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 126ᵒC 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.
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