What are the major species present in \(0.250 M\) solutions of each of the following acids? Calculate the \(\mathrm{pH}\) of each of these solutions. a. \(\mathrm{HOC}_{6} \mathrm{H}_{5}\) b. HCN

HOC6H5 is an organic acid, which dissociates in water as follows: \[ \ce{HOC6H5 <=> H+ + OC6H5^-} \] The major species present in a 0.250 M solution of HOC6H5 are HOC6H5, H+ ions, and OC6H5- ions.

Since HOC6H5 is a weak acid, we need to write the ionization constant expression (Ka) for the acid and use it to calculate the pH. The Ka expression for HOC6H5 dissociation is as follows: \[ \ce{Ka = [H+] [OC6H5^-]/ [HOC6H5]} \] However, to calculate the pH, we need to find the concentration of H+ ions in the solution. To do this, we will assume that the initial concentration of dissociated ions is negligible and write the equilibrium concentrations as follows: - [H+] is x - [OC6H5-] is x - [HOC6H5] is (0.250 - x) Now we can substitute these concentrations into the Ka expression: \[ Ka = x^2 / (0.250 - x) \] We need the Ka value of HOC6H5 to solve this equation, which should be provided or found in a table of acid ionization constants. With the Ka value, we can solve for x, which represents [H+], using approximation or iterative methods. Once x is found, we can calculate the pH using the formula: \[ pH = -\log_{10} [H+] \]

HCN is a weak acid that dissociates in water as follows: \[ \ce{HCN <=> H+ + CN^-} \] The major species present in a 0.250 M solution of HCN are HCN, H+ ions, and CN- ions.

Similar to HOC6H5, we need to write the ionization constant expression (Ka) for HCN. The Ka expression is as follows: \[ \ce{Ka = [H+] [CN^-]/ [HCN]} \] Again, we will assume that the initial concentration of dissociated ions is negligible and write the equilibrium concentrations as follows: - [H+] is x - [CN-] is x - [HCN] is (0.250 - x) Now we can substitute these concentrations into the Ka expression: \[ Ka = x^2 / (0.250 - x) \] We need the Ka value of HCN, which should be provided or found in a table of acid ionization constants. With the Ka value, we can solve for x (the concentration of H+ ions) using approximation or iterative methods. Once x is found, we can calculate the pH using the formula: \[ pH = -\log_{10} [H+] \] By following these steps, the pH of each acid solution can be found.