Methyl amine is a weak base with a pKb=3.35. Consider the titration of 30.0mL of .030M of Methyl amine with 0.025M HCl.
a) Write the appropriate equation for the reaction.
b) Calculate K for the reaction in part (a).
c) Calculate pH of the initial methyl amine solution (0mL added HCl)
d) calculate pH of solution with addition of 10mL HCL
To answer these questions, we need to first analyze the chemical equation, calculate the equilibrium constant (K), and then determine the pH of the solution.
a) The appropriate equation for the reaction can be written as:
CH3NH2 (aq) + HCl (aq) → CH3NH3+ (aq) + Cl- (aq)
b) To calculate K, we need to consider the balanced equation and the concentrations of the products and reactants. In this case, the concentration of CH3NH2 is given as 0.030 M, and the concentration of HCl is 0.025 M. Since both are in the same solution and their stoichiometric coefficients are equal (1:1), we can treat them as initial concentrations. Thus, we can write the expression for K:
K = [CH3NH3+][Cl-] / [CH3NH2][HCl]
c) To calculate the pH of the initial methyl amine solution (before any HCl is added), we need to find the concentration of OH- ions in the solution and then convert it to pH. Since methyl amine is a weak base, we need to calculate the hydroxide ion concentration using the Kb expression:
Kb = [OH-][CH3NH3+] / [CH3NH2]
Given that pKb = 3.35, we can calculate Kb:
Kb = 10^(-pKb) = 10^(-3.35)
Now, let's solve for the hydroxide ion concentration ([OH-]):
[OH-] = sqrt(Kb * [CH3NH2])
Finally, we can convert the hydroxide ion concentration to pH using the equation:
pOH = -log10([OH-])
pH = 14 - pOH
d) After the addition of 10 mL of HCl, we need to consider the amount of HCl reacted with CH3NH2 to calculate the concentration of the remaining reactants and products. In this case, 30 mL of the initial methyl amine solution reacts with 10 mL of HCl. Assuming complete reaction, we can calculate the concentrations of CH3NH3+ and Cl- ions and then convert it to pH using the same process as in part (c).
Note: The above calculations assume that the volumes are additive and that the solution is at standard conditions (25°C, 1 atm pressure).