Chemical Principles in the Laboratory

Emil J. Slowinski, Wayne C. Wolsey, Robert C. Rossi

Chapter 25 pH Measurements - Buffers and Their Properties - all with Video Answers

Educators

Chapter Questions

00:19

Problem 1

A solution of a weak acid was tested with the indicators used in this experiment. The colors observed were as follows:
$\begin{array}{llll}\text { Methyl violet } & \text { violet } & \text { Congo red } & \text { violet } \\ \text { Thymol blue } & \text { orange } & \text { Bromcresol green } & \text { yellow } \\ \text { Methyl yellow } & \text { red } & & \end{array}$
What is the approximate $\mathrm{pH}$ of the solution?

Aadit Sharma

Numerade Educator

01:33

Problem 2

An aqueous solution of $\mathrm{NH}_{3}$ has a pH of $11.6 .$ The ammonia (NH, $_{3}$ ) molecule is the conjugate base of the NH_t (called "ammonium") ion. Write the net ionic equation for the reaction that makes an aqueous solution of $\mathrm{NH}_{3}$ basic. (Eq. 5.)

Sima Sarker

Numerade Educator

08:38

Problem 3

The pH of a 0.10 M HOBr solution is 4.8.
a. What is $\left[\mathrm{H}^{+}\right]$ in that solution?
b. What is $\left[\mathrm{OBr}^{-}\right] ?$ What is [HOBr]? (Where do the $\mathrm{H}^{+}$ and $\mathrm{OBr}^{-}$ ions come from?)
c. What is the value of $K_{\mathrm{a}}$ for HOBr? What is the value of $\mathrm{pK}_{\mathrm{a}} ?$

Jennifer Hudspeth

Numerade Educator

02:51

Problem 4

Formic acid, HFor, has a $K_{a}$ value equal to about $1.8 \times 10^{-4} .$ A student is asked to prepare a buffer having
a pH of 3.90 from a solution of formic acid and a solution of sodium formate having the same molarity. How many milliliters of the NaFor solution should she add to $20 .$ mL of the HFor solution to make the buffer? (See discussion of buffers.)

Himanshu Kushwaha

Numerade Educator

04:46

Problem 5

How many mL. of 0.10 M NaOH should the student add to 20 mL 0.10 M HFor if she wished to prepare a buffer with a pH of 3.90, the same as in Problem 4?

David Collins

Numerade Educator