Question

A chemistry graduate student is given 125. mL of a 0.30 M methylamine (CH3NH2) solution. Methylamine is a weak base with K= 4.4 x 10 . What mass of CH3NH2Cl should the student dissolve in the CH3NH, solution to turn it into a buffer with pH = 10.30? You may assume that the volume of the solution doesn't change when the CH NH2Cl is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits. x s ?

Answer 1

Soln. Given- Achemistry graduate student is given 125 ml of a 0.30M methylamine (CMNM) solution. Methylamine a weak base with kn 4.4x10" what CH₃NH₂Cl should be student dissolve in the CH₃NH2 solution to turn it into a buffer with pH=10.30? - Volume of solution does not changes when the CH₂ NHU is dissolwed in it. formula used- H = asi) pH = pka + log [Aud] pka + log [Base? pka xp ks = 10th moles of solute Molar arity Vilume of solestiae (L) - cilin Moler- Giver mass Moler- Given mass molar mass using i 4 dll) we get of many volume duhet Molarity Criver man -iv) Now, Ion buffer solution CH₃NH₂ - Base CH₃NH₂Cl - Acid 1. pka = -logka kaxky = 10-14 I 10th pha= -log (14 pka = 10.644 ka = 1 4.48104

PH= PH: pka + log [CH₃NH₂7 " ( [CH, NH, 1/3 10.30 = 10.644 + log [CH, NHECI] = 0.6624 M molar mass of CH₂ NH₃U = 67.518 g/mol Voleine of solution = 125ml 11: 1sooml - 125ml = 125 L 1000 = 0,1252 mass of CH3NH, 016624 x 67.518 x 0.125 g (using (iv)) = 5.599 25.69 Hence, ' mass of CH3NH2U added is 5.69.