One has a solution Sa of ethanoic acid of concentration Ca=1×10^-2 mol/l and pH=3.4
One mixes a volume Va=60ml of the solution Sa of ethanoic acid with a volume Vb1=20ml of the Sb1 solution of ammonia of concentration Cb1=2×10^-2 mol/l. The pH is 5
One has a soutions of weak bases : Sb1 solution of ammnia
Sb2 of mythelamine .Cb2=1.5×10^-2
Is ammonia a weaker base than methylamine. Justify
To determine if ammonia is a weaker base than methylamine, we need to compare their respective dissociation constants (Kb values). A higher Kb value indicates a stronger base, while a lower Kb value indicates a weaker base.
The Kb value for ammonia (NH3) can be calculated using its concentration (Cb1) and the pH of the resulting solution after mixing it with the ethanoic acid solution. The pH can be converted to the concentration of hydroxide ions (OH-) using the formula: [OH-] = 10^(-pH).
Since the concentration of hydroxide ions is equal to the concentration of ammonium ions (NH4+) in the solution (as they are produced in a 1:1 ratio), we can write an expression for the Kb of ammonia:
Kb(NH3) = [NH4+][OH-] / [NH3]
We have the concentration of ammonia (Cb1), which is 2×10^-2 mol/l, the volume of ammonia solution (Vb1), which is 20 ml, and the volume of the mixed solution (Va + Vb1), which is 60 ml.
Using these values, we can determine the concentration of NH4+ by dividing the moles of ammonia (Cb1 * Vb1) by the total volume of the mixed solution (60 ml).
Now that we have the concentration of NH4+ and the concentration of OH- (calculated from pH), we can calculate the value of Kb(NH3).
Similarly, we can repeat the same calculations for methylamine (CH3NH2) using its concentration (Cb2), the resulting pH (5), and the volume of the mixed solution.
After calculating the Kb values for both ammonia and methylamine, we can compare them. If the Kb value for ammonia is lower than that of methylamine, that means ammonia is a weaker base. Conversely, if the Kb value for ammonia is higher, it is a stronger base.
It is important to note that the pH of a solution alone cannot determine the relative strength of bases. The Kb values take into account concentration and other factors to determine the relative strength of bases.