Hydrogen Fluoride
Hydrogen fluoride is an acid compound with the chemical formula HF. Hydrogen fluoride he a colorless, fuming liquid with the boiling point of 20 degree Celsius.
The boiling point of hydrogen fluoride is the highest among other hydrogen halide compounds. The high boiling point is due to the presence of hydrogen bonds between hydrogen fluoride molecules.
Between other hydrogen halide molecules, eg HCl, there is also a hydrogen bond. However, the hydrogen bonds formed by fellow hydrogen fluoride molecules are much stronger.
Why is the hydrogen bond in the hydrogen fluoride stronger?
The answer relates to the electronegativity value of the halogen elements. As we know, fluorine is the element that has the highest electronegativity value among all the elements in the periodic table. So the hydrogen bond formed with the fluorine atom is the strongest of all.
When we mix hydrogen fluoride with water, we produce hydrofluoric acid. Hydrofluoric acid is a weak acid with a positive pKa value. Acid strength of hydrofluoric acid differs from other hydrohalic acids such as HCl, HBr, and HI. These three acids are strong acids.
Why is hydrofluoric acid a weak acid?
The answer is related to the single covalent bonding force formed between the hydrogen atom and the halogen atom.
Acid strength depends on the easy or difficulty of a compound to release hydrogen ions. The easier the hydrogen ion is released, the acid strength will be stronger.
Since the fluorine atom is the most electronegative atom among all other halogen elements, the single bond between H-F will be much stronger than H - Cl, H - Br or H - I. This makes HF more difficult to remove hydrogen ions than HCl, HBr and HI. Hence, HF is a weak acid.
Although hydrofluoric acid is a weak acid, it is a highly corrosive acid compound. Hydrofluoric acid can even melt glass. Because it is highly corrosive, hydrofluoric acid is always stored in plastic bottles.
Hydrofluoric acid is widely used by people to paint on glass. The reaction between hydrofluoric acid and glass produces hexafluorosilicate ions.
SiO2 (s) + 6HF (aq) ==> SiF63- (aq) + 2H + (aq) + 2H2O (l)
Globally, about 10 ^ 6 tons of hydrofluoric acid is produced annually. Hydrogen fluoride is made by heating calcium fluoride with concentrated sulfuric acid.
The reaction is:
CaF2 (s) + H2SO4 (l) ==> HF (g) + CaSO4 (s)
The above reaction takes place endothermically (need energy).
The formed HF gas will then be cooled to turn into a liquid or mixed with water to form hydrofluoric acid.
Making hydrogen fluoride is one of the most dangerous compounds. This is because hydrogen fluoride is highly toxic.
In the past, before anyone knew the dangers of hydrogen fluoride, many chemists were researching this compound without protection. As a result, some of these chemists were found dead by inhaling hydrogen fluoride gas and most others experiencing respiratory problems.
Inhaling hydrogen fluoride gas can cause pneumonia. Hydrofluoric acid exposed to the skin can cause tissue damage.
Because it is so dangerous, hydrogen fluoride should be used with extreme caution.
In addition to painting glass, most of the production of hydrofluoric acid is used to synthesize other compounds containing fluorine atoms.
As an example :
Sodium fluoride is prepared by reacting sodium hydroxide with hydrofluoric acid
Note: All pictures are taken from wikimediacommons.org
The boiling point of hydrogen fluoride is the highest among other hydrogen halide compounds. The high boiling point is due to the presence of hydrogen bonds between hydrogen fluoride molecules.
Between other hydrogen halide molecules, eg HCl, there is also a hydrogen bond. However, the hydrogen bonds formed by fellow hydrogen fluoride molecules are much stronger.
Why is the hydrogen bond in the hydrogen fluoride stronger?
The answer relates to the electronegativity value of the halogen elements. As we know, fluorine is the element that has the highest electronegativity value among all the elements in the periodic table. So the hydrogen bond formed with the fluorine atom is the strongest of all.
When we mix hydrogen fluoride with water, we produce hydrofluoric acid. Hydrofluoric acid is a weak acid with a positive pKa value. Acid strength of hydrofluoric acid differs from other hydrohalic acids such as HCl, HBr, and HI. These three acids are strong acids.
Why is hydrofluoric acid a weak acid?
The answer is related to the single covalent bonding force formed between the hydrogen atom and the halogen atom.
Acid strength depends on the easy or difficulty of a compound to release hydrogen ions. The easier the hydrogen ion is released, the acid strength will be stronger.
Since the fluorine atom is the most electronegative atom among all other halogen elements, the single bond between H-F will be much stronger than H - Cl, H - Br or H - I. This makes HF more difficult to remove hydrogen ions than HCl, HBr and HI. Hence, HF is a weak acid.
Although hydrofluoric acid is a weak acid, it is a highly corrosive acid compound. Hydrofluoric acid can even melt glass. Because it is highly corrosive, hydrofluoric acid is always stored in plastic bottles.
Hydrofluoric acid is widely used by people to paint on glass. The reaction between hydrofluoric acid and glass produces hexafluorosilicate ions.
SiO2 (s) + 6HF (aq) ==> SiF63- (aq) + 2H + (aq) + 2H2O (l)
Globally, about 10 ^ 6 tons of hydrofluoric acid is produced annually. Hydrogen fluoride is made by heating calcium fluoride with concentrated sulfuric acid.
The reaction is:
CaF2 (s) + H2SO4 (l) ==> HF (g) + CaSO4 (s)
The above reaction takes place endothermically (need energy).
The formed HF gas will then be cooled to turn into a liquid or mixed with water to form hydrofluoric acid.
Making hydrogen fluoride is one of the most dangerous compounds. This is because hydrogen fluoride is highly toxic.
In the past, before anyone knew the dangers of hydrogen fluoride, many chemists were researching this compound without protection. As a result, some of these chemists were found dead by inhaling hydrogen fluoride gas and most others experiencing respiratory problems.
Inhaling hydrogen fluoride gas can cause pneumonia. Hydrofluoric acid exposed to the skin can cause tissue damage.
Because it is so dangerous, hydrogen fluoride should be used with extreme caution.
In addition to painting glass, most of the production of hydrofluoric acid is used to synthesize other compounds containing fluorine atoms.
As an example :
Sodium fluoride is prepared by reacting sodium hydroxide with hydrofluoric acid
Note: All pictures are taken from wikimediacommons.org
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