[theunproblemist]

A student performed an experiment to determine the molar mass of carbon dioxide. He heated a known mass of copper carbonate in a test tube. The solid will undergo thermal decomposition, release carbon dioxide and leaving copper oxide.
The chemical equation for the reaction taking place in the tube is given below
CuCO3 (s) --> CuO (s) + CO2 (g)
The carbon dioxide gas given off will be collected by displacement of water from an inverted glass tube.
The following results were recorded:
Mass of the boiling tube and copper carbonate before heating (g) ± 0.001 = 45.675
Mass of boiling tube and copper carbonate after heating (g) ± 0.001 = 45.623
Volume of gas collected (cm3) ±0.1 = 37.3
Temperature (C) ±0.1 = 25.0
Pressure (kPa) ±0.1 = 99.7

a) Calculate the percentage error in the mass of carbon dioxide produced.
b) Deduce the absolute uncertainty of the temperature in Kelvin.
c) Using the above data, calculate the molar mass of carbon dioxide.
d) Calculate the percentage experimental error in the calculated molar mass.

[Babcock_Hall]

Would you show us your calculations so far?

[theunproblemist]

Would you show us your calculations so far?

To be quite honest, I have no idea what to actually do.
For (a), I subtract the mass of boiling after and before heating to find the mass of the gas. Then use n=m/ Mr to find the moles and use n= V/Vm to find the volume. Then proceeded to divide that by the volume of gas collected to find the percentage error. But I do not think that is correct.

[Orcio_87]

For (a), I subtract the mass of boiling after and before heating to find the mass of the gas. Then use n=m/ Mr to find the moles and use n= V/Vm to find the volume. Then proceeded to divide that by the volume of gas collected to find the percentage error. But I do not think that is correct.

Why did you not used the pV = nRT equation to calculate the mass of colected gas ?

Percentage error is the ratio of difference between mass of the collected gas and change of mass of CuCO₃ to the change of mass of the CuCO₃.

Because the second one (change of the mass of CuCO₃) is more reliable here (serves as the base for calculating error).

[mjc123]

You can't use PV = nRT to calculate the mass of gas without knowing the molar mass, which is what you are trying to find. You have to assume that the mass of gas is equal to the change in mass of CuCO₃. You work out the percentage error using the given uncertainty in the mass measurements.

[theunproblemist]

You can't use PV = nRT to calculate the mass of gas without knowing the molar mass, which is what you are trying to find. You have to assume that the mass of gas is equal to the change in mass of CuCO₃. You work out the percentage error using the given uncertainty in the mass measurements.

Would you be able to show me how to do this?
Because if I am correct, I will have to use PV=nRT in question (c) anyway right?