Rates of reaction part 2: measure change in colour or turbidity
Investigate how changes in concentration affects the rates of reactions by measuring change in colour or turbidity.
In this required practical, students use a change in colour or turbidity to see how quickly Hydrochloric Acid reacts with Sulfuric Acid to give a cloudy solution.
This follows the rates of reaction by measuring the volume of gas produced practical, which tests two different concentrations of acid to see how quickly and how much gas is produced when it is reacted with a set length of Magnesium Ribbon.
Equipment (per participant)
• Safety goggles
• 100ml conical flask
• 25ml measuring cylinder x 2
• Stopwatch
• Paper square with a cross
• Washing up bowl (for use as a stop bath containing 0.5M Sodium Carbonate and Phenolphthalein solution)
• Sodium Thiosulfate (40g/L)
• Hydrochloric Acid (1M)
• CLEAPSS Hazcards: 32, 47A, 59A, 95A
Method
- Students should collect the necessary equipment and place a 100ml conical flask onto a square of white paper onto which a large cross has been drawn.
- They should measure 10mls of Sodium Thiosulfate solution and put this into the conical flask. They then need to add 40mls of water to dilute the Sodium Thiosulfate solution a little and ensure the conical flask is put back onto the cross.
- Using a clean measuring cylinder, students should measure 10mls of Hydrochloric acid. This is added to the flask and the flask is swirled to mix whilst starting the stopwatch. The flask must be placed back onto the cross after the solution is mixed.
- Students must now observe the solution from above (at a distance), taking care not to inhale any sulfur fumes given off. They should watch for when the cross disappears. As soon as the cross disappears, the students must stop the stopwatch. They then record this time in a suitable table.
- The waste solution from the reaction should be emptied into the stop bath provided containing 0.5M Sodium Carbonate solution, to keep the sulfur fumes in the laboratory to a minimum.
- The students then repeat steps 2-5 of the process using 20mls, 30mls, 40mls and 50mls of Sodium Thiosulfate (& 30mls, 20mls, 10mls and 0mls of water to dilute the Sodium Thiosulfate). The total amount of solution in the flask each time should total 50mls.
- They must then carry out a complete repeat two further times to produce results from which a mean average can be taken, and their results can be plotted on a graph.
Technician tips
• A washing up bowl should be provided as a stop bath. A Sodium Carbonate solution (0.5M) is added to the washing up bowl, and students can empty the waste from their experiments into this so that it stops the reaction between the acid and the Thiosulfate. This will also help to reduce the sulfur fumes in the laboratory.
• In order to make the Sodium Carbonate solution for the stop bath, 53g of Sodium Carbonate anhydrous is dissolved in 1L of water. Phenolphthalein should be added, and the stop baths should be checked periodically and be refreshed as needed to ensure they are still reacting to neutralize the waste products.
• 40g/L Sodium Thiosulfate solution is made up wearing eye protection by dissolving 10g of the solid in 250mls of water.
To do this practical you will need
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Reaction Colour Changes GCSE Chemistry
Rates of reaction part 2: measure change in colour of turbidity
Investigate how changes in concentration affects the rates of reactions by measuring change in colour or turbidity.
In this required practical, students use a change in colour or turbidity to see how quickly Hydrochloric Acid reacts with Sodium Thiosulfate to give a cloudy solution.
This follows the rates of reaction by measuring the volume of gas produced practical, which tests two different concentrations of acid to see how quickly and how much gas is produced when it is reacted with a set length of Magnesium Ribbon.
Equipment (per participant)
• Safety goggles
• 100ml conical flask
• 25ml measuring cylinder x 2
• Stopwatch
• Paper square with a cross
• Washing up bowl (for use as a stop bath containing 0.5M Sodium Carbonate and Phenolphthalein solution)
• Sodium Thiosulfate (40g/L)
• Hydrochloric Acid (1M)
• CLEAPSS Hazcards: 32, 47A, 59A, 95A
Method
Preparation and Setup
- Gather Equipment
- Collect the necessary equipment, including a 100ml conical flask, a trough, a 100ml measuring cylinder, a delivery tube, a stopwatch, a retort stand (if needed), and a small piece of magnesium ribbon.
- Prepare the Trough and Cylinder
- Fill the trough two-thirds full with water.
- Fill the 100ml measuring cylinder completely with water, then invert it into the trough, ensuring the opening is submerged underwater.
- Secure the inverted measuring cylinder in a vertical position using a retort stand if necessary.
- Set Up the Delivery System
- Position the delivery tube so that its end is inside the underwater opening of the measuring cylinder.
Conducting the Experiment
- Add Hydrochloric Acid
- Measure 50ml of 1M Hydrochloric Acid using a measuring cylinder and pour it into the 100ml conical flask.
- Start the Reaction
- Add a small piece of magnesium ribbon to the acid in the flask.
- Immediately seal the flask with a bung and start timing with the stopwatch.
- Record Gas Volume
- Choose a time interval (e.g., every 10 seconds).
- At each interval, read and record the volume of gas collected in the inverted measuring cylinder. Record these results in a suitable table.
- Continue Until Completion
- Continue measuring and recording gas volumes until the volume stops increasing (indicating the reaction has completed).
Repeating the Experiment
- Repeat with Different Acid Concentration
- Repeat steps 4–7 using 50ml of 1.5M Hydrochloric Acid.
Analysis
- Plot the Results
- Plot the results for each acid concentration on a graph, with time on the x-axis and volume of gas on the y-axis.
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Technician tips
• A washing up bowl should be provided as a stop bath. A Sodium Carbonate solution (0.5M) is added to the washing up bowl, and students can empty the waste from their experiments into this so that it stops the reaction between the acid and the Thiosulfate. This will also help to reduce the sulfur fumes in the laboratory.
• In order to make the Sodium Carbonate solution for the stop bath, 53g of Sodium Carbonate anhydrous is dissolved in 1L of water. Phenolphthalein should be added, and the stop baths should be checked periodically and be refreshed as needed to ensure they are still reacting to neutralize the waste products.
• 40g/L Sodium Thiosulfate solution is made up wearing eye protection by dissolving 10g of the solid in 250mls of water.
To do this practical you will need
Need Chemistry inspiration and help?
