Scientific Measurement

Measurementp A measurement is a quantity that has

both a number & a unit.p Examples: 67, 154, & 70 are just

numbers.p 67inches, 154 pounds, & 70 miles per

hour, are measurements!

Precision vs. AccuracypPrecision: the ability to reproduce the

same value in a measurement. In other words, how repeatable measurements are.

pAccuracy: The agreement between a measured value & the true value. In other words, how close a measurement comes to the actual value (the target).

p Precise does not always mean accurate.

Precision vs. Accuracy cont.p

Significant Figures/Digitsp Significant Figures are all the digits in a

number that are known & the last digit that is estimated.

p They determine where to round off a calculation.

Significant Figures Rules:

1. Non-zero numbers are always significant.

2. Zeros between digits are always significant.

3. Initial zeros are not significant. (Example: 0.0003 has only 1 sf.)

4. Zeros at the end of the number are significant IF there is a decimal point.(24.0 cm has 3 sf)

Scientific NotationpPurpose: to express very large or very

small values easily.p Ex. 1,000 = 1 x 103 0.001 = 1 x 10-3

p To convert-nMove the decimal point until there is only one

digit (number) before the decimal point.n The number of moves = the exponent

pMove to the left = positive exponentpMove to the right = negative exponent

Scientific Notation cont.p Let your calculator do the work (use

the EE (or exp) button)p Examples:

5,280 = 3 moves to the left so, 5.28 x103

0.0899 = 2 moves to the right so, 8.99 x 10-2

SI Units

• There are two types of units:– fundamental (or base) units;– derived units.

• There are 7 base units in the SI system.- We only use 4-5

Metric System Quantity Unit Symbol

Mass* Gram g

Length* Meter m

Time* Second s

Temperature* Kelvin K

Amount* Mole mol

SI Units

Metric Tablemega kilo hecto deca Base

Unitdeci centi milli micro

M k H da d c m u1,000,000 1,000 100 10 Gram g

Liter LLength m

0.1 0.01 0.001 0.000001

1.0 x106 1.0 x103 1.0 x 102 1.0 x101 1.0x10-1 1.0x10-2 1.0x10-3 1.0x10-6

Derived UnitspDerived Unit is a combination of other

units to reach a measurement. There are 2 common derived units we will use.nVolume = cm3 or m3 = formula (L x W x H)nDensity = g/cm3 = from formula (D = m/v)

Volume

• The units for volume are given by (units of length)3.– SI unit for volume is 1 m3.

• Common: 1 mL=1 cm3.

• Other volume units:1 L = 1 dm3 = 1000 cm3 =

1000mL.

Volume

Density

• A physical property.• Defined as mass divided by volume:

• Units: g/cm3 or g/mL• Originally based on mass (density was defined as

the mass/vol. of 1.00 g of pure water).

volumemassDensity =

SI Units

TemperatureThere are three temperature scales:• 1. Kelvin Scale

– Used in science.– Same temperature increment as Celsius scale.– Lowest temperature possible (absolute zero) is zero Kelvin. – Absolute zero: 0 K = −273 oC.

Temperature

• 2. Celsius Scale– Also used in science.– Water freezes at 0 oC and boils at 100 oC.– To convert: K = oC + 273.

• 3. Fahrenheit Scale– Not generally used in science.– Water freezes at 32 oF and boils at 212 oF.– To convert: Look up the formula – then forget it.

( )32-F95C °=° ( ) 32C

59F +°=°

Temperature Scalesp Know MP and BP of water in all three.

What the Heck is a Mole?Atoms & molecules are too tiny & numerous

to count. (Imagine counting grains of sand!) It is much easier to weigh atoms & molecules. Chemists use a mole to represent a specified number of particles. One mole of an element =6.02 x 1023 =the atomic mass. (See periodic table)

Kind of like a dozen = 12. Except a mole =

Dimensional Analysis

• Method of calculation utilizing a knowledge of units.

• Conversion factors are simple ratios (fractions):

unitgiven unit desired factor Conversion aswritten

Using a Conversion Factor

• Example: convert length in meters to length in centimeters:

• 3.25 meters x 100 cm = 325 cm1 m

Using Two or More Conversion Factors

• Example to convert length in meters to length in inches:

• 3.00 meters x 100 cm x 1 inch = 118 in1 m 2.54 cm

This takes practice. Be patient.

pPercent Error – used to compare data (observed values) to accepted/true values in a meaningful way

p │ Obs – Acc│ x 100 = % errorAcc