In a chemical reaction, the law of conservation of mass states that mass is neither created nor destroyed. This means that the total mass of the reactants will equal the total mass of the products.
In this case, the scientist starts with 30 grams of calcium carbonate (\( \text{CaCO}_3 \)). When heated, it decomposes into carbon dioxide (\( \text{CO}_2 \)) and calcium oxide (\( \text{CaO} \)).
Since there are no additional substances added or lost during the process (assuming it's conducted in a closed system), the total mass of the products will equal the initial mass of the reactant:
Total mass of products = Total mass of reactants = 30 grams.
Thus, the total mass of the products is 30 grams.