The Chemistry Behind H2SO4 + As2S3: 15 Facts You Should Know

As2S3 a lyophobic colloid occurs as an orpiment of deep yellow red in color. H2SO4 king of all acids is known as the oil of vitriol. Let us see how the As2S3 reacts with the H2SO4.

As2S3 is a mono clinic crystal and a negatively charged sol with 3.46 g/cm3 density. It is used in glass, oil cloth, linoleum and intrinsic p – type semiconductors. Sulfur in H2SO4 is sp3 hybridized with a C2 point symmetry group and tetrahedral shape. It is reactive to metals, ionizes 100 %, and acts as a battery acid.

In this article, we will discuss important facts about H2SO4 + As2S3 chemical reactions such as reaction enthalpy, the heat required, the product formed, the type of reaction, the type of intermolecular forces between their compounds, etc.

What is the product of H2SO4 and As2S3

Arsenic acid (H3AsO4), Sulfur dioxide (SO2), and H2O (water) are formed when Arsenic trisulfide (As2S3) reacts with sulfuric acid (H2SO4).

As2S3 + 11 H2SO4 → 2 H3AsO4 + 14 SO2 + 8 H2O

What type of reaction is H2SO4 + As2S3

H2SO4 + As2S3 falls under Double Displacement (Salt metathesis), redox, and exothermic reaction.

How to balance H2SO4 + As2S3

The unbalanced molecular equation for H2SO4 + As2S3 is.

As2S3 + H2SO4 →H3AsO4 + SO2 +H2O

To balance this equation, we should follow the steps given below:

  • Here, the number of H, O, As and S atoms is not the same on both sides of the reaction. So we will multiply these atoms with some coefficients so that they become equal.
  • The total number of As atoms on the reactant side is 2 while on the product side it is 1.
  • So, we multiply the H3AsO4 with a coefficient of 2 on the product side so that the number of As atoms become 2 on both sides of the reaction.
  • As2S3 + H2SO4 → 2 H3AsO4 + SO2 +H2O
  • Now, 2 H atoms are present on the reactant side while it is 8 on the product side of the reaction.
  • So, we multiply H2SO4 with a coefficient of 11 on the reactant side and H2O multiply with 8 on the product side so that the number of H atoms becomes 22 on both sides of the reaction.
  • As2S3 + 11 H2SO4 → 2 H3AsO4 + SO2 +8 H2O
  • 14 S and 44 O atoms are present on the reactant side while it is 1 on the product side so we multiply SO2 with a 14 coefficient so that the number of S and O atoms becomes 14 and 44 respectively on both sides of the reaction.
  • Finally, the balanced equation is:
  • As2S3 + 11 H2SO4 → 2 H3AsO4 + 14 SO2 + 8 H2O

H2SO4 + As2S3 titration

The titration of H2SO4 is not valid against As2S3.

H2SO4 + As2S3 net ionic equation

The net ionic equation of H2SO4 + As2S3 is as follows:

As2S3 (s) +16 H+ (aq) +11SO42– (aq) = 6 AsO4 (aq) + 14SO2 (g) + H2O (l)

To get the net ionic equation for H2SO4 + As2S3, we should follow the steps given below:

  • Write the general balanced molecular equation.
  • As2S3 + 11 H2SO4 → 2 H3AsO4 + 14 SO2 + 8 H2O
  • Now the solubility equation for H2SO4 + As2S3 is written by labeling the state or phase (s, l, g or aq) of each substance in the balanced molecular equation of H2SO4 + As2S3.
  • As2S3 (s) + 11 H2SO4 (aq) → 2 H3AsO4 (aq) + 14 SO2 (g) + 8 H2O (l)
  • Break all aquatic soluble ionic substances into their corresponding ions to get the balanced ionic equation.
  • As2S3 (s) +22 H+ (aq) +11SO42– (aq) = 6H+ (aq)+6 AsO4(aq)+14SO2 (g)+H2O(l)
  • To get the net ionic equation, remove spectator ions (H+) from the reactant and product side of the balanced ionic equation.
  • Finally, the net ionic equation for H2SO4 + As2S3 is:
  • As2S3 (s) +16 H+ (aq) +11SO42– (aq) = 6 AsO4 (aq) + 14SO2 (g) + H2O (l)

H2SO4 + As2S3 conjugate pairs

The conjugate pairs (compounds differ by one proton in their respective pair) in H2SO4 + As2S3 are:

  • The conjugate base of H2SO4 acid is HSO4.
  • The conjugate base of H2O is OH.
  • The conjugate base of H3AsO4 is H2AsO4.
  • As2S3 and SO2 do not have their conjugate pairs because both compounds do not contain hydrogen atom that can remove as proton ion.

H2SO4 and As2S3 intermolecular forces

The intermolecular forces that work on H2SO4, As2S3, H3AsO4, SO2 and H2O are-

  • Dipole-dipole force, London dispersion force, and hydrogen bonding are present in H2SO4 molecules due to their polar and unsymmetrical nature.
  • Van der Waals forces are present in polar covalent As2S3.
  • The hydrogen bonding present in H3AsO4 is due to three OH groups present in it.
  • The dipole dipole interaction is present in SO2 as it is a polar molecule.
  • Hydrogen bonds, dipole-induced dipole forces, and London dispersion forces exist in H2O due to their strong polar and ionic nature.

H2SO4 + As2S3 reaction enthalpy

The net enthalpy change of the reaction H2SO4 + As2S3 is -28.60 kJ/mol. The value is gained from the following mathematical calculation.

CompoundStandard Formation Enthalpy (ΔfH°(Kj/mol))
H2SO4 -735.13
Standard Formation Enthalpy of Compounds
  • ΔH°f = ΣΔH°f (products) – ΣΔH°f (reactants) (kJ/mol)
  • ΔHf = [2*( -904.6 ) +8 *(-285.83) +14 *(-297) -(11* (-735.13) +(-169 )] kJ/mol
  • ΔHf = -28.60 kJ/mol

Is H2SO4 + As2S3 a buffer solution

As2S3 + H2SO4 is not a buffer solution because H2SO4 is a strong acid and a buffer solution contains a weak acid and its conjugate base or a weak base and its conjugate acid.

Is H2SO4 + As2S3 a complete reaction

As2S3 + H2SO4 is a complete reaction because in this reaction As2S3 and H2SO4 are completely consumed and converted into the final product (H3AsO4, SO2 ) successfully.

Is H2SO4 + As2S3 an exothermic or endothermic reaction

As2S3 + H2SO4 reaction is an exothermic reaction because the net change of enthalpy is negative (i.e., ΔHf < 0, -28.60 kJ/mol) where the -ve sign interprets the following facts about the reaction:

  • 28.60 kJ/mol heat is released by the reactants As2S3 and H2SO4  due to the formation of less energetic acid H3AsO4
  • Heat emission by As2S3 and H2SO4 rises the energy of surroundings and makes the products stable.

Is H2SO4 + As2S3 a redox reaction

H2SO4 + As2S3 is a redox reaction where As2S3 is a reducing agent, H2SO4 is an oxidizing agent, and the electron transportation occurs as follows:

  • As+3 – 2 e → As+5 (oxidation)
  • S-2 – 6 e →  S+4 (oxidation)
  • S+6 + 2 e → S+4 (reduction)

Is H2SO4 + As2S3 a prcipitation reaction

As2S3 + H2SO4 is not a precipitation reaction because the completion of the reaction provides the H3AsO4 as the main product that is dissolved in reaction media. 

Is H2SO4 + As2S3 reversible or irreversible reaction

As2S3 + H2SO4 is an irreversible reaction because the products H3AsO4 and SO2 are stable so they do not need to react with each other to form reactants back.

Is H2SO4 + As2S3 displacement reaction

As2S3 + H2SO4 is a double displacement reaction because, in this reaction, sulfate ion (SO42–) and sulfide ion (S2- ) exchange their places with each other to form new products, H3AsO4 and SO2.


This article concludes that As2S3 + H2SO4 reaction is carried out through a double displacement mechanism and produces more stable H3AsO4 and SO2 by emitting approximately 28 KJ/mol energy. The As2S3 + H2SO4 reaction displays the cyclic voltammograms due to electron transportation.

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