6.2a - Effect of Temperature on Reaction Rate using Sodium Thiosulphate and Hydrochloric Acid

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Experiment Summary

This experiment investigates the effect of temperature on the rate of reaction between sodium thiosulphate ( $Na₂S₂O₃$ ) and hydrochloric acid ( $HCl$ ).

As the temperature increases, the rate of reaction is expected to increase due to higher kinetic energy, which leads to more frequent and energetic collisions between reactant particles.

The reaction forms a precipitate of sulfur, which clouds the solution and obscures a cross placed beneath the reaction flask. The time taken for the cross to disappear is used to measure the reaction rate.

The reaction is:

\text{2HCl (aq) + Na}_2\text{S}_2\text{O}_3\text{(aq)} \rightarrow 2\text{NaCl (aq)} + \text{SO}_2\text{(aq)} + \text{S (s)}↓ + \text{H}_2\text{O (l)}

Materials and Apparatus Required

Chemicals

0.05 M sodium thiosulphate solution
3 M hydrochloric acid

Apparatus

Conical flasks (250 cm³)
Graduated cylinders (100 cm³)
Bunsen burner with tripod and wire gauze
Thermometer
Stop-clock
White paper marked with a cross

Safety Precautions

Wear safety glasses at all times.
Hydrochloric acid is corrosive; avoid contact with skin and eyes.
Sulfur dioxide ( $SO₂$ ) is released during the reaction and can irritate the lungs and eyes. Ensure the experiment is conducted in a well-ventilated area.
Handle hot liquids with care to prevent burns.

Method

Measure 100 cm³ of 0.05 M sodium thiosulphate solution and pour it into a conical flask.
Gently heat the flask using a Bunsen burner until the temperature of the solution reaches approximately 20°C.
Measure the temperature using a thermometer.
Add 5 cm³ of 3 M hydrochloric acid to the conical flask and start the stop-clock simultaneously.
Swirl the flask and place it on a piece of white paper marked with a cross.
Record the time taken for the cross to disappear.
Repeat the experiment, heating the sodium thiosulphate solution to different temperatures: 30°C, 40°C, 50°C, and 60°C.
For each trial, add hydrochloric acid once the desired temperature is reached and measure the reaction time.
For each temperature, calculate the reaction rate as the reciprocal of the time (1/time).
Plot a graph of 1/time (rate) against temperature to analyze the effect of temperature on the reaction rate.

Results

Temperature (°C)	Reaction Time (s)	1/Time (s⁻¹)
20	105	0.0095
30	46	0.0217
40	36	0.0278
50	18	0.0556
60	12	0.0833

Example Questions with Answers

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Q1: What effect does increasing the temperature have on the reaction time?

Increasing the temperature decreases the reaction time, meaning the cross disappears faster as the temperature rises.

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Q2: How does temperature affect the rate of reaction?

As the temperature increases, the rate of reaction increases.

This is because particles have more kinetic energy, resulting in more frequent and energetic collisions.

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Q3: What are the two main reasons why the rate of reaction increases with temperature?

The particles move faster, leading to more collisions per unit time.
A greater proportion of collisions have the activation energy needed for the reaction to occur.

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Q4: Why is it not recommended to carry out the experiment at temperatures higher than 60°C?

At temperatures above 60°C, the reaction occurs too quickly to measure the time accurately.

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Q5: Why is sulfur dioxide produced during the reaction, and why must the experiment be done in a well-ventilated area?

Sulfur dioxide is a by-product of the reaction and is harmful if inhaled.

Conducting the experiment in a well-ventilated area reduces the risk of exposure.

a - Effect of Temperature on Reaction Rate using Sodium Thiosulphate and Hydrochloric Acid Simplified Revision Notes for Leaving Cert Chemistry

6.2a - Effect of Temperature on Reaction Rate using Sodium Thiosulphate and Hydrochloric Acid

Experiment Summary

Materials and Apparatus Required

Chemicals

Apparatus

Safety Precautions

Method

Results

Example Questions with Answers

Q1: What effect does increasing the temperature have on the reaction time?

Q2: How does temperature affect the rate of reaction?

Q3: What are the two main reasons why the rate of reaction increases with temperature?

Q4: Why is it not recommended to carry out the experiment at temperatures higher than 60°C?

Q5: Why is sulfur dioxide produced during the reaction, and why must the experiment be done in a well-ventilated area?

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