What is the pH of the mixture before the addition of any base?

Verified step by step guidance

Identify the components of the mixture. Determine if the mixture is an acid, a base, or a buffer solution. This will guide the approach to calculating the pH.

If the mixture is a strong acid or base, use the concentration of the acid or base to calculate the pH directly. For a strong acid, pH = -log[H⁺], and for a strong base, pOH = -log[OH⁻] and then pH = 14 - pOH.

If the mixture is a weak acid or base, use the equilibrium expression to find the concentration of hydrogen ions [H⁺] or hydroxide ions [OH⁻]. For a weak acid, use the expression: \( K_a = \frac{[H^+][A^-]}{[HA]} \) to solve for [H⁺].

If the mixture is a buffer solution, use the Henderson-Hasselbalch equation: \( pH = pK_a + \log\left(\frac{[A^-]}{[HA]}\right) \), where [A⁻] is the concentration of the conjugate base and [HA] is the concentration of the acid.

Calculate the pH using the appropriate method based on the type of mixture identified in the previous steps. Ensure all concentrations are in molarity (mol/L) and use the correct values for any constants like \( K_a \) or \( K_b \).

Key Concepts

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

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is considered neutral, while values below 7 indicate acidity and values above 7 indicate alkalinity. Understanding the pH scale is essential for determining the nature of a solution and its behavior in chemical reactions.

Acid-Base Chemistry

Acid-base chemistry involves the study of substances that can donate protons (acids) or accept protons (bases). The strength of an acid or base is often quantified by its dissociation constant (Ka or Kb), which influences the pH of a solution. Recognizing the properties of acids and bases is crucial for predicting the pH of a mixture.

Buffer Solutions

Buffer solutions are mixtures that resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. Understanding how buffers work is important for predicting the pH of a mixture before any base is added, especially in biological and chemical systems.

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Buffer Solutions

Related Practice

Textbook Question

Ethylenediamine (NH2CH2CH2NH2, abbreviated en) is an organic base that can accept two protons: (a) Consider the titration of 30.0 mL of 0.100 M ethylenediamine with 0.100 M HCl. Calculate the pH after the addition of the following volumes of acid, and construct a qualitative plot of pH versus milliliters of HCl added: (i) 0.0 mL (ii) 15.0 mL (iii) 30.0 mL (iv) 45.0 mL (v) 60.0 mL (vi) 75.0 mL

Textbook Question

A 40.0 mL sample of a mixture of HCl and H₃PO₄ was titrated with 0.100 M NaOH. The first equivalence point was reached after 88.0 mL of base, and the second equivalence point was reached after 126.4 mL of base. (a) What is the concentration of H₃O⁺ at the first equivalence point?

Textbook Question

A 40.0 mL sample of a mixture of HCl and H₃PO₄ was titrated with 0.100 M NaOH. The first equivalence point was reached after 88.0 mL of base, and the second equivalence point was reached after 126.4 mL of base. (b) What are the initial concentrations of HCl and H₃PO₄ in the mixture?

Textbook Question

A 40.0 mL sample of a mixture of HCl and H₃PO₄ was titrated with 0.100 M NaOH. The first equivalence point was reached after 88.0 mL of base, and the second equivalence point was reached after 126.4 mL of base. (c) What percent of the HCl is neutralized at the first equivalence point?