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Candidates preparing for their CSIR UGC NET exam might need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point, We at BYJU'S Exam Prep come up with short notes on the Soft Acid and Base concept, which comes under the Chemical Science syllabus. It includes the most important concepts from the CSIR-NET exam perspective. Our experienced subject-matter experts have meticulously designed this set of short notes for Chemical Sciences to give you the most standard set of study materials to focus upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them learn and for their future. Here we are offering the best study notes that are reliable and can be used by the students during their preparations for the upcoming CSIR-NET 2021 exam.
Soft Acid and Base concept
Hard-soft Acid-Base Concept
According to the HSAB principle, soft base tends to combine with soft acid while hard base combines with hard acid. Let us discuss each term one by one:
Soft base: Large ionic radius, highly polarizable, intermediate electronegativity, low energy HOMOs. Ex- RNC, CO, RSH, H-
Soft acid: Large ionic radius, low positive charge, low energy Lumos. Ex- Ag+, Cs+,Pd2+
Hard acid: Small ionic radius, high positive charge, high energy Lumos. Ex-K+, H+, Al3+.
Hard base: Small ionic radius, high electronegativity, weakly polarizable, high energy HOMOs. Ex- H2O, R2O, NH3.
Borderline Acid and Base: They have intermediate properties between hard acid/base and soft acid/base. Ex- Aniline, N2, pyridine
Some important points regarding the Stability of Compound formed:
- Higher the electronegativity difference between hard acid and hard base, stronger will be ionic interactions.
- Due to almost the same electronegativity of soft acid and soft base, they have covalent interactions.
- When hard acid and soft base or vice-versa combine, the interaction between them is polar covalent, making them reactive.
Applications of HSAB:
1. Hydrogen Bonding: H- bonding is possible when H is attached to highly electronegative elements such as N, O, or F. In cases of NH3, H2O, or HF, H-bonding is possible.
2. Linkage of Ambidentate ligand to Metal Atom: Ambidentate ligand can use its different elements to bind with metal. Example- SCN-. It can bInd with metal both as M-NCS or M-SCN. Now which atom will combine depends on the nature of the acid or base.
Symbiotic effect: The hard-soft nature of metal ions can be changed by the presence of other groups.
3. Predict the direction of inorganic reactions: Let us understand this concept by taking 1 example:
Consider the reaction between AsF3 and PI3:
AsF3+ PI3→ AsI3+ PF3
This reaction will go in the right direction as As3+ is softer and P3+ and I- is softer than F-.
4. Solubility in water: The polar compound will be soluble in water while non-polar will be insoluble. Now, when soft acid combines with a soft base, the compound formed has covalent nature, due to which it will be less soluble in water.
5. Precipitation reaction: Soft and borderline acids can be precipitated in the form of sulfides from their aqueous solution.
Limitations of the HSAB principle:
According to Fazan’s rule, salts of Be are covalent in nature, but according to the HSAB principle, Be compounds show ionic nature. This is not true.
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Also Read :
CSIR NET Chemical Science - Short Notes on Organometallic Compounds
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