Bromine is a nonmetal and the third lightest halogen that exists in diatomic (Br2) in pure state. Nitric acid (HNO3) is a strong mineral acid. Let us focus on their chemical action.
Br2 is a reddish-brown liquid at room temperature and reacts readily due to high electron affinity. It occurs naturally in the form of its salt. HNO3 is a colorless, corrosive and fuming liquid. It is a powerful oxidizing agent and is used as an oxidizer in liquid-fueled rockets.
In this section, let us discuss the mechanism of the reaction between nitric acid and bromine, products formed, reaction enthalpy, type of reaction, balancing method etc.
What is the product of HNO3 and Br2?
Bromic acid (HBrO3), Nitrogen Dioxide (NO2) gas and Water (H2O) are obtained when HNO3 is added to dibromine.
10HNO3 + Br2 —-> 2HBrO3 + 10NO2 + 4H2O
What type of reaction is HNO3 + Br2?
HNO3 + Br2 is a redox reaction as oxidation and reduction of elements take place simultaneously.
How to balance HNO3 + Br2?![]( "15 Facts on HNO3 + Br2: What, How To Balance & FAQ’s 1")
The general chemical reaction of HNO3 + Br2 can be represented as:
HNO3 + Br2 —-> HBrO3 + NO2 + H2O
We have to balance the above equation in the following way –
- First, we label all the reactants and products by A, B, C, D and E, as there are five different molecules in this reaction.
- A HNO3 + B Br2 = C HBrO3 + D NO2 + E H2O
- Equate the coefficients for the same type of elements.
- When the coefficients of the same elements are rearranged according to their stoichiometric proportion, we obtain,
- H : A = C = 2E, N : A = D, O : 3A = 3C = 2D = E, Br : 2B = C
- By applying the Gaussian elimination and equating each of the obtained equations, we get, A = 10, B = 0, C = 2, D = 10, and E =4.
- The overall balanced equation will be,
- 10HNO3 + Br2 —-> 2HBrO3 + 10NO2 + 4H2O
HNO3 + Br2 titration
The titration of HNO3 and Br2 will not yield any significant result. However, quantitative estimation of free bromine is possible by titrating it with sodium thiosulphate solution in the presence of potassium iodide and starch indicator.
HNO3 + Br2 net ionic equation
The net ionic equation between HNO3 + Br2 is represented as –
8H+ (aq)+ 10NO3– (aq) + Br2 (l) = 2BrO3– (aq) + 10NO2 (g) + 4H2O (l)
Following are the steps to determine the net ionic equation –
- Write the balanced chemical equation and indicate the physical states (s, l, aq, g) of each molecule participating in the reaction.
- 10HNO3 (aq) + Br2 (l) = 2HBrO3 (aq) + 10NO2 (g) + 4H2O (l)
- Substances that are strong acids, bases, and salts break down into ions in their aqueous forms but not those in their liquid or gaseous forms.
- Now, represent the complete ionic equation of HNO3 + Br2 as –
- 10H+ (aq)+ 10 NO3– (aq) + Br2 (l) = 2H+ (aq) + 2BrO3– (aq) + 4H2O (l) + 10NO2 (g)
- Cancel the spectator ions (H+) that appears on either side of the equation, and make sure that the charge is conserved too. Thus, the net ionic equation is –
- 8H+ (aq)+ 10NO3– (aq) + Br2 (l) = 2BrO3– (aq) + 10NO2 (g) + 4H2O (l)
HNO3+ Br2 conjugate pairs
HNO3 and Br2 reaction has the following conjugate pairs,
- The conjugate pair of HNO3 is NO3–.
- No conjugate pair exists for Br2.
HNO3 + Br2 intermolecular forces
HNO3 + Br2 has the following intermolecular forces,
- Electrostatic, Van der Waal’s, Dipole interaction, and Covalent forces are the acting forces in HNO3.
- Weak Van der Waal’s forces exist in bromine molecule.
HNO3 + Br2 reaction enthalpy
HNO3 + Br2 reaction enthalpy is +1996.4 KJ/mol, and the enthalpy values are listed below:
| Reactants and Products | Enthalpy in KJ/mol |
|---|---|
| HNO3 | -207.36 |
| Br2 | 0 |
| HBrO3 | 367.1 |
| H2O | -285.8 |
| NO2 | 33.18 |
- ∆Hf°(reaction) = ∆Hf°(products) – ∆Hf°(reactants)
= -77.2 – (-2073.6)
= +1996.4 KJ/mol
Is HNO3 + Br2 a buffer solution?
The combination of HNO3 + Br2 will not function as a buffer solution, because it is neither a combination of a weak base and its conjugate acid nor a weak acid and its conjugate base.
Is HNO3 + Br2 a complete reaction?
HNO3 + Br2 is a complete reaction, as the products are completely formed at equilibrium and will not proceed further since one of the products is a gas (NO2) that gets expelled during the reaction.
Is HNO3 + Br2 an endothermic reaction?
The reaction HNO3 + Br2 is an endothermic reaction as the reaction enthalpy is positive, thereby absorbing energy from the surroundings in the form of heat.
Is HNO3 + Br2 a redox reaction?
The reaction between HNO3 and Br2 is a redox reaction, because N gets reduced, and bromine gets oxidized in this reaction. Here HNO3 acts as an oxidizing agent, whereas Br2 acts as a reducing agent.
Is HNO3 + Br2 a precipitation reaction?
HNO3 + Br2 is not a precipitation reaction as the products are not precipitated in the system.
Is HNO3 + Br2 an irreversible reaction?
HNO3 + Br2 is an irreversible reaction as the forward reaction is favored owing to the increase in entropy due to the liberation of NO2 gas.
Is HNO3 + Br2 a displacement reaction?
The reaction between HNO3 + Br2 is not an example of a displacement reaction, as there is no swapping of ions involved in the product formation.
Conclusion
The reaction of HNO3 with Br2 forms colorless bromic acid or hydrogen bromate, a powerful oxidizing agent which has diverse applications in organobromine chemistry. Reddish brown nitrogen dioxide gas is also observed.
Read more about following HNO3:
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