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

Hydrogen iodide (HI) is a colorless gas. When dissolved in water, it transforms into a strong acid. Let us look at the reactivity of HI with Mn(OH)2 in this article.

HI is used as a reducing agent and an analytical reagent. It is also used in manufacturing pharmaceuticals, disinfectants and other chemicals. Mn(OH)2 is a white solid, although samples darken quickly upon exposure to air owing to oxidation.

This article will discuss important facts and FAQs about HI + Mn(OH)2 chemical reactions, such as heat required, product formed, reaction enthalpy, type of reaction and intermolecular forces between their compounds, etc.

What is the product of HI and Mn(OH)2

The reaction of hydrogen iodide (HI) with manganese(II) hydroxide (Mn(OH)2 will give the manganese(II) iodide (MnI2) and Water (H2O). The reaction is

2HI + Mn(OH)2 → MnI2 + 2H2O

What type of reaction is HI + Mn(OH)2

HI + Mn(OH)2 reaction is a double replacement reaction. This type of reaction is commonly called as a metathesis or exchange reaction.

How to balance HI + Mn(OH)2

Balance the equation HI + Mn(OH)2 = MnI2 + H2O using the algebraic method.

  • In the equation, label each compound (reactant or product) with a variable representing the unknown coefficients.
  • aHI + bMn(OH)2 = cMnI2 + dH2O
  • Make an equation for each element (H, I, Mn, O), with each term representing the number of atoms of that element in each reactant or product.
  • H: 1a = 2d; I: 1a = 2c; Mn: 1b = 1c; O: 2b  = 1d
  • Solve for All Variables using gauss elimination and simplify the result to get the lowest, whole integer values.
  • a = 2 (HI); b = 1 (Mn(OH)2); c = 1 (MnI2); d = 2 (H2O)
  • Substitute Coefficients and Verify Result
  • 2HI + Mn(OH)2 = MnI2 + 2H2O
  • Since there is an equal number of each element in the reactants and products of 2HI + Mn(OH)2 = MnI2 + 2H2O, the equation is balanced.

HI + Mn(OH)2 titration

The information below will provide a general idea of the titration of HI and Mn(OH)2.

Apparatus used

Beaker, burette, burette stand, conical flask, pipette,  dropper, and measuring cylinder.


The phenolphthalein indicator can be used because it is a strong acid versus strong base reaction, and its endpoint is colorless to pink.


Standardized HI is added to the burette, and Mn(OH)2 is placed in a conical flask. Titration is then started by adding drops of HI one at a time, and an indicator is added in the middle. Titration is continued until the solution turns pink.

It is the equivalence point; record the readings, and use the formula V1N1=V2N2 to calculate the normality of MnI2.

HI + Mn(OH)2 net ionic equation

The HI + Mn(OH)2 net ionic equation is

2H+(aq) + 2I(aq) + Mn2+(aq) + 2OH(aq) → Mn2+(aq) + 2I(aq) + 2H+(l) + 2OH(l)

The steps to writing a net ionic equation are as follows:

  • The chemical states are indicated in the equation
  • HI (aq) + Mn(OH)2 (aq) → MnI2 (aq) + H2O (l)
  • Balance the molecular equation
  • 2HI (aq) + Mn(OH)2 (aq) → MnI2 (aq) + 2H2O (l)
  • HI will be ionized as proton and iodide as it is strong acid and electrolyte.
  • Then that Mn(OH)2 also dissociates into Mn2+ ion and OH ion as it is also a strong base
  • In the product part, MnI2 is ionized into Mn2+ and I as it is a strong electrolyte and salt.
  • H2O ionized into proton and hydroxide ion., Hence the reaction can be
  • 2H+(aq) + 2I(aq) + Mn2+(aq) + 2OH(aq) → Mn2+(aq) + 2I(aq) + 2H+(l) + 2OH(l)

HI + Mn(OH)2 conjugate pairs

HI + Mn(OH)2 Conjugate pairs will be the corresponding de-protonated and protonated forms of that species, which are listed below.

  • The conjugate base of HI is I ion.
  • Mn(OH)2  is a base in water. The hydroxide ion’s conjugate acid is H3O+.

HI and Mn(OH)2 intermolecular forces

HI and Mn(OH)2 have the following intermolecular forces

  • HI is a polar molecule, and it has strong dipole-dipole interactions and hydrogen bonding between hydrogen and iodide.
  • Mn(OH)2 has covalent force.
  • water has Hydrogen bonds, dipole-induced dipole forces and London dispersion forces.
  • MnI2 has van der Waal’s forces present.

HI + Mn(OH)2 reaction enthalpy

HI + Mn(OH)2 reaction enthalpy is -195.34 KJ/mol, which can be calculated using the following formula: enthalpy of products – enthalpy of reactants.

  • Enthalpy of formation of HBr = 26.5 kJ/mol
  • Enthalpy of formation of Mn(OH)2 = −695.4 kJ/mol
  • Enthalpy of formation of MnI2 = -266.1 kJ/mol
  • Enthalpy of formation of H2O = -285.82 kJ/mol
  • Enthalpy of reaction = (-(285.82*2)-266.1) – (-695.4 + (2*26.5) kJ/mol
  • = -837.74 + 642.4 kJ/mol
  • = -195.34 kJ/mol

Is HI + Mn(OH)2 a buffer solution

HI + Mn(OH)2 will not give a buffer solution as it is not a combination of weak acid and salt of its conjugate base because HI is a strong acid and Mn(OH)2 is a base.

Is HI + Mn(OH)2 a complete reaction

This is a complete reaction. HI and Mn(OH)2 will react to form MnI2 and H2O.

Is HI + Mn(OH)2 an exothermic or endothermic reaction

An exothermic reaction occurs when two moles of HI react with one mole of Mn(OH)2.

  • Enthalpy of reaction is calculated to be negative (i.e., ΔHf<0) from the above calculations.
  • HI + Mn(OH)2 reaction is liberated heat due to the formation of a MnI2 which increases the energy of the surroundings.
exothermic 2
Exothermic reaction

Is HI + Mn(OH)2 a redox reaction

HI + Mn(OH)2 is not a redox reaction because the oxidation states of elements do not change during the reaction.

Is HI + Mn(OH)2 a precipitation reaction

HI + Mn(OH)2 is not a precipitation reaction as MnI2 produced in the reaction readily dissolves in water; thus, no precipitate remains in the reaction.

Is HI + Mn(OH)2 reversible or irreversible reaction

HI + Mn(OH)2 is an irreversible reaction because the products MnI2 and H2O do not react with each other to produce the original reactants under the same conditions.

Is HI + Mn(OH)2 displacement reaction

HI + Mn(OH)2 is a double displacement reaction because, in this reaction, iodine ion (I) and hydroxide ion (OH ) exchange their places with each other to form new products, MnI2 and H2O.

Displacement Reaction


The reaction between HI and Mn(OH)2 is an exothermic, double displacement, and irreversible reaction which produces MnI2.It can be used as a pink pigment or as a manganese or iodide ion source. It is frequently employed in the lighting industry.