Measurement & Measurement & ConversionsConversions

Get ready for some math!!!!

Scientific NotationScientific NotationUsed for very large or very small

numbersAll numbers are represented by a

number between 1 and 10 multiplied by a power of 10

The number of places the decimal point has moved determines the power of 10. ◦ If the power is positive, the decimal point

will move to the ◦ If the power is negative, the decimal point

will move to the left

MeasurementMeasurementMeasurements and calculations

allow for some of the properties of substances to be determined (mass, density)

Scientific Notation is often used because measurements in chemistry can be very large or very small

Convert the following numbers Convert the following numbers to scientific notationto scientific notation

24500

356

0.000985

0.222

12200

Convert the following scientific Convert the following scientific notation numbers to regular notation numbers to regular numbersnumbers

4.2 x 103

2.15 x 10-4

3.14 x 10-6

9.22 x 105

9.57 x 102

Significant FiguresSignificant FiguresAll measured quantities are

generally reported in a way that the last digit is UNCERTAIN.

All other digits are considered SIGNIFICANT.

Rules for Sig FigsRules for Sig Figs

1. Nonzero digits are always significant.

22.6 kg has 3 significant figures453.9 m has 4 sig figs

2. Zeros between nonzero digits are significant.

20.3 kg has 3 sig figs87009 L has 5 sig figs

Rules for Sig Figs cont’dRules for Sig Figs cont’d

3. Zeros in front of nonzero digits are not significant (they simply are decimal place holders)

0.0009876 has 4 sig figs 0.0008 has 1 sig fig4. Zeros both at the end of a

number and to the right of a decimal point are significant

85.00 kg has 4 sig figs 9.0700000000 has 11 sig figs

Rules for Sig Figs cont’dRules for Sig Figs cont’d5. Zeros both at the end of a number

but to the left of a decimal point may not be significant. If a zero has not been measured or estimated, it is NOT SIGNIFICANT. A decimal point placed after zeros indicates that the zeros are significant.

2000 m has one significant figure

2000. m has four sig figs

Rules for CalculationsRules for CalculationsMultiplication or Division –

◦Final answer has the smallest # of sig figs

◦DO NOT ROUND UNTIL THE VERY END.

Addition or Subtraction – ◦Result cannot have more decimals

places than the unit with the smallest # of decimal places

Rules for CalculationsRules for CalculationsIf a calculation has both

multiplication (or division) and addition/subtraction, round after each operation.

EXACT VALUES HAVE UNLIMITED SIG FIGS

2 MOLECULES ARE 2 MOLECULES. = COUNT VALUE

SI UnitsSI Units

MeasurementMeasurement SymbolSymbol UnitUnit AbbreviationAbbreviation

LengthLength ll metermeter mm

MassMass MM kilograkilogramm

kgkg

TimeTime tt secondsecond ss

Therm. TempTherm. Temp TT kelvinkelvin KK

Amount of Amount of substancesubstance

nn molemole molmol

PrefixesPrefixes

PrefixPrefix SymbolSymbol MeaningMeaning

MegaMega MM 101066

KiloKilo KK 101033

DeciDeci DD 1010-1-1

CentiCenti CC 1010-2-2

MilliMilli MM 1010-3-3

MicroMicro 1010-6-6

Conversion in MetricsConversion in Metrics

K H D M D C M

Find the number of m in 2.35 km.

Find the number of km in Find the number of km in 756 m756 m

Conversion FactorsConversion FactorsA ratio that is derived from the

equality of two different units that can be used to convert from one unit to the other

5 dozen eggs = how many individual eggs?1 dozen = 12

individual

5 dozen x 12 individual = 60 individual eggs

1 dozen

CONVERSION FACTOR

How many g is 8503 mg?How many g is 8503 mg?

How many mm is 0.331 How many mm is 0.331 km?km?

Derived UnitsDerived UnitsUnits derived from the seven base unitsVolume= l x w x h (m3) Volume

◦ The most common used unit for volume is cm3.◦ 1cm3 = 1ml ◦ 1000cm3 = 1dm3 = 1000ml = 1L.

density◦ Density is the ratio of the mass of an object to its volume◦ Density = mass volume

Precision vs. AccuracyPrecision vs. AccuracyAccuracy- the accuracy of a

measurement is how close the measurement is to the true or actual value

Precision – is how closely several measurements made agree with one another.

Percent Error Analysis Percent Error Analysis

% Error = Measured value – Accepted Value

Accepted value