Starter quiz
- Which method would be most suitable for measuring the rate of a reaction that produces a gas as one of its products?
- end-point method
- gas collection method ✓
- titration method
- combustion method
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- How can we measure the amount of gas produced in a chemical reaction?
- using an inverted measuring cylinder ✓
- using a stopwatch
- using a gas syringe ✓
- using a burette
- using a conical flask
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- Typically what happens to the rate of reaction during a reaction?
- the rate of reaction increases
- the rate of reaction decreases ✓
- the rate of reaction remains at zero
- the rate of reaction remains constant
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- When measuring the volume of gas produced in a chemical reaction, what effect will gas escaping to the surroundings have on the results?
- The measured volume of gas produced will be higher than the true value.
- The measured volume of gas produced will be lower than the true value. ✓
- There will be no effect on the volume of gas recorded.
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- How can we calculate the instantaneous rate of reaction from a volume of gas produced versus time graph?
- calculating the area under the graph
- reading the maximum amount of gas produced
- measuring how long the reaction took to reach completion
- calculating the gradient at specific points ✓
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- Match the type of error to the correct definition.
- zero error⇔occurs when an instrument does not reset to zero ✓
- systematic error⇔is caused by the equipment used ✓
- parallax error⇔occurs when a measurement is not taken at eye-level ✓
- random error⇔made by the investigator such as timing incorrectly ✓
Exit quiz
- What is a potential error that could affect the accuracy of end-point measurements?
- contamination ✓
- colour changes
- bubbling
- a temperature change
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- What type of error could affect the accuracy of measuring the volume of gas over time?
- timing errors ✓
- colour changes
- pH measurement errors
- temperature changes
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- Which apparatus set-up can cause errors when measuring volumes of gas produced?
- incorrect temperature
- gas displaced by the bung ✓
- incorrect pH
- an inverted measuring cylinder
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- Why is measuring an end-point in a reaction useful?
- It allows direct and simple comparison of reaction rates. ✓
- It changes the temperature of the reaction.
- It alters the reactants used.
- It measures the pH of the solution.
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- How can you reduce subjectivity in observing the end-point of a reaction?
- using automated sensors such as light sensors ✓
- rely on human judgement
- get a different person to take each reading
- ignore observations
- change the reactants
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- Which key term is used for results that are close to the true or standard value?
- accurate ✓
- precise
- repeatable
- reproducible
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- Measuring volume of gas produced throughout a reaction allows the changing rate of reaction to be calculated.
- Errors in measuring volumes of gas over time include timing, reading volumes in real time and gas displaced by the bung.
- Measuring an end-point in a reaction allows direct and simple comparison of reaction rates.
- Errors in measuring end-points include subjectivity of observations, measuring times and volumes, and contamination.
Common misconception
Adding a bung to the top of a conical flask does not affect volume measurements.
The bung can displace a small volume of gas, which can affect the accuracy of the measurements. It is essential to account for the volume displaced by the bung in calculations.
Keywords
Accuracy - Accuracy refers to how close a measured value is to the true or standard value.
Repeatable - A method is described as repeatable if a person uses the same method and obtains the same/similar results when repeating the experiment.
Parallax error - A parallax error occurs when a measurement is not taken at eye-level.
Systematic error - A systematic error is caused by the equipment used.
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