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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 can be expressed mathematically as:
ext{Rate} = - rac{d[ ext{Reactant}]}{dt} = rac{d[ ext{Product}]}{dt}
This indicates how quickly reactants are converted into products, reflecting the speed at which a chemical reaction occurs.
Step 2
Describe and explain the change observed in the conical flask during the reaction.
Answer
During the reaction between sodium thiosulfate and hydrochloric acid, a noticeable change occurs as the mixture becomes cloudy. This cloudiness results from the formation of sulfur precipitate. As the reaction proceeds, the sulfur particles scatter light, making the solution opaque, which can be visually observed.
Step 3
Describe how this observed change was used to obtain the reaction times.
Answer
The time for the reaction was measured by observing when the mixture turned cloudy. A stopwatch was started upon adding the acid, and the time recorded when the distinct cloudiness made a cross mark on a piece of paper beneath the flask invisible. This provided a reliable measure of the time taken for sufficient sulfur to form.
Step 4
Plot a graph of rate of reaction (1/time) versus temperature.
Answer
To plot the graph, first calculate the rate of reaction (1/time) for each temperature. The data can be plotted on a graph with 'Temperature (°C)' on the x-axis and 'Rate of Reaction (1/time in s^{-1})' on the y-axis. Ensure to label each axis correctly and plot points accurately, connecting them to illustrate the trend.
Step 5
Describe and explain the relationship shown in your graph between rate of reaction and temperature.
Answer
The graph shows that the rate of reaction increases with temperature, often exponentially. This is because higher temperatures provide more energy to the reactant particles, resulting in increased collision frequency and more successful collisions. Consequently, the rate approximately doubles with every 10 °C rise in temperature, as more molecules possess sufficient energy to surpass the activation energy barrier.
Step 6
Use your graph to find the value for the reaction time at 35 °C.
Answer
From the graph, at 35 °C, the reaction time can be interpolated or calculated based on the plotted points. It is found that the reaction time is approximately 66-72 seconds, hence you would state it as 66 seconds for clarity.
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 with 0.025 M sodium thiosulfate solution, the reaction times would be longer. This is because a lower concentration of thiosulfate results in fewer reactant molecules available to collide. Consequently, the rate of reaction would decrease, leading to an increase in the time taken for the solution to turn cloudy.