1. CHEM-111CHEM-111
General ChemistryGeneral Chemistry
Unit OneUnit One
Scientific MeasurementScientific Measurement
Department of ChemistryDepartment of Chemistry
February-2007February-2007

2. Contents
Scientific MeasurementsScientific Measurements
• Measurement and Units
• System of Measurement
• Scientific Notation
• Significant figures in measurements
• Length and Volume
• Converting Units
• Unit of Mass
• Density and Specific Gravity
• Units of Heat and Heat Capacity of
Matter

3. Metric Units
Metric System is used by scientists and
health professionals
Type Name symbol
Mass Gram g
Length Meter m
Volume Liter L
Time Second s
Temperatue Celsius 0
C

4. Systems of Measurements
International System of Units
(SI Units)
Base Quantity Name Symbol
Length Meter m
Mass Kilogram kg
Time Second s
Electric current Ampere A
Temperature Kelvin K
Luminous intensity Candela cd
Amount of substance Mole mol
The seven SI base units

5. Name Symbol Value in SI units
minute (time) min 1 min = 60 s
hour h 1 h = 60 min = 3600 s
day d 1 d = 24 h = 86 400 s
liter L 1 L = 1 dm3
= 10-1
m3
metric ton t 1 t = 1x103
kg
unified atomic mass
unit u
1 u = 1.66054 x 10-27
kg, approximately
1 meter = 3.3 feet
. Units Outside the SI That are Accepted for Use
with the SI

6. Commonly-used metric prefixes
Prefix Name Prefix Symbol Prefix Value
giga G 1 billion or 1 000 000 000 109
mega M 1 million or 1 000 000 106
kilo k 1 thousand or 1000 103
deci d 1 tenth or 1/10 or 0.1 10-1
centi c 1 hundredth or 1/100 or 0.01 10-2
milli m 1 thousandth or1/1000 or 0.001 10-3
micro µ 1/1 000 000 or 0.000 001 10-6
nano n 1/1 000 000 000 or 0.000 000 001 10-9
Prefixes that increase the size of the unit
Prefixes that decrease the size of the unit

7. Prefixes and
equalities
Measuring
length 1 meter
10 dm
100 cm
1000 mm
Some Length Equalities
1 m = 100 cm
1 m = 1000 mm
1 cm = 10 mm
Measuring Volume
1 L = 10 dL
1 L = 1000 mL
1dL = 100 mL
1cm3
= 1 cc = 1 mL

8. Mass and Weight
In commercial and everyday use, and especially in
common parlance, weight is usually used as a synonym for
mass.
How are weight and mass differ?
1) Mass is a measurement of the amount of matter
something contains,
while Weight is the measurement of the pull of gravity
on an object.
2) Mass is measured by using a balance comparing a
known amount of matter to an unknown amount of
matter. Weight is measured on a scale.
3) The Mass of an object does not change when an
object's location changes.
Weight, on the other hand does change with location .

9. Measuring mass
In metric system, the unit for mass is grams (g)
The SI unit of mass, the kilogram (kg), is used for larger
masses.
1 kg = 2.20 lb
454 g = 1 lb
Some mass equality
1 kg = 1000g
1 g = 1000mg
1 mg = 1000µg

10. Scientific Notation
Scientists have developed a shorter method to express very large
numbers.
This method is called scientific notation. Scientific Notation is based on
powers of the base number 10.
The number 123,000,000,000 in scientific notation is written as 1.23 x 1011
Example
93,000,000 = 9.3 X 107
miles
these two digits are
retained 93,000,000 miles
7 digits
instruction: move decimal point
9.3 x 107
miles seven(7) digits to the right
exponent
9.3 x 107

11. Scientific Notation for very large Numbers
The number 2,398,730,000,000 can be written in
scientific notation as:
(the starred representation is most common)
0.239873 x 1013
****2.39873 x 1012
****
23.9873 x 1011
239.873 x 1010

12. A paper clip weighs a bit more than one thousandth of a
pound (0.0011 Lb).
This would be expressed in scientific notation as 1.1 x 10-3
lb.
The negative sign indicates that the decimal point is
moved to the left.
Scientific notation for very small numbers
0.0011 kg = 1.1 x 10
-3
kg
0.0 0 11 kg
0 1 2 3 4
1.1 x 10
-3
kg
these two digits are
retained
instruction: move decimal point
three digits to the left

13. The number 0.003,483 can be written in scientific notation
as
(the starred representation is most common):
0.3483x 10-2
****3.483 x 10-3
****
34.83x 10-4
348.3x 10-5
3483.x 10-6
Scientific notation for very small numbers
Conventional Notation Scientific Notation
0.012 1.2 x 10-2
0.000541 5.41 x 10-4
0.000007 7 x 10-6
0.0010 1.0 x 10-3

14. value significant figures rule
16.74 g 4 sig. figs non zero digits are significant
0.003 m 1 sig. fig
a zero at the beginning of a decimal
number is not significant
2500 km 2 sig. figs
a zero at the end of a large number
without
a decimal point after is not significant
25.0 ml
50. L
3 sig. figs
2 sig. figs
a zero at the end of a decimal number is
significant
405 3 sig. figs
zeros between non zero digits are
significant
Number of Significant Figures

15. Number of Significant Figures
• According to these rules, all of these
numbers have three significant digits:
123
123,000
0.000123
• 12.3
1.23 x 106
0.000123
67.2units = three significant figures
uncertain
digit
certain
digit

16. Remember- Rules for zeros
1. Leading zeros are not significant.
0.523– three significant figuresLeading zeros
2. Captive zeros are significant.
5016 – four significant figures
Captive zeros
3.Trailing zeros are significant.
315.60–five significant figures
Trailing zeros
4. A zero at the beginning of a decimal number is not significant
0.008 - one significant figure
Zero at the beginning of a decimal number

17. Scientific notation can be used to clearly express
significant figures.
A properly written number in scientific notation
always has the proper number of significant
figures.
0.00524=5.24x 10-3
Three significant figures
378 000 3.78 x 10 5
Three
8931.5 8.9315 x 10 3
Five
0.000 593 5.93 x 10 -4
Three
0.000 000 4 4 x 10 -7
One
Conventional Notation Scientific Notation significant figures
Scientific notation and significant figures

18. Temperature
The temperature of an object tells us how hot or cold an object is (intensity
of heat).
In metric system temperature is measured on the Celsius temperature
scale.
On Celsius thermometer, freezing point of water is 0 0
C and boiling point of
water is 100 0
C.
On a Fahrenheit scale, freezing point of water is 320
F and boiling point of
water is 212 0
F.
• 0
F = 1.8 (0
C) + 32
Kelvin Temperature scale
In SI system, temperature is based on Kelvin (K) temperature scale.
• K = 0
C + 273

19. 180
Fahrenheit
degrees
100
Celsius
degrees
100
Kelvins
degrees
FahrenheitCelsiusKelvin
Normal body
temperature
Freezing point
of water
Boiling
water
373 K 100 0
C 212 0
F
310 K 37 0
C 98.6 0
F
273 K 0 0
C 32 0
F
Boiling point
of water
Comparison of the Fahrenheit, Celsius,
and Kelvin Temperature

20. Accuracy
Accuracy indicates how close a measurement is to the
accepted value. For example, we'd expect a balance to
read 100 grams if we placed a standard 100 g weight on
the balance. If it does not, then the balance is
inaccurate.
Accuracy
100 g
100.00
100 g
98.89
InaccurateAccurate
Measurements and Units

21. Which Factors effect on
Accuracy & Precision
Predict the effect on accuracy and precision:
1. Instrument not “zeroed” properly
2. Reagents made at wrong concentration
3. Temperature in room varies “widely”
4. Lab partner is not properly trained

22. Precision
• Precision indicates how close together or how
repeatable the results are. A precise measuring
instrument will give very nearly the same result
each time it is used.
Precision
More precise
Trial # Mass (g)
1 100.00
2 100.01
3 99.99
4 99.99
Average 100.00
Range 0.01
Std. Dev. 0.05
Less precise
Trial # Mass (g)
1 100.10
2 100.00
3 99.88
4 100.02
Average 100.00
Range 0.11
Std.
Dev.
0.09

23. Measurements and Units
Accuracy with PrecisionPrecision with mistake Accuracy with mistake
Accuracy and Precision of Measurements

24. The box that has more balls has more mass per
unit of volume. This property of matter is called
density
Each box has the same volume If each ball has the same mass,
which box would weigh more? Why?
What is Density
More Dense Less Dense

25. Density is a measure of mass per unit of volume.
The higher an object's density, the higher its mass per
volume.
The average density of an object equals its total
mass divided by its total volume.
A denser object (such as iron) will have less volume
than an equal mass of some less dense substance
(such as water).
Common units are : g/ mL or g/ cm3
or kg/L (kg/m3
)
( cm3 = ml)
DensityDensity
Density =
mass
volume
d =
m
v
or

26. Density is a characteristic property of a substance.
Air 0.0013 g/L Bone 1.7-2.0 g/ml
Water 1.0 g/ml Urine 1.01-1.03 g/ml
Gold 19.3 g/ml Gasoline 0.66-0.69 g/ml
DensitySubstance Substance
Density of some common substance
Density

27. 1. An Iron ball was weight and found to have a mass of 42.6 g. Its
volume was measured to be10.00 mL. What is the density of Fe?
SOLUTION: Density is the ratio of mass to volume. Using the
symbol d for density, therefore, we obtain
d =
mass
volume
42.6g
10.00mL
4.26g/mL
=
=
Density Calculation
Mass
Volume
=Density
15.69g
1 5mL
= 1.046g/mL=
2.What is the density of 15.00 mLof urine if it has a mass of 15.69 grams?

28. Density calculation
What would be the mass of 3.00 liters of this milk sample?
The density was 3.02 g/mL
Mass
Volume
=Density
mass = 9.06x 103 g
mass = volume x density

29. Specific gravity
The density of a substance compared to a
reference substance is known as specific gravity.
Specific Gravity =
density of substance
density of reference
Specific gravity is unit less.
Reference material is commonly water at 40
C.
At 40
C, density = specific gravity.

30. Specific gravity measurement
Hydrometer
Float height will be
based on Specific Gravity.
Hydrometer is used to know density of
urine by health care workers.
The specific gravity of a liquid can be
determined with a hydrometer, a hollow,
sealed, calibrated glass tube.
The depth to which the hydrometer sinks
is inversely proportional to the
specific gravity of the liquid.

31. Units of Heat
• Heat is the energy associated with the
motion of particles in a substance.
• Heat is commonly measured in calories.
• A Calorie (cal): is the amount of heat
needed to raise the temperature of exactly
1 g of water by exactly 10
C.
• 1 Kcal = 1000 calories
• 1 cal = 4.18 j ( Joule, pronounced jewel)
• 1 kJ = 1000 J

32. Specific Heat
• All substances absorb energy.
• Some need less amount of heat to
become hot and others need more.
• The amount of heat that raises the
temperature of 1 g of a substance by 10
C
is known as its specific heat.
Specific heat =
Amount of heat (Cal)
1 gm x 1 0C

33. Specific Heats of some Substances
. All substances absorb energy, but some need only small
amount of heat to become hot and others need more
Substances Specific Heat (cal/g0
C)
Water 1.00
Ethanol 0.58
Sand 0.19
Iron 0.11
Copper 0.093
Silver 0.057
Gold 0.031

34. Some Relationships to find
The Mass
Heat Change
Temperature Change
and Specific Gravity
Specific heat
Amount of heat ( cal )
=
1 g x 1 0
C
Heat gain or loss = (mass) x(temperature
change(ΔT)
) X (specific heat)
Heat (calories) = g x 0
C x
g 0
C
cal
1.
2.
3.
g 0
C
calg 0
C

35. Exercise
1. Write the following measurements in scientific notation.
a. 350 g b. 0.00016 L
c. 5220000 m d. 0.0086
2. What is the name of the unit and the type of measurement
( mass, volume, length, or temperature) indicated for each
of the following quantities.
a. 4.8 m b. 325 g
c. 1.5mL d. 373K
3. How many significant figure are in each of the following
numbers
a. 4.5 b. 205 c. 5.082 d. 0.0004

36. 4. Complete the following metric relationship:
a. 1m = cm b. 1 km = m
c. 1mm = m d. 1L = mL
e. 1 kg = g f. 1mL = L
g. 1 g = kg h. 1 g = mg
5. For each of the following pairs, which is the smaller unit
a. mg or kg b. mL or µL
c. cm or km d. kL or dL
6. Choose the larger unit
a. mg or g b. cm or m
c. ml or dL d. mm or µm