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

Video transcript

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.