Lab 3
Determination of Density
of Liquids and Solids
Uncertainties in Scientific Measurement
Systematic Errors
(Determinate Errors)
• Bias an experimentally determined value in one
direction
• Have a definite value and an assignable cause
• Influence experimental accuracy
• May be avoided altogether
OR
measured and corrected (“correction factor”)
Uncertainties in Scientific Measurement
Random Errors
(Indeterminate Errors)
• Errors may be high or low
• Arise from uncertainties in measurement that are
either unknown or uncontrollable by the
experimenter
• Effect experimental precision
Reducing Your Error
(Mass measurements)
• Do not touch the object to be weighed with
bare hands
• Clean the outside of object to be weighed
(wipe; wash & dry), prior to weighing
• Tare the balance to avoid recording an
irrelevant mass (e.g., the container)
Reducing Your Error
(Volume Measurements)
• Carefully read volumes: Avoid parallax error!
• Carefully transfer fluids (or an object into fluid)
to avoid splashing; tilt container containing the
fluid for easier transfer
• Gently tap side of fluid container to dislodge air
bubbles
Parallax Error occurs when you read the
volume anywhere BUT at the “bottom” of the
meniscus (for most liquids) or “top” of the
meniscus (for mercury).
CORRECT (“true”)
reading is at the
meniscus (“curve”) in the
center of the cylinder.
Actual Densities
• Rubbing alcohol and Rubber stopper:
correct densities will not be given
• Metal: correct densities of all unknowns
will be posted
Remember significant figures!!!!
Do problem and adjust (round)
final answer.