Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 16: Problem 17

Calculate the \(\mathrm{pH}\) of the \(0.20 \mathrm{M} \mathrm{NH}_{3} / 0.20 \mathrm{M} \mathrm{NH}_{4} \mathrm{Cl}\) buffer. What is the pH of the buffer after the addition of \(10.0 \mathrm{~mL}\) of \(0.10 \mathrm{M} \mathrm{HCl}\) to \(65.0 \mathrm{~mL}\) of the buffer?

Short Answer

Expert verified
The initial pH of the buffer is 9.25. After addition of 10.0 mL of 0.10 M HCl, the pH of the buffer is 9.22.

Step by step solution

01

Calculate the initial pH of the buffer using the Henderson-Hasselbalch equation

The Henderson-Hasselbalch equation is given by \(pH = pKa + \log{\left(\frac{[NH3]}{[NH4+]}\right)}\). pKa is the negative log of the Ka of the NH4+. Given that the Ka of NH4+ is \(5.56 \times 10^{-10}\), the pKa is -log(Ka) = 9.25. The molarities of NH3 and NH4Cl in the buffer are both 0.20 M. Substituting these values into the equation gives \(pH = 9.25 + \log{\left(\frac{0.20}{0.20}\right)} = 9.25\)
02

Determine the molar concentrations after addition of HCl

When the strong acid HCl is added to the buffer, it reacts with the weak base NH3 to form more NH4+. The reaction can be written as NH3 + HCl -> NH4Cl. The number of moles of NH3 and HCl are needed to know how much NH4+ is produced. This is calculated by multiplying the volume (in liters) by the molarity. The initial number of moles of NH3 is 0.20 M * 0.065 L = 0.013 mol. The number of moles HCl added is 0.10 M * 0.01 L = 0.001 mol. So, 0.001 mol of NH3 reacts with the HCl, leaving 0.012 mol of NH3, and forming an additional 0.001 mol of NH4+.
03

Recalculate the pH after the addition of HCl

The new total volume of the solution after addition of HCl is 0.065 L + 0.01 L = 0.075 L. This means the new molarities of NH3 and NH4+ are 0.012 mol / 0.075 L = 0.16 M for NH3 and (0.20 M * 0.065 L + 0.001 mol) / 0.075 L = 0.176 M for NH4+. The new pH can be calculated using the Henderson-Hasselbalch equation again: \(pH = 9.25 + \log{\left(\frac{0.16}{0.176}\right)} = 9.22\). The pH of the buffer has slightly decreased due to the addition of the strong acid HCl.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

A student mixes \(50.0 \mathrm{~mL}\) of \(1.00 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\) with \(86.4 \mathrm{~mL}\) of \(0.494 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4} .\) Calculate the mass of \(\mathrm{BaSO}_{4}\) formed and the \(\mathrm{pH}\) of the mixed solution.

The molar solubility of \(\mathrm{Pb}\left(\mathrm{IO}_{3}\right)_{2}\) in a \(0.10 \mathrm{M} \mathrm{NaIO}_{3}\) solution is \(2.4 \times 10^{-11} \mathrm{~mol} / \mathrm{L} .\) What is \(K_{\mathrm{sp}}\) for \(\mathrm{Pb}\left(\mathrm{IO}_{3}\right)_{2} ?\)

Which of the following solutions can act as a buffer: (a) \(\mathrm{KCN} / \mathrm{HCN}\) (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4} / \mathrm{NaHSO}_{4}\) (c) \(\mathrm{NH}_{3} /\) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\), (d) \(\mathrm{Nal} / \mathrm{HI}^{2}\)

In a titration experiment, \(12.5 \mathrm{~mL}\) of \(0.500 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) neutralize \(50.0 \mathrm{~mL}\) of \(\mathrm{NaOH}\). What is the concentration of the \(\mathrm{NaOH}\) solution?

Find the approximate \(\mathrm{pH}\) range suitable for the separation of \(\mathrm{Fe}^{3+}\) and \(\mathrm{Zn}^{2+}\) ions by precipitation of \(\mathrm{Fe}(\mathrm{OH})_{3}\) from a solution that is initially \(0.010 \mathrm{M}\) in both \(\mathrm{Fe}^{3+}\) and \(\mathrm{Zn}^{2+}\). Assume a 99 percent precipitation of \(\mathrm{Fe}(\mathrm{OH})_{3}\)
See all solutions

Recommended explanations on Chemistry Textbooks

Kinetics

Read Explanation

Physical Chemistry

Read Explanation

Nuclear Chemistry

Read Explanation

Chemical Reactions

Read Explanation

Organic Chemistry

Read Explanation

Chemistry Branches

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free