Determine the pH of each solution. a. 0.10 M NH₄Cl

검증된 단계별 안내

Step 1: Identify that NH4Cl is a salt and will dissociate completely in water to form NH4+ and Cl-. The NH4+ ion is the conjugate acid of the weak base NH3, and will therefore react with water to form NH3 and H3O+.

Step 2: Write the chemical equation for the reaction of NH4+ with water: NH4+ + H2O -> NH3 + H3O+.

Step 3: Set up an ICE (Initial, Change, Equilibrium) table to keep track of the concentrations of each species. Initially, the concentration of NH4+ is 0.10 M, and the concentrations of NH3 and H3O+ are 0. At equilibrium, the concentration of NH4+ will have decreased by x, and the concentrations of NH3 and H3O+ will have increased by x.

Step 4: Write the expression for the equilibrium constant of the reaction, Ka, which is equal to [NH3][H3O+] / [NH4+]. Since NH4+ is the conjugate acid of NH3, Ka can be found by taking the inverse of the Kb for NH3 and using the relationship Kw = Ka * Kb.

Step 5: Substitute the equilibrium concentrations from the ICE table into the Ka expression and solve for x, which represents the concentration of H3O+ at equilibrium. The pH of the solution can then be found by taking the negative logarithm of the H3O+ concentration.

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주요 개념

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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 basicity. The scale is logarithmic, meaning each whole number change represents a tenfold change in hydrogen ion concentration.

Ammonium Chloride (NH4Cl) as a Weak Acid

Ammonium chloride is a salt formed from the weak base ammonia (NH3) and the strong acid hydrochloric acid (HCl). In solution, NH4Cl dissociates into NH4+ and Cl-. The NH4+ ion can donate a proton to water, forming NH3 and H3O+, which contributes to the acidity of the solution, thus lowering the pH.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a solution to the concentration of an acid and its conjugate base. For weak acids, it is expressed as pH = pKa + log([A-]/[HA]). This equation is useful for calculating the pH of buffer solutions and can be adapted to find the pH of solutions containing weak acids or their salts, like NH4Cl.

Determine the pH of each solution. a. 0.10 M NH4Cl