Chapter 25
Chemical Principles in the Laboratory · 3 exercises
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.)
4 step solution
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 \(\mathrm{pK}_{\mathrm{a}} ?\)
4 step solution
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.)
5 step solution