Question

What mass of NH C1 A chemistry graduate student is given 250. mL of a 0.40 M ammonia (NH) solution. Ammonia is a weak base with K = 1.8 x 10 should the student dissolve in the NH, solution to turn it into a buffer with pH = 8.66? You may assume that the volume of the solution doesn't change when the NH C1 is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits. x s ?

Answer 1

L Number of moles of NH, = 250.0mL – *0.40 mol 1000 m =0.1000 mol pH of a buffer = 8.66 pH+pOH=14.00 pOH=14.00- pH =14.00 -8.66 =5.34 K, of NH, = 1.8x10$ PK, =- log K =-log(1.8x10) =5.00 – log1.8 =5.00 -0.26 = 4.74 According to Henderson equation salt º [base] *NH.] pOH =pK, +log . [NH, pOH =pK, + [NH] 5.34 =4.74+log [NH] ΝΗ, log =5.34 -4.74 *[NH,] = 0.600 [NH 7. (NH3] = 100.600 = 3.98 [NH7=3.98x0.1000 mol =0.398 mol Mass of NH C1=0.398mol x Pa mol = 21.3g = 21g gammonium chloride need to be added. Hence, 2.1