Unit 2Unit 2

Chapters 3 & 4Chapters 3 & 4

ReviewReview

Qualitative measurementQualitative measurement• Uses descriptive wordsUses descriptive words

Quantitative measurementQuantitative measurement• Uses numbersUses numbers

Exact vs. Measured NumbersExact vs. Measured Numbers

Exact numbers - counting numbersExact numbers - counting numbers• Not measurementsNot measurements• A stated value that is certainA stated value that is certain

Example: 100 years = 1 centuryExample: 100 years = 1 century

Measured numbers- have uncertainty Measured numbers- have uncertainty because of the equipment/device because of the equipment/device used and the observerused and the observer

Scientific NotationScientific Notation

Expresses numbers as a multiple of Expresses numbers as a multiple of two factorstwo factors

1.1. A number between 1 and 10A number between 1 and 10

2.2. 10 raised to a power (X) or exponent10 raised to a power (X) or exponent

# times 10 x

How can you tell if the power is How can you tell if the power is negative or positive?negative or positive?

If the number you are converting is…If the number you are converting is…• LESS than 1, the exponent will be LESS than 1, the exponent will be

NEGATIVENEGATIVEExample: 0.025 = 2.5 x 10 Example: 0.025 = 2.5 x 10 -2-2

• MORE than 1, the exponent will be MORE than 1, the exponent will be POSITIVEPOSITIVE

• Example: 7300 = 7.3 x 10 Example: 7300 = 7.3 x 10 33

Converting to Scientific NotationConverting to Scientific Notation# x 10# x 10xx

How? 4 steps:How? 4 steps:1.1. Move the decimal so that the front number Move the decimal so that the front number

is a single digit. (between 1 and 10)is a single digit. (between 1 and 10)

2.2. Count how many places the decimal moves. Count how many places the decimal moves. That number represents x in That number represents x in 10x..

3.3. If you move the decimal to the left, If you move the decimal to the left, then x is positive.then x is positive.

4.4. If you move the decimal to the right, If you move the decimal to the right, then x is negative.then x is negative.

Remember your vocabulary:Remember your vocabulary: The The xx in in 10x is called the is called the exponentexponent..

Converting to Scientific NotationConverting to Scientific Notation# x 10# x 10xx

Common Sense Double Check:Common Sense Double Check:1.1. If your answer has a If your answer has a negative negative

exponentexponent, then your original number , then your original number must be must be less than zeroless than zero..

Example: 1.0 x 10-2 = 0.01

2.2. If your answer has a If your answer has a positive exponentpositive exponent, , then your original number must be then your original number must be more than zeromore than zero..

Example: 1.0 x 102 = 100

Scientific NotationScientific Notation

Do the practice problemsDo the practice problems

Precision vs. AccuracyPrecision vs. AccuracyWhat’s the difference?What’s the difference?

Accuracy refers to the closeness of a Accuracy refers to the closeness of a measurement/measured value to the measurement/measured value to the accepted or known value.accepted or known value.• Accuracy = CorrectAccuracy = Correct

Precision refers to the agreement Precision refers to the agreement among several measurements/ among several measurements/ measured valuesmeasured values• Precision = ConsistencyPrecision = Consistency

Precision vs. AccuracyPrecision vs. Accuracy

Can an instrument be precise and not Can an instrument be precise and not be accurate?be accurate?

Bull’s EyeBull’s Eye

When is it precise but NOT accurate?When is it precise but NOT accurate?• Hits the same spot over and over but Hits the same spot over and over but

not near the Bull’s eyenot near the Bull’s eye When it is accurate but NOT precise?When it is accurate but NOT precise?

• Hit Bull’s eye once, and then not ever hit Hit Bull’s eye once, and then not ever hit it againit again

When is it accurate AND precise?When is it accurate AND precise?• Hit the Bull’s eye over and over again!!Hit the Bull’s eye over and over again!!

Example 1: Accuracy vs Example 1: Accuracy vs PrecisionPrecision

Example 2: Accuracy vs Example 2: Accuracy vs PrecisionPrecision

QuantityQuantity

A quantity includes both a number A quantity includes both a number and a standard unitand a standard unit

Examples: 14.5 g 12 miExamples: 14.5 g 12 mi

A quantitative measurement!!!!A quantitative measurement!!!!

Units of MeasurementsUnits of Measurements

Units used by scientists (everywhere) Units used by scientists (everywhere) and people (outside of the US)and people (outside of the US)

SystSystèème Internationale d’ Unitme Internationale d’ Unitéés or s or SI unitsSI units

Seven Base Units in SISeven Base Units in SI

QuantityQuantity Base UnitBase Unit

TimeTime Second (s)Second (s)

LengthLength Meter (m)Meter (m)

MassMass Kilogram (Kg)Kilogram (Kg)

TemperatureTemperature Kelvin (K)Kelvin (K)

Amount of a Amount of a substancesubstance

Mole (mol)Mole (mol)

Electric current Electric current Ampere (A)Ampere (A)

Luminous intensityLuminous intensity Candela (cd)Candela (cd)

Derived UnitsDerived Units

A combination of base units A combination of base units

Examples:Examples:

• Speed: meters/s or miles/hoursSpeed: meters/s or miles/hours

• Density: g/cmDensity: g/cm3 3 or g/mLor g/mL

Metric PrefixesMetric Prefixes

Powers of 10Powers of 10 Know the Metric Prefix to Power of 10Know the Metric Prefix to Power of 10 Mega (10Mega (1066) to pico (10) to pico (10-12-12)) Show chart and Practice Examples on Show chart and Practice Examples on

boardboard

ConversionsConversions The middle “man”The middle “man”

• Grams (g)Grams (g)• Liters (L)Liters (L)• Meters (m)Meters (m)

Set the Set the biggerbigger prefix as 1 when determining prefix as 1 when determining the conversion factors you needthe conversion factors you need• Example 1Example 1: how many kilograms are in 25 grams?: how many kilograms are in 25 grams?

Conversion factor: 1 kilogram = 1x10Conversion factor: 1 kilogram = 1x103 3

gramsgrams

• Example 2Example 2: how many micrograms are in 25 : how many micrograms are in 25 grams?grams?

Conversion factor: 1 gram = 1x10Conversion factor: 1 gram = 1x1066 microgramsmicrograms

DensityDensity

A ratio that compares the mass of an A ratio that compares the mass of an object to its volume orobject to its volume or

How much mass takes up a certain How much mass takes up a certain amount of volumeamount of volume

Density of an substance will NOT Density of an substance will NOT changechange• If the mass changes, then the volume will If the mass changes, then the volume will

change alsochange also• What kind of property is density?What kind of property is density?

Common Units of DensityCommon Units of Density

grams/ cmgrams/ cm33

grams/ mLgrams/ mL

Important Conversion to Know:Important Conversion to Know:

1 mL = 1 cm1 mL = 1 cm33

The Standard for All DensityThe Standard for All Density

Water!!Water!!

The density of water is 1.0 g/mLThe density of water is 1.0 g/mL

The End!!The End!!

Work on the Scientific and Standard Work on the Scientific and Standard Notation HandoutNotation Handout

HW:HW:• Complete Handout – scientific and Complete Handout – scientific and

standard notation only, not sig figs yetstandard notation only, not sig figs yet• Read Chapter 5.1 and complete Read Chapter 5.1 and complete

problems on page 164 #9-34; Some are problems on page 164 #9-34; Some are difficult. Don’t give up. Try every difficult. Don’t give up. Try every problem.problem.

Error Error The difference between an accepted value The difference between an accepted value

and an experimental value is ERRORand an experimental value is ERROR• Take the absolute valueTake the absolute value

No negative valuesNo negative values

| experimental – accepted | = error| experimental – accepted | = error

• Accepted- what you are “suppose” to Accepted- what you are “suppose” to getget

• Experimental- what you “actually” getExperimental- what you “actually” get

% Percent Error %% Percent Error %

Percent error- the ratio of an error to Percent error- the ratio of an error to an accepted valuean accepted value

Equation:Equation:

100% xlueAcceptedVa

ErrorError

Practice ProblemPractice ProblemSuppose you calculate your semester grade in Suppose you calculate your semester grade in

chemistry as 90.1, but you receive a grade chemistry as 90.1, but you receive a grade of 89.4.of 89.4. • What is your percent error?What is your percent error?

ErrorError

90.1- 89.4 = 0.790.1- 89.4 = 0.7

Percent errorPercent error

0.7/ 90.1 times 100 = 0.78%0.7/ 90.1 times 100 = 0.78%

Significant FiguresSignificant Figures

The The # of digits reported in a # of digits reported in a measurement indicates how precise measurement indicates how precise the measurement isthe measurement is

The more digits reported, the more The more digits reported, the more precise the measurementprecise the measurement

The digits reported are called SIG The digits reported are called SIG FIGSFIGS

Sig Fig’s cont’dSig Fig’s cont’d

The accuracy of the final answer to a The accuracy of the final answer to a problem problem depends upon the accuracy depends upon the accuracy of the numbers usedof the numbers used to express each to express each measurement usedmeasurement used

Digits in answers that are more Digits in answers that are more accurate than the measurements accurate than the measurements justify are NOT significant and justify are NOT significant and must must be droppedbe dropped

Significant FiguresSignificant Figures

If no decimalIf no decimal Start from the right Start from the right

until you hit the 1st until you hit the 1st non-zero numbernon-zero number

Examples: Examples:

31003100

20502050

405405

123123

If decimal is presentIf decimal is present

Start from the left Start from the left until you hit the 1st until you hit the 1st non-zero numbernon-zero number

Examples: Examples:

1.351.35

0.350.35

0.02400.0240

2.102.10

When are numbers significant?When are numbers significant?

ALL NONZEROALL NONZERO numbers are numbers are significant!!significant!!

When are ZEROS significant?When are ZEROS significant?

1. All zeros between NONZERO numbers 1. All zeros between NONZERO numbers are significantare significant

2. If a decimal is 2. If a decimal is NOT presentNOT present, the zero at , the zero at the end of the number is NOT significantthe end of the number is NOT significant

3. Zero that act as place holders are NOT 3. Zero that act as place holders are NOT significantsignificant

4. If a decimal is 4. If a decimal is presentpresent, zeros following , zeros following NONZERO numbers are significantNONZERO numbers are significant

5. All digits to the 5. All digits to the LEFTLEFT of the 10 of the 10xx (in (in scientific notation) are Significant!!scientific notation) are Significant!!

Sig Fig Measurement ExampleSig Fig Measurement Example

Significant Digits in CalculationsSignificant Digits in Calculations

When adding or subtracting, the When adding or subtracting, the answer may ONLY contain the answer may ONLY contain the LEASTLEAST accurate accurate decimal placedecimal place

Let’s do the example problemsLet’s do the example problems

Significant Digits in CalculationsSignificant Digits in Calculations

When multiply or dividing, the When multiply or dividing, the answer will have the answer will have the LEAST amount LEAST amount of significant digitsof significant digits

Let’s do the practice problemsLet’s do the practice problems

Specific GravitySpecific Gravity

Specific gravity is a comparison of Specific gravity is a comparison of the density of a substance with the the density of a substance with the density of a reference substance, density of a reference substance, usually at the same temperature.usually at the same temperature.

Water is the reference or standard = Water is the reference or standard = 1 (no units) 1 (no units)

Specific GravitySpecific Gravity

A hydrometer is the device that A hydrometer is the device that measures specific gravity.measures specific gravity.

Applications: urinalysis tests & Applications: urinalysis tests & antifreeze testsantifreeze tests

TemperatureTemperature

Used to describe how hot or cold an Used to describe how hot or cold an object feelsobject feels

2 scales commonly used: Celsius and 2 scales commonly used: Celsius and KelvinKelvin

One Kelvin is equal to one degree on One Kelvin is equal to one degree on the Celsiusthe Celsius

ConversionsConversions

To convert from Celsius to KelvinTo convert from Celsius to Kelvin

# °C + 273 = _____ Kelvin# °C + 273 = _____ Kelvin

To convert from Kelvin to CelsiusTo convert from Kelvin to Celsius

# Kelvin – 273 = _____ # Kelvin – 273 = _____ CelsiusCelsius

Practice ProblemsPractice Problems

0 degrees Celsius = ______ Kelvin0 degrees Celsius = ______ Kelvin

500 Kelvin = ________ Celsius500 Kelvin = ________ Celsius