Chapter 2
Quantitative measurements
give results in a definite form, usually a
number
Example
Thermometer
Qualitative measurements
gives results in a descriptive form
non-numeric value
Example
Color of a reaction
Accuracy
How close a measurement comes to the
true value
Precision
Reproducibility of the measurement
Significant Figures
include all digits that can be known
accurately plus a last digit that is
estimated
Rules for Significant Figures
1. Every nonzero digit in a recorded
measurement is significant
Examples
65.2
0.268
(All have 3 Sig. Figs.)
126
2. Zeros between nonzero digits are
significant
Example
2004
60.39
8.602
(All have 4 Sig. Figs.)
3. Zeros in front of all nonzero digits are
NOT significant. They act as placeholders.
Examples
0.0062
0.58
(2 Sig. Figs.)
0.00027
4. Zeros at the end of a number and to
the right of a decimal point are significant
Examples
61.00
1.030
(4 Sig. Figs.)
8.000
Zeros at the end of a measurement and
to the left of the decimal can be
confusing.
If they are place-holders to show the
magnitude of a number, they are not
significant
Examples
300
700
27210
ambiguous
If the zeros were measured- significant
700.
To avoid confusion use scientific notation
3.00 x 10
2
How Many Sig. Figs.?
123 
3
40,506  5
0.123  3
9.8000 x 10 4  5
98,000  2
0.07080  4
0.078  2
Sig. Figs in calculations
If digit following last sig fig is <5, all
digits are dropped
If digit following last sig fig is >5, digit in last
sig fig place is increased by one
Round These…….
314.721
4 sig figs
314.7
0.001775
2 sig figs
0.0018
1 sig fig
60 x 10
or 6
64.32 x 10
-1
-1
Addition and Subtraction
The answer cannot contain any more
digits to the right of the decimal point
than are contained in the measurement
with the least number of digits to the
right of the decimal point
Sample Problem
12.52
+
349.0
+
8.24
369.8 or 3.698 x 10 2
Multiplication and Division
Answer must contain no more sig figs than the
measurement with the least number of sig figs.
*Decimal point has nothing to do with
determining this!
Example Problems
755 x .034 = 26
3 sig. figs.
2 sig. figs
2 sig. figs
2.4526  8.4 = 0.29
►Metric
►SI
System
system (International
System of Units)Developed in 1790 in
France
Quantity
SI Unit
Non-SI
Length
m
Volume
m3
Liters
Mass
kg
grams
Density
g/cm³, g/ml
Temperature
K
Time
s
Pressure
Energy
pa (pascal)
J (joules)
oC
atmospheres, mm Hg
calories
Units of Measurement – Meter (m)
Prefix
kilo
hecto
deca
unit
deci
centi
milli
micro
nano
pico
Symbol
Magnitude
K
h
da
m, L, g
d
c
m
u
n
p
1000x
100x
10x
x
.1x
.01x
.001x
1 x 10 -6 x
1 x 10 -9 x
1 x 10-12 x
Units of Volume – Liter (L)
 Volume of a cube-10 cm x 10 cm x
10 cm= 1000 cm 3
► 1 L = 1 dm 3 = 1000 cm 3
1 cm 3 = 1 mL
Units of Mass – (g)
► Mass-
quantity of matter
► Weight- a force
► Unit of mass – gram (g) =
mass of 1 cm 3 of H2O at 4 ºC
►Density-
ratio of mass of an object
to volume
D= M = g/mL or g/cm 3
V
Specific Gravity
►Specific
Gravity- comparison of
the density of a substance to
the density of a reference
substance
Specific Gravity Cont’d
 Sp. Gravity = density of substance g/cm 3
density of H2O g/cm 3
 Sp. Gravity of a liquid is measured with a
hydrometer
► Temperature-
Degree of hotness or
coldness of an object
 Determined direction of heat
transfer
► Heat transfer- occurs when two
objects at different temperatures
contact each other
 Heat goes from high temperature
to low temp
Temperature Scales
Fahrenheit
32ºF - FP of H2O
212ºF - BP of H2O
Celsius (centigrade)
0ºC - FP of H2O
100ºC - BP of H2O
Kelvin
273 K - FP of H2O
373 K - BP of H2O
K = oC + 273
Heat
► Heat-
measured in joule (J) or calories
(cal)
 One calorie is the quantity of heat
that raises the temperature of 1 g of
H2O 1ºC
►1
cal = 4.18 J
 Calorie in nutritional terms means
kilocalorie
Heat Cont’d
► Heat
Capacity- quantity of heat
required to change an objects
temperature by exactly 1ºC
 Depends on mass and type of substance
Specific Heat
►The
quantity of heat required to raise
1g of a substance 1ºC
 Sp. Heat = heat
mass x T
Units of Specific Heat:
J/g°C or cal/g°C
=
q
(m) (T)
Chapter 2B
Problem Solving in Chemistry
Three easy steps to problem
solving. . .
►
Step 1 : Analyze
►
Identify a known
 Determine where you are starting from.
 What information do you already have to
work with?
Step 1 cont’d…
► Identify
an unknown
 Where are you going?
 What are you looking for?
► Plan a solution
 How are you going to get there?
Step 2: Calculate
May involve substituting known quantities
and doing the arithmetic needed to solve for
unknown.
► You may also need to convert.
►
Step 3: Evaluate
►
Go over your answers
 Does the answer make sense?
 Did you use correct units?
► Check
your work
 Make sure you copied down the given
information correctly.
Sample Problem
►What
is the mass, in grams,
of a piece of lead that has a
volume of 19.84 cm³?
Step 1 : Analyze
► List
Knowns and Unknowns
 Knowns :
►Volume of lead: 19.84 cm³
►Density of lead = 11.4 g/cm³ (according
to table 3.7)
►Density = mass
volume
 Unknowns: mass = ?g
Step 2: Calculate
►
Density = mass -or- Mass = volume x density
volume
► Mass
= 19.84 cm ³ x 11.4 g/cm ³
= 226.176 g
Mass = 226 g
Step 3: Evaluate
► Has
the unknown been found?
 Yes, problem asks for mass
► Do
you have the correct units?
 Yes, units canceled correctly to yield grams (g)
► Is
the number of sig figs correct?
 Yes, answer has 3 sig figs
Mass = 226 g
What is the volume, in cubic
centimeters of a sample of
cough syrup that has a mass
of 50.0g? The density of
cough syrup is 0.950g/cm³.
Volume = mass
density
Volume = 50.0g
= 52.6316 cm³
0.950g/cm³
Volume = 52.6 cm³
Your school club has sold 600 tickets
to a chili-supper fundraising event,
and you have volunteered to make
chili. You have a chili recipe that
serves 10. The recipe calls for two
teaspoons of chili powder. How
much chili powder do you need for
600 servings?
Servings Needed = 600
10 servings = 2 tsp chili powder
Amount of chili powder = ? tsp
600 servings
x
2 tsp chili powder =
10 servings
1200 tsp chili powder = 120 tsp chili powder
10
►How
many cups are in 120
teaspoons of chili powder?
120 tsp
x
120 cups =
48
1 tbs
3 tsp
x
2.5 cups
1 cup
16 tbs
=
►Express
750 dg in grams
Mass = 750 dg
1 g = 10 dg
Mass = ?g
750 dg x
1g
10 dg
= 75 g
►What
is 0.073 km in cm?
0.073 km x 1000 m x 100 cm =
1 km
1m
7300 cm = 7300 cm
1
►
How many seconds are in
one day?
1 day x
24 h x
1 day
86400 s =
1
60 min x 60 s =
1h
1 min
8.64 x 104 s