Certainly! Let's analyze the experiment and predict the trend in the time taken for the cross to become invisible due to the formation of the yellow precipitate.
The given experiment involves hydrochloric acid (HCl) reacting with sodium thiosulfate, forming a yellow precipitate that causes the cross at the base of the flask to become invisible. The variables in the experiment include the volume of hydrochloric acid, sodium thiosulfate, and water in different flasks. The time taken for the cross to become invisible is recorded in the table, and we are provided with one example: Flask 1, which takes 14 seconds when it contains 10 mL of sodium thiosulfate and 40 mL of water.
### Factors Affecting Reaction Rate
1. Concentration of Reactants: Increasing the concentration of reactants generally increases the rate of reaction. This is because a higher concentration means more reactant particles in a given volume, leading to more frequent collisions and, therefore, a faster reaction.
2. Volume of Sodium Thiosulfate: By increasing the volume of sodium thiosulfate while keeping the total solution volume constant, we are effectively increasing the concentration of sodium thiosulfate in the reaction mixture.
### Analysis of the Experimental Record
- Flask 1: 10 mL Sodium Thiosulfate, 40 mL Water → 14 seconds
- Flask 2: 20 mL Sodium Thiosulfate, 30 mL Water
- Flask 3: 30 mL Sodium Thiosulfate, 20 mL Water
- Flask 4: 40 mL Sodium Thiosulfate, 10 mL Water
### Predicted Trend Analysis
- Flask 1: Already measured at 14 seconds.
- Flask 2: The volume of sodium thiosulfate is doubled from Flask 1 (20 mL compared to 10 mL), leading to an increased concentration of sodium thiosulfate. Therefore, the rate of reaction will be faster, and the time taken for the cross to become invisible will be less than 14 seconds.
- Flask 3: The volume of sodium thiosulfate is tripled from Flask 1 (30 mL compared to 10 mL). This further increase in concentration will make the reaction even faster. Thus, the time taken will be less than that of Flask 2.
- Flask 4: The volume of sodium thiosulfate is quadrupled from Flask 1 (40 mL compared to 10 mL). This will result in the highest concentration of sodium thiosulfate, and therefore, the fastest reaction rate among the four flasks. The time taken will be the shortest of all.
### Conclusion
As the volume of sodium thiosulfate increases from Flask 1 to Flask 4, the time taken for the cross to become invisible will decrease. This is due to the increased concentration of sodium thiosulfate, which increases the rate of reaction. Consequently, the predicted trend in the last column of the experimental record is as follows:
- Flask 1: 14 seconds (given)
- Flask 2: Time < 14 seconds
- Flask 3: Time < Time in Flask 2
- Flask 4: Time < Time in Flask 3
This trend shows that the reaction rate increases with the increase in sodium thiosulfate concentration, leading to a decrease in the time taken for the cross to become invisible.
