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Standards for Measurement. Preparation for College Chemistry Columbia University Department of Chemistry. The Scientific Method. http://antoine.fsu.umd.edu/chem/senese/101/intro/scimethod-quiz.shtml. Observations. Laws. (analysis). Hypothesis. (explanation). Experiment. (measurement).

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standards for measurement

Standards for Measurement

Preparation for College Chemistry

Columbia University

Department of Chemistry

slide2

The Scientific Method

http://antoine.fsu.umd.edu/chem/senese/101/intro/scimethod-quiz.shtml

Observations

Laws

(analysis)

Hypothesis

(explanation)

Experiment

(measurement)

(analysis)

Theory

(Model)

slide3

1

2

3

4

5

6

7

8

Measurement and Interpretations

Direct Measurement

Interpretation Step

Diameter = 2.5 cm

Radius = Diameter/2

Area =  x r2 = 8.04 cm2

Art of Chemical Measurement:

  • Recognize what can be measured directly
  • Devise a way to obtain the desired information from
  • measurement data
slide4

mV

ms

y

x

Na+

K+

Na+

Na+

K+

Na+

K+

+

+

+

+

+

+

-

-

-

-

-

-

Na+

K+

Na+

Na+

K+

Na+

K+

-

-

-

-

-

-

Na+

K+

Na+

Na+

K+

Na+

K+

+

+

+

+

+

+

Na+

K+

Na+

Na+

K+

Na+

K+

Resting Potential (Squid Experiment)

40

-65

slide6

Experimentation

Measured Data

Basic

UNIT

Derived

Resting Potential = -65 mV

Affected by Uncertainty

  • Accuracy
  • Precision

NUMERICAL VALUE

  • Resolution
  • Noise
significant figures sig figs
The mass of an object weighed on a triple beam balance (precision + 0.1g) is found to be 23.6 g.

This quantity contains 3 significant figures, i.e., three experimentally meaningful digits.

If the same measurement is made with an analytical balance (precision + 0.0001g) , the mass might be 23.5820 g (6 sig. fig.)

Significant Figures (Sig. Figs.)
evaluating zero
Evaluating Zero

Zero is SIGNIFICANT when:

Is between nonzero digits: 61.09 has four sig Figs.

Appears at the end of a number that includes a decimal point 0.500 has three sig. Figs.; 1000. has four sig. Figs.

Zero is NON SIGNIFICANT when:

Appears before the first nonzero digit. 0.0025 has two sig. Figs. Leading Zeros are non significant

Appears at the end of a number without a decimal point. 1,000 has one sig. Fig.; 590 has two sig. Figs.

slide9

Exact Numbers

Defined numbers, like 12 inches in a foot, 60 minutes in an hour, 1,000mL in one liter.

Numbers that occur in counting operations.

Exact numbers have an infinite number of sig. figs.

Exact numbers do not limit the number of sig. figs. in a calculation.

scientific notation
Scientific Notation

Number written as a factor between 1 and 10 multiplied by 10 raised to a power.

Useful to unequivocally designate the significant figures.

multiplication or division
Multiplication or Division

The answer must contain as many significant figures as in the least precise quantity (measurement with least precision).

What is the density of a piece of metal weighing 36.123 g with a volume of 13.4 mL?

Drop these three digits

Round off to 7

ANSWER:

addition or subtraction
Addition or Subtraction

Keep only as many digits after the decimal point as there are in the least precise quantity

Ex. Add 1.223 g of sugar to 154.5 g of coffee:

Total mass = 1.2 g + 154.5 g = 155.7 g

addition or subtraction13
Addition or Subtraction

Note that the rule for addition and subtraction does not relate to significant figures.

The number of significant figures often decreases upon subtraction.

Mass beaker + sample = 52.169 g (5 sig. figs.)

- Mass empty beaker = 52.120 g (5 sig. figs.)

Mass sample = 0.049 g (2 sig figs)

syst me international si the metric system

Physical Quantity Name Symbol

Length meter m

Mass kilogram kg

Time second s

Electric current ampere A

Temperature kelvin K

Amount of substance mole mol

Luminous intensity candela cd

Système International (SI) The Metric System

Based on seven DIMENSIONALLY INDEPENDENT quantities

length
Length

Base unit is the meter (m)

1790s: 10-millionth of the distance from the equator to the North Pole along a meridian.

1889: Distance between two engraved lines on a Platinum-Iridium alloy bar maintained at 0°C in Sevres-France.

1960-1983: 1,650,763.73 wavelengths of the orange-red emision of 18Kr at standard conditions

Since 1983: 1/299,792,458 of the distance traveled by light in 1 second through vacuum.

length18
Length

Engineering dimensions

1 km = 103 m 1 in. = 2.54cm

1 cm = 10-2 m 1 mile = 1.61km

1 mm = 10-3 m

1 µm = 10-6 m

Atomic dimensions

1 nm = 10-9 m

1 Å = 10-10 m

mass base unit is the kilogram kg
1 kg = 103 g; 1 mg = 10-3 g

A mass of 1 kg has a terrestrial weight of 9.8 newtons (2.2 lbs)

Depending on the precision required and the amount of material, different balances are used:

The Quadruple Beam Balance (+ 10 mg)

The Top Loading Balance (+ 1 mg).

The Analytical Balance (+ 0.1 mg).

MassBase unit is the kilogram (kg)

International prototype: a platinum-Iridium cylinder maintained in Sevres-France.

slide20

Fahrenheit

Kelvin

Celsius

212

373.15

100

180

100

100

32

273.15

0

Comparison of Temperature Scales

K = °C + 273.15

°C= (°F - 32) / 1.8

°F= (1.8 x °C) + 32

Boiling point of water

Freezing point of water

temperature conversion
K = °C + 273.15

°F= (1.8 x °C) + 32

°C= (°F - 32) / 1.8

Ex. 2.20 Convert 110°F to °C and K

°C= (68° – 32°) / 1.8 = 20°C

K = 20 + 273 = 293 K

Temperature Conversion
derived units

Physical quantity Name Symbol Definition

Frequency Hertz Hz s-1

Force newton N m.kg.s-2

Pressure, stress pascal Pa N.m-2 = m-1.kg.s-2

Energy work, heat joule J N.m = m2.kg.s-2

Electric charge coulomb C A.s

Electromotive Force volt V J.C-1 = m2.kg.s-3.A-1

Electric Resistance ohm  V.A-1 = m2.kg.s-3.A-2

Derived Units
conversion factors
Conversion Factors

Two conversion factors

dimensional analysis pp 23 24
Dimensional Analysis (pp. 23 - 24)
  • Read Problem. What needs to be solved for? Write it down
  • Tabulate data given. Label all factors with proper units
  • Determine principles involved and unit relationships
  • Set up the problem deciding for the proper conversion factor
  • Perform mathematical operations
  • Check if the answer is reasonable
simple one step conversions
CBS News reported the barometric pressure to be 99.6 kPa. Express this in mm Hg.

760 mm Hg

101.3 kPa

Simple, One Step Conversions

Conversion factor : 101.3 kPa = 760 mm Hg

Unit needed

pressure (mmHg) = 99.6kPa

x

= 747mmHg

Unit given

Unit given

simple one step conversions27

2.54 cm

1 in

Simple, One Step Conversions

A rainbow trout is measured to be 16.2 in. long. What is the length in cm?

x

= 41.1 cm

length in cm = 16.2 in

Note the cancellation of units. To convert from centimeters to inches, the conversion factor would be 1 in / 2.54 cm.

multiple conversion factors

1 h

3600 s

miles

hour

1.609 x 10–3m

1 mile

Multiple Conversion Factors

A baseball is thrown at 89.6 miles per hour. What is the speed in meters per second?

m/s

Mile/hour

m/hour

1 mile = 1.609 km = 1.609 x 10-3 m; 1 h = 3600 s

x

speed = 89.6

= 40.0 m / s

x

Three sig. figs.

slide30

Extensive Properties

Vary with the amount of material

  • Mass
  • Volume
  • Internal Energy
  • Enthalpy
  • Entropy
slide31

Intensive Properties

Independent of the amount of material

Density (mass per unit volume)

Temperature (average energy per particle)

slide32

Chemical vs. Physical Properties

Chemical Properties

Molecules or ions undergo a change in structure or composition

Physical Properties

Can be studied without a change in structure or composition

density conversion factor mass volume

25.598

3.460g

5.00 mL

-22.138

3.460g

= 0.692g / mL

d =

1 mL

0.692g

V = 10.00g x

= 14.5 mL

Density: Conversion factor mass volume

An empty flask weighs 22.138 g. You pipet 5.00 mL of octane into the flask. The total mass is 25.598 g. What is the density?

Octane amount in g:

What is the volume occupied by ten grams of octane?

solubility
Solubility

Expressed as grams of solute per 100 g of solvent in the CRC (Chemical Rubber Company) Chemistry and Physics Handbook.

For lead nitrate in aqueous solution:

solubility35

100g water

140g lead nitrate

Solubility

How much water is required to dissolve 80 g of lead nitrate at 100°C?

Mass water = 80g lead nitrate

x

= 57g water

Conversion factor

(from table)

slide36

50g lead nitrate

100g water

Cool the solution to 10°C. How much lead nitrate remains in solution?

x

= 28g lead nitrate

Mass of lead nitrate = 57g water

28g lead nitrate remain in solution

80g lead nitrate were initially in solution

80g – 28g = 52g lead nitrate crystallizes out of solution

slide37

Elements

Compounds

Mixtures

Classification of Matter

slide38

States of Matter

Solid

Liquid

Gas

Plasma

slide39

Matter Classification

Matter

Mixtures

Pure Substances

Compounds

Homogeneous

One Phase

(Solutions)

Elements

Heterogeneous

More than one phase

slide42

H

1

He

2

Li

3

Be

4

5

B

C

6

7

N

8

O

F

9

Ne

10

Na

11

12

Mg

13

Al

Si

14

P

15

S

16

Cl

17

Ar

18

K

19

20

Ca

21

Sc

Ti

22

V

23

Cr

24

25

Mn

Fe

26

Co

27

Ni

28

Cu

29

Zn

30

31

Ga

32

Ge

33

As

Se

34

Br

35

36

Kr

Rb

37

Sr

38

39

Y

40

Zr

Nb

41

42

Mo

Tc

43

44

Ru

Rh

45

46

Pd

Ag

47

Cd

48

49

In

50

Sn

51

Sb

52

Te

53

I

Xe

54

Cs

55

Ba

56

57

La

Hf

72

Ta

73

W

74

75

Re

76

Os

77

Ir

78

Pt

Au

79

80

Hg

8l

Tl

Pb

82

83

Bi

Po

84

85

At

Rn

86

Fr

87

88

Ra

Ac

89

104

Rf

Ha

105

Sg

106

107

Bh

Hs

108

Mt

109

Ce

58

Pr

59

Nd

60

Pm

61

62

Sm

63

Eu

64

Gd

Tb

65

Lu

71

70

Dy

Yb

Tmi

Ho

67

69

66

68

Er

Th

90

91

Pa

92

U

Np

93

94

Pu

Am

95

96

Cm

Bk

97

102

103

Cf

Es

Fm

Md

101

99

100

Lr

98

No

, Nonmetals,

Metals

Metalloids

Main-Group Elements

Main-Group Elements

Transition Metals

Inner-Transition Metals

Lantanides

Actinides

slide44

Depending upon Bonding type

Compounds

Ionic

(Coulombic forces)

Molecular

(Covalent bonds)

Molecules

Cations

Anions

slide45

Compounds

Contain two or more elements with fixed mass percents

Covalent:

Glucose: 40.00% C

6.71% H

53.29% O

Ionic:

Sodium chloride: 39.34% Na

60.66% Cl

slide46

Information in a Chemical Formula

Ca(NO3) 2

Calcium atom

Nitrate group: two nitrate groups

Per each calcium atom

Total elements: 1 Ca

2 N

6 O

slide47

Allotropic Forms (Allotropes)

Graphite

Carbon

Diamond

Buckyballs (C60 )

Nanotubes

slide49

Energy in Chemical Changes

Heat: Quantitative Measurement

Energy

slide50

Is the energy available but not being used or is it in use?

Types of Energy

Forms of Energy

Kinetic Energy (Motion Energy)

Radiant (light)

Thermal (heat)

Energy

Chemical

(Capacity to do work)

Potential Energy (Stored Energy)

Electrical

  • Position,
  • Composition
  • Condition

Mechanical

Law of Conservation of Energy:

In any chemical or physical change, energy can be converted from one form to another, but it is neither created nor destroyed

slide51

Heat Energy and Specific Heat

Units of Energy:

Joule :

Amount of kinetic energy possessed by a 2kg object moving at a speed of 1m/s. Substituting these values in the equation that defines kinetic energy:

Equivalent to the amount of energy you will

feel if you drop 4.4 lb from about 4 in. onto your foot.

calorie (cal) :

Amount of heat energy needed to raise the temperature of one gram of water by one degree Celsius measured between 14.5 and 15.5°C.

slide52

Units of Energy

1 cal = 4.3184 J

The joule and calorie are rather small units.

The large calorie (Cal, C) is used to express the energy content of foods.

1kcal = 4.3184kJ

1C = 1kcal = 103 cal

140,000 cal of energy is released when the soft drink is metabolized within the body.

Sprite™ contains 140 C:

1 BTU (British Thermal Unit):

Amount of heat needed to raise the temperature of a lb of water one °F

1BTU =.818 kcal

slide53

Heat Capacity and Specific Heat

Joseph Black (~1750):

“Amount of heat needed to raise the temperature of a substance by the same amount depends on the substance”

Amount of heat needed to raise the temperature of a given quantity of substance in a specific physical state.

Heat Capacity

Amount of heat needed to raise the temperature of 1 g of a substance in a specific physical state by 1°C

Specific Heat

  • Units: cal /g °C or J/g °C
slide54

The specific heat of a substance changes when the physical state of the substance changes

Ex.

Water (ice)

Water (liquid)

Water (steam)

2 .1 J / g °C

4 . 18 J / g °C

2 . 0 J / g °C

The higher the specific heat of a substance, the less its temperature will change when it absorbs a given amount of heat.

  • metals heat up quickly, but cool quickly

At the beach, sand has a lower specific heat than water, so it heats up while water stays cool.

slide55

Solving problems

Heat transferred = mass x Specific heat x ∆T

q = m x Cs x ∆T

Amount of heat energy needed to cause a fixed amount of a substance to undergo a specific temperature change without causing a change of state.

Transfer of heat from one body to another.

Heat always flows from the warmer body to the colder body.

The heat loss by the warmer body is equal to the heat gained by the colder body.

Generalizations:

slide56

Potential energy

Potential energy

H2

H2

O2

O2

+

+

time

time

Heat in Chemical Change

Electrolysis

Direct synthesis

H2O

H2O

Potential Energy Diagrams