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

The reaction between HCl and Zinc hydroxide is a reaction between a strong acid and a weak base. Let us see the mechanism behind the reaction between HCl and Zn(OH)2.

When strong acids like HCl react with the weak base like zinc hydroxide then weak salt is formed by hydrolysis. The reaction does not require any type of catalyst, because the nature of HCl is so strong that it can be ionized and carry forward the reaction. The reaction also not required temperature and pressure.

By this reaction, we can estimate the strength of the HCl or the amount of chloride present in the given molecule. In this article, we will learn more about reactions like enthalpy, redox reaction, intermolecular force, conjugate pairs, etc with an explanation in the following part of the article.

1. What is the product of HCl and Zn(OH)2?

Zinc chloride formed as a major product when HCl reacted with Zn(OH)2 along with water molecules due to hydrolysis.

Products of the Reaction
Between HCl and Zn(OH)2

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

HCl + Zn(OH)2 is an acid-base and hydrolysis reaction. There are also redox reactions, displacement reactions, and also precipitation reactions that occur at certain pH. The former is strongly acidic but the latter is weakly basic so, a buffer reaction is also observed.

3. How to balance HCl + Zn(OH)2?

HCl + Zn(OH)2 = ZnCl2 + H2O this reaction is not balanced yet because the L.H.S of the reaction is not equal to the R.H.S., so we have to balance the equation in a few steps,

  • Step 1 – Labelling all the reactants and products by the required number of alphabets
  • First, we labeled all the molecules in the part of the reactant as well as the product side by A, B, C, and D as there is a total of four molecules present in both sites in unbalanced form. Now the reaction reduces to,        
  •  A HCl + B Zn(OH)2= C ZnCl2 + D H2O
  • Step 2 – Equating all the Coefficients for all the same type of elements by rearranging them
  • Comparing all the same elements by their stoichiometric proportion and coefficients in this reaction we get,
  • H = A = 2D, Cl = A = 2C, Zn = B = C, OH = 2B = 2D
  • Step 3 – Using Gaussian elimination to determine the coefficient values
  • Using the Gaussian elimination and equating all the equations we get,
  • A = 2, B = 1, C = 1, D = 2
  • Step 4- now write the whole equation in the balanced form
  • The overall balanced equation will be,
  • 2HCl + Zn(OH)2=  ZnCl2 +  2H2O

4. HCl + Zn(OH)2 titration

To estimate the quantity of chloride and strength of HCl we can perform a titration between Zn(OH) 2 and HCl in the following way,

Apparatus used

We need a burette, conical flask, burette holder, volumetric flask, and beakers for this titration.

Titre and titrant

HCl versus Zn(OH)2, HCl acts as titrant which is taken in the burette and the molecule to be analyzed is Zn(OH)2which is taken in a conical flask.


The whole titration is done in an acidic medium or acidic pH so the best suitable indicator will be phenolphthalein which gives perfect results for this titration at given pH.


The burette was filled with standardized HCl and Zn(OH) 2 was taken in a conical flask along with the respective indicator. Then the titration was started by adding HCl dropwise to the conical flask and the flask was shaking constantly. After a certain time when the endpoint arrived and the indicator changes its color.

We repeat the titration several times for better results and then we estimate the quantity of chloride and strength of HCl by the formula V1S= V2S2.

5. HCl+ Zn(OH)2 net ionic equation

The net ionic equation between HCl+ Zn(OH)2 is,

2H+ + 2Cl + Zn2+ + 2OH = Zn2+ + 2Cl + 2H+ + 2OH

6. HCl+ Zn(OH)2 conjugate pairs

The conjugate pairs formed during the reaction between HCl + Zn(OH)2 are,

  • Conjugate pair of HCl = Cl
  • Conjugate pair of H2O = OH

7. HCl and Zn(OH)2 intermolecular forces

The ionic and electrostatic forces are present in HCl as also dipole interaction and for the Zn(OH)2. There are coulombic forces along with covalent interaction present with the molecule. Strong H-bonding is present in H2O and for ZnCl2 there is ionic interaction along with van der waal’s interaction present.

MoleculeActing force
van der Waals,
Zn(OH)2Coulombic ionic,
van der waal’s
ZnCl2Ionic, Strong
H2OThe electrostatic force,
Intermolecular Forces

8. HCl + Zn(OH)2 reaction enthalpy

The reaction enthalpy between HCl + Zn(OH)2 is, -86.4 KJ/mol which can be obtained by the formula enthalpy of products – enthalpy of reactants, and here the change in enthalpy is negative.

Reaction Enthaply

9. Is HCl + Zn(OH)2 a buffer solution?

The reaction between HCl + Zn(OH)2 gives a buffer solution of ZnCl2 and water which can control the pH of the solution as it has both acidic as well as basic characteristics at certain pH.

10. Is HCl + Zn(OH)2 a complete reaction?

HCl + Zn(OH)2 is a complete reaction that gives two complete products ZnCl2 and H2O which indicates that reactants are utilized properly and ends with two complete products.

11. Is HCl + Zn(OH)2 an exothermic or enothermic reaction?

HCl + Zn(OH)2 is an exothermic reaction based on thermodynamics because the enthalpy for the reaction came negative. On the other hand, the reactant released heat in the course of the reaction or we can say δH = HProducts-Hreactans < 0.

Energy Profile Curve for
Exothermic Reaction

12. Is HCl + Zn(OH)2 a redox reaction?

HCl + Zn(OH)2 is a redox reaction where the oxidation number of several elements is changed like Cl gets reduced whereas O and H get oxidized.

Redox Schematic of Reaction
Between HCl and Zn(OH)2

13. Is HCl + Zn(OH)2 a precipitation reaction

HCl + Zn(OH)2 is a precipitation reaction where ZnCl2 is precipitated at the acidic pH. The optimum pH for the precipitation of ZnCl2 is 6.6 and the total titration was done in an acidic medium so ZnCl2 precipitated in this reaction.

14. Is HCl + Zn(OH)2 reversible or irreversible reaction?

HCl + Zn(OH)2 is irreversible reaction because that reaction proceeds only forward direction at that particular pH.

15. Is HCl + Zn(OH)2 displacement reaction?

HCl + Zn(OH)2 is a double displacement reaction because Zn is displaced by HCl and Cl is also displaced by Zn(OH)2.


To estimate the quantity of Cl we can use the titration between Zn(OH)2 and HCl. By this reaction, we also estimate the strength of HCl as well. The reaction does not require any catalyst or temperature because it is an endothermic reaction.

Biswarup Chandra Dey

Hi......I am Biswarup Chandra Dey, I have completed my Master's in Chemistry from the Central University of Punjab. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.

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