Chemistry- Laboratory #1
Name: ____________________________ Partner: ______________________________
ACCURACY AND PRECISION IN MEASUREMENTS
Introduction:
In this experiment, the volume of the graduated cylinder up to the 50-mL
graduation will be calculated using the measurements of its internal diameter and height
to the graduation. The mass of measured volume of water will be calculated from its
density and then determined by weighing. The error and percentage error in each of the
experiment will be calculated on the basis of the accepted value.
Experimental error = observed value - accepted value
% Error =
(accepted value-experimental value) x 100
accepted value
The sign of the experimental error and the percentage error may be either positive (the
experimental result is too low) or negative (the experimental result is too high).
Safety Alert/MSDS:
Before beginning part of the experiment, take the necessary safety precautions.
Wear safety goggles, and apron. It is important to use good safety techniques while
conducting experiments.
Objectives:
1. 1. To learn the importance of accuracy and precision in scientific
measurements and the difference between them.
2. 2. To calculate values from experimental measurements.
3. 3. To understand percentage error.
Materials List:
Balance
cylinders
Celsius thermometer
ruler- metric
lead) Water
100 mL and 10 mL graduated
100-mL beaker
Metal shot (aluminum, copper or
Pre Lab Questions:
1. 1. What is the formula for the calculation of density?
__________________________
2. 2. What does percentage error mean? What is the formula used to calculate
this quantity?
______________________________________________________________
Procedure 1:
1. 1. Examine the centimeter scale of the plastic ruler. What are the smallest
divisions? To what fraction of a centimeter are you expected to be able to
make a measurement with such a ruler?
2. 2. Using the ruler, measure the inside diameter of the 100-mL graduated
cylinder. Similarly, measure the inside height of the cylinder to the 50-mL
graduation. Record these measurements in Data Table 1.
Data Table 1
Inside diameter of graduated cylinder
Inside height of graduated cylinder (h)
Chemistry Honors- Laboratory #1
Name: ____________ Partner: ____________ Date: ____________ Period:
____________
cm
cm
Procedure 2:
1. 1. Examine the gram scale of the triple-beam balance. What are the smallest
divisions? _________
2. 2. Using the balance, determine the mass of the dry 100-mL cylinder. Record the
mass in Data Table 2. Fill the beaker half-full of water and determine its temperature
to the nearest degree. Look up the density of water for this temperature and record
both the temperature and water density. Fill your graduated cylinder to some value
between 10 and 15 mL; accurately read and record the volume. Determine the mass
of the water plus the cylinder. Then, record this value in Data Table 2. Save the water
in the graduated cylinder for use in Procedure 3.
Data Table 2
Mass of empty graduated cylinder
Temperature of water
Density of water
Volume of water
Mass of graduated cylinder + water
g
c
g/cm3
mL
g
Procedure 3:
1. 1. Add a sufficient quantity of the assigned metal shot to the cylinder containing the
water (from procedure 2) to increase the volume by at least 5 mL. Determine the
volume and then the mass of the shot, water, and cylinder, and record your
measurements in Data Table 3.
2. 2. At the end of the experiment, all the equipment back in the lab drawer should be
clean, dry and arranged in an orderly fashion. Ask your teacher for the proper waste
container for the metal shot. Wash your hands before leaving the lab.
Data Table 3
Volume of water (from Procedure 2)
Mass of water + graduated cylinder
Volume of metal and water
mL
g
mL
Mass of metal + water + graduated cylinder
g
Calculations:
Show your calculations. Place your answers in the appropriate Calculations Table.
Part I:
a. Calculate the volume of the cylinder to the 50 mL graduation (v = 3.14 (r2 )(h).
b. Assume the accepted value is 50 cm3. Calculate the error and percentage error.
Calculations Table
Volume of graduated cylinder (computed)
Error
Percentage error
cm3
cm3
%
Part 2:
a. Calculate the mass of the water as determined by the balance.
b. Calculate the mass of the water from its measured volume and its density (m= d X
V).
c. Using the mass determined by the use of the balance as the accepted value,
calculate error and percentage error.
Calculations Table
Mass of water (observed)
Mass of water (calculated: m= D x V)
Error
Percentage error
g
g
g
%
Part 3:
a. Use volume displacement to determine the volume of the metal.
b. Determine the mass of the metal.
c. Calculate the density of the metal.
d. Look up the specific gravity (density) of the metal in a handbook. Then calculate
error and percentage error for the density of the metal shot you determined in .
Calculations Table 3
Volume of the metal
Mass of metal
Density of metal (computed)
Density of metal (accepted)
Error
cm3
g
g/cm3
g/cm3
%
Percentage Error
Post-Lab. Questions:
1. What value of a measurement must be available if the accuracy of a measurement is
to be determined?
2. What are the possible sources of experimental errors in this experiment?
%