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

Hydrochloric acid Sulfuric acid
The molecular formula of hydrochloric acid is HCl 
The molecular formula of sulfuric acid is H2SO4
Its molecular mass is 36.45 g/mol Its molecular mass is 98.0 g/mol  
HCl has a pungent smell 
H2SO4 is odorless
The specific gravity or density of hydrochloric acid is 1.18 g/cm3
The specific gravity or density of sulfuric acid is 1.83 g/cm3
HCl has a pKa value of -6.3
H2SO4 has a pKa value of -2.8
It is a monoprotic acid (releases one proton per molecule)  It is a diprotic acid (releases two protons per molecule) 
HCl is stronger than H2SO4
H2SO4 is weaker as compared to HCl

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.

HCl - hydrochloric acid

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.

H2SO4 - sulphuric acid

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) → SO2 (g) 

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

Oxidation reduction of sulfuric acid

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

H2SO4 (aq) + SO3 (g),→ H2S2O7 (l) 

H2S2O7 (l) + H2O(l)  → 2H2SO4 (aq) 

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 (SO42-) in water.

H2SO4 (aq) + H2O (l) → HSO4 (aq) + H3O+ (aq) 

HSO4 (aq)  + H2O(l) → SO42-(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 pKa 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)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

HCl vs H2SO4 - 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.

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