Chemistry 121 3/14/2014
Factors Affecting Acid Strength
1.
The more polar the H–X bond, the more acidic the compound.
A molecule containing H
will behave as an acid only if the bond is polarized this way:
Hydrides such as NaH, do not react as acids, because H has a negative charge. CH
4
is not an acid
because the C-H bond is not polar.
2. The weaker the H–X bond, the more acidic the compound.
Bond strength of halides: HF(567kJ/mol)>HCl(431KJ/mol)>HBr(366kJ/mol)>HI(299KJ/mol).
HF is the least acidic, HI is the most acidic.
3. The greater the stability of the conjugate base, the stronger the acid.
The strength of an acid is often a combination of all three factors.
Binary Acids
•
For a series of binary acids H-X (X represents members of the same group), the strength
of the H-X bond is the most important factor in determining the acid strength.
•
The strength of the H-X bond decreases down a group.
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•
For a series of binary acids H-X (X represents members of the same period), the polarity
of the H-X bond is the most important factor in determining the acid strength.
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- Fall '14
- Alam,MohammadSajja
- Chemistry, Mole, acidity increases, binary acids H-X
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