Name
____________________________ Block _________ Date __________
Precision
Fine Tuning
Chemcatalyst:
Do you believe
everything you read? How would you
check up on facts you read on the internet?
Part
I, Problem:
There are rules
regulating how many digits you are allowed to document while doing chemical
measurements and calculations. We need
to make sense of those rules.
Materials:
lab
stations with various measurement tools.
Lab
Safety:
Wear goggles – we are using
glassware.
Be safe – keep aisles clear.
Procedure:
There are a number of
lab stations around the room. Your job
is to visit each lab station and correctly measure the item identified. You are to enter your measurement in the
data table. Once this is done, circle
the digit which you estimated (guessed, if any). It might be a good idea to have your teacher
check your data table after you have visited the first few stations.
Data
Table: significant figures for several stations of measurement tools.
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Questions: - Answer each of these
questions to the best of your ability.
1. To what decimal place
can mass be measured using the triple beam balance?
2. To what decimal place
can temperature be measured on our thermometers?
3. What determines to how
many decimal places volume can be measured?
4. Significant digits are
those you wrote down off the tools in the lab.
What generalization can you make as to when non-zero digits are
considered significant?
5.
If
you were asked to measure a volume of 20.5 mL, what size graduated cylinder
would you use? Explain your answer.
6.
Write
a rule (or set of rules) which state(s) when zeroes are significant and when
they are not. Provide an example for each situation.
Name
_________________________ Block _____ Date
_______________
Homework
Convert the following numbers from scientific
notation to standard English or English to scientific notation. Then underline
all of the significant digits.
1) 0.0084876
2) 30393000000
3) 0.004059586
4) 100
5)* 1
6) Write the rules of
math in chemistry we learned yesterday.
7) Which tools from the
“Precision Fine Tuning” lab measured volume?
8) Which tools from the
“Precision Fine Tuning” lab measured mass?
9) Which tools from the
“Precision Fine Tuning” lab measured a non-SI unit?
10) Explain the
difference between “precision” and “accuracy”?
If you were counting your money, which would you be more concerned
about, precision or accuracy? Explain.
Working With Math in Chemistry Notes
UNITS –
RULE #1 – NEVER WRITE A
NUMBER IN CHEMISTRY WITHOUT A UNIT. IT
WILL BE WRONG!
Liters (L) – Volume, you will also see cc, cm3,
dm3, (anything cubed is volume!!!!!)
Meter (m) – length, all lengths will be in meters or its
metric derivatives (mm, nm)
Gram (g) – mass, all masses (we can use “weight” in this
class for mass) will be in grams or its metric derivative (mg, kg)
Please notice that L is capitalized, m and g are
not. It does matter!
A few helpful hints:
1 gram of water = 1 mL = 1cm3 (We defined these terms to make your life
easier!)
1kg of water = 1L = 1dm3 (this is the same
statement as above with larger units)
Memorize the following –
you will be asked to know these on just about every quiz and exam. Please notice that they are lined up to make
memorization easier. (The blank boxes
are units not often used in chem. so I left them out to make your life easier.)
1,000,000nm = 1m 1000mm
= 1 m 100cm = 1m 10dm = 1m 1000m
= 1km
1000ml = 1L 10dL
= 1L
1000mg = 1g 1000g
= 1kg
MAKING MEASUREMENTS –
RULE #2 – ALWAYS
ESTIMATE 1/10 OF THE SMALLEST MARK ON THE TOOL YOU ARE USING.
If you are using a graduated cylinder that is marked
every 1mL, write an estimated digit in tenths
of
a mL.
If
you are using a beaker marked every 50mL, estimate a digit to 5mL.
Digital
balances have 1 estimated digit given to you on the display.
VOCABULARY –
Precise measurements give you the same
number every time you measure.
Accurate measurements give you a number
that is very close to the actual number.
Significant digits (sig. figs.) – any
number you record off a measuring tool (including the
estimated
digit)
ATLANTIC/PACIFIC RULE
(for sig figs.) - count digits in a
number from the first non-zero number.
If a decimal point is Present, count from the Pacific
side (left). If a demical is Absent,
count from the Atlantic side (right).
Example: How many significant
figures are present in the following numbers…
1200mL
Decimal is absent, count
from the first non-zero from the Atlantic side.
2 sig figs.
0.0831 L
Decimal is present, count
from the first non-zero from the Pacific side.
3 sig figs.
Zeros inside a number are always counted.
101.3kPa has 4 sig figs.
Math
in chemistry notes – Day 2.
Calculating with Sig
Figs –
RULE – WHEN MULTIPLYING
OR DIVIDING, THE ANSWER CAN ONLY HAVE THE NUMBER OF SIG FIGS AS THE FEWEST SIG
FIGS IN THE PROBLEM.
RULE – ONLY MEASUREMENTS
COUNT. (1000mm – 1m is not counted as a
sig fig because you did not measure these number, they are a definition.)
Ex.
0.75m x
100.3m = 75.225m2
I
can only write 75m2 because 0.75m only has two sig figs.
SCIENTIFIC NOTATION
Ex. How would you write 602,200,000,000,000,000,000 in scientific
notation?
602,200,000,000,000,000,000
is the most
famous number in chemistry. But it is
too messy to write. So we use scientific notation.
HOW TO WRITE A NUMBER IN
SCIENTIFIC NOTATION
1. Move the decimal
until there is one digit on the left of the decimal.
6.022
2. Write x10 then the
exponent equal to the number of spaces you moved your decimal.
6.022 X1023
3. If the original
number was bigger than one, the exponent is positive. If the number was smaller than one, the exponent is negative.
Helpful hints
4. Using your
calculator. – Do not use x
10 yx 23
, your
answer will often be wrong.
Your calculator has a
button marked EXP or EE.
a. Set your calculator to SCI mode.
b. write 6.022 EXP 23
Your calculator reads EXP as x10x.
CACLULATE PERCENTS – We
will do this in many ways this year.
Percent = Part x 100
Whole
Ex. What was your grade
on homework.
You earned x100 7 x100 = 70%
Possible 10