Textbook Question
Find the pH of each mixture of acids. a. 0.115 M in HBr and 0.125 M in HCHO2
Ch.16 - Acids and Bases
Chapter 16, Problem 79b,c,d
Find the pH of each mixture of acids. b. 0.150 M in HNO2 and 0.085 M in HNO3 c. 0.185 M in HCHO2 and 0.225 M in HC2H3O2 d. 0.050 M in acetic acid and 0.050 M in hydrocyanic acid
Verified step by step guidance1
Step 1: Identify the acids in each mixture and determine their strengths. HNO_3 is a strong acid, while HNO_2, HCHO_2, HC_2H_3O_2, and hydrocyanic acid (HCN) are weak acids.
Step 2: For each mixture, calculate the contribution of the strong acid to the pH. Since strong acids dissociate completely, the concentration of H^+ ions from the strong acid is equal to its initial concentration.
Step 3: For the weak acids, use the acid dissociation constant (K_a) to calculate the concentration of H^+ ions. Set up an equilibrium expression for each weak acid: K_a = [H^+][A^-]/[HA].
Step 4: For each mixture, add the concentration of H^+ ions from the strong acid to the concentration of H^+ ions from the weak acids to find the total [H^+].
Step 5: Calculate the pH of each mixture using the formula pH = -log[H^+].
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Theory
Acid-base theory explains the behavior of acids and bases in solution. According to the Brønsted-Lowry theory, acids are proton donors while bases are proton acceptors. This concept is crucial for understanding how different acids interact in a mixture and how they affect the overall pH of the solution.
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Bronsted-Lowry Acid-Base Theory
pH Scale
The pH scale quantifies the acidity or basicity of a solution, ranging from 0 to 14. A pH less than 7 indicates an acidic solution, while a pH greater than 7 indicates a basic solution. The pH is calculated using the negative logarithm of the hydrogen ion concentration, making it essential for determining the acidity of the mixtures in the question.
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Weak vs. Strong Acids
Understanding the difference between weak and strong acids is vital for calculating pH. Strong acids, like HNO3, completely dissociate in solution, while weak acids, such as acetic acid, only partially dissociate. This distinction affects the concentration of hydrogen ions in the solution and, consequently, the pH of the mixtures.
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