Base strength, inherent

You might have noticed the numbers for ammonia and acetic acid are the same, but don t be misled to believe these numbers are universal for all weak acids and bases. It is entirely coincidental that the numbers for acetic acid and ammonia are the same. The degree of ionization is dependent on the inherent acid or base strength of the species. This is a topic we will consider shortly. 

Hardness and softness refer to special stability of hard-hard and soft-soft interactions and should be carefully distinguished from inherent acid or base strength. For example. both OH and F are hard bases yet the basicity of the hydroxide ion is about lO times that of the fluoride ion. Similariy, both S( and EtjP may be considered soft bases however, the latter is 10 times as strong (toward CHjHg ). It is possible for a strong acid or base to displace a weaker one, even though this appears to violate the principle of hard and soft acids and bases. For example, the stronger, softer base, the sulfite ion, can displace the weak, hard base, fluoride ion, from the hard add. the proton, H -... 

More detailed comparisons are possible, but another factor, called the inherent acid-base strength, must also be kept in mind in these comparisons. An acid or a base may be either hard or soft and at the same time be either strong or weak. The strength of the acid or base may be more important than the hard-soft characteristics both must be considered at the same time. If two soft bases are in competition for the same acid, the one with more inherent base strength may be favored unless there is considerable difference in softness. As an example, consider the following reaction. Two hard-soft... 

Drago s system emphasized the two factors involved in acid-base strength (electrostatic and covalent) in the two terms of his equation for enthalpy of reaction. Pearson s system put more obvious emphasis on the covalent factor. Pearson proposed the equation log K = + o- ag, with the inherent strength S modified by a soft-... 

Polyetherimides are suitable for applications that require high temperature stability, high mechanical strength, inherent flame resistance with extremely low smoke evolution, outstanding electrical properties over a wide frequency and temperature range, chemical resistance to aliphatic hydrocarbons, acids and dilute bases, UV stability, and ready processability on conventional equipment. 

The H30 /H20/0H reference for quantifying relative acid and base strengths is only useful when the examined acid is inherently weaker than H30 or the examined base is weaker than OH. Hydronium ion and hydroxide ion are the strongest acid and base. 

Tensile Strength. The inherent tensile strength of a single asbestos fiber, based on the strength of Si—O—Si bonds ia the siUcate chain, should be near 10 GPa (1.45 x 10 psi) (18). However, iadustrial fibers exhibit substantially lower values, because of the presence of various types of stmctural or chemical defects. 

The copolymer-silica adhesives also follow a similar trend but fail much earlier than the terpolymer-based adhesives. This is because of two factors (1) the increase in the inherent strength of the adhesive due to more favorable terpolymer rubber-silica interaction and (2) chemisorption in much higher magnitude between the polar substrates and the nanocomposites. 

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