Arrhenius Acid Concept in Chemistry

Acids and bases are chemical compounds showing distinct properties which make them usable in certain scenarios. For instance, automobile batteries use sulphuric acid, few fertilisers and detergents use acids for its composition. Likewise, bases like Calcium Hydroxide find its application in the manufacturing of bleaching powder. These acids and bases have numerous applications in chemical units, industries, and day to day life. 

While these have numerous applications, exposure to strong acids and bases can be harmful to you. Therefore, it is important to adhere to the safety measures while handling these corrosive chemicals. 

Now, an acid or base can be defined in multiple ways as there are three proposed theories –

1. Arrhenius acid and base theory. 

2. Bronsted-Lowry definition. 

3. Lewis theory. 

Here, we will discuss Arrhenius theory of acids in details. 

Arrhenius Acid and Base Definition

A Swedish scientist Svante Arrhenius, in the year 1884, proposed acid and base as the two classifications of compounds. According to him, an acid is a compound which can readily give up protons or Hydrogen ion in aqueous or water solution. 

For instance, take this equation into consideration. 

HCl(aq) → H+(aq) + Cl–(aq) 

Here, the solution of Hydrochloric acid with water entirely dissociates them into Hydrogen and Chlorine ions. When this aqueous solution of HCl is mixed with water, it releases hydronium ions as shown by the equation below – 

HCl(aq) + H2O(l) → H3O+(aq) + Cl–(aq) 

In a similar manner, acids such as HBr, CH3COOH (acetic acid), HNO3 (Nitric acid), HI (Hydro-iodic acid), H2SO3 (sulphurous acid), H2SO4 (sulphuric acid), H3PO4 (Phosphoric acid), H2CO3 (Carbonic acid), HCIO4 (Perchloric acid), HF (Hydrofluoric acid) follow the Arrhenius concept. 

According to the theory, a compound is known as Arrhenius base if it dissociates into OH– ions in its aqueous or water solution form. 

For instance, consider this equation to understand this theory. 

NaOH (aq) → Na+ (aq) + OH– (aq) 

Here, the aqueous solution of NaOH produces Hydroxide ions exhibiting the property of base. 

Basicity Property of Arrhenius Acids 

The basicity of any acid is the measure of H+ ions it can release. Further, understand this concept with the help of the following reaction – 

H3PO4 → H+ + H2PO4–

H2PO4– → H+ + HPO42–

HPO42– → H+ + PO43–

From the above equations, it is clear that H3PO4 releases three Hydrogen ions in its aqueous or water solution. Therefore, the basicity of H3PO4 acid will be equal to 3. 

Further, look at the table drawn below that shows the basicity values of different acids. 

Arrhenius Acid as Electrolytes 

Arrhenius was trying to learn the reason behind the conduction of electricity in solutions. He found out that the reason for conductivity was ions, primarily. His observation led to the speculation that acids like HNO3, HCl, H2SO4, etc. behave as electrolytes when they are dissolved in water. 

As per the Arrhenius definition of acid, for an ideal strong electrolyte solution, if 100 molecules of HCl are mixed with water, then it releases 100 H+ & 100 Cl– ions. Ideally, there is no molecule of HCl in the solution as this acts as strong acid and reacts with water to produce ions. 

1. Strong Acid 

A strong acid has the capability to get completely dissociated or ionised in the aqueous solution so that it increases the number of protons or H+ ions in the solution. Here, the acid dissociation constant is represented as Ka and is proportional to the strength of an acid. Therefore, a strong acid has a high magnitude of Ka. 

2. Weak Acid 

Few compounds fail to dissociate completely when added to the aqueous solution. These are known as weak acids which are a solution of un-dissociated weak acid along with partially dissociated ions. In the solution, the number of H+ ions are extremely low and hence their pH value is greater than that of strong acids. For weak acids, magnitude of Ka or the value of acid-dissociation constant is lesser than strong acids. 

Arrhenius Acid Example

The list of acids which qualify Arrhenius theory for acids is included in the table mentioned below. Have a look. 

In the solid or pure state, these exist as covalent compounds as the hydrogen ions are generated only when these are mixed with water as per Arrhenius acid base theory. 

Multiple-Choice Questions 

1. Choose the appropriate option which is true for Arrhenius acid. 

1. It is a compound which accepts hydrogen ions. 

2. When mixed with water, these release hydroxide ions. 

3. When mixed with water, these accept hydroxide ions. 

4. It is a compound which releases hydrogen ions in the solution. 

2. Choose the appropriate option which states the property of strong acid. 

1. The bond between hydrogen atoms and other elements is stronger in case of strong acids. 

2. Strong acids can easily bond with water. 

3. Strong acids are capable of dissociating entirely in the solution. 

4. Strong acids barely dissociate when mixed in the form of solution. 

3. If you pour an Arrhenius base into a beaker full of water, which ions will you find inside it? 

1. Hydroxide ions. 

2. Hydronium ions. 

3. Hydrogen ions. 

4. Water. 

4. Choose the appropriate option which depicts the hydronium ion formation. 

1. HCl (aq) ---> H+ (aq) + Cl- (aq)

2. HCl(aq) + NaOH(aq) ---> H20(l) + NaCl(aq)

3. H3O+(aq) ---> H+(aq) + H20(l)

4. HCl(aq) ---> H3O+(aq) + Cl-(aq)

5. Choose the appropriate option for application of pH scale. 

1. It is used to neutralise bases and acids. 

2. It is used for describing the chemical reaction between bases and acids. 

3. It is a scientific theory which helps determine the nature of bases and acids at a molecular level. 

4. It is utilised for measuring the concentration of hydrogen ions or hydronium ions in an aqueous solution.

6. Choose the right option for an aqueous solution whose pH range is in between 1 and 6. 

1. A base. 

2. An acid. 

3. A hydrocarbon. 

4. A neutral solution. 

7. Choose the appropriate equation depicting acid base neutralisation reaction. 

1. H3O+ (aq) ---> H+(aq) + H20 (l)

2. HCl (aq) ---> H+ (aq) + Cl

3. HCl (aq) + NaOH (aq) ---> H20 (l) + NaCl (aq)

4. HCl (aq) ---> H3O+ (aq) + Cl- (aq)

8. What is the effect of strong acid on litmus paper? 

1. It turns the red litmus paper blue. 

2. It turns the blue litmus paper blue. 

3. It turns the blue litmus paper blue. 

4. It turns the red litmus paper red. 

Now, get familiar with the important concepts related to Arrhenius with these study notes. You will be able to perform better in your examination and improve your knowledge about the two segregations of chemical compounds. So, if you want to give Arrhenius definition of an acid and a base precisely, refer to these study notes and learn with examples. You can also download Vedantu’s app for a more comprehensive learning approach. Refer to the study notes prepared by professional tutors and progress in your academic venture.