# Day 1 Introduction to Chemistry and Measurement ```Can you hit the bull's-eye?
Three targets
with three
arrows each to
shoot.
How do
they
compare?
Both
accurate
and precise
Precise
but not
accurate
Neither
accurate
nor precise
Can you define accuracy and precision?
Accuracy:
A measure of how close a
measurement comes to the
actual or true value of whatever
is measured.
Precision:
A measure of how close a series
of measurements are to one
another.
Three students measure the volume to be 10.2
ml, 10.3ml and 10.4 ml .
• If the actual value of volume is 10.5ml
• Were they precise?
No
• Were they accurate?
No
Weight Trial
Result
1
2.486g
2
2.487g
3
2.487g
4
2.487g
5
2.487g
Are these values precise?
Yes
High precision among several
measurements is an indication
of accuracy only if systematic
error is absent .
Calculates the error in a measurement
Table T of Reference Tables
Accepted value = the correct value based on
reliable references.
Experimental value = the value measured in
Error = accepted value – exp. value
Can be positive or negative
Percent Error = the absolute value of the error
divided by the accepted value, then
multiplied by 100%
Problem:
What is the percent error of a
measured value of 187 lb. if the
person’s actual weight is 175
lb.?
Solution:
187 lb -175 lb X 100%
175 lb
Percent Error = 12 X 100%
175
.0685 X100% = 6.85%
Problem:
Measured density from lab
experiment is 1.40 g/mL.
The correct density is
1.36 g/mL.
• Find the percent error.
From an experiment the data for the
molar mass of oxygen is 30.0g. From
the periodic table the mass is 32.0g.
What is the percent error?
30.0g – 32.0g
X 100% = 6.3%
32.0g
A technician experimentally
determined the boiling point for
sodium (Na) to be 1105 K.
Calculate the percent error.
Solution = 4.4%
```