CCEA A-Level Life and Health Sciences 0008
Experimental Techniques
Human Body Systems
Physical Chemistry in Industrial Processes
Brain ScienceDouble Award
Material ScienceDouble Award
Medicine, Drugs and Clinical TrialsDouble Award
Scientific Method, Investigation, Analysis and Evaluation
Organic Chemistry
Medical PhysicsA2 option
Sound and LightA2 option
Genetics, Stem Cell Research and CloningA2 option
MicrobiologyDouble Award
Oral Health and DentistryDouble Award
Histology and PathologyDouble Award
Analytical Chemistry TechniquesDouble Award
Enabling TechnologyDouble Award
Experimental Techniques
Rates of reaction and organic preparations
- 3 things to know
- AS 1
Overview
Measuring rate with gas syringes and the disappearing cross, initial rate, fair tests, reflux and distillation, percentage yield with a worked example, purity checks and risk assessment.
What you need to know
Answer each one before you reveal it.
How can a gas syringe be used to follow a reaction rate?
How is the initial rate found from a graph of product against time?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How can the rate of a reaction be measured?
Model answer
The rate can be found by measuring how quickly a reactant is used up or a product forms. Gas volume, mass loss or colour change can be measured over time.
- 2
How can a gas syringe be used to follow a reaction rate?
Model answer
The gas syringe collects the gas produced, and its volume is read at regular time intervals. A graph of volume against time shows the rate.
- 3
How is the initial rate found from a graph of product against time?
Model answer
A tangent is drawn to the curve at time zero. The gradient of the tangent gives the initial rate.
- 4
A reaction produces 48 cm³ of gas in the first 30 seconds. What is the mean rate over that time?
Model answer
The mean rate is 1.6 cm³ per second. The working is 48 ÷ 30 = 1.6 cm³/s.
- 5
How does a disappearing-cross experiment measure rate?
Model answer
The time taken for a precipitate to hide a cross under the flask is recorded. A shorter time means a faster rate.
- 6
Why must only one variable be changed in a rate investigation?
Model answer
Changing one variable at a time shows its effect alone. Other variables, such as temperature and volume, must be controlled.
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