Question

A 0.500 g sample containing Ag2O and inert material is heated, causing the silver oxide to decompose according to the following equation:

2 Ag2O(s) → 4 Ag(s) + O2(g)

If 13.8 mL of gas are collected over water at 27°C and 1.00 atm external pressure, what is the percentage of silver oxide in the sample? The partial pressure of water is 26.7 mm Hg at 27°C.

a.) 25.1%

b.) 51.9%

c.)12.5%

d.) 50.1%

Answer 1

answer : d.) 50.1%

solution :

volume = 13.8 mL = 0.0138 L

temperature = T = 27 + 273 = 300 K

pressure water + O2 = 1 atm =760 mmHg

partial pressure of O2 = 760 - 26.7

                                  = 733.3 mm Hg

                                 = 0.965 atm

P V = n R T

0.965 x 0.0138 = n x 0.0821 x 300

n = 5.41 x 10^-4

2 moles Ag2O ------------------------> 1 mole O2

X moles Ag2O ---------------------------> 5.41 x 10^-4 moles O2

X = 2 x 5.41 x 10^-4

X = 1.08 x 10^-3

moles of Ag2O = 1.08 x 10^-3

mass of Ag2O = 1.08 x 10^-3 x 231.7

                       = 0.2505 g

mass % of Ag2O = mass of Ag2O x 100 / sample mass

                           = 0.2505 x 100 / 0.500

                          = 50.1 %