Here's what I got.
Notice that the problem is asking for
total volume of gas, measured at
#29^@"C"#and #"769 torr"#
which can only mean that your goal here to find the volume of carbon dioxide,
So why carbon dioxide and not sodium carbonate,
Now, the problem provides you with mass of sodium bicarbonate,
This is just a tricky way of saying that all the mass of sodium bicarbonate reacted to produce sodium carbonate. However, sodium carbonate is not the only product of the reaction.
Water and carbon dioxide will also be produced when the sample of sodium bicarbonate undergoes decomposition.
As you can see in the solution, you can ignore the sodium carbonate completely because it is not important here.
Once you convert the mass of sodium bicarbonate to moles, you can use the
Once you know that, the ideal gas law equation helps you find the needed volume.