GCSE Core Practical Temperature and Reaction Rates

Summary

In this experiment, the effect of temperature on the reaction rate between sodium thiosulfate and hydrochloric acid is observed. The reaction produces a sulfur precipitate, causing the mixture to become increasingly cloudy, eventually obscuring a cross placed beneath the conical flask. By timing how long it takes for the cross to disappear at various temperatures, the experiment aims to demonstrate how temperature affects reaction speed. The results, recorded at different temperatures, help evaluate the impact of heat on the rate of reaction, with sulfur formation as the key indicator.

Takeaways

• 😀 The experiment is called the 'Disappearing Cross Experiment' and aims to examine the effect of temperature on reaction rate.
• 😀 The reaction involves mixing sodium thiosulfate with hydrochloric acid to observe a color change as a result of the reaction.
• 😀 The experiment focuses on measuring how long it takes for the cross, placed under the conical flask, to disappear due to the reaction.
• 😀 The key indicator of the reaction's progress is the formation of a precipitate, which makes the solution turn cloudy and eventually hides the cross.
• 😀 A set amount of sodium thiosulfate (10 cm³) is measured and combined with 40 cm³ of water in the conical flask.
• 😀 Hydrochloric acid (5 cm³) is measured separately and added to the mixture in a test tube before being combined with the flask contents.
• 😀 The experiment investigates the effect of temperature by using a water bath to heat the chemicals to different temperatures before mixing.
• 😀 A makeshift water bath is used in the experiment, heating the test tube and conical flask to a desired temperature (e.g., 50°C).
• 😀 Once the chemicals reach the target temperature, the mixture is observed and the time is recorded until the cross is no longer visible.
• 😀 The experiment has been repeated at different temperatures to track the time taken for the cross to disappear, allowing the effect of temperature on the reaction rate to be analyzed.
• 😀 The precipitate formed during the reaction is sulfur, which causes the cloudiness in the mixture, and the time it takes for the cross to disappear correlates to the rate of sulfur production.

Q & A

What is the purpose of the disappearing cross experiment?

The purpose of the disappearing cross experiment is to study the effect of temperature on the rate of reaction between sodium thiosulfate and hydrochloric acid. The reaction produces a precipitate that makes the solution opaque, and the disappearance of a cross beneath the flask is used as a visual indicator of the reaction's progress.

What is the visual indicator used in the experiment?

The visual indicator is a cross placed under the conical flask. As the reaction occurs and the precipitate forms, the solution becomes increasingly opaque. Once enough precipitate is formed that the cross is no longer visible, the reaction is considered to have reached the desired point.

What chemicals are used in the experiment?

The chemicals used in the experiment are sodium thiosulfate and hydrochloric acid. These chemicals react to produce a precipitate, sulfur, and change the appearance of the solution.

Why is water added to the sodium thiosulfate in the experiment?

Water is added to the sodium thiosulfate to dilute the solution, ensuring that the concentration of sodium thiosulfate is consistent for each trial. This helps to make the reaction's rate more comparable when studying the effect of temperature.

How is the effect of temperature on reaction rate studied?

The effect of temperature on reaction rate is studied by conducting the experiment at different temperatures. The temperature of the chemicals is controlled using a water bath, and the time taken for the cross to disappear is recorded at each temperature.

How is the temperature of the chemicals controlled during the experiment?

The temperature of the chemicals is controlled by placing the test tube and conical flask in a water bath. In the video, a makeshift water bath consisting of a jug of water heated to 50°C is used to ensure the chemicals reach the desired temperature before the reaction begins.

Why is it important to record the actual temperatures used in the experiment?

It is important to record the actual temperatures to ensure that the experiment is being conducted accurately. This allows for a clear comparison between different trials and helps in drawing valid conclusions about the relationship between temperature and reaction rate.

What product is formed during the reaction between sodium thiosulfate and hydrochloric acid?

The product formed during the reaction is sulfur, which appears as a precipitate. This precipitate makes the solution cloudy, and the reaction is considered complete when enough sulfur has been produced to obscure the cross beneath the flask.

What happens to the appearance of the solution as the reaction progresses?

As the reaction progresses, the solution becomes increasingly cloudy due to the formation of a sulfur precipitate. The more precipitate that forms, the less light can pass through the solution, eventually making the cross beneath the flask disappear.

How does the experiment measure the rate of the reaction?

The rate of the reaction is measured by timing how long it takes for the cross beneath the flask to disappear. This time is used as an indicator of how fast the reaction is progressing, and it is compared across different temperatures to analyze the effect of temperature on the reaction rate.