Consider the titration of a 25.0-mL sample of 0.175 M CH 3 NH 2 with 0.150 M HBr. Determine each quantity. e. the pH at the equivalence point

Hi everyone here we have a question asking us to calculate the ph at the equivalence point for this hydration of a 50.0 millimeter sample of 0.125 moller ammonia was 0.1 to zero molar hydrochloric acid. So the malls of our base is going to equal the molds of our acid is going to equal, the moles of ammonium Is going to equal 0. moles per leader Equals 6.2. 5 Times 10 to the -3 moles. Our mold of ammonium equals our moles of hydrochloric acid Equals 6.25 Times 10 to the -3 moles. Our volume of hydrochloric acid equals 6.25 Times to the -3 moles Divided by 0.120 moles per liter Equals 0.05. To readers. And now we need to calculate our polarity. So our concentration of ammonium Equals 6.25 Times to the -3 moles Divided by zero 052 l Plus 0.05 l Equals 0.0613 Malaria. And now we need to set up an ice chart. So we have ammonium plus water goes back and forth from ammonia plus H 30. And we have our initial our change and our end. So for ammonium our initial is 0.0613 more. Our water doesn't matter because it's a liquid, not a crease. Our ammonia starts out at zero and our H 30 starts out at zero. Our change is -1 and plus X. And plus X. And our end is 0. minus X. For ammonia. It is X. And H 30. It is X. R. K B Equals 1.8 Times 10 to the negative 5th R. K. A equals the concentration of ammonia times H. divided by ammonium, R. K. W. Divided by K. B. Equals ammonia Times H. 30. Divided by ammonium 1.0 Times 10 to the -14 Divided by 1. Times 10 to the negative 5th equals X squared divided by 0. -1. 5.56 times to the negative 10 equals X squared Divided by 0. minus X. And now we have to check if X is ineligible in the denominator. So 0. divided by 5.56 times to the negative 10 Equals 1. times 10 to the 8th which is greater than 500. So it is negligible. Now we have 5. times 10 to the negative 10 equals X squared Divided by 0.0613. So X equals the square root of five . times 10 to the negative 10th Times 0. And that equals five 0. Times 10 to the -6 Malaria T. So X equals H Equals 5.84 Times 10 to the -6 Polarity. So the ph equals the negative log of H equals the negative log of 5.84 Times 10 to the -6. More clarity Equals 5.234. And that is our final answer. Thank you for watching. Bye.

Ch.18 - Aqueous Ionic Equilibrium

All textbooks

Tro 6th Edition

Ch.18 - Aqueous Ionic Equilibrium

Problem 79e

Chapter 18, Problem 79e

Consider the titration of a 25.0-mL sample of 0.175 M CH₃NH₂ with 0.150 M HBr. Determine each quantity. e. the pH at the equivalence point

Verified step by step guidance

Identify the reaction: CH_3NH_2 (aq) + HBr (aq) \rightarrow CH_3NH_3^+ (aq) + Br^- (aq).

Determine the moles of CH_3NH_2 initially present using the formula: \text{moles} = \text{concentration} \times \text{volume}.

Calculate the volume of HBr needed to reach the equivalence point using the stoichiometry of the reaction and the concentrations given.

At the equivalence point, all CH_3NH_2 is converted to CH_3NH_3^+. Determine the concentration of CH_3NH_3^+ in the solution.

Use the K_b of CH_3NH_2 to find the K_a of CH_3NH_3^+ and calculate the pH using the formula: \text{pH} = -\log[H^+].

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

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

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant (a solution of known concentration) to a sample until the reaction reaches its equivalence point, where the amount of titrant equals the amount of substance in the sample. Understanding the stoichiometry of the reaction is crucial for calculating concentrations and pH at various points during the titration.

Equivalence Point

The equivalence point in a titration is the stage at which the amount of titrant added is stoichiometrically equivalent to the amount of substance present in the sample. At this point, the reaction between the acid and base is complete, and the pH of the solution can change dramatically. For a weak base like methylamine (CH3NH2) being titrated with a strong acid like HBr, the pH at the equivalence point will be determined by the properties of the resulting salt and the hydrolysis of its ions.

pH Calculation

The pH of a solution is a measure of its acidity or basicity, calculated as the negative logarithm of the hydrogen ion concentration. At the equivalence point of a titration involving a weak base and a strong acid, the resulting solution will contain the conjugate acid of the weak base, which can affect the pH. To find the pH at this point, one must consider the concentration of the conjugate acid and its dissociation in water, often requiring the use of the acid dissociation constant (Ka) for accurate calculations.