Question

The compound Nd₂(C₂O₄)₃ decomposes when heated according to the equation below.

Nd₂(C₂O₄)₃(s) ➝ 2 Nd (s) + 6 CO₂(g)

An impure sample of material contains a small amount of Nd₂(C₂O₄)₃ . The sample is heated and the gas produced collected by downward displacement of water. A total of 166.5 ml of gas is collected at a temperature of 22.0ºC when the atmospheric pressure is 680.0 torr.
[The vapor pressure of water at 22.0ºC is 19.83 torr.]

Calculate the number of grams of Nd₂(C₂O₄)₃ present in the impure sample.

Answer 1

Given:

P = 660.17 torr

= (660.17/760) atm

= 0.8686 atm

V = 166.5 mL

= (166.5/1000) L

= 0.1665 L

T = 22.0 oC

= (22.0+273) K

= 295 K

find number of moles using:

P * V = n*R*T

0.8686 atm * 0.1665 L = n * 0.08206 atm.L/mol.K * 295 K

n = 5.975*10^-3 mol

From reaction,

moles of Nd2(C2O4)3 recated = (1/6)*moles of CO2 formed

= (1/6)*5.975*10^-3 mol

= 9.958*10^-4 mol

Molar mass of Nd2(C2O4)3,

MM = 2*MM(Nd) + 6*MM(C) + 12*MM(O)

= 2*144.2 + 6*12.01 + 12*16.0

= 552.46 g/mol

use:

mass of Nd2(C2O4)3,

m = number of mol * molar mass

= 9.958*10^-4 mol * 5.525*10^2 g/mol

= 0.5501 g

Answer: 0.550 g