Types of Observations and
Measurements
 We make QUALITATIVE observations of
reactions — changes in color and physical
state.
 We also make QUANTITATIVE
observations that involve
MEASUREMENTS with numbers and
units.
A measurement always has two parts:
A value (this is the number)
A unit of measure (this tells what you
have)
Example:
200 meters; 15 ml; 13.98 grams
 In Chemistry we use SI Units of measure
International System of Units
 These are the base units that we will be working with:
 From these base units, we can combine them using
mathematical operations to obtain derived units.
 Some of the derived units we will be using include:
 Density (g/ml)
 Area (m2)
 Volume (m3)
Prefixes Used in the SI System
.
Metric Prefixes
 Kilo- means 1000 of that unit
 1 kilometer (km) = 1000 meters (m)
 Centi- means 1/100 of that unit
 1 meter (m) = 100 centimeters (cm)
 1 dollar = 100 cents
 Milli- means 1/1000 of that unit
 1 meter (m) = 1000 millimeters (mm)
To convert from one metric unit to
another – remember this pneumonic:
King Henry Died (Unexpectedly)
Drinking Chocolate Milk
You must also know…
…how to convert within the Metric System.
Here’s a good device:
On your paper draw a line and add 7 tick marks:
Next:
Above the tick marks write the abbreviations
for the King Henry pneumonic:
k
h
d
(u )
d
m
l
g
Write the units in the middle under the “U”.
c
m
Let’s add the labels for
meter, liters, and grams:
k
h
d
u
d
c
m
km
hm
dam
m
dm
cm
mm
kl
hl
dal
l
dl
cl
ml
kg
hg
dag
g
dg
cg
mg
Deca can also be dk or da
How to use this device:
1.
Look at the problem. Look at the unit
that has a number. On the device put
your pencil on that unit.
2.
3.
Move to new unit, counting jumps and noticing the direction of
the jump.
Move decimal in original number the same # of spaces and in
the same direction.
Example #1:
(1) Look at the problem: 56 cm = _____ mm
Look at the unit that has a number 56 cm
On the device put your pencil on that unit.
k
km
h
hm
d
u
d
dam
m
dm
c
cm
m
mm
Example #1:
2.
Move to new unit, counting jumps and noticing the direction of
the jump! Be careful NOT to count the spot you start from,
where you put your pencil point. Only count the jumps!
k
km
h
hm
d
dam
u
m
d
c
m
dm
cm
mm
One jump to the right!
Example #1:
3.
Move decimal in original number the same # of spaces and in
the same direction.
56 cm = _____ mm
56.0.
One jump
to the right!
Move decimal one jump to the right.
Add a zero as a placeholder.
Answer:
56cm = 560 mm
Example #2:
(1) Look at the problem. 7.25 L = ____ kL
Look at the unit that has a number. 7.25 L
On the device put your pencil on that unit.
k
h
d
kl
hl
dal
u
L
d
c
m
dl
cl
ml
Example #2:
2. Move to new unit, counting jumps and
noticing the direction of the jump!
k
h
d
u
kL
hL
daL
L
d
dL
c
m
cL
Three jumps to the left!
mL
Example #2:
(3) Move decimal in original number
the same # of spaces and in the same
direction.
7.25 L = ____ kL
.007.25
Move decimal to the left three jumps.
Add two zeros as placeholders.
Answer: 7.25 L = .00725 kL
Three jumps
to the left!
Learning Check
1. 1000 m = 1
___
a) mm
b) km c) dm
2.
___
a) mg
b) kg
c) dg
___
a) mL
b) cL
c) dL
a) mm
b) cm c) dm
0.001 g = 1
3. 0.1 L = 1
4.
0.01 m = 1 ___
1. 1000 m = 1
___
2.
___
0.001 g = 1
3. 0.1 L = 1
4.
___
0.01 m = 1 ___
a) mm
a) mg
b) km c) dm
b) kg
c) dg
a) mL
b) cL
c) dL
a) mm
b) cm c) dm
Measurement
 Accurate means "capable of providing a correct
reading or measurement."
 In Chemistry: it means 'correct‘. How close you are to
the accepted value.
Measurement
Accurate
Measurement
Precise
X X
X X X
X
Measurement
Can you be neither
accurate or precise?
Measurement
x
This is a random like
pattern, neither precise
nor accurate. The darts
are not clustered together
and are not near the bull's
eye.
x
x
x
x
Measurement
This is an accurate
pattern, but not precise.
The darts are not
clustered, but their
'average' position is the
center of the bull's eye.
x
x
x
x
x
Measurement
This pattern is both
precise and accurate. The
darts are tightly clustered
and their average position
is the center of the bull's
eye.
x
xxx
x