Fe(OH)3, called Ferric oxyhydroxide, is a transition metal hydroxide, and HBr (hydrobromic acid) is a powerful mineral acid. Let us look into their reaction thoroughly.
HBr has a pKa of -9 which makes it more acidic than hydrochloric acid. Fe(OH)3 is a weak base and occurs naturally as mineral bernelite. It exhibits polymorphism comprising 4 forms, namely α, β, γ, and δ also known to form hydrates.
This article emphasizes the reaction products, type, molecular forces, and enthalpy corresponding to the reaction HBr + Fe(OH)3.
What is the product of HBr and Fe(OH)3
FeBr3 (Ferric bromide) and water molecules are obtained by the reaction HBr + Fe(OH)3.
HBr + Fe(OH)3 → FeBr3 + H2O
What type of reaction is HBr + Fe(OH)3
HBr + Fe(OH)3 is a neutralization reaction where the acid HBr is neutralizing the base Fe(OH)3 to form the salt FeBr3.
How to balance HBr + Fe(OH)3
HBr + Fe(OH)3 is balanced through the step-to-step approach
HBr + Fe(OH)3 → FeBr3 + H2O
- In the first step, the elements are counted.
| Elements involved | Reactants side | Products side |
|---|---|---|
| H | 4 | 2 |
| O | 3 | 1 |
| Br | 1 | 3 |
| Fe | 1 | 1 |
- The elements are further balanced using the coefficients. 3 is added before HBr and H2O respectively and thus the balanced equation is
- 3HBr + Fe(OH)3 → FeBr3 + 3H2O
HBr + Fe(OH)3 titration
HBr + Fe(OH)3 represents an acid-base titration where Fe(OH)3 which is a weak base is titrated against the strong acid HBr.
Apparatus required
Burette, conical flask, measuring cylinder, pipette, conical flask, volumetric flask.
Indicator
Methyl orange is used as an indicator as it is red in color in a highly acidic medium and then changes to orange in slightly acidic and finally gives yellow color in the basic medium.
In2- (yellow color) = HIn– (red color)
Procedure
- Fe(OH)3 solution is prepared in the volumetric flask and about 20 ml of this solution is pipette out in the conical flask.
- The standard HBr solution is taken in the burette with the help of a funnel.
- 3-4 drops of methyl orange are added to the conical flask containing Fe(OH)3 solution.
- HBr is added dropwise into the Fe(OH)3 solution and the color change is noted.
- The yellow color solution gradually changes to orange and then becomes red due to excess of HBr.
- The readings are taken and are further used in the calculation using the formula M1V1 = M2V2.
HBr + Fe(OH)3 net ionic equation
HBr + Fe(OH)3 net equation is
3H+(aq) + Fe(OH)3(s) → Fe3+(aq) + 3H2O(l)
The net ionic equation for the above reaction is derived using the following steps
- Balanced equation is written first.
- 3HBr + Fe(OH)3 → FeBr3 + 3H2O
- Representation of the phases of the involved species is done in the second step.
- 3HBr(aq) + Fe(OH)3(s) → FeBr3(aq) + 3H2O(l)
- Strong electrolytes are dissociated into the ions. H2O is a weak electrolyte so it will not split.
- 3H+(aq) + 3Br–(aq) + Fe(OH)3(s) → Fe3+(aq) + 3Br–(aq) + 3H2O(l)
- After crossing out the spectator ions we get the net ionic equation as
- 3H+(aq) + Fe(OH)3(s) → Fe3+(aq) + 3H2O(l)
HBr + Fe(OH)3 conjugate pairs
HBr + Fe(OH)3 is not a conjugate-acid base pair as they do not conjugate with each other ,however Br– is the conjugate base of HBr.
HBr and Fe(OH)3 intermolecular forces
The intermolecular forces present in HBr and Fe(OH)3 are
- Ionic interactions are found in the molecules of Fe(OH)3.
- Dipole-dipole interactions and London dispersion forces exist between HBr molecules.
HBr + Fe(OH)3 reaction enthalpy
HBr + Fe(OH)3 enthalpy of the reaction is -1.8KJ/mol. Using the tabulated values we can calculate the reaction enthalpy by putting them in the formula below
| Species present | Enthalpy in KJ/mol |
|---|---|
| HBr | -101.2 |
| Fe(OH)3 | -820.2 |
| FeBr3 | -268.2 |
| H2O | -285.8 |
∆Hf°(reaction) = ∆Hf°(products) – ∆Hf°(reactants)
= -1125.6 – (-1123.8) KJ/mol
= -1.8 KJ/mol
Is HBr + Fe(OH)3 a buffer solution
HBr + Fe(OH)3 will not make a buffer as weak acid is required for the buffer solution while HBr is a strong acid.
Is HBr + Fe(OH)3 a complete reaction
HBr + Fe(OH)3 is a complete reaction as completely reduced products are formed which will not react further to give off new species.
Is HBr + Fe(OH)3 an exothermic or endothermic reaction
HBr + Fe(OH)3 is an exothermic reaction as the liberation of heat is observed during the reaction and it can be further signified by the negative value for the enthalpy.
Is HBr + Fe(OH)3 a redox reaction
HBr + Fe(OH)3 is not a redox reaction as the elements present in the reactants suffer no change in their oxidation states.
Is HBr + Fe(OH)3 a precipitation reaction
HBr + Fe(OH)3 is not a precipitation reaction because the reaction gives soluble products and thus no precipitate is formed.
Is HBr + Fe(OH)3 reversible or irreversible reaction
HBr + Fe(OH)3 is an irreversible reaction as the hydrogen being less reactive will not be able to displace iron from its salt and hence the backward reaction is not feasible.
Is HBr + Fe(OH)3 displacement reaction
HBr + Fe(OH)3 is a double-displacement reaction as the highly reactive metal Fe displaces the less reactive hydrogen from its salt to form ferric bromide and hydrogen further combines with OH– ions.
Conclusion
The reaction is slightly exothermic and irreversible. Fe(OH)3 is wide applications in the dyeing and cosmetic sectors. It is used as a phosphate binder in water purification and also acts as efficient adsorbent in nano range.
Hi! I am Lubna Khan. I have done my Postgraduation in Chemistry at Jamia Millia Islamia, New Delhi. I have been in academia for years and have always welcomed new opportunities, lifestyles, and cultures coming my way.
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