How is Lab Glassware Used For Students_113_revised S19v3-1.pdf

Arizona State University CHM 113 S19 School of Molecular Sciences 1
How is Lab Glassware Used?
BACKGROUND
The glassware and equipment/apparatus used in our general chemistry labs to measure
a quantity has inherent limitations. There are also differences in how people make the
same measurement. Uncertainties always exist in measured quantities and we use the
terms accuracy and precision to better understand them.
Accuracy is how close a measured value is to the actual (true) value. The degree of
uncertainty in any measured value will depend on the apparatus or glassware used.
Precision is measured by repeating measurements under unchanged conditions and
comparing how widely the results vary. The precision of the measurements may be
expressed qualitatively or by calculations in terms of the standard deviation.
When we perform a measurement in the laboratory, we should remember that there is
always some uncertainty in the last digit reported for that measured quantity. All digits of
a measured quantity, including the uncertain one, are called significant figures .
A more precise measuring device allows for measurements to be made with more
significant figures. The precision of an experimental result is no more precise than the
measuring device used with the least precision.
√
Precision
√
Precision
❌
Precision
❌
Precision
√
Accuracy
❌
Accuracy
√
Accuracy
❌
Accuracy
Percent Error
A percent error calculation tells us about the accuracy of an experimental measurement
(or an experimental result).
% ????? =
|?????𝑖????𝑎? 𝑉𝑎??? − 𝐴??????? 𝑉𝑎???|
𝐴??????? 𝑉𝑎???
× 100

Arizona State University CHM 113 S19 School of Molecular Sciences 2
Performing Measurements Using Common Glassware
Lab equipment used to measure volumes varies in size, types, and purpose. Some
common glassware used in lab include: beakers, burets, graduated pipets, graduated
cylinders, and volumetric flask.
Figure 1. Some common glassware equipment used in lab .
Each of these pieces of glassware are commonly used in the laboratory. Each type of
glassware is used to either hold or deliver certain volumes of liquids, but they vary in the
amounts and accuracy with which they can measure these volumes.
The glassware used to measure volumes has some degree of uncertainty, therefore,
when reading a measurement you should estimate one more digit past the smallest
division on the measuring device being used. For example, a buret or a 10mL graduated
cylinder has gradations of a tenth of a milliliter (0.1 mL), therefore, volumes should be
estimated to the hundredths place (0.01 mL).
When measuring out a specific volume using graduated glassware, be sure to line up the
desired volume line with the bottom of the meniscus.

Arizona State University CHM 113 S19 School of Molecular Sciences 3
Figure 2. Graduated cylinder reading
Some glassware such as volumetric flasks and volumetric pipettes only have a single line
to indicate volume. This is because they are made to measure just one specific volume
and will have two significant figures after the decimal point (i.e. 10.00 mL and 50.00 mL).