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Chapter 16: Problem 86

An unknown salt is either \(\mathrm{KBr}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{KCN},\) or \(\mathrm{K}_{2} \mathrm{CO}_{3} .\) If a \(0.100 M\) solution of the salt is neutral, what is the identity of the salt?

Short Answer

Expert verified
The salt is KBr.

Step by step solution

01

Understand the Properties of the Salts

First, recall the properties of each salt in solution. - \( ext{KBr}\) is neutral since both potassium \( ext{K}^+\) and bromide \( ext{Br}^-\) ions are neither acidic nor basic.- \( ext{NH}_4 ext{Cl}\) is acidic due to the ammonium ion \( ext{NH}_4^+\).- \( ext{KCN}\) is basic because the cyanide ion \( ext{CN}^-\) reacts with water to produce OH鈦�.- \( ext{K}_2 ext{CO}_3\) is basic as the carbonate ion \( ext{CO}_3^{2-}\) also reacts with water to form OH鈦�.
02

Identify the Solution's pH Level

Since the 0.100 M solution is neutral, the pH level is 7. This means the solution neither has an excess of hydrogen ions (acidic) nor hydroxide ions (basic).
03

Determine the Neutral Salt

Based on the properties, \( ext{KBr}\) is the only salt that results in a neutral solution. The other options, \( ext{NH}_4 ext{Cl}\), \( ext{KCN}\), and \( ext{K}_2 ext{CO}_3\), either form acidic or basic solutions.

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Key Concepts

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

Understanding pH Levels
The pH level is a numerical scale used to specify the acidity or basicity of an aqueous solution. It ranges from 0 to 14, with 7 being considered neutral. A pH less than 7 indicates an acidic solution, while a pH greater than 7 indicates a basic solution. This distinct scale helps determine the concentration of hydrogen ions ([H^+]) present in a solution.
The pH is calculated using the formula: \[ \text{pH} = -\log_{10} [\mathrm{H^+}] \] where \([\mathrm{H^+}]\) is the concentration of hydrogen ions in moles per liter. In a neutral solution, \([\mathrm{H^+}]\) equals \([\mathrm{OH^-}]\), which results in a pH of 7.
Key Points:
  • pH indicates the acidic or basic character of a solution.
  • 7 is neutral, below 7 is acidic, and above 7 is basic.
Neutral Solution Explained
A neutral solution is a special kind of aqueous solution where the concentrations of hydrogen ions (\(\mathrm{H^+}\)) and hydroxide ions (\(\mathrm{OH^-}\)) are equal. In neutral solutions, the pH is exactly 7. This means there is no dominance of acidic or basic properties.
For example, pure water at 25掳C is a neutral solution because its hydrogen ion concentration is equal to its hydroxide ion concentration. This balance ensures no excess of acidic or basic properties.
When dealing with salts, if the pH of their aqueous solution is 7, the salt is often termed as forming a neutral solution. This aids in identifying specific salts, as demonstrated in the exercise where among , , , and , only led to a neutral pH.
Neutral Solution Characteristics:
  • pH level is 7.
  • Equal concentration of \(\mathrm{H^+}\) and \(\mathrm{OH^-}\).
  • No excess of either acidic or basic ions.
Exploring Chemical Properties
Chemical properties define how a substance reacts with other chemicals, involving changes in chemical composition. When a salt is dissolved in water, its chemical properties influence whether the solution becomes acidic, basic, or remains neutral.
Each salt comprises a cation (positively charged ion) and an anion (negatively charged ion) whose interaction in water largely determines the pH of the solution.Examining Chemical Properties of Salts:
  • KBr: Both \(\mathrm{K^+}\) and \(\mathrm{Br^-}\) ions do not react with water, resulting in a neutral solution.
  • NH4Cl: Releases \(\mathrm{NH_4^+}\) ions, which make the solution acidic.
  • KCN: The presence of \(\mathrm{CN^-}\) ions tends to make the solution basic due to their interaction with water producing \(\mathrm{OH^-}\) ions.
  • K2CO3: Releases \(\mathrm{CO_3^{2-}}\) ions, which also form a basic solution through similar interactions.

Understanding these properties of salts allows one to predict the nature of their aqueous solutions, which is crucial when identifying unknown substances based on their chemical behavior.

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Most popular questions from this chapter

Label each of the following as being a strong base, a weak base, or a species with negligible basicity. In each case write the formula of its conjugate acid, and indicate whether the conjugate acid is a strong acid, a weak acid, or a species with negligible acidity: \((\mathbf{a}) \mathrm{F}^{-}(\mathbf{b}) \mathrm{Br}^{-}(\mathbf{c}) \mathrm{HS}^{-}(\mathbf{d}) \mathrm{ClO}_{4}^{-}(\mathbf{e}) \mathrm{HCOO}^{-}\)

Butyric acid is responsible for the foul smell of rancid butter. The \(\mathrm{p} K_{b}\) of the butyrate ion is 9.16. (a) Calculate the \(K_{a}\) for butyric acid. (b) Calculate the pH of a \(0.075 \mathrm{M}\) solution of butyric acid. (c) Calculate the pH of a \(0.075 \mathrm{M}\) solution of sodium butyrate.

Benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)\) and aniline \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\right)\) are both derivatives of benzene. Benzoic acid is an acid with \(K_{a}=6.3 \times 10^{-5}\) and aniline is a base with \(K_{a}=4.3 \times 10^{-10}\) (a) What are the conjugate base of benzoic acid and the conjugate acid of aniline? (b) Anilinium chloride \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3} \mathrm{Cl}\right)\) is a strong electrolyte that dissociates into anilinium ions \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}\right)\) and chloride ions. Which will be more acidic, a \(0.10 \mathrm{M}\) solution of benzoic acid or a 0.10 \(M\) solution of anilinium chloride? (c) What is the value of the equilibrium constant for the following equilibrium?

Arrange the following \(0.10 \mathrm{M}\) solutions in order of increasing acidity: (i) \(\mathrm{HCOONH}_{4},\) (ii) \(\mathrm{NH}_{4} \mathrm{Br}\), (iii) \(\mathrm{NaNO}_{3}\), (iv) \(\mathrm{HCOOK},(\mathrm{v}) \mathrm{KF}\).

Calculate \(\left[\mathrm{OH}^{-}\right]\) for each of the following solutions, and indicate whether the solution is acidic, basic, or neutral: (a) \(\left[\mathrm{H}^{+}\right]=0.00010 \mathrm{M} ;(\mathbf{b})\left[\mathrm{H}^{+}\right]=7.3 \times 10^{-14} \mathrm{M} ;(\mathbf{c})\) a solu- tion in which \(\left[\mathrm{OH}^{-}\right]\) is 100 times greater than \(\left[\mathrm{H}^{+}\right]\).
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