15 Facts on HCl + ZnS: What, How To Balance & FAQs

Zinc sulfide (ZnS) is a solid and white-colored compound that is soluble in HCl. Let us see the products obtained from the reaction between ZnS and HCl.

ZnS is a metal sulfide, and it reacts with strong hydrochloric acid (HCl) and forms Zinc chloride (ZnCl2) and hydrogen sulfide gas (H2S). H2S evolved from the reaction medium as bubbles.

This article discusses different relevant topics on type, balancing method, enthalpy, net ionic equation, and conjugate pairs of this reaction in detail.

What is the product of HCl and ZnS?

The product of the reaction between ZnS and HCl is zinc chloride (ZnCl2) and hydrogen sulfide gas (H2S).

ZnS (aq) + 2HCl (aq) = ZnCl2 (aq) + H2S (g)

What type of reaction is HCl + ZnS?

  • The reaction between HCl + ZnS is one type of Endothermic reaction (change of enthalpy is positive).
  • The reaction between HCl + ZnS is one type of a displacement reaction.

How to balance HCl + ZnS?

To balance a chemical reaction the following three steps should be followed.

  • The unbalanced equation of the reaction with a right arrow sign is written first as it is not balanced yet. ZnS (aq) + HCl (aq) ZnCl2 (aq) + H2S (g)
  • Mole numbers of the respective species will be determined on both the reactant and product sides.
ElementsReactant sideProduct side
Mole numbers of each of the chemical species
  • To balance the reactant and product sides we have to multiply 2 with the mole number of HCl. Therefore, mole numbers of hydrogen, as well as chlorine, will be balanced on both sides.
  • equation after balancing will be – ZnS (aq) + 2HCl (aq) = ZnCl2 (aq) + H2S (g).

HCl + ZnS Titration

Complexometric titration is performed between HCl and ZnS to perform the qualitative analysis of Zn2+ in any sample solution.


Erlenmeyer flask, 10 ml pipette, burette, and conical flask.


Eriochrome Black T (EBT) is used as the indicator in the complexometric titration of Zn2+.


  1. Zinc sulfide solution is prepared in dilute HCl and transferred into an Erlenmeyer flask.
  2. Dilute the solution with 100 mL distilled water and add 2 mL of ammonia buffer solution of pH 10.
  3. Add a very small amount of EBT indicator with NaCl (100 mg EBT + 20 g of analytical grade NaCl).
  4. Titrate this solution against standard EDTA solution. The color changes from purple blue to wine-red.

HCl + ZnS Net Ionic Equation

The net ionic equation of the chemical reaction between ZnS and HCl is-

 Zn2+ (s) + S2- (aq)+ 2H+ (aq) + 2Cl (aq) = Zn2+ (aq) + 2Cl (aq) + H2S (g)

HCL + ZnS Conjugate Pairs

The conjugate pair equation of HCl and ZnS is HCl + ZnS = Cl + HZnS+. The conjugate pair of acids is the anion after removing the H+ ion from acids and for the base, the positive ion formed after accepting an H+ ion from an acid.

HCl and ZnS Intermolecular Forces

The intermolecular forces act on HCl and ZnS are-

  • ZnS is an ionic metal sulfide. Therefore, the electrostatic force of attraction (Columbic force) is working between the zinc (Zn2+) and sulfide ion (S2-).
  • HCl is a covalent and polar molecule. Therefore, dipole-dipole, London Dispersion forces, and Van der Waals force is working in HCl.

HCl + ZnS Reaction Enthalpy

The enthalpy changes of the reaction between ZnS and HCl is 31.91 KJ/mol. The below mathematical calculation is done to calculate the change of enthalpy.

  • The enthalpy of the product side is -488.2 KJ/mol (for ZnCl2) and -20.17 KJ/mol (for H2S). The enthalpy values for the reactant side are -205.98 (ZnS), and -167.15 (HCl) KJ/mol.
  • The change of enthalpy = Total enthalpy of products – Total enthalpy of reactants = [-488.2 – 20.17– {-205.98 + 2×(-167.15)}] KJ/mol. = 31.91 KJ/mol.

Is HCl + ZnS a buffer solution?

HCl + ZnS is not a buffer solution because it is not the mixture of a weak acid and its conjugate base (CH3COOH and CH3COONa) or a weak base and its conjugate acid (NH4OH and NH4Cl). It is a displacement reaction between a metal sulfide and a strong acid.

Is HCl + ZnS a complete reaction?

HCl +ZnS can only be a complete reaction if it is written with its desired and actual products which are zinc chloride and hydrogen sulfide. The reaction will be completed when the concentration of the reactants becomes zero which indicates the reactants will be finished.

ZnS (s) + 2HCl (aq) = ZnCl2 (aq) + H2S (g)

Is HCl + ZnS an exothermic or endothermic reaction?

HCl + ZnS is an endothermic reaction because the change of enthalpy of this reaction is positive having the value of +31.9 KJ/mol and heat is absorbed on the product side and generated on the reactant side. It indicates that by increasing the temperature, the reaction equilibrium will shift toward the forward direction or product side.

Is HCl + ZnS a redox reaction?

HCl + ZnS is not a redox reaction because zinc, hydrogen, sulfur, and chlorine does not change their oxidation states from the reactant side to the product side. Therefore, no transfer of electrons occurs in this reaction between zinc sulfide and HCl. It is rather a displacement reaction.

Is HCl + ZnS a precipitation reaction?

HCl + ZnS is not a precipitation reaction because no precipitation of any of the two products forms in the reaction medium. Some amount of H2S evolves from the reaction medium and the rest of the H2S dissolves in the reaction medium along with ZnCl2.

Is HCl + ZnS reversible or irreversible reaction?

HCl + ZnS is an irreversible reaction because a gas (H2S) is produced on the product side. A gas always possesses a greater amount of entropy than solids and liquids. Therefore, the reaction becomes very fast, and the reaction equilibrium is shifted toward the forward direction (product side).

Is HCl + ZnS displacement reaction?

HCl + ZnS is a double-displacement reaction because, in this reaction, Zn2+ displaces the hydrogen ion from HCl and hydrogen also displaces the zinc ion (Zn2+) from ZnS and forms zinc chloride (ZnCl2) and hydrogen sulfide. Therefore, two displacements occur simultaneously between the reactants in this reaction.

hcl + zns
Double Displacement Reaction


Zinc sulfide also reacts with strong base, NaOH to give zinc hydroxide [Zn(OH)2] and sodium sulfide (Na2S). Not only zinc sulfide, but metal zinc also reacts with HCl and forms zinc chloride (ZnCl2) with hydrogen gas (H2).

Aditi Roy

Hello, I am Aditi Ray, a chemistry SME on this platform. I have completed graduation in Chemistry from the University of Calcutta and post graduation from Techno India University with a specialization in Inorganic Chemistry. I am very happy to be a part of the Lambdageeks family and I would like to explain the subject in a simplistic way. Let's connect through LinkedIn-https://www.linkedin.com/in/aditi-ray-a7a946202

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