Question

help?

Buffer. Finding the amount of a conjugated pair to obtained a nxeu pe value b) How many grams of sodium acetate will be added to a 40.00 mL of .4500 M CHCOOH solution to obtain a pH of 3.55? K. = 1.80 x 10-5 ammonium chloride will be added to a 100.00 mL of 2500 M NH Solutions

Answer 1

Ka = 1.8*10^-5

pKa = - log (Ka)

= - log(1.8*10^-5)

= 4.745

use formula for buffer

pH = pKa + log ([CH3CO2Na]/[CH3CO2H])

3.55 = 4.7447 + log ([CH3CO2Na]/[CH3CO2H])

log ([CH3CO2Na]/[CH3CO2H]) = -1.1947

[CH3CO2Na]/0.45 = 0.0639

[CH3CO2Na] = 0.0287

volume , V = 40 mL

= 4*10^-2 L

use:

number of mol,

n = Molarity * Volume

= 2.874*10^-2*4*10^-2

= 1.15*10^-3 mol

Molar mass of CH3CO2Na,

MM = 2*MM(C) + 3*MM(H) + 2*MM(O) + 1*MM(Na)

= 2*12.01 + 3*1.008 + 2*16.0 + 1*22.99

= 82.034 g/mol

use:

mass of CH3CO2Na,

m = number of mol * molar mass

= 1.15*10^-3 mol * 82.03 g/mol

= 9.431*10^-2 g

Answer: 9.43*10^-2 g