Correct Answer - Option 1 : Not a buffer but pH <7
Concept:
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pH (Power of Hydrogen): The degree of acidity or alkalinity of a substance is expressed in pH value.
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pH is a scale (0 to 14) used to specify the acidity or basicity of an aqueous solution.
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Lower pH values of solutions represent more acidic in nature,
- While higher pH values of solutions represent more basic or alkaline.
pH = - log [H+] For acid
pOH = - log [OH-] For base
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Buffer solution: A buffer solution contains either a weak acid and its salt with a strong base or a weak base and its salt with strong acid. Buffers resist a change in pH when acids or bases are added to them.
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Buffer can be classified into two types;
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Acidic Buffer: The buffer is formed from the solution of a weak acid and its salt of a strong base. acid. Acidic buffers generally have a pH of less than 7. Example of the acidic buffer is CH3COOH and CH3COONa.
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Basic Buffer: The buffer is formed from the solution of a weak base and its salt with a strong acid. basic buffers have a pH of more than 7. An example of a basic buffer is NH4OH and NH4Cl.
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For buffer solution,
\({\rm{pH}} = {\rm{pKa}} + \log \left[ {\frac{{{\rm{salt}}}}{{{\rm{acid}}}}} \right] = {\rm{pKa}}\)
Explanation:
- Given is a solution of 1M NaCl and 1M HCl.
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NaCl is formed by the reaction of strong base NaOH and strong acid HCl.
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NaCl is a salt of strong acid and a strong base. whereas HCl is a strong acid.
- When equimolar amounts of them are mixed together, they do not form a buffer because a strong acid the salt of the strong acid does not form the buffer.
- The solution of 1M NaCl and 1M HCl cannot resist the change in pH when acid or base are added to it.
- Also, the mixture is strongly acidic because, upon hydrolysis, NaCl gives NaOH and HCl, and HCl is also present there.
- So there is twice the amount of HCl as compared to NaOH. This renders the solution acidic in nature.
- Hence, the pH of the solution will be less than 7.
Hence, the correct answer is an aqueous solution of 1M NaCl and 1M HCl is not a buffer but pH < 7.
