To find the concentration of potassium ions ([K+]) in the solution, we need to calculate the number of moles of potassium hydroxide (KOH) dissolved in 250.0 ml of solution.
Step 1: Calculate the moles of KOH
Given the mass of potassium hydroxide (KOH) is 0.140 g and the molar mass of KOH is 56.11 g/mol (from the periodic table), we can calculate the moles of KOH using the formula:
moles = mass / molar mass
moles = 0.140 g / 56.11 g/mol
Step 2: Calculate the concentration ([K+])
The concentration is given in moles per liter (mol/L). Since we are given the volume as 250.0 ml, we need to convert it to liters by dividing by 1000:
volume = 250.0 ml / 1000
volume = 0.250 L
Then, we can calculate the concentration ([K+]) using the formula:
concentration = moles / volume
Now we can substitute the values we found into the formula:
concentration = (0.140 g / 56.11 g/mol) / 0.250 L
Finally, calculate the value to find the [K+] concentration.
For the second question, to find the pH of the solution, we need to determine the pKa value for aniline using the given Kb value. The pKa is related to Kb by the formula:
pKa + pKb = 14
Rearranging the formula, we find:
pKa = 14 - pKb
From the given value, Kb = 7.4 × 10-10, we can calculate pKa:
pKa = 14 - log(Kb) = 14 - log(7.4 × 10-10)
Once we have the value of pKa, we can calculate the concentration of the anilinium ion, [C6H5NH3+], using the Henderson-Hasselbalch equation:
pH = pKa + log([C6H5NH3+]/[C6H5NH2])
Since we have the concentration of aniline as 0.570 M, we can calculate the pH using the formula:
pH = pKa + log([C6H5NH3+]/0.570)