. The inorganic bases are mainly alkali and alkaline earth hydroxides dissolved in water, such as sodium hydroxide (NaOH), potassium hydroxide (KOH) and magnesium hydroxide (Mg (OH) 2 ). In addition, some oxygen compounds such as phosphates (PO 4 3− ) and carbonates (CO 3 2− ) are known strong bases. There are also sulfides (S 2− ), such as sodium sulfide .

Strong organic bases

In the organic bases , there are few strong bases. Some amines and naphthalenes are strong bases. However, this depends on the other substituents that are in the vicinity of the basic group.

Individual evidence

  1. ^ A b Charles E. Mortimer, Ulrich Müller: Chemistry . Thieme, Stuttgart 2010, ISBN 978-3-13-484310-1 , p. 310 f .
  2. ↑ a b c T. L. Brown; HE LeMay; BE Bursten: Chemistry, study compact . Pearson Verlag, Munich 2011, ISBN 978-3-86894-122-7 .
  3. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 245.
  4. ↑ Gerhart Jander , Karl Friedrich year, Gerhard Schulze, Jürgen Simon (eds.): Measure analysis. Theory and practice of titrations with chemical and physical indications. 16th edition. Walter de Gruyter, Berlin a. a. 2003, ISBN 3-11-017098-1 , p. 81.
  5. ↑ PW Atkins, TL Overton, JP Rourke, MT Weller, FA Armstrong: Shriver & Atkins' inorganic chemistry. 5th edition. Oxford University Press, Oxford New York 2010, ISBN 978-0-19-923617-6 , p. 115.
  6. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 , p. 241.
  7. ↑ Jerry March : Advanced Organic Chemistry. Reactions, Mechanisms, and Structure. 3. Edition. Wiley, New York NY et al. a. 1985, ISBN 0-471-88841-9 , p. 222.
  8. ↑ List of some pKb values .