Hydrogen bromide is a strong acid, reacts exothermically with bases. Calcium is a reactive alkaline earth metal. Let us check relevant facts for the following reaction of HBr+Ca.
Anhydrous HBr is corrosive, colorless, irritant to smell, and heavier than air. It is highly soluble in water and is a powerful acid (CAS 10035-10-6) with 48 to 62% dissolution. Calcium exists in Group 2 of the periodic table, known as alkaline earth metal with atomic number 20 and a mass of 40.08 g/mol.
In this article, we will focus on the plausible changes of HBr in presence of Ca metal and vice versa in the terms of reaction like ionic equation, intermolecular forces, reaction enthalpy etc.
What is the product of HBr and Ca?
Calcium (II) bromide (CaBr2) salt in aqueous medium along with hydrogen gas are produced from HBr solution and solid calcium metal.
Ca(s)+HBr(aq)→CaBr2(aq)+H₂(g)
What type of reaction is HBr + Ca?
HBr+Ca is a redox reaction because of transfer of electrons from calcium (0) to hydrogen ion (H+) due to more reactive nature of calcium metal than its ionic form.
How to balance HBr + Ca?
Step 1: Let’s write down the reaction.
Ca0(s)+H+Br−(aq)→Ca2+Br−2(aq)+H₂0(g)
The reaction can be balanced using ion exchange method.
Step 2: We need to find out the changes in oxidation number (ON) of elements.
| Elements | ON before reaction | ON after reaction | Net change |
|---|---|---|---|
| Ca | 0 | +2 | Loss of two electrons |
| H | +1 | 0 | Gain of one electron |
| Br | -1 | -1 | No change |
Step 3: So, the total increase of ON is 2 and the decrease is 1. Therefore, H+ ion should be multiplied with 2 to balance in the hydrogen atom number in both reaction sides.
Step 4: Check the other atoms in the reaction has been balanced automatically or are needed to be balanced.
Ca0(s)+2H+Br−(aq)→Ca2+Br−2(aq)+H₂0(g)
After adding 2 in front of HBr molecule, Br ion is balanced automatically and any extra ion or atom is not there, hence the equation is balanced now.
HBr + Ca titration
HBr + Ca do not undergo titration because of absence of equivalence point. However, HBr solution is strong acid and responses in titration in presence of any strong base like, KOH.
HBr + Ca net ionic equation
HBr is a strong acid, it can fully dissociate into ionic components in aqueous solution, hence its ionic form can be written as:
2H+(aq)+Ca (s)→Ca2+(aq)+H₂(g)
HBr + Ca conjugate pairs
The conjugate pair is mentioned below:
The conjugate base of Hr is Br−ion, whereas Ca does not have any conjugate pair.
- The conjugate base of HBr is Br− ion, whereas Ca does not have any conjugate pair.
HBr and Ca intermolecular forces
HBr and Ca intermolecular forcesAnhydrous HBr exerts dipole-dipole intermolecular forces and aqueous HBr can furnish cation (H+) and anion (Br−) very easily.
Ca metal exists with metallic bond in 3D arrangement which is known as crystal lattice. The outermost shell electrons and metal cations attract each other.
During reaction between HBr (aq) and Ca metal (s) molecules, all the above-mentioned bonds dissociate and rearrange the atoms along with new chemical bonds between Ca and Br and H atoms.
CaBr2 exists with ionic bonding forces between molecules because of their ionic nature. However, as Br− ion is larger than Ca2+ ion so, as per Fajan’s rule, there exists some extent of covalent bonding force as well.
H₂ molecules contains weak london forces of attraction, which are known as dipole-induced dipole forces.
HBr + Ca reaction enthalpy
The standard reaction enthalpy of HBr+Ca is −554.2 kJ/mol. The standard heat of formation (∆H0f) value of each molecule can be used in the calculation of reaction enthalpy the reaction.
| Molecules in the reaction | Number of moles | ∆H0f (kJ/mol) |
|---|---|---|
| HBr (aq) | 2 | -120.8 |
| Ca (s) | 1 | 0 |
| CaBr2(aq) | 1 | -675.0 |
| H₂(g) | 1 | 0 |
The table contains details of enthalpy values at standard conditions of temperature and pressure.
∆Hf=ΣHproducts−ΣHractants
∆H0f=(∆H0CaBr2+∆H0H2) –(∆H0HBr+∆H0Ca)
={−675−(−120.8)}kJ/mol=-554.2 kJ/mol
Hence, the standard reaction enthalpy of HBr+Ca is −554.2 kJ/mol.
Is HBr + Ca a buffer solution?
HBr+Ca mixture solution is not a buffer solution because it contains strong acid without any conjugated base part in the solution.
Is HBr + Ca a complete reaction?
HBr + Ca is a complete reaction as no reactant is left after reaction.
Is HBr + Ca an exothermic reaction?
HBr+Ca is an exothermic reaction which shows an enthalpy value of 554.2 kJ/mol.
Is HBr + Ca a redox reaction?
HBr+Ca is a redox reaction, as the reactants change their oxidation state or number after the reaction.
Is HBr + Ca a precipitation reaction?
HBr+Ca is not a precipitation reaction. The product molecules are CaBr2 and H₂. CaBr2 is ionic in nature and well soluble in aqueous solution, and H₂ is a gas which cannot be precipitated.
Is HBr + Ca irreversible reaction?
HBr+Ca is irreversible reaction as we cannot reverse the direction of reaction, i.e. extract reactant from product.
Is HBr + Ca displacement reaction?
HBr+Ca is a single displacement reaction where the strong molecule displaces the weaker one from its compound. Ca metal is more reactive than H according to the metal activity series. So, strong metal displaces H atom and forms CaBr2 and H₂ gas.
A+B−C→A−C+B, reactivity: A˃B
Conclusion
HBr is widely used in pharma and agricultural industries for its strong acidic nature. It is also used in production of bromine gas in industry scale. Calcium ions are found in living body. Calcium ions are also widely used in cement, toothpaste, and mineral industries.
Hi……I am Sanchita Baitalik, I have completed my Ph.D. in Chemistry from Jadavpur University, West Bengal. My area of specialization is Inorganic Chemistry. I am here to share my best knowledge about chemistry as a part of science. I believe the concept of chemistry can be easy and interesting if we have the ability to present it’s each concept in simple words. So, I am here to share my concept in simple but meaningful words.
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