Precautions & Source of Error

• Take readings with eye perpendicular to scale (avoid parallax error)
• Take readings from the bottom of the meniscus
• Leave all test tubes in a water bath to equilibrate
• Hot test tube (Use tongs to hold the test tube)
• Stir a solution to distribute all the components evenly
• While taking readings from a measuring cylinder, place it on a flat surface
• Wear a lab coat
• Stand while performing experiment
• Don’t expose an alcohol/reagent to a flame directly; heat it using a water bath
• Use burette/pipette instead of measuring cylinder
• In photosynthesis experiment, use a heat shield (beaker of water) placed between the plant and the lamp to prevent the temperature from changing due to the changing light intensity
• Heat using water bath (often used in Benedict’s test for reducing sugars)
• While using a knife use a solid surface to cut on, cut away from fingers
• The same type of plant/fruit may not be used; use same species
• Measurement Error (Use a graduated pipette)
• Water loss from tubes was not accounted for; cover the tubes
• A subjective/non-quantifiable variable was measured; measure a more quantifiable variable for accurate results
• Subjective Colour Nature (Use a colorimeter)
• No repeats; repeat the experiment 3 times and find the average (to

  remove anomalies)
• Mass/volume/size/shape of pieces is not the same
• Volume of each drop could vary; measure volume used instead of number of drops
• Temperature of water may change; maintain water temperature using a thermostatically controlled water bath
• Heat may be lost through gaps in lid/cork; make sure lid perfectly fits container
• When a variable (eg potato) is cut into smaller pieces, the smaller pieces are not measured into equal sizes
• Number of bubbles counted; measure volume of gas as the volume of each bubble may vary
• Uneven crushing; use a mortar and a pestle
• Reuse of syringe; (causes contamination) use a new syringe each time