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Chapter 5: Problem 206

The \(\mathrm{pH} 0.1 \mathrm{M}\) solution the following salts increases in the order a. \(\mathrm{NaCl}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCN}<\mathrm{HCl}\) b. \(\mathrm{HCl}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCl}<\mathrm{NaCN}\) c. \(\mathrm{NaCN}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCl}<\mathrm{HCl}\) d. \(\mathrm{HCl}<\mathrm{NaCl}<\mathrm{NaCN}<\mathrm{NH}_{4} \mathrm{Cl}\)

Short Answer

Expert verified
The correct answer is b: \(\mathrm{HCl}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCl}<\mathrm{NaCN}\).

Step by step solution

01

Understand the Salts

Analyze the given salts and their nature of acidity or basicity. Consider the dissociation of each salt in water and identify the resulting ions, focusing on their acid or base properties. \(\mathrm{NaCl}\) is a neutral salt resulting from a strong acid and a strong base, \(\mathrm{NH}_4\mathrm{Cl}\) is acidic due to \(\mathrm{NH}_4^+\), \(\mathrm{NaCN}\) is basic due to \(\mathrm{CN}^-\), and \(\mathrm{HCl}\) is a strong acid.
02

Determine the Nature of the Solution

Recognize that the pH of the solution depends on the strength of the acids or bases formed upon hydrolysis. \(\mathrm{HCl}\) will completely dissociate into \(\mathrm{H}^+\) making it the most acidic, \(\mathrm{NH}_4\mathrm{Cl}\) releases \(\mathrm{NH}_4^+\) which partially dissociates into \(\mathrm{NH}_3\) and \(\mathrm{H}^+\), \(\mathrm{NaCN}\) hydrolyzes to form the basic ion \(\mathrm{CN}^-\), and \(\mathrm{NaCl}\) does not affect pH as it is neutral.
03

Arrange the Salts by pH

Based on the previous analysis, arrange the salts in order of increasing pH from acidic to neutral to basic. Since \(\mathrm{HCl}\) is the most acidic, it will have the lowest pH, followed by \(\mathrm{NH}_4\mathrm{Cl}\) (slightly acidic), then \(\mathrm{NaCl}\) (neutral), and \(\mathrm{NaCN}\) will be the highest due to its basicity.
04

Select Correct Option

Compare the sequence obtained with the given options. The correct sequence of increasing pH is \(\mathrm{HCl}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCl}<\mathrm{NaCN}\), which matches option b.

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Key Concepts

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

Acidic and Basic Salts
Salts can be categorized as acidic, basic, or neutral. This classification is based on how they dissociate and interact in a water solution. When salts dissolve in water, they separate into their respective cations and anions. The nature of these ions determines whether the solution becomes acidic or basic.
For instance, acidic salts often result from the combination of a strong acid and a weak base, leading to the presence of cations that react with water to release hydrogen ions, \(\text{H}^+\), making the solution acidic. A classic example is ammonium chloride, \(\text{NH}_4\text{Cl}\), where \(\text{NH}_4^+\) influences the acidity.
  • Neutral salts, like sodium chloride \(\text{NaCl}\), arise from the reaction of strong acids and strong bases, typically showing no effect on the pH of the solution.
  • Basic salts, like sodium cyanide \(\text{NaCN}\), are produced from strong bases and weak acids. The anions react with water to form hydroxide ions, \(\text{OH}^-\), increasing the pH.
Hydrolysis of Salts
Hydrolysis is the process through which salts react with water to form either acidic or basic solutions. It depends on the ions present within the salt when it is dissolved.
When dealing with hydrolysis, it's essential to understand the behavior of the salt's cation and anion:
  • Cations from weak bases in salts, such as \(\text{NH}_4^+\) from \(\text{NH}_4\text{Cl}\), tend to make solutions more acidic as they react with water releasing protons.
  • Anions derived from weak acids in salts, like \(\text{CN}^-\) from \(\text{NaCN}\), usually make the solution more basic as they generate \(\text{OH}^-\) when hydrolyzing.
Understanding these interactions is crucial to determine the pH nature of the resulting solution after dissolution.
Acid-Base Properties
The core of acid-base chemistry lies in understanding how substances react to donate or accept protons. Strong acids, such as \(\text{HCl}\), dissociate completely in water to release\(\text{H}^+\) ions, greatly influencing pH.
Acid-base properties are also crucial in assessing the behavior of salts in solution:
  • Strong acids combined with weak bases yield acidic salts.
  • Strong bases with weak acids lead to basic salts.
  • Both strong acid and base interactions can yield neutral salts with no substantial pH effect, like in \(\text{NaCl}\).
The interplay of these interactions determines the passage of ions in solution affecting the pH level.
pH Calculation
Calculating the pH of a solution gives us insight into its acidic or basic nature. The formula for pH is given by \(\text{pH} = -\log[\text{H}^+]\).
Factors influencing the pH of salt solutions include the strength of its component acid and base:
  • For acidic salts, the higher concentration of \(\text{H}^+\) from hydrolysis decreases pH.
  • For basic salts, the presence of \(\text{OH}^-\) raises pH resulting from hydrolyzed anions.
  • The calculated pH serves as a direct indicator of whether the salt solution is acidic, neutral, or basic.
By understanding how ions interact in water, accurate pH measurement is achievable, illustrating the overall acidity or basicity of the solution.
Strong Acids and Bases
Strong acids and bases are essential in understanding salt behavior because of their complete dissociation in water. This property dictates the resulting pH of the solution.
When strong acids such as \(\text{HCl}\) dissolve, they completely disintegrate into ions giving high concentrations of \(\text{H}^+\). This results in lower pH.
Contrary, strong bases like sodium hydroxide release significant amounts of \(\text{OH}^-\), making solutions highly basic.
  • The neutralization between strong acids and bases results in neutral salts, like \(\text{NaCl}\), carrying no significant pH change.
  • Understanding these extremes in acid and base strength allows the prediction of how salt solutions will behave once dissolved in water.
This knowledge is fundamental for predicting and adjusting pH in various practical applications.

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Most popular questions from this chapter

Which of the following statement is/are correct for a reversible reaction? a. At a given temperature both \(Q\) and \(K\) vary with the progress of the reaction. b. When \(Q>K\), the reaction proceeds in backward direction before coming to stand still. c. Reaction quotient (Q) is the ratio of the product or arbitrary molar concentrations of the products to those of the reactants. d. \(Q\) may be \(<>=K\).

(A): When \(\mathrm{CaCO}_{3}(\mathrm{~s})\) is heated, the loss of \(\mathrm{CO}_{2}\) (g) from the system causes the reaction to go almost to completion to leave a residue of \(\mathrm{CaO}(\mathrm{s})\) (R): Heating causes gas particles to move with more energy.

What is the correct sequence of active masses in increasing order in gaseous mixture containing one gram per litre of each of the following? I. \(\mathrm{NH}_{3}\) II. \(\mathrm{N}_{2}\) III. \(\mathrm{H}_{2}\) IV. \(\mathrm{O}_{2}\) Select the correct answer using the codes given below: a. III, I, IV, II b. III, IV, II, I c. II, I, IV, III d. IV, II, I, III

(A): For the reaction \(\mathrm{A}+\mathrm{B} \leftrightarrow \mathrm{C}, \mathrm{Kc}=2\). If we start with 1 mol each of \(A, B\), and \(C\) in \(5 L\) flask, then at equilibrium, molar concentration of \(\mathrm{A}\) and \(\mathrm{B}\) decreases and that of \(\mathrm{C}\) increases. (R): Reaction quotient \(\mathrm{Q}>\mathrm{Kc}\) with given quantity of \(\mathrm{A}, \mathrm{B}\), and \(\mathrm{C}\) hence reaction is reversed.

(A): The value of \(\mathrm{K}\) gives us a relative idea about the extent to which a reaction proceeds. \((\mathbf{R}):\) The value of \(\mathrm{K}\) is independent of the stoichiometry of reactants and products at the point of equilibrium.
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