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If 0.158 g of a white, unknown solid carbonate of a group 2A metal (M) is heated and the resulting CO2 is transferred to a 285 ml sealed flask and allowed to cool to 25 degrees Celsius, the pressure in the flask is 69.8 mmHg. What is the identity of the carbonate?

Respuesta :

using the ideal gas law equation we can find the number of moles of COā‚‚ formedĀ 
PV = nRT
whereĀ 
P - pressure - 69.8 mmHg x 133 Pa/mmHg = 9 283 Pa
V - volume - 285 x 10ā»ā¶ mĀ³
n - number of molesĀ 
R - universal gas constant - 8.314 Jmolā»Ā¹Kā»Ā¹
T - temperature in Kelvin - 25Ā Ā°C + 273 = 298 K
substituting these values in the equationĀ 
9283 Pa xĀ 285 x 10ā»ā¶ mĀ³ = n xĀ 8.314 Jmolā»Ā¹Kā»Ā¹ x 298 K
n = 1.067 x 10ā»Ā³ mol

decomposition of metal carbonate is as followsĀ 
MCOā‚ƒ ---> MO + COā‚‚
stoichiometry of MCOā‚ƒ to COā‚‚ is 1:1
therefore number of moles of MCOā‚ƒ heated = number of COā‚‚ moles formedĀ 
number of MCOā‚ƒ moles = 1.067 x 10ā»Ā³ mol
molar mass = mass / number of molesĀ 
molar mass = 0.158 g / 1.067 x 10ā»Ā³ mol = 148 g/molĀ 
since carbonate molar mass is known -
Ā (molar mass of C x 1 C atom)Ā + (molar mass of O x 3 Ā O atoms)Ā Ā 
12 + 16x 3 = 12 + 48 = 60Ā 
then mass of metal M - 148 - 60 = 88
group IIĀ metal with molar mass of 88 is Ra - RadiumĀ