Sure, let's break down the given observations and determine the solubility of both substances from the data recorded in the table.
### Part 1: Which, if any, substance is soluble in water?
Based on the observations, we have the following data for the mass of undissolved substances at different temperatures:
- Substance A: 50 g (remaining the same at all temperatures: 20°C, 40°C, 60°C, and 80°C)
- Substance B: 10 g at 20°C, 8 g at 40°C, 5 g at 60°C, and 2 g at 80°C
From analyzing this data, we can conclude the following:
- Substance A is not soluble in water.
- Substance B is soluble in water.
### Part 2: Explanation of Solubility Determination
#### Substance A:
- For Substance A, the mass of undissolved substance remains constant at 50 g across all temperatures (20°C, 40°C, 60°C, and 80°C).
- Because the undissolved mass of Substance A does not change with increasing temperature, we can infer that none of the Substance A is dissolving in water irrespective of the temperature.
- In other words, Substance A does not dissolve in water at these temperatures, indicating that it is insoluble.
#### Substance B:
- For Substance B, the mass of undissolved substance decreases as the temperature increases: 10 g at 20°C, 8 g at 40°C, 5 g at 60°C, and 2 g at 80°C.
- This trend shows that as the temperature of the water increases, more of Substance B dissolves, leading to a decreasing amount of undissolved mass.
- The decrease in the undissolved mass of Substance B with increasing temperature is a clear indication that Substance B is soluble in water. It dissolves more effectively at higher temperatures.
### Conclusion:
- Substance A is not soluble in water at temperatures from 20°C to 80°C because the undissolved mass remains unchanged.
- Substance B is soluble in water at these temperatures, with its solubility increasing as the temperature rises, as evidenced by the decreasing undissolved mass.
