Hydrofluoric acid (HF) is a strong acid, while ferric hydroxide (Fe(OH)3) is a weak base. Let us explore the chemical reactivity of HF and Fe(OH)3.
HF is a colorless fuming liquid that can be dissolved in water. HF is used in making refrigerants, electrical components, and high-octane gasoline, besides glass etching. Fe(OH)3 or iron(III) hydroxide is a dark orange crystal insoluble in water and is mainly used as a heavy-metal adsorbent.
In this article, let us focus on more details about the reaction between HF and Fe(OH)3, like the product, enthalpy change, type, the balancing method, etc.
What is the product of HF and Fe(OH)3?
Ferric fluoride (FeF3) and water (H2O) are formed when ferric hydroxide reacts with hydrofluoric acid.
Fe(OH)3 + 3HF —-> FeF3 + 3H2O
What type of reaction is HF and Fe(OH)3?
HF + Fe(OH)3 is classified as a neutralization (acid-base) reaction since a strong acid neutralizes a weak base to produce salt and water.
How to balance HF and Fe(OH)3?
The steps to balance HF + Fe(OH)3 are as follows –
- The general equation is HF + Fe(OH)3 = FeF3 + H2O
- Count the number of moles of each element involved in the entire reaction (reactant and product sides of the equation).
| Elements | Reactant side | Product side |
|---|---|---|
| H | 4 | 2 |
| F | 1 | 3 |
| Fe | 1 | 1 |
| O | 3 | 2 |
- The product side is deficient of 2 moles of the hydrogen atom, 1 mole of oxygen atom, and 2 moles of fluorine atoms.
- To balance the number of elements in the reactant and product side, add 3 moles of water on the product side and 3 moles of HF on the reactant side and
- Hence, the overall balanced reaction is given by –
- 3 HF + Fe(OH)3 = FeF3 + 3H2O.
HF + Fe(OH)3 titration
HF + Fe(OH)3 titration is not possible because there is no significant change in the titration curve. Hence, it is impossible to accurately detect the equivalence point in the titration.
HF + Fe(OH)3 net ionic equation
The net ionic equation between HF + Fe(OH)3 is –
3H+ (aq) + Fe(OH)3 (s) = Fe3+ (aq) + 3H2O (l)
The following are the steps to derive the net ionic equation:
- The first step is to balance the given molecular equation to get –
- 3HF + Fe(OH)3 = FeF3 + 3H2O
- Indicate the substances existing in aqueous form and capable of complete dissociation in water and write their ionic form. The complete ionic equation of HF + Fe(OH)3 is –
- 3H+ (aq) + 3F– (aq) + Fe(OH)3 (s) = Fe3+ (aq) + 3F– (aq) + 3H2O (l)
- The net ionic equation is got by canceling the spectator ions (3F–) on both sides of the equation.
- 3H+ (aq) + Fe(OH)3 (s) = Fe3+ (aq) + 3H2O (l)
HF + Fe(OH)3 conjugate pairs
- In HF, the conjugate acid-base pairs are HF and F–.
- In Fe(OH)3, OH– and H2O are the conjugate acid-base pairs.
HF + Fe(OH)3 intermolecular forces
- The intermolecular forces in HF are strong hydrogen bonding and dipole-dipole interactions exist. The dipole interactions are more predominant due to the presence of a highly electronegative fluorine atom.
- Interionic Columbic forces and electrostatic forces of attraction exist between Fe+3 and OH– ions.
HF + Fe(OH)3 reaction enthalpy
HF + Fe(OH)3 standard reaction enthalpy is -115.77 KJ/mol. The enthalpy of formation values is listed below –
| Reactants and Products | Enthalpy in KJ/mol |
|---|---|
| HF | -332.63 |
| Fe(OH)3 | -824 |
| FeF3 | -986.6 |
| H2O | -285.8 |
∆Hf°(reaction) = ∆Hf°(products) – ∆Hf°(reactants)
= -1272.4 – (-1156.63)
= -115.77 KJ/mol
Is HF + Fe(OH)3 a buffer solution?
HF + Fe(OH)3 is not a buffer solution because HF is a strong acid, and Fe(OH)3 is not the conjugate base of HF.
Is HF + Fe(OH)3 a complete reaction?
HF + Fe(OH)3 is a complete reaction, as it produces ferric fluoride and water after complete neutralization.
Is HF + Fe(OH)3 an exothermic reaction?
HF + Fe(OH)3 is an exothermic reaction, as the reaction enthalpy calculated for this reaction is negative.
Is HF + Fe(OH)3 a redox reaction?
The reaction between HF + Fe(OH)3 is not a redox reaction, as the oxidation states are the same for all the elements before and after the reaction.
Is HF + Fe(OH)3 a precipitation reaction?
HF + Fe(OH)3 is not a precipitation reaction as FeF3 formed is a pale green solution slightly soluble in water.
Is HF + Fe(OH)3 an irreversible reaction?
HF + Fe(OH)3 is an irreversible reaction because the ferric fluoride and water formed do not react together to form the reactants.
Is HF + Fe(OH)3 a displacement reaction?
The reaction between HF + Fe(OH)3 is an example of a double displacement reaction because the anion (OH–) from Fe(OH)3 gets displaced to HF by removing F–, leading to the formation of FeF3 and H2O.
Conclusion
This article summarizes the reaction between HF and Fe(OH)3. The green crystalline ferric fluoride formed in this reaction is used as a fluorinating agent and in the production of ceramics and pottery.
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