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

HBr, or hydrobromic acid, is an inorganic acid, and ZnS (zinc sulfide) is a naturally occurring salt. Let us briefly discuss how they react to each other.

HBr is a powerful mineral acid with a pKa of -9 making it even more acidic than HCl. ZnS shows polymorphism and has two crystalline forms named zinc blende and wurtzite. Both forms are intrinsic with a wide band gap around 3.5 to 3.9 eV.

This article will primarily focus on the reaction products and the factors governing the reaction of HBr and ZnS.

What is the product of HBr and ZnS

ZnBr2 (zinc bromide) and H2S (hydrogen sulfide) are produced in the reaction HBr + ZnS.

HBr + ZnS → ZnBr2 + H2S

What type of reaction is HBr + ZnS

HBr + ZnS represents a double-displacement reaction.

How to balance HBr + ZnS

Following steps are followed to balance the above reaction HBr + ZnS.

HBr + ZnS → ZnBr2 + H2S

  • Counting the elements in the reactants and products is done in the first step.
Elements present Reactant sideProduct side
Number of elements
  • The elements being unequal in the equation are balanced using stoichiometric coefficients. 2 is added before HBr to balance the bromine and hydrogen and hence the balanced equation is
  • 2HBr + ZnS → ZnBr2 + H2S

HBr + ZnS titration

HBr + ZnS titration is an example of complexometric titration where the Zn2+ ion can be estimated qualitatively in a given simple.

Apparatus required

Burette, pipette, conical flask, Erlenmeyer flask.


Eriochrome Black T is the indicator used in this titration. The blue color indicator gives wine red color on complexation with the zinc ion.

HIn2- (blue color) + Zn2+ (colorless) = ZnIn (wine red)


  • Zinc sulfide solution is prepared by diluting it with the acid HBr to make a homogenous solution.
  • 25 ml of the solution is taken into the Erlenmeyer flask and diluted using distilled water.
  • To it about 2 ml of pH 10 buffer is added (this pH is required for the reaction) and 3 to 4 drops of the indicator are also added.
  • The resulting wine-red solution is titrated against a standard EDTA solution until the color again changes to blue. .
  • The color change is observed because EDTA displaces the indicator and forms a colorless complex with the zinc as Zn-EDTA is more stable than Zn-indicator complex.
  • The concordant readings are taken to calculate the amount of zinc ion present in the sample.

HBr + ZnS net ionic equation

The net ionic equation of HBr + ZnS is-

2H+(aq) + ZnS(s) → Zn2+(aq) + H2S (g)

The net ionic equation is derived by the below-listed steps.

  • The equation is balanced and written.
  • 2HBr + ZnS → ZnBr2 + H2S
  • Indicate the phases of the reactants and products is done in the next step.
  • 2HBr(aq) + ZnS(s) → ZnBr2(aq) + H2S(g)
  • The electrolytes (strong) are dissociated into ions afterward.
  • 2H+(aq) + 2Br(aq) + ZnS(s) → Zn2+(aq) + 2Br(aq) + H2S (g)
  • After crossing out the spectator ions we get the net ionic equation as-
  • 2H+(aq) + ZnS(s) → Zn2+(aq) + H2S (g)

HBr + ZnS conjugate pairs

HBr + ZnS forms a conjugate acid-base pair as-

HBr + S2- = H2S + Br

  • H2S is the conjugate acid of the base S2-.
  • Br serves as the conjugate base of HBr (acid).

HBr and ZnS intermolecular forces

The intermolecular forces present in HBr + ZnS are-

  • Dipole-dipole forces are observed between the molecules of HBr.
  • Ionic interactions are found in ZnS molecules.

HBr + ZnS reaction enthalpy

HBr + ZnS enthalpy of reaction is -7.05 KJ/mol. Using the values listed below and substituting them in the formula will give the reaction enthalpy.

Components involvedEnthalpy in KJ/mol
ZnBr2 397
Values of enthalpy
  • ∆Hf°(reaction) = ∆Hf°(products) – ∆Hf°(reactants)
  • = -417.27 – (-410.22) KJ/mol
  • = -7.05 KJ/mol

Is HBr + ZnS a buffer solution

HBr + ZnS will not act as a buffer solution as HBr is a strong acid and for the buffer, a weak acid is used.

Is HBr + ZnS a complete reaction

HBr + ZnS is a complete reaction because the products formed will not undergo any further reaction to give new species.

Is HBr + ZnS an exothermic or endothermic reaction

HBr + ZnS is an exothermic reaction due to the liberation of heat during the reaction and negative reaction enthalpy signifies the same.

Exothermic reaction

Is HBr + ZnS a redox reaction

HBr + ZnS is not a redox reaction as the elements do not show any change in their oxidation states during the process.

Is HBr + ZnS a precipitation reaction

HBr + ZnS is not a precipitation reaction due to the formation of the water-soluble salt (ZnBr2).

Is HBr + ZnS reversible or irreversible reaction

HBr + ZnS is an irreversible reaction as the equilibrium shifts towards the product’s side due to an increase in entropy attributed to the formation of a gaseous product (H2S).

Is HBr + ZnS displacement reaction

HBr + ZnS is a double-displacement reaction where Zn being more reactive displaces the H+ ion from its salt and forms ZnBr2 and the hydrogen ion takes up sulfide ions to form H2S.


HBr and ZnS reacted in an irreversible manner giving off heat. ZnS is widely used as a pigment and as a luminescent material in cathode-ray tubes and X-ray screens. The optical properties of ZnS are utilized in manufacture of optical windows.

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