Honors Chemistry
Chapter 3
Objectives—Chapter 3

Understand and be able to explain the nature of
measurement







Qualitative, quantitative
Accuracy, Precision, Error
Demonstrate a knowledge of significant figures through
problem solving.
Demonstrate an ability to solve problems with scientific
notation
To use proper scientific (metric) units.
Be able to calculate density of various objects
Convert temperature to a different scale.
Vocab—give example of
formula when appropriate!
Scientific Notation
 Precision
 Accuracy
 Error
 Kelvin
 Density
 Metric Units

Joke of the day
what does a chemist say when he finds two
helium molecule?
 HeHe

What is wrong with this
picture?




A group of Civil Engineers were at a conference being held
in Central Australia. As part of the conference
entertainment, they were taken on a tour of the famous
rock, Uluru. "This rock", announced the guide, "is 50 000
004 years old."
The engineers - always impressed by precision in
measurement - were astounded.
"How do you know the age of the rock so precisely?" asked
one of the group.
"Easy!", came the reply. "When I first came here, they told
me it was 50 million years old. I've been working here for
four years now."
Rules for Scientific
Notation

1.
Example: 3427g to scientific notation.
Move the decimal point until the ”root” number is
between 1 and 10

2.
3.
3427  3.427
Count the number of places the decimal moved.
Move to the left.

Multiply the “root” number times 10 raised to the
positive power that the decimal moved
 3.427 x 103
Rules for Scientific
Notation---Part B

1.
Example: 0.003427g to scientific notation.
Move the decimal point until the ”root” number is
between 1 and 10

2.
3.
.003427  3.427
Count the number of places the decimal moved.
If move to the right.

Multiply the “root” number times 10 raised to a negative
power = number of places moved.

0.003427  3.427 x 10-3
Recall--Exponents
am x an = a (m+n)
 am = a (m-n)
an
 (am)n = amn


1/an= a-n
Scientific Notation
• Addition and subtraction
– Exponents must be the same.
– Rewrite values with the same
exponent.
– Add or subtract coefficients.
Uncertainty in
Measurement

So what uncertainty would you have in a
qualitative (observation—color, smell…)
measurement?

What about quantitative (data taken with an
instrument—thermometer, scale…)
measurement, what would give rise to
uncertainty?
Types of Error
Random error is the error that a
measurement has an equal probability of
being high or low.
 Systematic error in the same direction each
time, either high or low.

Uncertainty in
Measurement
Certain v. uncertain in measurement.
 Always measure one beyond the scale of the
instrument
 The last digit is uncertain in a measurement
 In class demo. Let’s read this graduated
cylinder and see what everyone gets.

Precision and Accuracy
Accuracy is the agreement between a data
measurement and the true measurement.
 Precision refers to the degree of agreement
between several measurements.

Precision v. Accuracy
Evaluating Error

How do you measure discrepancy between
the true and experimental value?

Percent error—measures the magnitude of
error.

Percent Error= |true-experimental| x100%
true
Significant Figures
Error and Significant
Figures
The convention is to read a measurement
with certain numbers and one uncertain
number.
 This allows a scientist to indicate precision
within their data.
 Only as good as your least precise
instrument!!!

Rules for Counting
Significant Figures

Nonzero integers always count as
significant figures.
 3456
has
 4 sig figs.
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18
Rules for Zeros-#1

Leading zeros do not count as significant
figures.
0.0486 has
 3 sig figs.

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19
Rules for Zeros-#2

Captive zeros always count as
significant figures.


16.07 has
4 sig figs.
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Mifflin Company. All rights
20
Rules for Zeros-#3

Trailing zeros are significant only
if the number contains a decimal
point.




9.300 has
4 sig figs.
9,300 has
2 sig figs
21
Exact Numbers

Exact numbers count, they have an
infinite number of significant figures.
12 apples,
 1 inch = 2.54 cm, exactly

22
Rules for Counting Significant Figures
- Overview
1. Nonzero integers (always count)
2. Zeros
leading zeros (don’t count)
 captive zeros (always count)
 trailing zeros (sometimes count)

3. Exact numbers (always count)
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23
Rules for Significant Figures in
Multiplication and Division

Multiplication and Division: # sig figs in
the result equals the number in that has
the least sig figs.
 5.4meters =
 41.58 square meters  42 (2
sig figs)
 7.7meters
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24
Rules for Significant Figures in
Addition and Subtraction

Addition and Subtraction: # sig figs in the
result equals the number of decimal places
in the least precise measurement.
 6.8
+ 11.934 =
 18.734  18.7 (3 sig figs)
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25
Exponential Notation and
Scientific Figures

The Advantage of writing 1.00 x 102 in this
type of notation:
Easy to identify the sig figs.
 Convenient—a lot less zeros to write.

Nature of Measurement

Measurement - quantitative observation
consisting of 2 parts



Part 1 – number
Part 2 - scale (unit)
Examples:
20 grams
 6.63   Joule seconds

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27
SI System (King Henry Drinks Much
Dark Chocolate Milk)

Units of measurement
SI System
King Henry Drinks Much Dark Chocolate
Milk
 Allows for easy comparison of data across
the world.
 Based on 10 which makes conversions
simple and consistent

Most important units to
remember in chemistry

Volume is in mL or Liters


Mass is in grams


(1000ml = 1L)
(1kg = 1000g or 1g =1000mg)
Temperature Kelvin or Celsius

(273 + C = K)
Celsius and
Kelvin Scale
K = C + 273
 C = K - 273

Density
The mass of a substance that occupies a
given volume.
D= Mass
Volume
 The SI standard unit of volume is the cubic
meter (m3) but it is more practical to use
g/cm3 for liquids and g/dm3 for gases.
 Note cm3 = mL

Dimensional Analysis
Using Conversion Factors to Solve Problems!
What is
it?
How do I make a
conversion factor?
Using Conversion Factors or
proportionality to allow you
to change the unit without
changing the amount.
Using 2 units that equal the same amount or
quantity you make a fraction or "factor"
Example: 1 dollar = 4 quarters = 10 dimes = 20
Nickels = 100 pennys
1 dollar or 4 quarters
4quarters
1dollar
How do I use a
conversion
factor?
Example) 1000g or 1kg
1kg
1000g
.
How many quarters are in $ 3. 75?
$1 = 4 quarters
1 dollar or 4 quarters
4quarters
1 dollar
Start with given amount that is not
a conversion.
Kilo = 1000 base units
Hecta = 100 base units
Deka = 10 base units
Base Unit: meter, Liter, Grams
1 base unit = 10 deci
1 base unit = 100 centi
1 base unit = 1000 milli
How do I use a
conversion factor
cont..
How do I decipher a
problem?
How do I start a
problem?
$3.75
•
•
•
•
•
4 quarters =15 quarters
1$
Use the factor that
allows you to cancel out
the unit given and get
the desired unit.
1st: Identify Knowns
2nd: Identify Unknowns
3rd: Do I need to make any
conversions? Ifso what
conversion factors do I need?
If it is an equation, and
the units match, just
plug it in and solve for
unknown.
Make Sure Units Match!
If they don't match, use
conversion factors to
convert units.