1.07 Accuracy and Precision
My Goals for this Lesson:

Distinguish between accuracy and precision.

Determine the number of significant figures in a measurement.

Read and record measurements with the correct number of significant figures.
I’m preparing to complete a lab on Accuracy and Precision
Measurements must include an indication of its uncertainty or reliability. This lesson discusses
how measurements are reported and used.
Learn About Accuracy and Precision
_________ is the closeness of a measurement to the ________ or accepted value.
________ refers to the _________ among a set of measurements made of the same quantity in
the same way, or _________.
Suppose the new guy on the crew measured the width of the opening three times and got the
measurements:
These values have _____ ______, because
These values have _____ ______,
they are _____ ________ .
they _____ ________.
470cm is the ________ or _____ ______.
These values are
Random error
and
No error
and
Systematic error
Watch the video Measuring and recording data
http://streaming.discoveryeducation.com/index.cfm?guidAssetId=B29DB0D2-0316-4AC8-BB55DFBDB77A938E
When you ______ with a ruler, a thermometer, or a balance, you are ______ by the precision of
the instrument and you must use the _______ properly and read the ______ carefully.
Lab measurements should be recorded. A _____ is a convenient way to ______ your _____.
To indicate the precision of a measurement, we use __________ __________. These are all the
numbers that can be read from an _________ —like a ruler, a thermometer, or a balance—and
one ________ number. The more significant digits, the more precise the measurement.
Significant Digits
When _______ a defined ______ with a ruler, there is a source of _____ and the measurement
may need _______ or rounding between two points. When doing this estimation, it is possible to
_________ or _________ the measured value, meaning there is a possibility for ____ ____.
Here is a pencil whose length lies between ___ and ____. With an intermediate mark, the ruler
shows in greater detail that the pencil length lies somewhere between ____ and _____.
Therefore, one may reasonably approximate that the length of the pencil is _____.
How long is it? The end of the pencil is between the seventh and eighth mark. The third digit in
the measurement must be estimated: 6.73 cm
The significant figures in a measurement include all the digits known with certainty plus one final
digit that is estimated and uncertain.
Estimating the final digit
The graduations on this
The graduations on this
The graduations on this
thermometer go in 10 degree
thermometer mark off every
thermometer mark off every
increments, estimate the ones
one degree and can estimate to
tenth of a degree and can
place. The temperature is
the tenths place:
estimate to the hundredths
6°C, 7°C or 8°C.
3.6°C, 3.7°C or 3.8°C.
place:
0.69°C, 0.70°C or 0.71°C.
Determining significant figures
Determining the significant digits in the measurement 12.34 g is easy; just count the total
number of digits. This number has four sig figs.
When a number includes zeroes, like 0.00450 L or 270 m, some additional rules are needed for
determining the sig figs.
Review Significant Figures—Rules and Practice – Text only version
Practice - Determine the number of significant digits in each of the measurements below.
1 - 203 cg , 2 - 0.001710° C, 3 - 80 mm, 4 - 0.0530 g, 5- 2.700 × 105 L
Significant figures in Calculations
After taking measurements, sometimes scientists need to use those measurements in ________.
These calculations may include ______ several measurements together or _______ mass by
volume to get the density of an object. The results of the calculations are not ________to
appear more or less accurate than the ________ _____________ used.
For __________ and __________, the answer should be rounded off to the same
number of total _______ ______ as in the measurement with the _______ significant figures.
For _______ and ________, the answer should be rounded off so that the number of
_________ is the same as in the measurement with the _________ decimals.
In order to follow the significant figures rules for calculations, it is sometimes necessary
to round your answer or add zeros to the end of the answer to give it the proper number of
significant figures.
Complete the examples
Now it is time to try some calculations on your own. Calculate the answer to each question
and enter it below. Remember to round your answer to the correct number of sig figs.
Question 1: 6.821 m + 1.4 m + 1.05 m =
Question 2:26.50 g ÷ 9.67 mL =
Question 3: Convert 17.8 m/s to the unit km/hr
Question 4:12.50 Kg — 17.80 Kg + 13.0 Kg =
Complete the Measuring Lab
Use the lab worksheet provided at the end of these notes. Copy and paste it into a new document.
Measurement is an important skill used for data collection and data analysis. Careful
attention to the accuracy and degree of uncertainty of each measuring device is necessary for
proper data collection. Significant figures are used to record or report measurements accurately.
01.07 Accuracy and Precision: Balance Lab Worksheet
Measurement

Measurement is an important skill used for data collection and data analysis. Careful attention to
the accuracy and degree of uncertainty of each measuring device is necessary for proper data
collection. Significant figures are used to record or report measurements accurately.

This laboratory activity will give you the opportunity to get more familiar with some of the basic
measuring devices that are common in chemistry labs. You will use the measurements
performed in this lab to calculate density.
Procedure

Access the virtual lab and complete the experiments.
Data


Below is the table that you will complete for the virtual lab. Either type your results into this table
or print the table from the virtual lab (it must be submitted to receive full credit for this
assignment.)
To print from the virtual lab.
1. Be sure the data table is viewable.
2. Right-click (PC) or Command-Click (Mac) on the table and select print.
Part I: Density of Unknown Liquid
Trial1 Trial2 Trial3
Measure Mass of Empty 10 mL graduated cylinder (g)
Measure Volume of liquid (mL)
Measure Mass of graduated cylinder and liquid (g)
Calculate the mass of the liquid for each trial
Calculate the density of the unknown liquid for each trial
Average
Part II: Density of Irregular-Shaped Solid
Trial1 Trial2 Trial3
Measure Mass of solid (g)
Measure Volume of water (milliliters)
Measure Volume of water and solid (milliliters)
Calculate the volume of the irregular-shaped solid for each trial
Calculate the density of the irregular-shaped solid for each trial
Average
Part III: Density of Regular-Shaped Solid
Trial1 Trial2 Trial3
Measure Mass of solid (grams)
Measure Length of solid (centimeters)
Measure Width of solid (centimeters)
Measure Height of solid (centimeters)
Calculate the volume of the regular shaped solid for each trial
Calculate the density of the regular-shaped solid for each trial
Average
Calculations
Show all of your work for each of the following calculations and be careful to follow significant figure
rules in each calculation.
Part I: Density of Unknown Liquid
1. Calculate the mass of the liquid for each trial. (Subtract the mass of the empty graduated
cylinder from the mass of the graduated cylinder with liquid.)
 Trial 1

Trial 2

Trial 3
2. Calculate the density of the unknown liquid for each trial. (Divide the mass of the liquid
calculated above by the volume of the liquid.)
 Trial 1:

Trial 2:

Trial 3:
Part II: Density of Irregular-Shaped Solid
3. Calculate the volume of the irregular-shaped solid for each trial. (Subtract the volume of
the water from the total volume of the water and solid.)
 Trial 1:

Trial 2:

Trial 3:
4. Calculate the density of the irregular-shaped solid for each trial. (Divide the mass of the
solid by the volume of the solid calculated above.)
 Trial 1:

Trial 2:

Trial 3:
Part III: Density of Regular-Shaped Solid
5. Calculate the volume of the regular shaped solid for each trial.
(Multiply the length × width × height for each trial to get the volume in the unit cm3.)
 Trial 1:

Trial 2:

Trial 3:
6. Calculate the density of the regular-shaped solid for each trial. (Divide the mass of the
solid by the volume calculated above.)
 Trial 1:

Trial 2:

Trial 3:
Questions and Conclusions:
1. How would you determine the proper number of significant figures of a liquid
using a graduated cylinder?
2. Can just one measurement be considered precise? Can just one measurement be
considered accurate? Explain your answers completely.
3. In parts II and III of the lab you used different sized objects in each trial. Compare
the density values that you calculated for these items, how do the three trials
compare?