Final answer:
To calculate the mass of water that evaporates, we apply energy conservation between the heated iron block and the water. Heat transfers from the iron to the water until the water boils and some evaporates. Specific heat capacities and latent heat values are needed for a numerical solution.
Step-by-step explanation:
To calculate the mass of water that boiled off when a 5kg block of iron is heated to 800℃ and placed in a tub containing 2 liters of water at 15℃, we apply the concept of conservation of energy. The heat lost by the iron block will be equal to the heat gained by the water, which will result in water reaching its boiling point and some of it evaporating. The specific heat capacity of water, the heat of vaporization of water, and the specific heat capacity of iron are crucial to these calculations.
We can denote the mass of water that evaporates as m, and calculate the heat required to raise the temperature of the remaining water from 15℃ to 100℃ and convert the m grams of water at 100℃ into steam. However, we need additional data such as the specific heat capacities and the latent heat of vaporization for water to provide a concrete answer. Without the specific values, we can only describe the methodology.