The gram-formula mass of citric acid is 3(1)+6(12)+5(1)+16(7)=192 g/mol.
This means that in 13.00 grams of citric acid, there are 13.00/192 = 0.067 moles.
From the equation, we know that for every 1 mole of citric acid that is consumed, 3 moles of carbon dioxide are produced.
This means that there are 3(0.067)=0.203 moles.
Since the gram-formula mass of carbon dioxide is 12+2(16)=44 g/mol, meaning it has a mass of 0.203(44)=8.93 g
