Tuesday, June 23, 2020

Hydrobromic-acid-formula-properties-uses with pH calculation



What is hydrobromic acid in halogen chemistry


Hydrobromic acid is an important chemical in chemistry, especially in inorganic chemistry. It is polar covalent molecule with chemical formula, HBr.

The pKa value of HBr acid is –9. This means that hydrobromic acid is a strong mono basic hydracids and act as a strong reducing agent in many chemical reactions.


Hydrobromic acid formula and Lewis structure


Hydrobromic acid is a diatomic molecule which consists of hydrogen and bromine. The chemical formula in aqueous solution and Lewis structure of hydrobromic acid are shown below.


Physical properties of hydrobromic acid


Hydrobromic acid is a colorless with intense pungentsmelling gas. It is slightly heavier than air and creates brown smoke with wet air.

Hydrobromic acid is highly soluble in water. When it dissolved in water, it forms a constant boiling mixture with boiling point 399K.

An aqueous solution of hydrobromic acid contains 70% of hydrogen bromide gas at 126áµ’C temperature. The density of hydrobromic acid is 1.49 g/ml.

Hydrobromic acid pH calculation


The density of hydrobromic acid is 1.49 g/ml. That is, 1 ml aqueous solution of hydrobromic acid contains 1.49 g of HBr gas. Therefore, 1000 ml or 1 liter contains 1490 g of HBr gas.

Hence the strength of hydrobromic acid solution is [1490 / 80.91] = 18.4(M). Since hydrobromic acid is a strong acid, hence it is completely ionized in aqueous solution [HBr = H+ + Br ].



Physical state
Hydrogen bromide is a gas at room temperature. But it is easily compressed to colorless liquid. 

HBr gas is slightly heavier than air. When it comes in contact with aquatic air it creates brown smoke.

Melting and boiling point of hydrobromic acid


The melting point and boiling point of hydrobromic acid are, 185 K and 206 K respectively.
Due to less polarity of H–Br bond, hydrogen bromide can’t form inter molecular hydrogen bonding. 
That is, HBr molecules remain as an individual molecule. Hence, HBr is a gas at room temperature.
Consequently, the melting point and boiling point of hydrobromic acid is less than HI acids.

Bond dissociation energy and stability of hydrobromic acid


Bromine is a electronegative element than hydrogen. So, hydrobromic acid is a polar covalent molecule.
The bond dissociation energy of H – Br molecule is 363 Kj/mole which is higher than HI molecule but less than HF and HCl molecules.
This means that HBr is thermally more stable than HI molecule but less stable than HF and HCl molecule.
When HBr is heated on 1073 K temperature, it produces hydrogen and bromine molecules.
The hydrobromic acid is also dissociates into bromine and hydrogen gas when it is oxidized by air oxygen in presence of sunlight.

Chemical properties of hydrobromic acid


Reducing properties
Since the bond dissociation energy of H–Br bond is less than H–F and H–Cl bond, hence HBr acids act as a strong reducing agent.
Some oxidizing agent, such as KMnO4, K2Cr2O7 Pb3O4, PbO2etc, oxidize HBr acid to release bromine gas.

Hydrobromic acid reaction with metals

Some metals which are electropositive than hydrogen, react with dilute HBr and produced hydrogen gas.
For example, zinc, magnesium, iron, calcium etc


Hydromic acid strength 


Hydrobromic acid is a strong mono basic acid. It is mores stronger acid than HF or HCl. Because, HBr acid is ionized in aqueous solution completely.




The aqueous solution of hydrobromic acid changes the litmus paper color from blue to red. It reacts with metal oxide or hydroxide to form salt and water.



Hydrobromic acid laboratory preparation


Hydrogen bromide is prepared in laboratory by the reaction of red phosphorous, bromine and water.
This is two step process reactions. In the first step, bromine reacts with red ‘P’ to form phosphorous tri bromide and phosphorous penta bromide.

In the second step, the producing phosphorous tribromide and phosphorous pentabromide under goes hydrolysis, resulting in the formation of hydrogen bromide gas.
This hydrogen bromide gas produces hydrobromic acid when dissolved in water solvent.




Synthesis method for preparation of hydrobromic acid


When a mixture of hydrogen gas and bromine vapor is passed over ‘Pt’ catalyst at 473 K temperature, then hydrogen bromide gas is obtained. 

This method for preparation of hydrogen bromide gas is known as Synthesis method. On dissolving of this hydrogen bromide gas in water, hydrobromic acid is prepared.


 Hydrobromic acid uses in chemistry   


Hydrobromic acid play an important role in inorganic, organic and also in industrial chemistry. Some application of HBr acid is discussed below.

The potassium salt of HBr acid is used to prepare medicine in medicine industry.
The silver salt of HBr acid is used in photography.

In organic chemistry, hydrobromic acid is used to prepare bromo compound, Such as, bromo alkane, alkyl magnesium bromide, bromo benzene and other aromatic benzene derivative compound.

It is used as a reducing agent both in organic andinorganic chemistry. It is also used as a laboratory reagent.

Identification of hydrobromic acid


When a mixture of concentrated HBr acid and a little amount of concentrated sulfuricacid are heated in a test tube, a brown color of gas with pungent smell is evolved.
This emitted gas change the color of KI in starch solution, from brown to blue. This is best identification method of HBr acid.









Importance of Hydrobromic acid in chemistry.
Hydrobromic acid chemical formula and Lewis structure.
Physical properties of hydrobromic acid.
Hydrobromic acid pH calculation.
Melting and boiling point of hydrobromic acid.
Bond dissociation energy and stability of hydrobromic acid.
Chemical properties of hydrobromic acid.
Hydrobromic acid reaction with metals.
Hydrobromic acid laboratory preparation.
Hydrobromic acid uses in chemistry.  
Identification of hydrobromic acid.












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