15 Facts on HF + HNO3: What, How To Balance & FAQs

by

Nitric acid (HNO3) and hydrogen fluoride (HF) are weak and strong acids, respectively. Let us look at the reaction between HF and HNO3 in more detail:

Hydrogen fluoride (HF) is a fluorine-containing chemical compound. It can exist as a colourless gas, a fuming liquid, or as a dissolved substance in water. Nitric acid (HNO3) is a mineral acid that is extremely corrosive.

In this post, we will discuss a few facts about the reaction between HF and HNO3, such as the final product, molecular forces, the type of reaction, buffer solution, and so on.

What is the product of HF and HNO3

The reaction of hydrogen fluoride (HF) with nitric acid (HNO3) will give the H2NO3+ and fluoride ion (F–). The reaction involves following steps as given below.

HF can ionize by itself.

2HF ⇌ [H2​​F]++ F–

Hence, HNO3 acts as a base when dissolved in HF because it accepts a proton from the HF. The reaction is

HNO3​​​ + HF​ ⇌ H2NO3+ + F–​

What type of reaction is HF + HNO3

The reaction between HF and HNO3 is a reversible reaction where ​ the products (H2​​NO3+ + F–) simultaneously again form the reactant.

How to balance HF + HNO3

Balance the equation HNO3 + HF = F– + H2​​NO3+ using the algebraic method.

  • Each compound in the equation (reactant or product) should be labelled with a variable that represents the unknown coefficients.
  • aHNO3 + bHF = cF– + dH2​​NO3+
  • Make an equation for each element (H, N, O, F), with each term representing the number of atoms of that element in each reactant or product.
  • H: 1a + 1b = 2d; N: 1a = 1d; O: 3a =3d; F: 1b = 1c
  • Use substitution, gauss elimination, or a calculator to solve for each variable and simplify the result to get the lowest, whole integer values.
  • a = 1 (HNO3); b = 1 (HF); c = 1 (F–) d = 1 (H2​​NO3+)
  • Substitute Coefficients and Verify Result
  • HNO3 + HF = F– + H2​​NO3+
  • Since there is an equal number of each element in the reactants and products of HNO3 + HF = F– + H2​​NO3+, the equation is balanced.

HF + HNO3 titration

The HF + HNO3 titration system is not feasible because HF is a weak acid, and HNO3 is a strong acid that cannot perform acid-base titration.

HF + HNO3 net ionic equation

The HF + HNO3 net ionic equation is

H+ (aq) + H+ + NO3– (aq) → H2​​NO3+(aq)   

Writing a net ionic equation involves the following steps:

  • Convert reactants to formulas and impute products if the reaction is given in sentence form. Prior knowledge of reaction type nomenclature and classifications is required (e.g., here, a reversible reaction with subsequent cation formation).
  • HF (aq) + HNO3 (aq) → H2​​NO3+ (aq)+ F– (aq)   
  • Balance this molecular equation.
  • HF (aq) + HNO3 (aq) → H2​​NO3+ (aq)+ F– (aq)   
  • If the reaction is occurring in an aqueous solution, all ionic reactants and products that are present and are fully dissociated in the solution should be described as ions rather than molecules (because that is what they would be in the solution).
  • H+ (aq) + F– (aq) + H+ + NO3– (aq) → H2​​NO3+ (aq)+ F– (aq)          
  • Any components that exist on both sides should be removed.
  • H+ (aq) + F– (aq) + H+ + NO3– (aq) → H2​​NO3+ (aq)+ F– (aq)          
  • Neaten up: exclude the components you cancelled in previous step  and redo the equation.
  • H+ (aq) + H+ + NO3– (aq) → H2​​NO3+ (aq)   

HF + HNO3 conjugate pairs

HF + HNO3 has the following conjugate acid-base pair, which are the corresponding de-protonated and protonated forms of that particular species

  • Conjugate base pair of HF is fluoride ion (F–)
  • conjugate acid pair of F– is HF
  • Conjugate base pair of HNO3 is nitrate ion (NO3–)
  • conjugate acid pair of NO3– is HNO3
  • Conjugate base pair of H2​​NO3+ is HNO3
  • Conjugate acid pair of HNO3 is H2​​NO3+   

HF and HNO3 intermolecular forces

HF and HNO3 have following intermolecular forces

  • HF is a polar and covalent molecule. It has dipole-dipole forces and London Dispersion Forces since HF has an electronegative atom, F is bonded to an H atom, forming a Hydrogen bond between their molecules.
  • These hydrogen bonds between H and F allow HF molecules to exist in a liquid form.
  • HNO3 contains dipole-dipole interactions and dispersion interaction since it is a polar molecule.
  • HNO3 doesn’t have a hydrogen bond since it is a strong acid in an aqueous solution, as separated hydrogen ions and nitrate ions.
  • NO3– has Ion-induced dipole forces – Intermolecular force exist between an ion and a non-polar molecule. Here the charge of the NO3– ion creates a temporary dipole on the non-polar molecule.

HF + HNO3 reaction enthalpy

HF + HNO3 exhibits no reaction enthalpy in the literature search because the product formed (H2​​NO3+) changes abruptly, which is not possible to record.

Is HF + HNO3 a buffer solution

HF and HNO3 is not a buffer solution. Because HF is a weak acid and HNO3 is a strong acid.

Is HF + HNO3 a complete reaction

It is not a complete reaction. HF and HNO3 will react to form H2​​NO3+ and F–because the product (H2​​NO3+ and F–) formed in this reaction is unstable.

Is HF + HNO3 an exothermic or endothermic reaction

HF + HNO3 is a highly exothermic reaction. The heat is liberated in the process while mixing of concentrated acids HNO3 and HF together.

exothermic 3
Exothermic reaction

Is HF + HNO3 a redox reaction

HF + HNO3 is not a redox reaction, because neither the reactant nor the product side’s oxidation status of any element changes.

Is HF + HNO3 a precipitation reaction

HF + HNO3 is not a precipitation reaction because a precipitation reaction is when two soluble compounds combine to form an insoluble solid. There is no solid product (H2​​NO3+ and F–) when the interaction between HF and HNO3.

Is HF + HNO3 reversible or irreversible reaction

HF + HNO3 is a reversible reaction as the products (H2​​NO3+ and F–) will be converted back into the reactants (HF and HNO3).

Is HF + HNO3 displacement reaction

HF + HNO3 is not a displacement reaction because displacement reactions are irreversible reactions when a more reactive ingredient removes a less reactive element from a combination. There is no elemental displacement during the reaction between HF and HNO3.

Conclusion

HNO3 is used to produce ammonium nitrate, a major component of fertilizers. HF is used to make fluorescent light bulbs, refrigerants, pharmaceuticals, high-octane gasoline and electrical components. Mixtures of HF and HNO3 are used to clean and etch the saw damaged silicon lattice on top of the multi-crystalline Silica wafer.