Accuracy and
Precision
Accuracy
O
refers to how close a measured or
calculated value is to the correct or
accepted value of the quantity measured
O the closer the darts land the the bull’s
eye the more accurate they are thrown
Precision
O
refers to how close repeated
measurements of the same quantity are
to each other
O the closer the darts land to one another
the more precisely they were thrown
Accuracy and Precision
O Scientists repeat measurements as a
way to reduce uncertainty. If a number
of measurements are very close to one
another, they have good precision and
the scientist can be assured that the
average of the measurements is likely
close to the actual value (accurate)
Percent
Error
Percent Error
O
the accuracy of an individual value or of
an average experimental value can be
compared quantitatively with the correct
or accepted value by calculating percent
error
The Ideal
Gas Law
The Ideal Gas Law
O
a gas sample can be characterized by
four quantities:
O volume
O pressure
O temperature
O moles
O
moles (mol) is a unit that scientists use
to measure the mass of an object
O 3.00 moles of little green peas would
cover 250 planets the size of Earth
1.00 m deep in green peas
O 1.00 mole of basketballs would fill a
bag the size of the Earth
O the ideal gas law is the mathematical
relationship among pressure, volume,
temperature, and the number of moles
of a gas
O
in the ideal gas law the constant R is
known as the ideal gas constant
O R= 0.082058 L x atm / (K x mol)