If 6.3 g of NaHCO3 arc added to 15.0 g of CH3COOH solution, the residue is found to weigh 18.0 g. What is the mass of CO2 released in the reaction ?

The correct option is 3.3g.

To find the mass of carbon dioxide (${\mathrm{CO}}_2$) released during the reaction, we can apply the Law of Conservation of Mass. This fundamental law of chemistry states that in any chemical reaction, the total mass of the reactants must be equal to the total mass of the products.

Let us first write down the chemical equation for the reaction between sodium bicarbonate (${\mathrm{NaHCO}}_3$) and acetic acid (${\mathrm{CH}}_3$COOH):
${\mathrm{NaHCO}}_3+{\mathrm{CH}}_3\mathrm{COOH}\to {\mathrm{CH}}_3\mathrm{COONa}+H_{2}O+{\mathrm{CO}}_2\uparrow$
In this reaction, the carbon dioxide gas (${\mathrm{CO}}_2$) escapes into the atmosphere, while the other products (sodium acetate and water) remain behind as the residue.

According to the Law of Conservation of Mass:
$\text{Total Mass of Reactants}=\text{Total Mass of Products}$

Here, the reactants are sodium bicarbonate and the acetic acid solution:
$\text{Mass of}{\mathrm{NaHCO}}_3=6.3\text{ g}$
$\text{Mass of}{\mathrm{CH}}_3\mathrm{COOH}\text{solution}=15.0\text{ g}$
Therefore, the total mass of the reactants is:
$\text{Total Mass of Reactants}=6.3\text{ g}+15.0\text{ g}=21.3\text{ g}$

The products consist of the solid residue left behind and the carbon dioxide gas that escapes:
$\text{Total Mass of Products}=\text{Mass of Residue}+\text{Mass of}{\mathrm{CO}}_2\text{released}$

We are given that the mass of the residue is $18.0\text{ g}$. Let the mass of ${\mathrm{CO}}_2$ released be $x$.
Substituting these values into our conservation equation:
$21.3\text{ g}=18.0\text{ g}+x$

Solving for $x$:
$x=21.3\text{ g}-18.0\text{ g}$
$x=3.3\text{ g}$

Thus, the mass of carbon dioxide released in the reaction is 3.3g.