Answer :
Let's analyze the given experimental setup and the factors affecting the rate of reaction to answer this question.
### Table Summary:
| Flask | Volume of H₂SO₄ | Volume of Sodium Thiosulfate | Volume of Water | Time |
|-------|------------------|-----------------------------|-----------------|--------------|
| 1 | 5 mL | 50 mL | 0 mL | 19 seconds |
| 2 | 5 mL | 40 mL | 10 mL | ? |
| 3 | 5 mL | 30 mL | 20 mL | ? |
| 4 | 5 mL | 20 mL | 30 mL | ? |
### Key Observations:
1. Volume of H₂SO₄: This is kept constant at 5 mL in each flask.
2. Volume of Sodium Thiosulfate: This decreases from 50 mL in Flask 1 to 20 mL in Flask 4.
3. Volume of Water: This increases from 0 mL in Flask 1 to 30 mL in Flask 4.
4. Time for Cross to Become Invisible: Given for Flask 1 (19 seconds) and unknown for other flasks.
### Trend Analysis:
- From Flask 1 to Flask 4, as the volume of sodium thiosulfate decreases (while keeping the volume of H₂SO₄ constant), we would expect the rate at which the cross becomes invisible to decrease.
- The concentration of sodium thiosulfate decreases from Flask 1 to Flask 4 because a larger volume of water is added, diluting the sodium thiosulfate solution.
- Rate of Reaction: Generally, for reactions involving a solid precipitate:
- Higher concentration of reactant (sodium thiosulfate) leads to a faster reaction.
- Lower concentration of reactant (sodium thiosulfate) leads to a slower reaction.
### Conclusion:
- Looking at the options provided:
- The volume of sulfuric acid increases, time decreases: Not applicable since H₂SO₄ volume is constant.
- The volume of sulfuric acid remains the same, time increases: Observing the trend, time should indeed increase as concentration of sodium thiosulfate decreases.
- As volume of sodium thiosulfate increases, time decreases: This matches our observed trend. More sodium thiosulfate means a faster reaction because of higher concentration, leading to less time for the cross to become invisible.
- The volume of sodium thiosulfate remains the same, time increases: Not applicable because the volume changes.
### Correct Answer:
As the volume of sodium thiosulfate increases, time decreases.
This conclusion is aligned with the trend that a higher concentration of sodium thiosulfate results in a faster reaction, making the precipitate form more quickly, which in turn makes the cross disappear faster.
### Table Summary:
| Flask | Volume of H₂SO₄ | Volume of Sodium Thiosulfate | Volume of Water | Time |
|-------|------------------|-----------------------------|-----------------|--------------|
| 1 | 5 mL | 50 mL | 0 mL | 19 seconds |
| 2 | 5 mL | 40 mL | 10 mL | ? |
| 3 | 5 mL | 30 mL | 20 mL | ? |
| 4 | 5 mL | 20 mL | 30 mL | ? |
### Key Observations:
1. Volume of H₂SO₄: This is kept constant at 5 mL in each flask.
2. Volume of Sodium Thiosulfate: This decreases from 50 mL in Flask 1 to 20 mL in Flask 4.
3. Volume of Water: This increases from 0 mL in Flask 1 to 30 mL in Flask 4.
4. Time for Cross to Become Invisible: Given for Flask 1 (19 seconds) and unknown for other flasks.
### Trend Analysis:
- From Flask 1 to Flask 4, as the volume of sodium thiosulfate decreases (while keeping the volume of H₂SO₄ constant), we would expect the rate at which the cross becomes invisible to decrease.
- The concentration of sodium thiosulfate decreases from Flask 1 to Flask 4 because a larger volume of water is added, diluting the sodium thiosulfate solution.
- Rate of Reaction: Generally, for reactions involving a solid precipitate:
- Higher concentration of reactant (sodium thiosulfate) leads to a faster reaction.
- Lower concentration of reactant (sodium thiosulfate) leads to a slower reaction.
### Conclusion:
- Looking at the options provided:
- The volume of sulfuric acid increases, time decreases: Not applicable since H₂SO₄ volume is constant.
- The volume of sulfuric acid remains the same, time increases: Observing the trend, time should indeed increase as concentration of sodium thiosulfate decreases.
- As volume of sodium thiosulfate increases, time decreases: This matches our observed trend. More sodium thiosulfate means a faster reaction because of higher concentration, leading to less time for the cross to become invisible.
- The volume of sodium thiosulfate remains the same, time increases: Not applicable because the volume changes.
### Correct Answer:
As the volume of sodium thiosulfate increases, time decreases.
This conclusion is aligned with the trend that a higher concentration of sodium thiosulfate results in a faster reaction, making the precipitate form more quickly, which in turn makes the cross disappear faster.