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Chapter 8: Problem 261

An aqueous solution of \(1 \mathrm{M} \mathrm{NaCl}\) and \(\mathrm{IM} \mathrm{HCl}\) is [2002] (a) not a buffer but \(\mathrm{pH}<7\) (b) not a buffer but \(\mathrm{pH}>7\) (c) a buffer with \(\mathrm{pH}<7\) (d) a buffer with \(\mathrm{pH}>7\)

Short Answer

Expert verified
(a) not a buffer but \( \mathrm{pH}<7 \).

Step by step solution

01

Understanding the Components

Identify the components in the solution: NaCl and HCl. NaCl is a neutral salt and does not affect the pH of the solution. HCl is a strong acid, which dissociates completely, contributing H鈦� ions.
02

Identifying Buffer Conditions

A buffer solution contains a weak acid and its conjugate base, or a weak base and its conjugate acid. Here, HCl is a strong acid and there is no conjugate base present in significant amounts from a weak acid to form a buffer.
03

Predicting the pH of the Solution

Because HCl is a strong acid, the solution will have an excess of H鈦� ions. Therefore, the solution is acidic, and the pH will be less than 7.
04

Final Analysis

Since the solution is neither a mixture of a weak acid and its conjugate base nor a weak base and its conjugate acid, it is not a buffer. Given that it contains a strong acid, the pH is less than 7.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Buffer Solutions
A buffer solution is a special type of solution that resists changes in its pH. It's a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid.
These solutions are crucial, especially in maintaining the pH necessary for various biological and chemical processes.
  • A buffer solution can maintain its pH even when a small amount of strong acid or strong base is added.
  • In contrast, solutions without these buffering components can undergo significant pH changes.
  • Buffer solutions are typically made by partially neutralizing a weak acid with a strong base, or vice versa.
When thinking about a solution鈥檚 ability to act as a buffer, it鈥檚 key to identify if both a weak acid/base and its conjugate are present in sufficient amounts.
This is because they work together to neutralize additional acids or bases.
Strong Acids
Strong acids are chemicals that dissociate completely in water, releasing protons (H鈦� ions) and increasing the hydrogen ion concentration of the solution.
This complete dissociation makes them very effective at lowering the pH of a solution.
  • Common examples include hydrochloric acid (HCl), sulfuric acid (H鈧係O鈧�), and nitric acid (HNO鈧�).
  • Unlike weak acids, which only partially dissociate, strong acids fully release their protons when dissolved.
In the context of the original exercise, the presence of strong acid like HCl means the solution's pH will be significantly below 7, indicating that the solution is acidic.
This is because there is an abundance of H鈦� ions, which are responsible for the acidic property.
Conjugate Base
The conjugate base of an acid is what remains after the acid has donated a proton. In other words, it's the substance formed when an acid loses an H鈦� ion.
An essential aspect of buffer solutions is the presence of sufficient quantities of both the weak acid and its conjugate base.
  • For example, the conjugate base of acetic acid (CH鈧僀OOH) is acetate (CH鈧僀OO鈦�).
  • A conjugate base is typically a weaker base than the strong bases found in solution.
In the context of the question discussed, the lack of a conjugate base from a weak acid, alongside the strong acid HCl, indicates the solution can鈥檛 function as a buffer.
This is because there is no equilibrium established between a weak acid and its conjugate base to adjust pH changes.

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Most popular questions from this chapter

When \(\mathrm{H}_{2} \mathrm{~S}\) is passed through an aqueous solution of an equilimolar mixture of \(\mathrm{Zn}^{2+}\) and \(\mathrm{Pb}^{2+}\) acidified with dilute acetic acid, \(\mathrm{ZnS}\) is not precipitated, because (a) \(\mathrm{K}_{\mathrm{sp}}(\mathrm{ZnS})<\mathrm{K}_{\mathrm{sp}}(\mathrm{PbS})\) (b) \(\mathrm{K}_{\mathrm{sp}}(\mathrm{ZnS})>\mathrm{K}_{\mathrm{sp}}^{\mathrm{sp}}(\mathrm{PbS})\) (c) \(\mathrm{H}_{2} \mathrm{~S}\) decreases the \(\mathrm{K}_{\mathrm{sp}}\) of \(\mathrm{ZnS}\) (d) \(\mathrm{H}_{2} \mathrm{~S}\) increases the \(\mathrm{K}_{\mathrm{sp}}\) of \(\mathrm{PbS}\)

\(1.75 \mathrm{gm}\) of solid \(\mathrm{NaOH}\) are added to \(250 \mathrm{ml}\) of \(0.1 \mathrm{M}\) \(\mathrm{NiCl}_{2}\) solution. Calculate the approximate \(\mathrm{pH}\) of final solution. \(\left(\mathrm{K}_{\mathrm{sp}}\right.\) of \(\left.\mathrm{Ni}(\mathrm{OH})_{2}=1.6 \times 10^{-14}\right)\).

The ionization constant of \(\left[\mathrm{NH}_{4}^{+}\right]\)in water is \(5.6 \times 10^{-10}\) at \(25^{\circ} \mathrm{C}\). The rate constant for the reaction of \(\left[\mathrm{NH}_{4}^{+}\right]\) and \(\left[\mathrm{OH}^{-}\right]\)to form \(\mathrm{NH}_{3}\) and \(\mathrm{H}_{2} \mathrm{O}\) is \(3.4 \times 10^{10}\) litmol \(\mathrm{sec}^{-1}\) at \(25^{\circ} \mathrm{C}\). The rate constant for the proton transfer form water to \(\mathrm{NH}_{3}\) in lit \(\mathrm{mol}^{-1} \mathrm{sec}^{-1}\) is (a) \(6.07 \times 10^{5}\) (b) \(6.07 \times 10^{-5}\) (c) \(6.07 \times 10^{-3}\) (d) \(6.07 \times 10^{-4}\)

An acid-base indicator has \(\mathrm{K}_{\mathrm{a}}=3.0 \times 10^{-5} .\) The acid form of the indicator is red and the basic form is blue. The \(\left[\mathrm{H}^{+}\right]\)required to change the indicator from \(75 \%\) red to \(75 \%\) blue is (a) \(8 \times 10^{-5} \mathrm{M}\) (b) \(9 \times 10^{-5} \mathrm{M}\) (c) \(1 \times 10^{-5} \mathrm{M}\) (d) \(3 \times 10^{-4} \mathrm{M}\)

A buffer solution contains monobasic acid and its salt of concentration \(3 \mathrm{M}\) ad \(0.3 \mathrm{M}\) respectively. If \(\mathrm{pK}_{\mathrm{a}}\) of acid is 5 , the \(\mathrm{pH}\) of the solution is
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