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Chapter 5: Problem 40

When solid potassium cyanide is added in water, then its a. \(\mathrm{pH}\) will decrease b. \(\mathrm{pH}\) will increase c. electrical conductivity will not change d. \(\mathrm{pH}\) will remain the same

Short Answer

Expert verified
The pH will increase (option b).

Step by step solution

01

Identify the Chemical Compound

Potassium cyanide (KCN) is an ionic compound composed of potassium ions (K鈦�) and cyanide ions (CN鈦�). When dissolved in water, it dissociates into these ions.
02

Analyze Ion Behavior in Water

The potassium ion (K鈦�) is a spectator ion and does not affect the pH of the solution. The cyanide ion (CN鈦�) is a weak base and will react with water to produce small amounts of hydroxide ions (OH鈦�), increasing the pH.
03

Determine the Effect on pH

Since CN鈦� acts as a weak base in aqueous solutions, it will increase the concentration of OH鈦� in the solution, leading to an increase in the pH value.
04

Consider Electrical Conductivity

When KCN dissociates into K鈦� and CN鈦� ions in water, they contribute to the electrical conductivity of the solution. Therefore, the conductivity will increase compared to pure water.
05

Conclusion and Answer Selection

Given that KCN will increase the pH when dissolved in water, the correct option is (b) pH will increase.

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Key Concepts

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

pH change
The pH value is a measure of how acidic or basic a solution is. It ranges from 0 to 14, with 7 being neutral. A pH less than 7 indicates an acidic solution, while a pH higher than 7 indicates a basic (alkaline) one.
When solid potassium cyanide (KCN) is added to water, it dissociates into potassium ions (K鈦�) and cyanide ions (CN鈦�). The cyanide ions, being a weak base, react with water to form small amounts of hydroxide ions (OH鈦�), a process that increases the pH of the solution. This makes the solution more basic.
  • A basic solution has a higher concentration of OH鈦� ions than H鈦� ions.
  • The increase in OH鈦� ions causes an increase in pH.
  • KCN causes such a change in pH because of the behavior of the cyanide ion as a weak base.
Therefore, adding KCN to water results in a pH increase, making the solution more alkaline.
ionic compounds
Ionic compounds are substances composed of positive and negative ions held together by strong electrostatic forces, known as ionic bonds. They are usually formed between metals and non-metals.
  • KCN is an example of an ionic compound, where potassium forms a positive ion (K鈦�), and cyanide forms a negative ion (CN鈦�).
  • When ionic compounds dissolve in water, they dissociate into their constituent ions.

For KCN, this dissociation means separating into K鈦� and CN鈦� ions. The separation of these ions is crucial for various chemical and physical properties, such as conducting electricity and altering pH levels. The free movement of charged ions in solution is what leads to changes in electrical conductivity as well as potential pH modifications, depending on the nature and interaction of the ions released.
weak base
Weak bases are substances that partially accept protons from water molecules. In other words, they do not completely ionize in solution.
  • A prime example is the cyanide ion (CN鈦�), which comes from the dissociation of KCN in water.
  • CN鈦� reacts with water slowly, forming small amounts of OH鈦� ions, which reduces the number of free positive hydrogen ions (H鈦�).
  • The reaction, however, does not go to completion. This partial reaction makes CN鈦� a weak base.

Weak bases thus increase the pH of their solutions, causing them to become more basic but not drastically so. The understanding of weak bases is essential for predicting chemical behaviors in solutions, especially how they influence the pH.
electrical conductivity
Electrical conductivity is the ability of a solution to conduct electricity, which relies on the presence of free ions that can move through the solution.
When solids like KCN dissolve in water dissociating into ions, they contribute to the electrical conductivity due to these free ions.
  • Conductivity increases as more ions are present in the solution, allowing for more charge carriers to flow.
  • K鈦� and CN鈦� ions from KCN both contribute to the increased electrical conductivity.
  • Pure water, on its own, has low conductivity because it has few ions available.
Hence, when KCN is added to water, the electrical conductivity of the solution increases significantly, thanks to the dissociated ions within the solution.

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Most popular questions from this chapter

The following two isomers of \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{NO}\) exist in equilibrium with each other in solution: If \(\mathrm{K}_{\mathrm{C}}=0.57\) at \(25^{\circ} \mathrm{C}\) and the initial concentration of the reactant is \(0.50 \mathrm{M}\) and the product is \(0.70 \mathrm{M}\), what are the concentrations at equilibrium? a. \([\) Reactant \(]=0.46 \mathrm{M}\) and \([\) Product \(]=0.28 \mathrm{M}\) b. [Reactant] \(=0.69 \mathrm{M}\) and \([\) Product \(]=0.48 \mathrm{M}\) c. \([\) Reactant \(]=0.96 \mathrm{M}\) and \([\) Product \(]=0.47 \mathrm{M}\) d. [Reactant \(]=0.76 \mathrm{M}\) and [Product \(]=0.44 \mathrm{M}\)

The equilibrium constant for gaseous reaction: \(\mathrm{A}+\mathrm{B} \rightleftharpoons \mathrm{C}+\mathrm{D}\) is 100 at \(25^{\circ} \mathrm{C}\). Consider the following statements in this regard. If the initial concentration of all the four species were \(1.0 \mathrm{M}\) each, then the equilibrium concentration of I. A would be \(0.182 \mathrm{~mol} / \mathrm{L}\) II. C would be \(0.818 \mathrm{~mol} / \mathrm{L}\) III. D would be \(1.818 \mathrm{~mol} / \mathrm{L}\) Of these statements: a. I and III are correct b. I and II are correct c. II and III are correct d. I, II and III are correct

The solubility product of AgI in water is \(4.9 \times 10^{-11}\) at a given temperature. The solubility of \(\mathrm{AgI}\) in \(0.001 \mathrm{M}\) KI solution is a. \(7.0 \times 10^{-7}\) b. \(4.8 \times 10^{-3}\) c. \(7.0 \times 10^{-8}\) d. \(5.9 \times 10^{-10}\)

(A): The \(\mathrm{pH}\) range of any indicator is form \(\mathrm{pK}_{\mathrm{ln}}-1\) to \(\mathrm{pK}_{\mathrm{ln}}+1\) (R): As the \(\mathrm{pH}\) of the indicator can be given as follows \(\mathrm{pH}=\mathrm{pK}_{\ln }+\log \frac{\left(\ln ^{-}\right)}{(\mathrm{Hln})}\) As \(\mathrm{pH}\) range depends upon the ratio of \(\left[\mathrm{ln}^{-}\right]\) to \([\mathrm{Hln}]\) which can not have value 10 to \(1 / 10\) for all indicators.

Match the following: Column I Column II A. Law of mass action (p) Guldberg wage B. Active mass of \(\mathrm{CaCO}_{3}\) (q) \(\mathrm{Kp}=\mathrm{Kc}(\mathrm{RT})\) (s) C. \(2 \mathrm{SO}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{SO}_{3}\) (r) 1 D. \(\mathrm{PCl}_{5} \leftrightarrow \mathrm{PCl}_{3}+\mathrm{Cl}_{2}\) (s) zero (t) \(\mathrm{Kp}=\mathrm{Kc}(\mathrm{RT})^{-1}\)
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