15 Facts on HBr + Zn(OH)2: What, How To Balance & FAQs

Zn(OH)2 is a hydroxide of zinc metal and occurs naturally in earth minerals, ashoverite, wulfenite, and sweetite. Let us see how Zn(OH)2 reacts with HBr through this article.

Zinc hydroxide (Zn(OH)2) is an amphoteric inorganic compound means it behaves as both an acid and base. Because of this dual nature, Zn(OH)2 is easily soluble in alkaline solutions as well as in strong acidic solutions. HBr is an anhydrous, strong acid that is used as a hydro bromination agent.

We will discuss important facts about the HBr + Zn(OH)2 reaction, like the products of the reaction, nature, enthalpy, intermolecular forces between their compounds, and the mechanism behind the reaction.

What is the product of HBr and Zn(OH)2 ?

During the reaction of HBr and Zn(OH)2, Zinc bromide (ZnBr2) and Water (H2O) are formed in which ZnBr2 is the major product. The chemical equation for the reaction is as follows:

2HBr + Zn(OH)2   = ZnBr2  + 2H2O

What type of reaction is HBr + Zn(OH)2 ?

HBr + Zn(OH)2   is a double displacement and acid-base (neutralization) reaction in which Zn(OH)2 is a weak base and HBr is acid.

How to balance HBr + Zn(OH)2 ?

Balanced chemical equation ofHBr + Zn(OH)2  is:

2HBr + Zn(OH)2   = ZnBr2  + 2H2O 

  • An unbalanced chemical equation is,
  • HBr + Zn(OH)2   → ZnBr2  + H2O
  • Make sure, the number of all atoms on both sides of the chemical reaction should be equal. Here, the number of oxygen, hydrogen, and bromine is not the same on both sides of the reaction.
  • Therefore, to balance them, HBr and H2O are multiplied by the coefficient of 2.
  • Hence, the balanced chemical equation is,
  • 2HBr + Zn(OH)2  = ZnBr2  + 2H2

HBr + Zn(OH)2 titration

Quantitative estimation of HBr can be estimated by performing the titration of HBr against Zn(OH), because HBr is a strong acid and Zn(OH)2 acts as a weak acid, so titration of this acid-base reaction is feasible.  For titration, the following procedure can be carried out,

Apparatus used

A burette, Pipette, measuring flask, glass funnel, clamp stand, measuring cylinder, volumetric flask, and beakers are required for this titration.

Analyte and titrant

In this procedure, HBr is taken in the burette as titrant and Zn(OH)2 is analyzed which is taken in a conical flask.


As this titration is performed in acidic media that is HBr therefore phenolphthalein will be used as an indicator for this titration.


The standard amount of HBr is filled into the burette and at the same time, the aqueous solution of Zn(OH) 2 with respective indicator is taken in a conical flask. Then HBr is added very carefully and dropwise into the conical flask. The constant shaking of Zn(OH)2  solution, provide the accurate endpoint. The procedure is repeated at least three times until a constant endpoint comes where the indicator changes its color. 

After the successful titration, the strength of hydrogen bromide and the quantity of bromide ions will be measured by the formula V1N= V2N2.

HBr + Zn(OH)2 net ionic equation

Net chemical ionic equation of HBr + Zn(OH)2 is as follows:

2H+(aq.) +2Br(aq.) + Zn(OH)2 (s) = Zn2+(aq.) + 2Br (aq.) + 2H2O (l)

  • Write the general balanced chemical equation.
  • 2HBr + Zn(OH)2   = ZnBr2  + 2H2O
  • Label the chemical state (s, l, g or aq) of each compound in the equation
  • 2HBr (aq)+ Zn(OH)2 (s) = ZnBr2 (aq) + 2 H2O (l)
  • Break the electrolytes into their corresponding ions only in an aqueous solution.
  • 2H+(aq.) +2Br(aq.) + Zn(OH)2 (s) = Zn2+(aq.) + 2Br (aq.) + 2H2O (l)
  • Balance the spectator ions to get the net ionic equation.
  • 2H+(aq.) + Zn(OH)2 (s) = Zn2+(aq.) + 2H2O (l)

HBr + Zn(OH)2 conjugate pairs

HBr and Zn(OH)2  and Zinc bromides do not have any conjugate pairs as they are totally polarized.

HBr and Zn(OH)2 intermolecular forces

HBr + Zn(OH)2 has the following intermolecular forces,

  • HBr is a polar molecule so it contains dipole – dipole interaction between its molecules.
  • Zn(OH)2 contains coulombic and ionic forces.
  • Electrostatic forces are present in ZnBr2 molecules.
  • H2O molecules in the given equation are held with each other through intra molecular hydrogen bonding.

HBr + Zn(OH)2 reaction enthalpy

HBr + Zn(OH)2 reaction enthalpy is 17.82 kJ/mol. The enthalpy of formation of reactants and products is as follows:

Compound Standard Formation Enthalpy (ΔfH°(Kj/mol) )
Zn (OH)2-642.00
Standard Formation Enthalpy of Compounds

ΔHf = Enthalpy of formation (product) – enthalpy of formation (reactant)

ΔHf = [2*(-120.77) – 642) – (-329.70 – 2*(285.83))

ΔHf = 17.82 kJ/mol.

Is HBr + Zn(OH)2 a buffer solution ?

The reaction between HBr + Zn(OH)2 provides a buffer solution of ZnBr2 and water which resist the change in its pH value if we add acid or base to it.

Is HBr + Zn(OH)2 a complete reaction ?

HBr + Zn(OH)2 is a complete reaction because in this reaction HBr completely neutralizes Zn(OH)2 molecules in its corresponding salt which is ZnBr2.

Is HBr + Zn(OH)2 an exothermic or endothermic reaction ?

HBr+ Zn(OH)2 is an endothermic reaction because the enthalpy of the reaction was found positive (i.e. ΔHf>0) from the above calculations. On the other hand, reactants absorb 17. 82kJ/mol heat during the reaction and provide the final products with higher energy.

 Is HBr+ Zn(OH)2 a redox reaction ?

HBr + Zn(OH)2 is not a redox reaction because the oxidation states of elements do not change during the reaction, given as below:

2HBr + Zn(O H)2   =  ZnBr2  + 2H2O

+1 -1    +2 -2 +1        +2 -1    +1   -2 (charges on each element of this reaction)

Is HBr + Zn(OH)2 a precipitation reaction ?

HBr+ Zn(OH)is not a precipitation reaction because not any product is in the solid phase after the completion of the reaction.

Is HBr + Zn(OH)2 reversible or irreversible reaction ?

HBr + Zn(OH)2 is an irreversible reaction.  Because at the same reaction conditions, the reactants can not be formed back.

Is HBr + Zn(OH)2 displacement reaction ?

HBr + Zn(OH)is a double displacement reaction because Zn from Zn(OH)2  and H from HBr displace each other’s positions to form different products.


From this article, it is clear that a strong acid like HBr reacts with weak base Zn(OH)2  through a double displacement mechanism and absorbs the heat from the surrounding. The amphoteric nature of Zn(OH)2  is changed to basic and the formation of ZnBr2 results in the removal of two hydroxides from Zn(OH)2.