1. Write the number 295 to two significant figures.
2. How many significant figures does the number
610. have?
3. Use the ruler below to determine the length of the
strip of metal using correct number of significant
figures.
Remember
When a measurement is recorded properly, all
of the digits that are read directly (certain)
and one estimated (uncertain) digit are called
significant digits. The number of allowable
significant digits is determined by the marks
or gradations of the instrument. Sometimes a
“0” is the estimated digit and must be
recorded.
MORE THAN 200,000 PEOPLE SIGN UP TO DIE
ON MARS
FIVE MONTHS AFTER THE NETHERLANDS-BASED PRIVATE SPACEFLIGHT
PROJECT MARS ONE ANNOUNCED IT WOULD BEGIN ACCEPTING
APPLICATIONS FOR A ONE-WAY TRIP TO THE RED PLANET, 202,586
PEOPLE FROM MORE THAN 140 COUNTRIES HAVE SUBMITTED VIDEOS
EXPLAINING WHY THEY SHOULD BE CHOSEN FOR THE MISSION.
THE FIRST OF FOUR SELECTION ROUNDS ENDED AUGUST 31. NOW, THE
MARS ONE SELECTION COMMITTEE WILL SPEND THE NEXT SEVERAL
MONTHS NARROWING DOWN THE APPLICANTS. THERE ARE EVEN
PLANS TO LAUNCH A REALITY TV SHOW TO CHOOSE THE FINAL
CANDIDATES. THE GOAL IS FOR 24 TO 40 PEOPLE TO BEGIN A SEVENYEAR TRAINING PROGRAM IN 2015. THEN, WORKING WITH THE
PRIVATE SPACE FLIGHT COMPANY SPACEX, MARS ONE HOPES TO SEND
THE PROSPECTIVE MARTIAN SETTLERS TO THE RED PLANET IN TEAMS
OF FOUR, BEGINNING IN 2023.
READ MORE ABOUT WHAT A HUMAN MARS COLONY WOULD BE LIKE
HERE. THEN CHECK OUT OUR Q&A WITH A LOS ANGELES-BASED VIDEO
GAME DESIGNER WHO APPLIED FOR THE PROGRAM EARLIER THIS YEAR.
Quiz on Friday
•
•
•
•
Scientific Notation
Significant Figures
Metric Conversions
Accuracy and Precision
Video
http://www.youtube.com/watch?v=xJG0ir9nDtc
&list=PL50300782DFB0AECF
After watching the video, what are 10 safety
procedures you learned? Be prepared to
discuss.
Video
http://www.youtube.com/watch?v=6aK2CKrdjb
E
After watching the video, what are 10 safety
issues that you saw? Be prepared to discuss
them.
Books Closed - QUIZ
1. What should you be wearing on your
face at all times during the lab?
2. Where is the eye wash station located
in the room?
3. What are two things you should
always do before leaving the lab?
4. What should you do if glassware
breaks or glassware is cracked?
5. What is never allowed in the lab?
NOTE OF THE DAY:
THIS WEEK IN SCIENCE ASSIGNMENT
Every week two people will be selected to present a current
news topic in the world of science. Research something that
interests you and is appropriate for class. Give approximately
a two minute presentation on your findings and be prepared
to answer questions. Students will present every Tuesday
until Christmas.
Marking Guide /5
Student is knowledgeable of topic. DON’T just read your
summary! /1
Student includes what it is, why they find it interesting, and
where they got their information. /3
Student hands-in a minimum of 1 page (double – spaced)
write up. This includes the what, the why and the source. /1
TOMORROW
When you come into class the lab instructions will be
on your desk. It is expected of you to read over the
instructions and become familiar with the procedure.
This is in place of the QUESTION OF THE DAY.
FRIDAY
On Friday there will be a quiz on scientific notation,
metric conversions, significant figures, and accuracy
and precision.
Yesterday
If you weren’t here yesterday then you missed a
quiz. It is up to you to come see me after class in
order to set up a time to write the quiz.
Powerpoints are on the wiki.
chemistry202013.wikispaces.com
Precision, Accuracy, and Type of Error
Precision, Accuracy & Types of Error
Precision refers to how close a series of measurements are
to one another; precise measurements show little variation
over a series of trials but may not be accurate.
Accuracy refers to how close a measured value is to an
accepted value.
Imagine you are doing an experiment with 10 individual
readings. To have high precision those 10 readings all have
to be close to each other. To have high accuracy those
readings must be close to the "true value" or the correct
answer.
Error
There are two types of error that are commonly
encountered in the lab random and systemic error.
Random error occurs for many reasons and is random.
Each time you take a measurement you have to decide
what that measurement is and each time it is and each
time it can change slightly. To compensate for random
error multiple trials are completed. While you may still
take measurements differently each time the average
will be a balance of high or low readings. Using
averages is the only way to get low precision but high
accuracy measurements.
The second type of error in the lab is systematic error. This
error arises in uncalibrated equipment or unfamiliarity with
that equipment. If you were to use a scale that you did not
calibrate and was off by 1.000 gram then all your results
would be off too. There would also be error if you were to take
readings in a burette wrong (from the top of the meniscus
instead of the bottom).
Average
Average, also referred to as the mean, is calculated by taking
the sum of a set of numbers and dividing it by how many
numbers you have. For example, if I want to calculate the
mean of 12, 13, 14, and 20 I would:
Step 1: Find the sum of the numbers.
12 + 13 + 14 + 20 = 59
Step 2: Divide the sum by the amount of numbers used.
59 ÷ 4 = 14.75
14.75 is the average or the mean.
Diameter
Volume
Common measurement of volume in chemistry is in mL or L.
When measuring volume it is important to know what the
units the instrument you are using uses.
When measuring volume you DO NOT measure from the
highest point of the liquid. Liquid usually forms a half moon
which can make it difficult to read. This half moon is called
the meniscus. When taking a measurement it is important to
measure form the bottom of the meniscus, or at the lowest
point of the half moon.
In your notes draw a picture of this in the box provided
Density
Density is a widely used characteristic used to characterize a
substance. It is the amount of mass per unit of volume, for
example, 1.00 g/mL. Or, density can be thought of as the
compactness of the substance. Keep in mind that density
changes based on the temperature (think of ice) so the
temperature should be reported as well. For example ethanol's
density at 25 Celsius is 0.79 g/mL.
Calculating Density
Density is calculated by dividing the mass of a
substance by the volume of the substance, this is
where g/mL is derived.
For example, if the mass of a substance is 13.4 g and
the volume of the substance is 20. ml, then what is the
density?
Calculate the density of a substance whose mass is
110. g and volume is 119 ml.
Calculating Percent Difference
Percent difference helps us to determine how
accurate our measurements are.
Percent Difference measures accuracy.
AcceptedValue  ExperimentalValue
PercentDifference 
 100%
AcceptedValue
Or, think of as “How much you’re off by, divided by
actual.”
Example: Jim is working in the lab to determine the density of
water at 25 °C. He makes three measurements which are
0.8972 g/mL , 0.8974 g/mL & 0.8973 g/mL. He wants to
know how close he is and find out that the true density is
0.9970 g/mL. Is Jim's work accurate or precise?
What is the percent difference if you measure the density
of an object to be 32g/cm3 and the actual density of the
object is 36 g/cm3.
Lab Report
Purpose:
• What are you trying to determine, prove, observe, etc?
Materials:
• What materials or equipment are you using to complete your
purpose?
Procedure:
• What are the steps are you completing to achieve your
purpose? In many cases this section will just need a reference
to the lab handouts.
Experimental Data:
• What results did you get? This section does not explain the
results, just recording of what you measured or saw during
the experiment. This is where you will make all your
experimental observations.
Questions:
• Answer the questions using the experimental
data.
Conclusion:
• Did you get the answer you were looking for?
What was it? If there are questions on the lab
handout make sure those are answered in your
conclusion or listed somewhere. This section
should also include any sources of error.
Equipment
Name
Beaker
Burette
Picture
How do I use it?
Beaker is used to
measure volume of a
liquid. Pour the desired
amount of liquid to the
desired line.
Use the stopcock to
dispense the desire
amount of liquid.
Note: The 0.00 ml mark
on a burette is at the top
and not the bottom.
Keep this in mind when
you are measuring
liquids using this
instrument.
Balance
Graduated Cylinder
Used to measure the
mass of an object or
substance. Make sure
the scale is zeroed
before massing an
object.
Used to measure the
volume of a liquid in
ml. This instrument
should only be used
when it is placed on a
flat surface.
Thermometer
When taking the
temperature of a liquid
you want to ensure that
the entire bottom of the
thermometer is
submerged in water
and the thermometer is
not touching the
glassware. Using a
thermometer,
temperature is
measured in 0C.