1.07 Accuracy
and Precision
Virtual Laboratory
The Plan
• Review how to read instruments with
accuracy and precision
• Complete 1 Trial of each Part of the Virtual
Lab via screen share/slides with teacher
• Use the data to calculate density using the
rules of accuracy/precision and significant
figures
• Discuss the analysis questions
• Complete the lab on your own
Before we Begin
• Please open your virtual lab in the course
Create/Download the Lab Form
• Copy and Paste the lab form into a document or
download the pre-made form from the Chemistry
Resource Center
https://sites.google.com/site/chemistryflvs/
READY?
Why use Significant Figures?
• The benefit of this agreement is the
consistency in the way all scientists read
and record measurements.
• You will always know exactly how many
digits your measurement should have
based on the instrument used.
• You will be able to determine what the
smallest graduations were on the
instruments used by others when they
share their data with you.
Please Open the Virtual Lab
* We will begin with Part I: Density of an unknown liquid
How do you measure properly?
• When measuring you will determine the number of sig
figs by estimating one digit past the smallest
measurement, or graduation, on the measuring tool.
• How many digits should our measurement have here?
What is this measurement?
Use the slides starting with the largest to make the balance even.
Make your measurement and record data
Add liquid to the cylinder and read the amount
What do you think this volume is? Record in your Notes
Take the mass of the full cylinder
• Let’s read this together. Record in your Notes
Repeat!
• You will need to complete two more trials
of this Part on your own
• Let’s keep moving!
Go back to the Menu
Move on to Part II: Density of an irregular shaped object
Mass is EASY here
Fill cylinder and record volume
How many digits should we have? What is the volume?
Place Solid into Liquid ~ Read and Record
• This is called the “displacement method”
NEXT!
• You will need to complete two more trials
of this Part on your own.
• Let’s move on to Part III
Part III: Density of a regular-shaped solid
Mass the Object. Read and Record
• What is the mass?
Use the ruler to measure length, width and height
• Remember the number digits is the same for the
instrument regardless of the measurement
What about width?
• What is this measurement?
Complete length on your own!
• After you measure the length, click Data
Table to review all of your information.
• How do your measurements compare?
• Did you use the correct number of digits?
Trial 1 Data
Remember to go back and complete 2 more trials for each Part
Calculations
• We now need to use our data to complete
the density calculations
• Density is mass divided by volume or
D= M/V
• If you have downloaded the pre-made lab
form it is color coded and numbered to
help you
Part I Density
• Part I: Density of Unknown Liquid
– Calculate the mass (g) of the liquid for each
trial (A). (Subtract the mass (g) of the empty
graduated cylinder [1] from the mass (g) of
the graduated cylinder with liquid [3])
• mass of the liquid = [3] - [1] = (A) g
• Trial 1:
35.58 g- 25.02g = ? How many significant
figures should our answer have?
Remember: Rules for Addition/Subtraction
• The final answer cannot have more places
after the decimal than any of the given
measurements.
• The final answer cannot have a final digit,
which represents the uncertain or
estimated place, farther to the right than
any of the final digits in the measurements
used.
• SO.. Our answer should have the same
number of decimal places as our
measurements when adding/subtracting.
Calculate Density
– Calculate the density (g/mL) of the unknown
liquid (B) for each trial. (Divide the mass (g) of
the liquid calculated above (A) by the volume
(mL) of the liquid [2])
• (A) / [2] = (B) g/mL
• Trial 1: Using our mass we just calculated
divide by volume from the data table.
10.56g/8.32 mL= ? g/mL
• How many digits should our answer have?
Remember: Rules for Multiplication/Division
• Only given measurements affect the number of sig figs allowed
in the final answer.
• If you are only given one measurement, the total number of sig
figs in that measurement equal the total number of sig figs
allowed in your final answer.
• If you are given more than one measurement to be used in a
calculation, the final answer must be rounded to the same total
number of sig figs as the measurement that has the least total
sig figs.
• SO.. Our answer should have the same number of figures as the
least significant figures in our data set when
multiplying/dividing.
• How do we know how many significant figures our data has?
Print your reference sheet! You will need it for the whole
course
Rules to Determine Sig Figs
What’s our density?
10.56g/8.32 mL= ? g/mL
• This is division so we follow the rules for
division and use the least number of
figures.
• 8.32 has 3 figures
• Our answer is 1.27g/mL when properly
rounded
• Remember to include your units or your
measurement is just a number!
Rules for Rounding up or down
• 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 sig figs.
Density for Trial 2
• Part II: Density of Irregular-Shaped Solid
– Calculate the volume (mL) of the irregularshaped solid (C) for each trial. (Subtract the
volume (mL) of the water [5] from the total
volume (mL) of the water and solid [6])
• [6] – [5] = (C) mL
• Trial 1:
59.2 mL – 54.9 mL = ?
Check your rules!!
What’s the answer?
• Remember to follow the rules for
subtraction.
• volume= 4.3 mL
– Calculate the density (g/mL) of the irregularshaped solid (D) for each trial. (Divide the mass
of the solid [4] by the volume of the solid
calculated above (C))
• [4] / (C) = (D) g/mL
• Trial 1: 38.718 g/4.3 mL = ?
• 9.0 g/mL
Part III
-Calculate the volume (cm3) of the regular
shaped solid (E) for each trial.
(Multiply the length [8] cm × width [9] cm ×
height[10] cm for each trial to get the volume
in the unit cm3.)
• [8] x [9] x [10] = (E) cm3
• Trial 1: 5.24cm x 3.00cm x 2.50cm =?
• 39.3 cm3
Density for Part III
– Calculate the density (g/ cm3)of the regularshaped solid (F) for each trial. (Divide the mass
(g) of the solid [7] by the volume (cm3)
calculated above (E))
• [7] / (E) = (F) g/ cm3
• Trial 1: 25.33 g/39.3 cm3
• 0.64 g/cm3
Analysis Questions
• #1~ How would you determine the proper
number of significant figures of a liquid
using a graduated cylinder?
Hmm.. Well, what did we have to do to read
our two different cylinders in this lab?
Analysis Questions
• #2~ Can just one measurement be
considered precise? Can just one
measurement be considered accurate?
Explain your answers completely.
- What is accuracy?
Precision?
Analysis Questions
• #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?
What was our density for Part II?
What about Part III?
How did our density compare? What the object in
Part II more or less dense then Part III?
Congrats!!
• Remember to go back and complete two
more trials and calculations for all three
Parts of this lab before submitting to your
teacher.
• Great job!
Questions?