1 Modern Chemistry Chapter 2 Measurements and Calculations Sections 1 - 3 Scientific Method Units of...

1

Modern Chemistry Chapter 2

Measurements and Calculations

Sections 1 - 3

Scientific Method

Units of Measurement

Using Scientific Measurements

Chapter 2 Section 1 Scientific Method pages 29-32

2

Chapte

r V

oca

bula

ryScientific methodSystemHypothesisModelTheoryQuantitySIWeightDerived unitVolumeDensityConversion Factor

Dimensional analysis

AccuracyPrecisionPercentage errorSignificant figuresScientific notationDirectly

proportionalInversely

proportional

3Chapter 2 Section 1 Scientific Method pages 29-32

Section 1

Scientific Method


Scientific MethodA logical approach to solving

problems by• OBSERVING AND COLLECTING DATA• FORMULATING HYPOTHESIS• TESTING HYPOTHESIS• FORMULATING THEORIES

that are supported by data.Not a fixed series of steps.


Scientific Method Image

p.

31


Sci

enti

fic

Meth

od

Anim

ati

on


Observation and Collecting DataWhat are we studying?A system is a specific portion of

matterin a given region of spacethat has been selected for

studyduring an experiment or

observation.


Observation and Collecting DataObservation –

use of senses to obtain informationQualitative – descriptiveQuantitative – numeric

Organize data and observations into tables and/or graphs.


Organizing Data into a Graphp.

30


Formulating Hypothesis• Generalizations about data or

observations can be used to make a hypothesis

• A hypothesis is a testable statement

• Often in an if-then statement• A prediction that is the basis for

testing by experiment


Testing Hypothesis• Controls – conditions that remain

constant (controlled variables)• Variable – any condition that

changes• Driven by the hypothesis• Test only one variable at a time• Identify variables to be held

constant


Theorizing• When data from experiments

support a hypothesis a theory and model are constructed

• A model in science is more than a physical object.It is often an explanation ofhow phenomena occur andhow data or events are related


Model A

nim

ati

on


Theorizing

• Models are a part of a theory.• A theory is

a broad generalizationthat explainsa body of facts or

phenomena.– not a fact; explains facts–modified with new discoveries


Section 1 Homework

Reading Notes #7-15 pages 33-43

18Chapter 2 Section 2 Units of Measurements pages 33-43

Section 2

Units of Measurement


QUANTITY UNIT STANDARD

Length Foot The king’s foot

Mass Kilogram

Kg prototype

Mass a.m.u. 1/12th of a carbon-12 atom

Something that has magnitude, size or amount

Objects or natural phenomena that are of constant value, easy to preserve and reproduce


Common SI Units Tablep.

33*


SI Measurements• Le Systeme’ International

d’Unites• 75 000 not 75,000 use spaces

not commas


Base SI Units Tablep.

34


SI Base UnitsComparing Mass and Weight

– Mass is the measure of the amount of mater in an object. •Unit = kg

– Weight is the measure of the gravitational pull on matter•Unit = N (newtons)•Dependant on gravity


SI Prefixesgiga G 1 Gm = 1 x 109 m

mega M 1 Mm = 1 x 106 m

kilo k 1 km = 1000 m

hecto h 1 hm = 100 m

deka da 1 dam = 10 m

1 m = 1 meter

deci d 1 dm = 0.1 m

centi c 1 cm = 0.01m

milli m 1 mm = 0.001m

micro μ 1 μm = 1 x 10-6 m

nano n 1 nm = 1 x 10 -9 m


SI Conversions Image

p.

40

*


Derived SI Units• Derived Units – a combination of

SI units• Example 1 kg/m∙sec2 = 1 pascal

(Pa)• Volume – the amount of space

occupied by an object– L x W x H = 1m x 1m x 1m = 1m3

– 1dm x 1dm x 1dm = 1dm3 = 1 liter– 1cm x 1cm x 1cm = 1cm3 = 1 mL


Derived Units Tablep.

36


Density• The ratio of mass to volume• D = M / V• Unit = kg/m3 or g/cm3 = g/mL• A characteristic physical property• Can be used to identify a

substance• Varies with temperature


Density Tablep.

38

Chapter x Section x Section title pages xx-xx

30

Densi

ty F

orm

ula

A

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Density1. What is the density of a block of

marble that occupies 310 cm3 and has a mass of 853 g?

2. Diamond has a density of 3.26g/cm3. What is the mass of a diamond that has a volume of 0.351 cm3?

3. What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given the density of mercury is 13.6 g/mL?

p. 4

0

1. 2.75 g/cm3 2. 1.14 g 3. 5.60 mL


A ratio derived from the equality between two different units that can be used to convert from one unit to another

Conversion Factors


• Conversion factors always equal 1.

• The numerator is equal to the denominator.

Conversion Factors

4 quarters1 dollar

= 1

12 inches1 foot

= 1

1 kilogram1000

grams

= 1


Convers

ion F

act

ors

A

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A mathematical techniquethat allows you to use unitsto solve a problem involving measurements

Dimensional Analysis



# given unit

xwanted

unitgiven unit= # wanted unit

Put in numbers to make the numerator

equal to the denominator



x x x x =

Arrange the units so that all cancel out except the last one, which should be the one you want.


Using Conversion Factors Imagep.

40

*


Dimensional Analysis• How many seconds in one week?


Dimensional Analysis1. Express a length of 16.45 m in

centimeters and in kilometers.2. Express a mass of 0.014 mg in

grams.

p.

40

1. 1645 cm and 0.01645 km 2. 0.000 014 g

41Chapter 2 Section 3 Using Scientific Measur. pages 44-57

Section 3

Using Scientific Measurements


Accuracy and Precision• Accuracy refers to

the closeness of measurements to the correct or accepted valueof the quantity measured

• Precision refers to the closeness of a set of measurementsof the same quantitymade the same way.


Acc

ura

cy &

Pre

cisi

on

Dart

s A

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on


Accuracy and Precision Imagep

. 4

4


Percent Error

• High percent error = low accuracy– Negative? Experimental is too low– Positive? Experimental is too high

Percentage error = Value

experimental-Value

accepted

Valueaccepted

100


Perc

ent

Err

or

Form

ula

Anim

ati

on


Percent Error1. Express a length of 16.45 m in

centimeters and in kilometers.2. Express a mass of 0.014 mg in

grams.

p.

40

1. 1645 cm and 0.01645 km 2. 0.000 014 g


Errors in Measurement• Skill of the measurer• Limitation of instruments• Estimation


Measu

ring L

iquid

s &

M

enis

cus

Anim

ati

on

Chapter 2 Section 3 Using Scientific Measur. pages 44-57

50

6.35 cm

p.

46

±0.01cm

certain

estimated

Plus or minus one of the estimated

decimal places

51Chapter x Section x Section title pages xx-xx

Affectionately called

“sig. figs.”


Brought to you by….


Nonzero integers always count as significant figures!


All the certain number in a measurement plus one estimated

figure.


There are three classes of zeros.

LEADING

CAPTIVE

TRAILING

http://www.youtube.com/watch?v=Nvc2PPTlW7k





These do not count

as significant figures.

0.00252.5 x 10-3


These count

as significant figures.

1.008


These do not count

as significant figures…

unless there is a decimal point.

100 vs. 100.1.00 x 102


These are determined by counting.

These have infinite significant figures.

2 atoms of H in H2O


These answer the question,

“What do we round to?”

There are two different rules:

Multiplication & Division

Addition & Subtraction


A team is only as good as its….

Your answer can only be as precise as your least precise (worst) piece of

data!

Practice!


The number of sig figs in the result is the same as the least precise

measurement used in the calculation.

13.54g /0.40ml =33.85 g/ml34 g/ml


The result has the same number of decimal places as the least precise

measurement used in the calculation.

13.85 + 0.0087 = 13.858713.86

+


In a series of calculations,

round at the very end.

LESS THAN

The preceding digit stays the same.

5 & GREATER

The preceding digit is increased by 1.



Significant Figures Rules Tablep.

47


Rule

s fo

r Sig

nifi

cant

Zero

s A

nim

ati

on


Roundin

g R

ule

s A

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on


Scientific Notation

M x 10n

Greater than or equal to 1 but less than

10

A whole number

A negative exponent means the number is smallA positive exponent means the number is large


Scientific Notation1. What is the volume, in

milliliters, of a sample of helium that has a mass of 1.73 x 10-3 g, given that the density is 0.178 47 g/L?

2. What is the density of a piece of metal that has a mass of 6.25 x 105 g and is 92.5cm x 47.3 cm x 85.4 cm?

p. 5

4

1. 9.69 mL 2. 1.67 g/cm3


Scientific Notation3. How many millimeters are there

in 5.12 x 105 kilometers?4. A clock gains 0.020 second per

minutes. How many seconds will the clock gain in exactly six months, assuming exactly 30 days per month?

p. 5

4

1. 5.12 x 1011 mm 2. 5.2 x 103 sec


Direct Proportions• Two quantities are directly

proportional to each other if dividing on by the other gives a constant value

• As Y increases; X increases

Y X

= k Y = k XThe equation for a

line!k is the slope.


Directly Proportional Graphp.

55

The line must go through the origin to be directly proportional


Inverse Proportions• Two quantities are inversely

proportional to each other if their product is constant.

• As X increases; Y decreases

X Y = k

produces a curve – a hyperbola


Inversely Proportional Graphp.

57


Dir

ect

ly P

roport

ional &

Invers

ely

Pro

port

ional

Gra

ph A

nim

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on

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