Hydrochloric acid vs. Sulfuric acid: The Differences

Acids are the species that donate protons. Hydrochloric acid and sulfuric acid both are strong acids but hydrochloric acid is stronger than the latter. The main difference between HCl and H₂SO₄ is that HCl is monoprotic whereas H₂SO₄ is a diprotic acid. Among many other differences between these acids, HCl is the one found in human bodies while H₂SO₄ is nowhere found inside our bodies.

HCl vs H₂SO₄

Molecular formula of HCl vs H₂SO₄

The molecular formula of hydrochloric acid is HCl. In this acid, hydrogen, and chlorine atoms are single bonded to each other.

Sulphuric acid has the molecular formula H₂SO₄. In this acid, the sulfur atom is present in the center and is bonded to the two (-OH) groups via single bonds and two oxygen atoms via double bonds. The configuration of sulfur in sulfuric acid is +6.

Read about single and double bonds.

The molar mass of HCl vs H₂SO₄

• HCl has a molar mass of 36.45 g/mol which means that it requires 36.45 grams of HCl in a dm³ solution to make a 1M hydrochloric acid solution.
• H₂SO₄ has a molar mass of 98.0 g/mol which means that it requires 98 grams of sulfuric acid in a dm³ solution to make a 1M sulfuric acid solution.

Preparation of HCl vs H₂SO₄

Preparation of Hydrochloric acid 

Hydrogen chloride is produced by the combination of chlorine with hydrogen. It is a gas and its acid solution is prepared by dissolving the hydrogen chloride gas in water.

Cl₂ + H₂ → 2HCl 

HCl can also be prepared by heating sodium chloride with concentrated sulfuric acid.

Preparation of Sulfuric acid 

Sulphuric acid is prepared by the contact process. This method was developed by Peregrine Phillips in the year 1831. Along with sulfuric acid, sulfur trioxide and oleum are also produced by this process.

In this method, the first step is the formation of sulfur dioxide (SO₂) by burning the sulfur over the air. 

S _(s) + O _(g) → SO_{2 (g)} 

SO₂ is oxidized into the SO₃ in the presence of catalyst V₂O₅ at 400-500 °C. 

The SO₃ obtained is converted into pyrosulfuric acid (oleum) by dissolving the 98% H₂SO₄. In the last step, the oleum is diluted with water to get any concentration of H₂SO₄. 

H₂SO_{4 (aq)} + SO_{3 (g)},→ H₂S₂O_{7 (l)} 

H₂S₂O_{7 (l)} + H₂O_(l)  → 2H₂SO_{4 (aq)} 

Related topics

• Uses of Hydrochloric acid
• Uses of Sulphuric acid
• Uses of Formic Acid
• Mineral acids

Dissociation in water for HCl vs H₂SO₄

Ionization of Hydrochloric acid 

HCl is a monoprotic acid and it dissociates into hydronium ion (H₃O⁺) and chloride ion (Cl^–) in water.

HCl _(g) + H₂O_(aq) → H₃O⁺_(aq) + Cl^–_(aq) 

Ionization of Sulfuric acid 

H₂SO₄ can donate 2H⁺ ions per molecule. It means that it is a diprotic acid. It dissociated into hydronium ion (H₃O⁺) and sulfate ion (SO₄^2-) in water.

H₂SO_{4 (aq)} + H₂O _(l) → HSO₄^– _(aq) + H₃O⁺ _(aq) 

HSO₄^– _(aq)  + H₂O_(l) → SO₄^2-_(aq) + H₃O⁺_(aq) 

Acidic strength of HCl vs H₂SO₄

Sulfuric acid and hydrochloric acids both are highly strong acids as compared to other acids but still, HCl is a stronger acid than H₂SO₄. This is because of the difference in the pK_a value of both acids. The pKa value of HCl is -6.3 while for H₂SO₄ it is -2.8. 

Reaction of lead nitrate with HCl vs H₂SO₄

Hydrochloric acid reacts with lead nitrate and produces lead chloride. It is insoluble in cold water but soluble in hot water. 

Pb(NO₃)₂ + HCl → PbCl₂ + 2HNO₃

Sulphuric acid reacts with lead nitrate and produces lead sulfate. It is insoluble in both hot and cold water. 

Pb(NO₃)₂ + H₂SO₄ → PbSO₄ + 2HNO₃ 

Although there are many other methods of differentiation for hydrochloric and sulfuric acids, this is an easy way. Lead nitrate Pb(NO₃)₂ dissolved in these acids will differ among them upon dissolution in hot water. In HCl, it will be a clear solution, but in the case of H₂SO₄, some precipitates will form.

Applications of HCl vs H₂SO₄

Hydrochloric and sulfuric acids are widely used in laboratories, for domestic and industrial purposes. Some of such applications are as follows:

Applications of Hydrochloric acid

1. HCl is used to remove rust or iron oxide from iron. 
2. The manufacture of oils involves HCl. 
3. It is used in the food industry such as for the production of corn syrups. 
4. It is used in the production of many organic chemicals. For example, polycarbonate resins, bisphenol A, etc. 
5. Purification of sand and clay is also accomplished in the presence of HCl, etc.
6. Removing metal stains is not difficult for hydrochloric acid.
7. The production of organic and inorganic compounds is a major function of HCl in lab chemistry.
8. It is used in the purification of table salt and its pH control.
9. HCl actively regulates drinking water production, sewage water treatment, and paper production.
10. Bleaching in the textile industry uses hydrochloric acid for the neutralization of alkaline agents, etc.

Applications of Sulfuric acid

1. H₂SO₄ is used as a drying agent. 
2. It is a major laboratory agent. 
3. Textile, leather iron, and steel industries specifically use H₂SO₄.
4. It is used in the manufacture of chemicals, dyes, plastics, paints, drugs, etc. 
5. The fertilizer industry uses sulfuric acid as a solvent.
6. Pigments and dyes are dissolved in sulfuric acid before application.
7. Petroleum refining is a major use of this acid.
8. It is an acid used in metallurgical processes.
9. Pharmaceutical industries use this acid to produce, purify and store drugs, etc.
10. Explosives contain sulfuric acid, etc.

Key Differences for Hydrochloric acid vs Sulfuric acid

Concepts Berg

Which one Is stronger HCl Or H₂SO₄?

HCl is a stronger acid than H₂SO₄. This is because HCl has a high value of the dissociation constant as compared to the H₂SO₄. The Ka value of HCl is 1.3 x 10⁶ while the H₂SO₄ has 1.0 x 10³. 

Is hydrochloric acid the strong acid?

Hydrochloric acid is a strong acid. This is because it dissociates completely into its ions in water. 

HCl_(aq) + H₂O_(l) → H₃O⁺_(aq) + Cl^–_(aq) 

Hydrochloric acid vs Sulfuric acid pH:

H₂SO₄ has a pH value lower than HCl. A lower pH value means more concentration of H⁺ ions. That is why HCl is a stronger acid than H₂SO₄. 

What would happen if you swallowed H₂SO₄?

If H₂SO₄ is swallowed then it causes severe damage to the esophagus and stomach. It can lead to the failure of many organs which may result in the death of a person.

What happens if we drink hydrochloric acid?

If we drink very dilute hydrochloric acid, it does not affect us. This is because our stomach also produces hydrochloric acid. But if it is very concentrated, it will burn our mouth and esophagus. 

Can hydrochloric acid melt or dissolve the PVC pipe?

Hydrochloric acid damages the PVC pipes. This is because it reacts with water excessively and produces a lot of heat which damages the PVC pipe.

References

• Uses of Sulphuric Acid By Arthur Edward Wells (Bureau of Mines, USA)
• Handbook of Clay Science By Faïza Bergaya (University of Orléans, France) and Gerhard Lagaly (Christian-Albrechts-Universität zu Kiel)
• Sulphuric, hydrochloric, nitric, and phosphoric acids (av.se)
• Dissociation of acids (Nottingham.ac.uk)