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Acids and Bases play an important role in chemistry. We see them everywhere in our day to day lives, from our cleaning agents; soaps and detergents, to baking soda. Acids and bases (alkaline earth metal chemical element) are 2 categories of corrosive substances. Any compound with a pH value between zero to seven is considered acidic, whereas a pH value between seven to fourteen is a base. An acid is called a proton donor, while a base is called a proton acceptor (Kolb, 1978).

Difference in Definition

Acid

An acid is a molecule or substance that has a pH value less than 7.0 when it is present in an aqueous solution. An aqueous solution is any solution where water is a solvent. Acids are termed as compounds that donate H+ (hydrogen ion) to another compound known as base.

Base

A base (alkaline) is a molecule or substance that has a pH value higher than 7.0 when present in an aqueous solution. Bases are the exact chemical opposite of acids. In chemistry. They are substances that, in aqueous solution, release hydroxide (OH) ions.

Arrhenius Concept (Ouertatani et al, 2007)

Acids

As per Arrhenius Concept, an acid elevates the concentration of Hydrogen ions when dissolved in water.

Bases

As per Arrhenius Concept, a base is a compound that increases the concentration of hydroxide ions (OH) when dissolved in water.

Bronsted-Lowry Concept (Kauffman, 1988)

Acids

In the Bronsted-Lowry Concept, acids are substances which donate protons

Bases

Bases, on the other hand, are substances which accept protons

Lewis Concept (Brewer, 1984)

Acids

Ions that accept the pair of electrons (electron pair acceptor – an electrophile), and possess vacant orbitals are termed ‘Lewis acid’.

Bases

Ions that donate a pair of electrons (electron pair donor – a nucleophile), and possess a lone pair of electrons are termed ‘Lewis base’.

Difference in Classification

Acids

Acids are classified as:

  • Strong acids, such as nitric acid (HNO3), sulfuric acid (H2SO4), and hydrochloric acid (HCl) respectively.
  • Strong Lewis acids, such as AlCl3 (anhydrous aluminium chloride) and BF3 (boron trifluoride).
  • Concentrated weak acids, such as acetic acid (CH3COOH) and formic acid (CH2O2).
  • Lewis acids with specific reactivity, for example; solutions of ZnCl2 (zinc chloride).
  • Superacids, which are extremely strong acids.

Bases

Bases are classified as:

  • Alkalis or Caustics, such as NaOH (sodium hydroxide) and KOH (potassium hydroxide).
  • Concentrated weak bases, such as NH3 (ammonia) in a concentrated solution.
  • Alkali metals in metallic form, (i.e. elemental sodium), and hydrides of alkaline and alkali earth metals, i.e. NaH (sodium hydride), which function as a strong hydrate and bases to produce caustics.
  • Superbases, which are extremely strong bases, such as metal amides, alkoxides, (i.e. NaNH2 – sodium amide) and C4H9Li (butyllithium), which is an organometallic base.

Difference in Chemical Formula

Acids

The chemical formula for most acids starts with H. For example, Nitric acid (HNO3), Carbonic acid in soft drink (H2CO3), Boric acid (H3BO3), Hydrochloric acid (HCl), Oxalic Acid (H2C2O4), Citric Acid or 2-Hydroxy-1,2,3-propanetricarboxylic acid (H3C6H5O7), and Sulfuric acid (H2SO4). However, there are exceptions like Acetic Acid (CH3COOH).

Bases

The chemical formula for most bases (compounds) has OH at the end. For example, Calcium hydroxide or slaked lime, Ca (OH)2 (paper, flocculant), Magnesium hydroxide (Mg (OH)2) or milk of magnesia, Sodium hydroxide (NaOH) or caustic soda (cleaning agent, pH regulator), Ammonium hydroxide (NH4OH) or ammonia water and KOH (Potassium hydroxide).

Difference in pH

Acids

Acids have a pH less than 7.0.

Bases

Bases have a pH higher than 7.0, and could even go up to 14 if the bases are very strong.

Strength of Acids and Bases

Acids

The strength of acids depends on the concentration of hydronium ions (Umansky, 1991).

Bases

The strength of bases depends on the concentration of hydroxide ions.

Differences in Physical Characteristics

Both acids and bases are different in their physical properties.

Acids

When dissolved in water, acids

  • Are Sticky
  • Have a burning sensation
  • Change blue litmus to red color
  • Are sour in taste
  • React with bases for neutralization of their properties
  • Conduct electricity
  • React with active metals to liberate H (Hydrogen)
  • Remain colorless when Phenolphthalein is added to the solution.

Bases

When dissolved in water, bases

  • Are bitter in taste
  • Are (except ammonia)
  • Change red litmus to blue color
  • Are slippery to the touch
  • React with acids to neutralize their respective properties
  • Turn pink when Phenolphthalein is added to the solution.

Difference in Ionization

Acids

Acids are species or compounds that break apart in H2O to form a hydrogen ion (H+). So, it can be said that acids form Hydronium ions on ionization (Schultz, 1997).

Bases

Bases result in Hydroxyl ions on ionization (Nyasulu et al, 2013).

Difference in Dissociation

Acids

Acids release H+ (Hydrogen ions) when mixed with water (H20).

Bases

Bases release OH (Hydroxide ions) when mixed with water (H20).

Differences in Uses

Acids

  • Used for household cleaning.
  • Used for industrial purposes: Acids, i.e. Sulfuric acid and Nitric acid are both commonly used in paints, dyes, fertilizers, and explosives.
  • Used as a metal dissolver: Hydrochloric acid (HCl) is used to make aqua regia, that assists in dissolving noble metals like platinum and gold (Jadhav & Hocheng, 2015).
  • Acids (i.e. Sulfuric acid) are used to make batteries for flashlights and cars. Sulfuric acid is also used in mineral processing (Ntengwe, 2010).
  • They are used to ward off rust and corrosion from metals, by means of a technique termed ‘pickling.’
  • In the chemical industry, acids are used as neutralizers in the production of salts. For example, nitric acid (HNO3) reacts with ammonia NH3 for production of ammonium nitrate – a fertilizer.

Bases

  • Sodium hydroxide (NaOH) is used in manufacturing soap, synthetic fiber rayon and paper. It is also used in manufacturing some medicines and petroleum-refining, in cleaning sinks, ovens and drains (Malkin, 2003).
  • Sodium bicarbonate (NAHCO3) is used in toothpaste, fire extinguisher, and baking soda.
  • Calcium hydroxide (slaked lime) is used in the manufacture of bleaching powder. It is mixed with water and sand to create mortar that is used in the construction of buildings. Slaked lime is also made use by the farmers on the fields for neutralizing the dangerous effects of acid rain. Calcium hydroxide also neutralizes the acid in water supplies, and is used as a dressing material for burns caused by acid, as an antidote for cases of food poisoning, in the making of fungicides, in the whitewash mixture, and in dentistry (Smith et al, 2014) (Mohammadi & Dummer, 2011).
  • Alkalis (Bases) are used in alkaline batteries like potassium hydroxide (Salkind, & Klein, 2000). They are also used in antiperspirant armpit deodorant, and in neutralizing soil acidity (Stenzaly‐Achtert et al, 2000) (Merry, 2009).
  • Ammonium hydroxide (NH4OH) is used to clean grease stains from clothes (Malanova et al, 2014).

Comparison Chart – Acids VS Bases

Characteristics

Acids

Bases

Definition

A substance, mostly liquid that donates a proton or accepts an electron pair in reactions. An acid increases the concentration of H+ ions.A base is a substance that releases hydroxide (OH-) ions in aqueous solution, donates electrons and accepts protons.

Bronsted Lowry Definition

An acid is a proton donor.A base accepts a proton.

pH (concentration of hydrogen ions in a solution)

Acids possess a pH value <7.Bases possess a pH value >7.

Phenolphthalein indicator

An acid remains colorless.A base gives a pink color.

Litmus paper test

Turns blue litmus paper to red color.Turns red litmus paper to blue color.

Chemical formula

The chemical formula begins with H in case of acids. For example, Hydrochloric acid (HCl).The Chemical formula ends with OH in case of bases. For example, Sodium Hydroxide (NaOH).

Strength

Depends on the concentration of hydronium ions.Depends on the concentration of hydroxide ions.

Dissociation

Acids dissociate to release hydrogen ions (H+) when mixed with water.Bases dissociate to release hydroxide ions (OH) when mixed with water.

Uses

Used as a household cleaning agent, in carbonated drinks, in processing leather, and in preservatives and fertilizers.Used in soaps, detergents, gastric medicines (antacid).

Conclusion

Acids and bases impact daily life because they play a major and important role in many reactions, from digesting food to removing soap scum off a shower wall. Acids and bases are significant in balancing the pH levels in the body so that it stays at a level of 7. When a person consumes acidic foods, the body uses a buffering system to neutralize the positive ions produced by the acids. On the other hand, bases are required to regulate and control the body from becoming too alkaline.

We conclude that both acids and bases are an important part of life, and are found in the environment, in foods, and in chemicals, including pharmaceuticals. They are vital, not only in the chemistry laboratory but also in our daily lives.

References

  1. Brewer, L. (1984). The generalized Lewis acid-base theory: Surprising recent developments.
  2. Jadhav, U., & Hocheng, H. (2015). Hydrometallurgical recovery of metals from large printed circuit board pieces. Scientific reports, 5, 14574.
  3. Kauffman, G. B. (1988). The Bronsted-Lowry acid-base concept. Journal of Chemical Education, 65(1), 28.
  4. Kolb, D. (1978). Acids and bases. Journal of Chemical Education, 55(7), 459.
  5. Malanova, N. V., Korobochkin, V. V., & Кosintsev, V. I. (2014). The application of ammonium hydroxide and sodium hydroxide for reagent softening of water. Procedia Chemistry, 10, 162-167.
  6. Malkin, H. M. (2003). Concept of acid-base balance in medicine. Annals of Clinical & Laboratory Science, 33(3), 337-344.
  7. Mohammadi, Z., & Dummer, P. M. H. (2011). Properties and applications of calcium hydroxide in endodontics and dental traumatology. International endodontic journal, 44(8), 697-730.
  8. Ntengwe, F. W. (2010). The leaching of dolomitic-copper ore using sulfuric acid under controlled conditions. Open Mineral Processing Journal, 3, 60-67.
  9. Nyasulu, F., McMills, L., & Barlag, R. (2013). Weak Acid Ionization Constants and the Determination of Weak Acid-Weak Base Reaction Equilibrium Constants in the General Chemistry Laboratory. Journal of Chemical Education, 90(6), 768-770.
  10. Ouertatani, L., Dumon, A., Trabelsi, M. A., & Soudani, M. (2007). Acids and bases: The appropriation of the Arrhenius model by Tunisian grade 10 students. International Journal of Science and Mathematics Education, 5(3), 483.
  11. Salkind, A. J., & Klein, M. (2000). Batteries, Alkaline Secondary Cells. Kirk‐Othmer Encyclopedia of Chemical Technology.
  12. Schultz, E. (1997). Ionization or dissociation? Journal of chemical Education, 74(7), 868.
  13. Smith, A. N. D. R. E. W., Verhelst, F. R. E. D. E. R. I. K., Denayer, C. H. R. I. S. T. O. P. H. E., & Givens, R. I. C. H. A. R. D. (2014). Quantifying the benefits of lime additions in cement-based mortars. In Proceedings of the IMC.
  14. Stenzaly‐Achtert, S., Schölermann, A., Schreiber, J., Diec, K. H., Rippke, F., & Bielfeldt, S. (2000). Axillary pH and influence of deodorants. Skin Research and Technology, 6(2), 87-91.
  15. Umansky, B., Engelhardt, J., & Hall, W. K. (1991). On the strength of solid acids. Journal of Catalysis, 127(1), 128-140.