Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (a) Write out the reaction that leads to this acidic pH.

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Write the dissociation reaction of pyridinium bromide in water: C_5H_5NHBr \rightarrow C_5H_5NH^+ + Br^-

Recognize that C_5H_5NH^+ is the conjugate acid of pyridine (C_5H_5N) and can donate a proton to water, leading to the acidic pH.

Write the reaction of C_5H_5NH^+ with water: C_5H_5NH^+ + H_2O \rightarrow C_5H_5N + H_3O^+

Identify that the formation of H_3O^+ (hydronium ions) is responsible for the acidic pH of the solution.

Understand that the pH of 2.95 indicates a relatively high concentration of H_3O^+ ions in the solution, confirming the acidic nature.

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Key Concepts

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

Electrolytes and Dissociation

Electrolytes are substances that dissociate into ions when dissolved in water, allowing the solution to conduct electricity. Strong electrolytes, like pyridinium bromide, completely dissociate into their constituent ions. In this case, pyridinium bromide dissociates into pyridinium ions (C5H5NH+) and bromide ions (Br-), which is crucial for understanding the resulting pH of the solution.

Acid-Base Chemistry

Acid-base chemistry involves the study of substances that can donate protons (H+) or accept protons. The pyridinium ion (C5H5NH+) acts as a weak acid in solution, donating protons to water and leading to an increase in hydrogen ion concentration. This process is essential for determining the acidic nature of the solution and calculating its pH.

pH Scale

The pH scale measures the acidity or basicity of a solution, with values ranging from 0 (very acidic) to 14 (very basic). A pH of 7 is considered neutral. In this case, a pH of 2.95 indicates a highly acidic solution, which can be attributed to the presence of free hydrogen ions from the dissociation of the pyridinium ion, reflecting the strength of the acid in the solution.

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The pH Scale

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Textbook Question

Using data from Appendix D, calculate 3OH-4 and pH for each of the following solutions: (b) 0.035 M Na2S

Textbook Question

Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (b) Using Appendix D, calculate the Ka for pyridinium bromide.

Textbook Question

Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (c) A solution of pyridinium bromide has a pH of 2.95. What is the concentration of the pyridinium cation at equilibrium, in units of molarity?