Transcript Chemistry, Matter and Measurements

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What is Chemistry?
 AKA the central science
 The study of matter and the changes that it undergoes
 Used in everything!
What’s it matter?
 Matter – anything that has mass and volume
 Mass – amount of matter
 Volume – space it takes up
 DON’T confuse mass with weight
 Weight – gravitational pull on a mass
 If I put you on the moon you weight less, however you
have the same mass
 If I cut your arm off you have less mass and
weight……(and blood pressure)
Macro vs Micro
 Much of what happens in chemistry is on the
macroscopic level
 What you can see, touch, smell etc.
 However , a lot happens on the submicroscopic level
 To be seen we must make models
 Model – a visual, verbal or mathematical explanation of
data (turning Micro  Macro)
Base Units
 Use international system of units (SI)
ame
 Manipulated by
powers of 10
Symbol
Distance
Mass
meter
kilogram
m
kg
Time
second
s
Electrical
current
ampere
A
Temperature kelvin
K
Amount of a
mole
substance
mol
lumination candela
cd
Derived Units
 Taken by manipulating base units
 Volume – space an object occupies
 L (m) x W (m) x H (m)
 Therefore, volume = m3
 10 cm3 = 1 Liter (L)
 Typical units:


Liters
cm3
Derived Units (continued)
 Density
 Amount of mass packed into a volume
 Density = Mass over volume (D = M/V)
 Typical units are g/cm3
More or less
What’s Scientific Notation?
My brain is on fire with the
crazy amount of info here
Rules of Sci. Not.
 Always between 1 and 10 and ten raised to a power.
 The power tells you how may times to multiply the 1st
number by 10.
 Ex:
 1.12 x 105 = 112,000
 9.167324 x 102 = 916.7324
 works the same in the opposite direction.
 Ex:
 4.5 x 10-4 = 0.00045
 9.9999 x 10-20 = 0.000000000000000000099999
Adding/Subtracting Sci. Not.
 Get all exponents to the same value, then add/subtract
the first number.
 Ex:



5 x 10-5m + 2 x 10-5m
1.26 x 104kg + 2.5 x 103kg
4.39 x 105kg – 2.8 x 104kg
Multiplying/dividing Sci. Not.
 1st multiply/divide the first number
 2nd add (multiplication)/subtract (division) the second
number
 Ex:
 (9 x 108)/(3 x 10-4) = (9/3) x 10(8 - -4)
 (2 x 103) x (3 x 102) = (2 x 3) x 10(3 + 2)
Practice
 Pg 32 14a-h
 Pg33 15a-d, 16a-d
Significant figures
 Include all known digits plus one estimated digit
 Rules
Rule
Ex.
Sig
Fig.
Non-zero numbers are always significant
72.3
535.112
3
6
Zeros between non-zero numbers are
always significant
50.001
17.02
5
4
All final zeros to the right of the decimal
place are significant
6.20
9.0
3
2
Zeros that act as placeholders are not
significant. Convert to Scientific notation
to remove the placeholder zeros.
0.0253
20000
4320
3
1
3
Counting numbers and defined constants
have an infinite number of sig. fig.
6 mol. ∞
60 s = 1 ∞
min
Measurement Reliability
 Accuracy – how close a value is to an accepted value
 Precision – how close a series of measurements are to
one another.
Ex:
Students were asked to find the density of an unknown powder.
The powder was table sugar which has a density of 1.59g/cm3
g/cm3
Student A Student B Student C
Which student was most precise?
Trail 1
1.54
1.40
1.70 Which student was most accurate?
Trial 2
1.60
1.68
1.69
Trail 3
1.57
1.51
1.71
Average
1.57
1.53
1.70
Percent Error
 Error -- Difference between experimental and
accepted values
 Percent error = (expected - actual)/accepted value x 100
g/cm3
Ex:
Error
g/cm3
Student A Student B Student C
Trail 1
1.54
1.40
1.70
Trial 2
1.60
1.68
1.69
Trail 3
1.57
1.51
1.71
Average
1.57
1.53
1.70
 Find the % error for
student A trial 1
Student A Student B Student C
Trail 1
0.05
0.19
-0.11
Trial 2
-0.01
-0.09
-0.10
Trail 3
0.02
0.08
-0.12