Al2(SO3)3 is a catalyst for many organic syntheses and has mild acid so it can react with a strong acid like HNO3. Let us focus on the mechanism of the above reaction.
Al2(SO3)3 or aluminium sulfite has a 3C-4e bond model due to electron deficiency on the central Al center. The Al-S bond becomes weaker due to the presence of two electronegative atoms and for this reason, the bond is easily cleaved and participates in the reaction. Whereas in nitric acid covalent bond is present.
Aluminium sulfite itself is a good catalyst so the reaction between HNO3 and Al2(SO3)3 does not require any external catalyst. Let us discuss the mechanism of the reaction between nitric acid and aluminium sulfite, the reaction enthalpy, the type of reaction, product formation, etc. in the following part of the article.
1. What is the product of HNO3 and Al2(SO3)3?
Aluminium nitrate is formed as a major product along with water as a by-product and sulfur dioxide gas is evolved when HNO3 and Al2(SO3)3 are reacted together.
HNO3 + Al2(SO3)3 = Al(NO3)3 + SO2 + H2O
2. What type of reaction is HNO3 + Al2(SO3)3?
HNO3 + Al2(SO3)3 reaction is an example of a salt formation reaction, single displacement reaction, and redox and precipitation reaction. Here, electrolytic salt is formed in the course of the reaction. It is also a hydrolysis reaction example.
3. How to balance HNO3 + Al2(SO3)3?
HNO3 + Al2(SO3)3 = Al(NO3)3 + SO2 + H2O this reaction is not balanced yet, we have to balance the 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 obtained for this reaction and the reaction looks like this,
- A HNO3 + B Al2(SO3)3 = C Al(NO3)3 + D SO2 + E H2O
- Equating the coefficients for the same type of elements by rearranging them.
- After the rearrangement of coefficients of the same elements by their stoichiometric proportion, we get,
- H = A = 2B, N = A = 3C, O = 3A = 9B = 9C =2D = E, Al = 2B = C, S =3B =D.
- Using the Gaussian elimination and equating all the equations we get, A = 6, B = 1, C = 2, D =3, and E = 3.
- The overall balanced equation will be,
- 6HNO3 + Al2(SO3)3 = 2Al(NO3)3 + 3SO2 + 3H2O
4. HNO3 + Al2(SO3)3 titration
To estimate the quantity of nitrate or acid strength, we can titrate Al2(SO3)3 and HNO3.
Apparatus used
We need a burette, conical flask, burette holder, volumetric flask, and beakers for this titration.
Titre and titrant
HNO3 versus Al2(SO3)3, HNO3 acts as a titrant taken in the burette and the molecule to be analyzed is Al2(SO3)3 taken in a conical flask.
Indicator
The whole titration is done in an acidic medium or acidic pH so the best suitable indicator will be phenolphthalein which gives perfect results for this titration at given pH.
Procedure
The burette is filled with standardized HNO3. Al2(SO3)3 is taken in a conical flask along with respective indicators. HNO3 is added dropwise to the conical flask and the flask is shaken constantly. After a certain time, when the endpoint arrives, the indicator changes its color and the reaction is done.
We repeat the titration several times for better results and then we estimate the nitrate quantity by the formula V1S1 = V2S2.
5. HNO3+ Al2(SO3)3 net ionic equation
The net ionic equation between HNO3 + Al2(SO3)3 is as follows,
H+(aq.) + NO3–(aq.) + Al3+(aq.) + SO3–(aq.) = Al3+(aq.) + NO3–(aq.) + H+(l) + OH–(l) +SO2(g)
- HNO3 will be ionized into H+ and nitrate as a counter ion as it is a strong electrolyte.
- Al2(SO3)3 dissociated into Al3+ and SO3– ions as it is strong electrolytes.
- In the product part Al(NO3)3 ionized into Al3+ and NO3–as it is a strong electrolyte.
- Water ionized into proton and hydroxide ion in a liquid state.
- Sulfur dioxide remains undissociated as it exists in a gaseous state.
6. HNO3+ Al2(SO3)3 conjugate pairs
In the reaction, HNO3 + Al2(SO3)3 conjugate pairs will be the corresponding de-protonated and protonated form of that particular species which are listed below-
- Conjugate pair of HNO3 = NO3–
- Conjugate pair of OH– = H2O
7. HNO3 and Al2(SO3)3 intermolecular forces
HNO3 + Al2(SO3)3 has the following intermolecular forces,
- The intermolecular force present in HNO3 is the strong electrostatic force between protons and nitrate ions.
- In Al2(SO3)3, electronic interactions and coulumbic force are present along with the metallic bond. It is also an electrostatic and ionic force in Al(NO3)3, as well as van der waal’s attraction.
| Molecule | Acting force |
| HNO3 | Electrostatic, van der waal’s Dipole interaction, Covalent interaction |
| Al2(SO3)3 | Metallic bond, strong electrostatic force, ionic interaction, Coulumbic force |
| Al(NO3)3 | Electrostatic force, ionic interaction |
| H2O | H-bonding, covalent force, ionic interaction |
| SO2 | Van der waal’s force, London dispersion force |
8. HNO3 + Al2(SO3)3 reaction enthalpy
HNO3 + Al2(SO3)3 reaction enthalpy is +582.82 KJ/mol which can be obtained by the formula: enthalpy of products – enthalpy of reactants. Here the change in enthalpy is positive.
| Molecule | Enthalpy (KJ/mol) |
| Al2(SO3)3 | -1676 |
| HNO3 | -207.36 |
| Al(NO3)3 | -206.60 |
| H2O | -68 |
| SO2 | -296.9 |
and Products
9. Is HNO3 + Al2(SO3)3 a buffer solution?
The reaction between HNO3 + Al2(SO3)3 gives a buffer solution of Al(NO3)3 and H2O which can control the pH of the reaction.
10. Is HNO3 + Al2(SO3)3 a complete reaction?
The reaction between HNO3 + Al2(SO3)3 is complete because it gives two major ones: a strong electrolyte and other is a water molecule along with a gaseous molecule.
11. Is HNO3 + Al2(SO3)3 an exothermic or endothermic reaction?
The reaction of HNO3 + Al2(SO3)3 is endothermic in terms of thermodynamics first law. This reaction released more energy and temperature to the surroundings, where δH is always positive.
12. Is HNO3 + Al2(SO3)3 a redox reaction?
HNO3 + Al2(SO3)3 reaction is a redox reaction because N gets oxidized and sulfur gets reduced in this reaction. Here HNO3 acts as a reducing agent whereas Al2(SO3)3 acts as an oxidizing agent.
HNO3 + Al2(SO3)3 Reaction
13. Is HNO3 + Al2(SO3)3 a precipitation reaction
The reaction between HNO3 + Al2(SO3)3 is a precipitation reaction because Al(NO3)3 gets precipitated in the solution at certain pH which can be removed by heating the solution.
14. Is HNO3 + Al2(SO3)3 reversible or irreversible reaction?
The reaction between HNO3 + Al2(SO3)3 is irreversible because it produced a gaseous molecule and the production of a gaseous molecule increases the entropy of the reaction. As a result, the equilibrium shifts towards the right-hand side only or forward directions.
HNO3 + Al2(SO3)3 —-> Al(NO3)3 + H2O +SO2↑
15. Is HNO3 + Al2(SO3)3 displacement reaction?
The reaction between HNO3 + Al2(SO3)3 is an example of a single displacement reaction. Because in the above reaction H+ was displaced by Al from HNO3.
Conclusion
The reaction between HNO3 and Al2(SO3)3 gives us an electrolytic salt Aluminium nitrate along with water and sulfur dioxide gas, where we can estimate the amount of nitrate. The reaction is commercially important for the production of aluminium nitrate salt and SO2. It is an irreversible endothermic reaction without using a catalyst.
Hi……I am Biswarup Chandra Dey, I have completed my Master’s in Chemistry from the Central University of Punjab. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.