You carefully measure 14.00 g of caco3 powder and add it to 56.70 g of hcl solution in a reaction flask of known mass. you notice bubbles as a reaction takes place. you then determine that the contents of the flask have a mass of 64.96 g . the relevant equation is

5.74 g

Explanation:

Using conservation of mass:

mass of the reactant = mass of the product if the system is closed

but in this case the bubbles must have been allow to leave the solution and the resulting mass after the reaction equals 64.96 g  

to find the mass of Co2 released

we subtract mass of the remaining product from the mass of the reactant

mass of reactant =14 g + 56.70 = 70.7 g

mass of carbon dioxide = 70.7 - 64.96 ( mass of the remaining product after the bubble) = 5.74 g