Chapter 25

A solution of a weak acid was tested with the indicators used in this experiment. The colors observed were as follows: Methyl violet\(\quad \) violet, Thymol blue \(\quad \) yellow, Methyl yellow\(\quad \) yellow, Congo red \(\quad\) orange-red, Bromcresol green \(\quad\) green What is the approximate \(\mathrm{pH}\) of the solution?_____

A solution of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) has a \(\mathrm{pH}\) of \(10 .\) The \(\mathrm{CO}_{3}^{2-}\) ion is the conjugate base of the \(\mathrm{HCO}_{3}^{-}\) ion. Write the net ionic equation for the reaction which makes a solution of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) basic. (Eq. \(7 .\) )

The pH of a 0.10 M HCN solution is 5.2. a. What is \(\left[\mathrm{H}^{+}\right]\) in that solution?______\(M\) b. What is \(\left[\mathrm{CN}^{-}\right] ?\) What is [HCN]? (Where do the \(\mathrm{H}^{+}\) and \(\mathrm{CN}^{-}\) ions come from?)_____\(M;\)_____\(M\) c. What is the value of \(K_{\mathrm{a}}\) for HCN? What is the value of \(\mathrm{pK}_{\mathrm{a}}\) ?_____ _____