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An experiment to investigate the effect of temperature on the rate of the reaction between 0.05 M sodium thiosulfate solution and an excess of 3 M hydrochloric acid solution was carried out as follows - Leaving Cert Chemistry - Question 3 - 2014
Question 3
An experiment to investigate the effect of temperature on the rate of the reaction between 0.05 M sodium thiosulfate solution and an excess of 3 M hydrochloric acid ... show full transcript
Worked Solution & Example Answer:An experiment to investigate the effect of temperature on the rate of the reaction between 0.05 M sodium thiosulfate solution and an excess of 3 M hydrochloric acid solution was carried out as follows - Leaving Cert Chemistry - Question 3 - 2014
Step 1
Explain the term rate of reaction.
Answer
The rate of reaction refers to the change in concentration of a reactant or product per unit time. It indicates how fast or slow a reaction occurs, and for a reaction involving the change in concentration of sodium thiosulfate, it can be expressed as:
where
- ( \Delta [Reactant] ) is the change in concentration of the reactant (sodium thiosulfate) and
- ( \Delta t ) is the change in time.
Step 2
Describe and explain the change observed in the conical flask during the reaction.
Answer
During the reaction, a cloudiness was observed in the conical flask due to the formation of sulfur as a precipitate. This change occurs as the sulfur is produced when sodium thiosulfate reacts with hydrochloric acid, resulting in a suspension that makes the solution opaque.
Step 3
Describe how this observed change was used to obtain the reaction times.
Answer
The cloudiness of the solution was used to time the reaction. A stopwatch was started when the hydrochloric acid was added, and the timer was stopped once the cross on the base of the flask (which was visible when the solution was clear) became obscured by the turbidity caused by the sulfur precipitate. The time recorded was then used to calculate the rate of reaction.
Step 4
Plot a graph of rate of reaction (1/time) versus temperature.
Answer
To plot the graph:
- Calculate the rate of reaction by taking the reciprocal of the time recorded.
- Prepare a graph with 'Temperature (°C)' on the x-axis and 'Rate of Reaction (1/time)' on the y-axis.
- Ensure both axes are appropriately labelled and use correct numerical scales based on the data collected.
- Plot the points for each temperature and connect them smoothly to represent the trend.
Step 5
Describe and explain the relationship shown in your graph between rate of reaction and temperature.
Answer
The graph should show that the rate of reaction increases with temperature. This relationship is typically exponential: as temperature increases, the rate of reaction tends to double with a 10 °C rise in temperature. This is due to the fact that increased temperature provides more energy to the molecules, resulting in more frequent and effective collisions, thereby leading to a higher reaction rate.
Step 6
Use your graph to find the value for the reaction time at 35 °C.
Answer
From the graph, the reaction time at 35 °C corresponds to the rate found by measuring. Based on the data, the time recorded for this temperature was approximately 6 seconds, as indicated on the graph. The value should be recorded to one decimal place as 6.0 s.
Step 7
What would be the effect on the reaction times if the experiment were repeated using 0.025 M sodium thiosulfate solution? Justify your answer.
Answer
If the experiment were repeated using 0.025 M sodium thiosulfate solution, the reaction time would likely increase. This is because a lower concentration of sodium thiosulfate results in fewer reactant particles, leading to a decreased frequency of collisions and a slower overall reaction rate. Consequently, the time taken for a visible change to occur would be longer.