Products
Bases are available as pure substances in pharmacies and drugstores. They are included in numerous medicines as active ingredients and excipients.
Definition
Bases (B) are proton acceptors. They accept a proton from an acid (HA), a proton donor, in the acid-base reaction. Thus, they lead to deprotonation:
- HA + B ⇄ HB
+
+ A
–
This reaction is reversible, resulting in equilibrium. Bases differ in the number of protons they can absorb. For example, a phosphate can bind three protons, while a hydrocarbonate can bind only one. Bases reduce the concentration of hydronium ions in water (H
3
O
+
):
- H
3
O
+
+ OH
–
2 H
2
O
Reaction with an acid
Typical bases include the hydroxides, hydrogen carbonates, carbonates and amines. A hydroxide reacts with an acid to form water and a salt:
- NaOH (sodium hydroxide) + HCl (hydrochloric acid) NaCl (sodium chloride) + H
2
O (water)
Carbonates react with acids to form carbon dioxide:
- Na
2
CO
3
(sodium carbonate) + 2 HCl (hydrochloric acid) 2 NaCl (sodium chloride) + H
2
O (water) + CO
2
(carbon dioxide)
Ammonia and water:
- NH
3
(ammonia) + H
2
O (water) NH
4
+
(ammonium ion) + OH
–
(hydroxide ion)
Organic amines:
- R-NH
2
(amine) + H
+
(proton) R-NH
3
+
(Protonated amine)
Strength of bases
Like acids, bases also differ in strength. For example, sodium hydroxide and potassium hydroxide are strong bases, while sodium hydrogen carbonate and ammonia are weak bases. The pKb value, the negative decadic logarithm of the dissociation constant (base constant) Kb, is used as a measure of strength. The lower the value, the stronger the base. pKb:
- Sodium hydroxide: -0.56
- Potassium hydroxide: -0.7
- Ammonia: 4.75
PH value
Aqueous solutions of bases have a pH above 7. The pH is the negative decadic logarithm of the hydronium ion concentration:
- pH = -log C(H
3
O
+
)
The pH scale ranges from 0 (acidic) to 14 (basic). Caution: A difference of 1 stands for the value 10 due to the logarithmic scale.
1
.
Application areas
Medical and pharmaceutical indications include:
- As a caustic, for example, for the treatment of dell warts (potassium hydroxide).
- Antacids and alkaline powders for the treatment of stomach burns and acid reflux.
- For the preparation of soaps from triglycerides (fats, fatty oils).
- As active pharmaceutical ingredients and excipients.
- For the preparation of buffer solutions.
- As reagents, for chemical syntheses.
- As cleaning agents.
Representative (examples)
- Aluminum hydroxide
- Amines
- Ammonia
- Ammonium hydrogen carbonate
- Ammonium hydroxide
- Calcium carbonate
- Calcium hydroxide
- Calcium oxide
- Guanidine
- Potassium hydrogen carbonate
- Potassium hydroxide
- Conjugate bases of acids
- Magnesium carbonate
- Magnesium hydroxide
- Sodium carbonate
- Sodium hydrogen carbonate
- Sodium hydroxide
- Sodium monohydrogen phosphate
- Triethanolamine
Many active ingredients are bases.
Adverse effects
Bases have corrosive and irritant properties and can cause burns to the skin, mucous membranes, and eyes. Ingestion of strong bases can be life-threatening. The appropriate precautions in the safety data sheet must be observed (e.g., protective gloves, fume hood, safety glasses, laboratory coat, respiratory protection).
