Final answer:
To find the mass of the solution after calcium reacts with water, the law of conservation of mass is applied. The total initial mass of calcium and water (140 g) minus the mass of hydrogen gas released (2 g) equals the mass of the remaining solution (138 g). Thus, the correct answer is 138 grams.
Step-by-step explanation:
The question involves a chemical reaction where calcium reacts with water to produce calcium hydroxide and hydrogen gas. According to the given reaction, when calcium reacts with water, we know that the reaction proceeds 100% to products, meaning all of the calcium and water react to form the stated products.
To find the total mass of the solution after the reaction, we have to consider the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction.
Therefore, the mass of the products will be equal to the mass of the reactants. The initial mass is 40 g of calcium plus 100 g of water which totals 140 g. Since hydrogen gas is released, we just need to subtract the mass of the hydrogen gas from 140 g to find the mass of the solution remaining after the reaction.
Calcium has a molar mass of about 40 g/mol, and produces 1 mol of H2 for every mole of calcium reacted. Since one mole of hydrogen gas has a mass of about 2 g, the release of hydrogen will be 2 g for the reaction of 40 g of calcium. Hence, we subtract the mass of hydrogen gas released (2 g) from the total initial mass (140 g).
140 g - 2 g = 138 g
Thus, the total mass of the solution that remains after the reaction is 138 g, which corresponds to choice C.