To determine the expected trend in the table based on the given experiment, let's examine the factors that affect the rates of chemical reactions, particularly focusing on the volumes of reactants used.
Experiment Details:
1. Four different flasks contain a constant volume of sulfuric acid (5 mL) but varying volumes of sodium thiosulfate and water.
2. A yellow precipitate is formed, and the time taken for the cross to become invisible is recorded.
Flask Data:
- Flask 1: 5 mL sulfuric acid, 50 mL sodium thiosulfate, 0 mL water, time = 19 seconds
- Flask 2: 5 mL sulfuric acid, 40 mL sodium thiosulfate, 10 mL water
- Flask 3: 5 mL sulfuric acid, 30 mL sodium thiosulfate, 20 mL water
- Flask 4: 5 mL sulfuric acid, 20 mL sodium thiosulfate, 30 mL water
Since the sulfuric acid volume remains constant across all trials, any changes in reaction time are predominantly influenced by the volume of sodium thiosulfate.
Trends in Chemical Reactions:
- Concentration of Reactants: The rate of a chemical reaction generally increases with an increase in the concentration of one or more reactants. In this case, the concentration is directly related to the volume of sodium thiosulfate, as the total volume is kept constant by compensating with water.
Analysis:
- Higher volume of sodium thiosulfate generally means a higher concentration of it in the reaction mixture.
- Higher concentration leads to an increased collision frequency among reacting molecules, thereby increasing the reaction rate.
- Higher reaction rate corresponds to shorter reaction time.
Observed Trend:
- Flask 1, with the highest volume of sodium thiosulfate (50 mL), has the shortest recorded time (19 seconds).
- As the volume of sodium thiosulfate decreases (from Flask 1 to Flask 4), the concentration decreases, leading to a slower reaction rate and hence a longer time for the cross to become invisible.
Based on this analysis, the correct description of the trend observed in the table is:
"As volume of sodium thiosulfate increases, time decreases."
