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Ch.18 - Aqueous Ionic Equilibrium
Chapter 18, Problem 56d

Determine whether or not the mixing of each pair of solutions results in a buffer. d. 150.0 mL of 0.15 M HCl; 135.0 mL of 0.25 M NaOH

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Identify the components needed for a buffer solution: a weak acid and its conjugate base, or a weak base and its conjugate acid.
Recognize that HCl is a strong acid and NaOH is a strong base, neither of which are suitable for forming a buffer directly.
Calculate the moles of HCl: \( \text{moles of HCl} = 0.15 \, \text{M} \times 0.150 \, \text{L} \).
Calculate the moles of NaOH: \( \text{moles of NaOH} = 0.25 \, \text{M} \times 0.135 \, \text{L} \).
Determine if there is an excess of either HCl or NaOH after the reaction, as a buffer requires a weak acid/base and its conjugate pair, not excess strong acid or base.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Buffer Solutions

A buffer solution is a system that resists changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffers are crucial in maintaining stable pH levels in various chemical and biological processes.
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Strong Acids and Bases

Strong acids, like HCl, completely dissociate in water, releasing all their hydrogen ions (H+), while strong bases, like NaOH, completely dissociate to release hydroxide ions (OH-). The complete dissociation of these substances means they do not contribute to the buffering capacity, as they do not exist in equilibrium with their conjugate forms.
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Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to produce water and a salt. In this case, HCl and NaOH will react to form water and sodium chloride (NaCl). The resulting solution's pH will depend on the relative amounts of acid and base, and if they are present in stoichiometric amounts, the solution will be neutral, not a buffer.
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