Arrhenius Acid: Definition, Examples, Uses, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 05:25 PM IST

The term "Arrhenius acid" refers to a material that contains a hydrogen atom and readily releases a hydrogen ion or proton when it is in contact with water. For instance, when hydrochloric acid dissolves in water, it produces the ions hydronium and chloride. Acetic acid (CH3COOH), which generates the acetate ion (CH3COO-) and the hydronium ion in its aqueous solution, functions similarly as an Arrhenius acid.

This Story also Contains

Arrhenius Acid
Arrhenius Base
Strong Electrolytes From Arrhenius Acid
A Strong Acid
Weak Acid
Arrhenius Acid Examples
Problems With The Arrhenius theory

Arrhenius Acid

Corrosive poisons typically affect the eyes and lungs. Burns caused by acids or bases may potentially harm the cornea. The respiratory system is corroded by air contaminants such as sulphur oxides, nitrogen oxides, chlorine, and ammonia.

Arrhenius Acid

Svante Arrhenius, a Swedish scientist, first put forth the Arrhenius hypothesis of acids and bases in 1884. He proposed categorising some substances as bases or acids based on the ions they produced when combined with water.

The concentration of protons or H+ ions is raised by the presence of Arrhenius acid in the aqueous solution. Taking hydrochloric acid in water as an illustration. As will be discussed below, HCl undergoes a dissociation reaction to produce the ions H+ and Cl-. By producing the hydronium ion, the H+ ion concentration is raised.

Examples:

HCl _{(aq)} \longrightarrow H^+_{(aq)} + Cl^-_{(aq)}

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HCl_{ (aq)} + H_2O_{(l)} \longrightarrow H_3O^+_{(aq)} + Cl^–_{(aq)}

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NHO_{3(aq)} + H_2O_{(l)} \longrightarrow H_3O^+_{(aq)} + No^-_3

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Arrhenius Base

A substrate that raises the number of hydroxide ions in an aqueous solution is known as an Arrhenius base. Highly soluble sodium hydroxide in water that separates into a sodium ion and hydroxide ion is an example of an Arrhenius base.

NaOH entirely dissolves to increase the concentration of hydroxide ions in an aqueous solution to produce sodium ions and hydroxide ions.

NaOH_{(aq)} \longrightarrow Na^+_{(aq)} + OH^–_{(aq)}

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Strong Electrolytes From Arrhenius Acid

When Arrhenius sought to understand why some solutions could carry an electric current, he discovered that conductivity resulted from the presence of ions. He noticed that the chemicals HCl, HNO3, and H2SO4 behave as potent electrolytes when dissolved in water. Ionization reactions in water produced this.

These compounds are known as strong acids because they are powerful electrolytes that generate H+ ions. Ionization reactions in water produced this.

According to studies, when HCl, HNO3, and H2SO4 are added to water, almost all of the molecules dissolve to produce ions. This means that 100 H+ ions and 100 Cl- ions are created when 100 HCl molecules are dissolved in water. Since these compounds are strong electrolytes that generate H+ ions and are hence referred to as strong acids, there are almost no HCl molecules in an aqueous solution.

A Strong Acid

In an aqueous solution, strong acids totally ionise and raise the concentration of protons (H+).

HA \longleftrightarrow H^+ + A^–

Acid dissociation constant is the name of the equilibrium constant for an acid's dissociation (Ka). Strong acids have a very high Ka magnitude. As a result, the relationship between an acid's strength and its dissociation constant is linear (Ka).

Weak Acid

Weak acids do not produce hydrogen ions because of partial or incomplete dissociation; instead, they exist as an equilibrium mixture of undissociated acid and the ions released after partial dissociation. Compared to strong acids, hydrogen ions have a high pH value and a very low quantity of them. When compared to strong acids, weak acids have a lower acid dissociation constant.

Arrhenius Acid Examples

Hydrochloric acid, or HCl, is an excellent illustration of an Arrhenius acid. The hydrogen ion and chlorine ion are formed when it dissolves in water:

HCl _{(aq)} \longrightarrow H^+_{(aq)} + Cl^-_{(aq)}

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Because of the dissociation's effect on the number of hydrogen ions in the aqueous solution, it is regarded as an Arrhenius acid.
Nitric acid, hydrobromic acid, and sulfuric acid () are further Arrhenius acids ().
Sodium hydroxide () and potassium hydroxide are examples of Arrhenius bases ().

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Problems With The Arrhenius theory

The Arrhenius theory only applies to aqueous solutions; for instance, it states that even if HCl gives an H+ ion to benzene, it is not an acid in aqueous solutions. Additionally, even though the amide ion deprotonates the ammonia, according to Arrhenius' definition, the sodium amide solution in liquid ammonia is not alkaline.

Frequently Asked Questions (FAQs)

1. What are the Arrhenius theory's drawbacks?

It falls short of explaining the basic properties of non-hydrogenated compounds like NH3, CaO, MgO, and others, as well as the acidic properties of non-hydrogenated molecules like CO2, SO2, and SO3.

2. What benefit does the Arrhenius hypothesis offer?

Aqueous media contain substances with acid-base properties. Acids and bases can be neutralised and hydrolyzed to varying degrees of strength.

3. How does it help Arrhenius define anything better?

An Arrhenius acid increases the concentration of hydrogen (H+) ions in an aqueous solution, whereas an Arrhenius base increases the concentration of hydroxide (OH-) ions. As a result, in Arrhenius acid-base reactions, the interaction between an acid and a base is a neutralisation reaction.

4. What Are Some of the Arrhenius Theory's Limitations?

By determining if an acid or base produces hydrogen ions or H+ ions, and an acid or base produces hydroxide ions, or OH- ions, the Arrhenius hypothesis for acids or bases only applies if the substance is dissolved in water or an aqueous solution. Any solution, not only aqueous ones, should have the same characteristics as an acid or base. Additionally, the Arrhenius theory is limited to aqueous solutions exclusively.

5. Is the Arrhenius basis robust or frail?

Strong bases are those that totally separate into the cation and OH- in water (hydroxide ion). Group I (alkali metals) and Group II (alkaline earth) metal hydroxides are typically regarded as strong bases. These Arrhenius bases are typical ones.

6. How do Arrhenius acids affect protein structure?

Arrhenius acids can denature proteins by disrupting their hydrogen bonds and electrostatic interactions. The increased H+ ion concentration can alter the ionization state of amino acid side chains, leading to changes in protein folding and potentially loss of function.

7. How do Arrhenius acids affect the freezing point of water?

Arrhenius acids, when dissolved in water, lower its freezing point. This is due to the colligative property of freezing point depression, where the presence of dissolved ions interferes with the formation of ice crystals, requiring a lower temperature for freezing.

8. How do Arrhenius acids contribute to the formation of coordination compounds?

Arrhenius acids can play a role in forming coordination compounds by providing an acidic environment that facilitates the dissociation of metal salts. The H+ ions can also compete with metal ions for ligands, influencing the stability and formation of metal complexes.

9. How do Arrhenius acids affect the boiling point of water?

Arrhenius acids increase the boiling point of water when dissolved in it. This is due to the colligative property of boiling point elevation, where the presence of dissolved ions increases the energy required for the liquid to vaporize.

10. What is the role of Arrhenius acids in the human digestive system?

Hydrochloric acid, an Arrhenius acid, is a key component of stomach acid. It helps in protein digestion by denaturing proteins and activating pepsin enzymes. The low pH created by this acid also helps protect against ingested pathogens.

11. What is an Arrhenius acid?

An Arrhenius acid is a substance that increases the concentration of hydrogen ions (H+) when dissolved in water. This definition, proposed by Swedish chemist Svante Arrhenius in 1884, forms the basis for understanding acid-base chemistry in aqueous solutions.

12. Can you explain the dissociation of an Arrhenius acid in water?

When an Arrhenius acid dissolves in water, it dissociates into its constituent ions. The hydrogen atom separates from the rest of the molecule, releasing H+ ions (protons) into the solution. This increases the concentration of H+ ions in the water, making the solution acidic.

13. What is the relationship between Arrhenius acids and hydronium ions?

When an Arrhenius acid dissociates in water, the released H+ ions quickly combine with water molecules to form hydronium ions (H3O+). In aqueous solutions, H+ ions exist primarily as hydronium ions, which are the actual acid species in solution.

14. How do Arrhenius acids participate in acid-catalyzed reactions?

Arrhenius acids can catalyze various chemical reactions by providing H+ ions. These ions can protonate reactants, making them more susceptible to nucleophilic attack or facilitating the removal of leaving groups. This is important in many organic synthesis reactions.

15. How do Arrhenius acids affect the solubility of gases in water?

Arrhenius acids can influence the solubility of gases in water. For some gases, like CO2, the presence of H+ ions can increase solubility by reacting with the dissolved gas. For others, the increased ion concentration may decrease gas solubility due to the salting-out effect.

16. What are some common examples of Arrhenius acids?

Common examples of Arrhenius acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3COOH), and phosphoric acid (H3PO4). These acids all release H+ ions when dissolved in water.

17. How do Arrhenius acids interact with metals?

Arrhenius acids can react with many metals to produce hydrogen gas and a metal salt. The H+ ions from the acid are reduced to H2 gas, while the metal is oxidized to form metal cations. This reaction is more vigorous with stronger acids and more reactive metals.

18. How do Arrhenius acids affect indicators?

Acid-base indicators change color depending on the pH of a solution. When an Arrhenius acid is added to water containing an indicator, the increased H+ ion concentration causes the indicator to change to its acidic form, resulting in a color change specific to that indicator.

19. How do Arrhenius acids contribute to acid rain?

Acid rain is primarily caused by the dissolution of acidic gases like sulfur dioxide and nitrogen oxides in atmospheric water. These gases form Arrhenius acids (sulfuric and nitric acids) when dissolved in rainwater, lowering its pH and causing environmental damage.

20. Can you explain the concept of acid-base titration involving Arrhenius acids?

Acid-base titration is a method to determine the concentration of an Arrhenius acid by neutralizing it with a base of known concentration. The endpoint is reached when the number of moles of H+ ions from the acid equals the number of moles of OH- ions from the base.

21. What is the relationship between Arrhenius acids and amphoteric substances?

Amphoteric substances can act as both acids and bases. In the context of Arrhenius theory, an amphoteric substance can produce H+ ions in some reactions (acting as an acid) and OH- ions in others (acting as a base), depending on the conditions and the other reactants present.

22. What is the concept of acid rain neutralization in relation to Arrhenius acids?

Acid rain neutralization involves counteracting the effects of Arrhenius acids (like sulfuric and nitric acids) in rainwater. This can be achieved by adding basic substances to affected water bodies or soil, or by reducing the emission of acid-forming pollutants into the atmosphere.

23. What is the role of Arrhenius acids in acid-base extraction techniques?

In acid-base extraction, Arrhenius acids are used to protonate basic compounds, making them more soluble in the aqueous phase. This technique is commonly used in organic chemistry to separate and purify compounds based on their acid-base properties.

24. What is the concept of acid-base homeostasis in biological systems?

Acid-base homeostasis refers to the maintenance of a stable pH in biological fluids, which is crucial for proper cellular function. It involves buffer systems that can neutralize small amounts of Arrhenius acids or bases, as well as physiological mechanisms for excreting excess acids or bases.

25. How does an Arrhenius acid differ from other acid definitions?

The Arrhenius definition is specific to aqueous solutions, while other definitions like Brønsted-Lowry and Lewis acids are more general. Arrhenius acids focus on the production of H+ ions in water, whereas Brønsted-Lowry acids are proton donors, and Lewis acids are electron pair acceptors.

26. Can you explain the concept of a conjugate base in relation to Arrhenius acids?

When an Arrhenius acid dissociates in water, the part of the molecule that remains after releasing the H+ ion is called the conjugate base. For example, when HCl dissociates, it forms H+ and Cl- ions. The Cl- ion is the conjugate base of HCl.

27. What is the role of water in the Arrhenius acid definition?

Water plays a crucial role in the Arrhenius acid definition as it provides the medium for dissociation. The polar nature of water molecules helps separate the H+ ions from the acid molecules and stabilizes them in solution. This is why the Arrhenius definition is specific to aqueous solutions.

28. What is the pH scale, and how does it relate to Arrhenius acids?

The pH scale measures the concentration of H+ ions in a solution, ranging from 0 to 14. Arrhenius acids have pH values below 7, with stronger acids having lower pH values. The pH scale is logarithmic, meaning each unit change represents a tenfold change in H+ concentration.

29. How do polyprotic Arrhenius acids behave in water?

Polyprotic Arrhenius acids can donate more than one H+ ion per molecule. They dissociate in steps, releasing one H+ ion at a time. Each step has its own dissociation constant, with the first dissociation typically being the strongest. Examples include H2SO4 and H3PO4.

30. What is the relationship between Arrhenius acids and electrical conductivity?

Arrhenius acids increase the electrical conductivity of water when dissolved. This is because the dissociation of the acid produces ions (H+ and the conjugate base) that can carry electric current. Stronger acids and higher concentrations generally result in higher conductivity.

31. How do Arrhenius acids affect the surface tension of water?

Arrhenius acids generally increase the surface tension of water when dissolved in it. This is due to the strong interactions between water molecules and the ions produced by the acid, which can strengthen the cohesive forces at the water's surface.

32. How do Arrhenius acids affect the viscosity of aqueous solutions?

Arrhenius acids generally increase the viscosity of water when dissolved in it. This is due to the increased interactions between water molecules and the ions produced by the acid, which can hinder the flow of the solution.

33. What is the concept of leveling effect in relation to Arrhenius acids?

The leveling effect occurs when a very strong Arrhenius acid is dissolved in water. Water acts as a base, accepting protons from the acid. As a result, the strongest acid that can exist in aqueous solution is the hydronium ion (H3O+), which "levels" the strength of all strong acids in water.

34. What is the role of Arrhenius acids in redox reactions?

In redox reactions, Arrhenius acids can act as oxidizing agents due to the presence of H+ ions. These ions can accept electrons, being reduced to hydrogen gas. This property is utilized in various chemical processes and in understanding corrosion mechanisms.

35. How does the strength of an Arrhenius acid relate to its dissociation?

The strength of an Arrhenius acid is determined by its degree of dissociation in water. Strong acids dissociate completely, releasing all their H+ ions, while weak acids only partially dissociate. The more H+ ions released, the stronger the acid.

36. How does temperature affect the behavior of Arrhenius acids?

Temperature can influence the dissociation of Arrhenius acids. Generally, as temperature increases, the degree of dissociation also increases, leading to a higher concentration of H+ ions in solution. This can result in a slight decrease in pH as temperature rises.

37. How does the concentration of an Arrhenius acid affect its pH?

As the concentration of an Arrhenius acid increases, more H+ ions are released into the solution, resulting in a lower pH. However, due to the logarithmic nature of the pH scale, a tenfold increase in acid concentration only decreases the pH by one unit.

38. What is the difference between a strong and weak Arrhenius acid?

Strong Arrhenius acids dissociate completely in water, releasing all their H+ ions. Weak Arrhenius acids only partially dissociate, reaching an equilibrium with a significant amount of undissociated acid molecules remaining. Strong acids have lower pKa values and produce more H+ ions in solution.

39. Can you explain the concept of acid dissociation constant (Ka) for Arrhenius acids?

The acid dissociation constant (Ka) is a measure of the strength of an Arrhenius acid in water. It represents the equilibrium constant for the dissociation reaction of the acid. A larger Ka value indicates a stronger acid, as it means more H+ ions are produced at equilibrium.

40. What is the role of Arrhenius acids in buffer solutions?

Arrhenius acids can be components of buffer solutions, which resist changes in pH when small amounts of acid or base are added. A weak Arrhenius acid and its conjugate base can form a buffer system, maintaining a relatively stable pH in the solution.

41. What is the concept of percent dissociation for weak Arrhenius acids?

Percent dissociation refers to the fraction of acid molecules that have dissociated into ions in solution. For weak Arrhenius acids, this value is less than 100% and depends on the acid's strength and concentration. It can be calculated using the acid's Ka value and initial concentration.

42. How do Arrhenius acids interact with carbonates and bicarbonates?

Arrhenius acids react with carbonates and bicarbonates to produce carbon dioxide gas, water, and a salt. This reaction is the basis for the fizzing observed when acids are added to baking soda (sodium bicarbonate) or limestone (calcium carbonate).

43. What is the concept of equivalent weight for Arrhenius acids?

The equivalent weight of an Arrhenius acid is the mass of acid that can provide one mole of H+ ions. For monoprotic acids, it's equal to the molecular weight. For polyprotic acids, it's the molecular weight divided by the number of ionizable H+ ions per molecule.

44. What is the concept of Lewis acidity in relation to Arrhenius acids?

While Arrhenius acids are defined by their ability to produce H+ ions in water, Lewis acidity is a broader concept. Many Arrhenius acids are also Lewis acids because the H+ ion (or H3O+) can accept an electron pair. However, not all Lewis acids are Arrhenius acids.

45. How do Arrhenius acids contribute to the formation of acid anhydrides?

Acid anhydrides are formed when water is removed from two molecules of an Arrhenius acid. For example, two molecules of sulfuric acid can form sulfur trioxide (an acid anhydride) and water. Anhydrides can react with water to reform the original Arrhenius acid.

46. What is the concept of acid strength in terms of electron-withdrawing groups?

The strength of an Arrhenius acid can be influenced by electron-withdrawing groups in its molecular structure. These groups pull electron density away from the H-X bond, making it easier for the H+ ion to dissociate, thus increasing the acid strength.

47. How do Arrhenius acids interact with zwitterions?

Zwitterions are molecules with both positive and negative charges. Arrhenius acids can protonate the negatively charged group of a zwitterion, potentially changing its overall charge and affecting its solubility and other properties.

48. What is the role of Arrhenius acids in the formation of coordination polymers?

Arrhenius acids can play a crucial role in the synthesis of coordination polymers by providing an acidic environment that influences the formation and stability of metal-ligand bonds. The pH can affect the protonation state of ligands and the solubility of metal ions.

49. How do Arrhenius acids contribute to the concept of supersaturation?

Arrhenius acids can induce supersaturation in some solutions by altering the solubility of compounds. For example, decreasing the pH can increase the solubility of certain salts, allowing a solution to hold more dissolved solute than it normally would at equilibrium.

50. What is the relationship between Arrhenius acids and the common ion effect?

The common ion effect occurs when an ion common to two solutes is added to a solution, affecting the solubility equilibrium. For Arrhenius acids, adding a salt with a common anion can suppress the dissociation of a weak acid, shifting its equilibrium towards the undissociated form.

51. How do Arrhenius acids affect the rate of chemical reactions?

Arrhenius acids can catalyze many chemical reactions by providing H+ ions. These ions can protonate reactants, making them more electrophilic and thus more reactive. This catalytic effect is important in various organic synthesis reactions and biological processes.

52. How do Arrhenius acids contribute to the formation of hydrogen bonds?

Arrhenius acids, particularly those with -OH groups, can form hydrogen bonds. The H+ ions produced by these acids can also participate in hydrogen bonding with water molecules or other species, influencing the properties of the solution and dissolved substances.

53. What is the role of Arrhenius acids in the process of acid hydrolysis?

Acid hydrolysis is a process where Arrhenius acids catalyze the cleavage of chemical bonds by water. This is important in various chemical reactions, including the breakdown of esters, amides, and glycosidic bonds in carbohydrates.

54. How do Arrhenius acids affect the solubility of ionic compounds?

Arrhenius acids can influence the solubility of ionic compounds in several ways. They can provide H+ ions that react with the anions of sparingly soluble salts, increasing their solubility. Conversely, for salts with anions of weak acids, increasing H+ concentration can decrease solubility due to the common ion effect.