Chemistry Chemistry Notes Notes

Unit 2 MeasurementUnit 2 MeasurementMetricsMetricsScientific NotationScientific NotationUncertainty Uncertainty

The Metric SystemThe Metric System

Created by the French in 1795Created by the French in 1795Two type of units Two type of units FundamentalFundamental – deals with single – deals with single

measurements that describes a single measurements that describes a single phenomenon phenomenon Ex: time, distance, massEx: time, distance, mass

DerivedDerived – deals with two or more – deals with two or more measurements that describe a single measurements that describe a single phenomenonphenomenon Ex: m/s, Kg*m/sEx: m/s, Kg*m/s22, m/s, m/s22, N*m, N*m

The Metric SystemThe Metric System The metric system is much easier than our The metric system is much easier than our

standard system of measurement because standard system of measurement because units with in the metric system Are powers units with in the metric system Are powers of ten.of ten. Ex: convert 1200 g to kgEx: convert 1200 g to kg

Answer Answer 1.20 kg (just move the decimal) 1.20 kg (just move the decimal)

Ex: convert 40 oz. Ex: convert 40 oz. lbs lbs Answer Answer 2 ½ lbs (have to do some math) 2 ½ lbs (have to do some math)

The Metric SystemThe Metric System Some basic units Some basic units see table 2.1 on page 29 see table 2.1 on page 29

Length Length meters meters Time Time seconds seconds Mass Mass kilogram kilogram

Metric Prefixes Metric Prefixes see table 2.2 on page 29 see table 2.2 on page 29 Micro-Micro- 0.000 001 m0.000 001 m Mill- Mill- 0.001 m0.001 m Centi- Centi- 0.01 m0.01 m Deci -Deci - 0.1 m0.1 m Kilo-Kilo- 1000 m 1000 m

The Metric SystemThe Metric System

Definitions of fundamental measurementDefinitions of fundamental measurement MassMass = the amount of matter in an object = the amount of matter in an object

Measured in kilograms (kg)Measured in kilograms (kg) Not to be confused weight. Weight is more Not to be confused weight. Weight is more

comparable to force,comparable to force, W = mgW = mg

A A balancebalance is an instrument used to is an instrument used to determine mass determine mass

The Metric SystemThe Metric System Mass v. WeightMass v. Weight

The Metric SystemThe Metric System

Definitions of fundamental measurementDefinitions of fundamental measurement

LengthLength = the distance covered by a straight = the distance covered by a straight line segment between two pointsline segment between two points Measured in meters (m)Measured in meters (m)

Time Time – interval between two occurrences – interval between two occurrences Measured in seconds (s)Measured in seconds (s)

The Metric SystemThe Metric System

Definitions of fundamental measurementDefinitions of fundamental measurement TemperatureTemperature = the average kinetic energy of = the average kinetic energy of

the particles that make of matter.the particles that make of matter. Measured in Kelvin (K)Measured in Kelvin (K)

Kelvin is a scale based on molecular motion.Kelvin is a scale based on molecular motion. We also use Celsius (We also use Celsius (ooC) C)

To convert from (To convert from (ooC) to K:C) to K: K = 273.15 + (K = 273.15 + (ooC) C) ((ooC) = K – 273.15 C) = K – 273.15

Example problem: convert 25Example problem: convert 25ooC to KelvinC to Kelvin Example problem: convert 400 Kelvin to 25Example problem: convert 400 Kelvin to 25ooCC

Scientific Notation Scientific Notation

Scientific NotationScientific Notation Used in science because Used in science because

scientist often work with very scientist often work with very large or very small numberslarge or very small numbers Ex: Astronomers, Ex: Astronomers,

Bacteriologists, ChemistsBacteriologists, Chemists

Scientific NotationScientific Notation To add and subtract numbers that are in To add and subtract numbers that are in

scientific notation you have to:scientific notation you have to: Be sure the Be sure the numbers are to the same powernumbers are to the same power Be sure numbers are in the Be sure numbers are in the same unitssame units

NOT one in grams and one in kilogramsNOT one in grams and one in kilograms

ExamplesExamples:: 2.30 X 102.30 X 101616 + 3.44 X 10 + 3.44 X 101414 = __________ = __________

1.14 X 101.14 X 1077 – 3.11 X 10 – 3.11 X 109 9 = __________ = __________

Scientific NotationScientific Notation

To multiply or divide numbers that are in To multiply or divide numbers that are in scientific notation you have to:scientific notation you have to: Add exponents if you are multiplyingAdd exponents if you are multiplying Subtract exponents if you are dividingSubtract exponents if you are dividing

ExamplesExamples (6.87 X 10(6.87 X 108787) (8.24 X 10) (8.24 X 107373) = _________) = _________

(4.87 X 10(4.87 X 103636) / (8.55 X 10) / (8.55 X 102121) = ________) = ________

UncertaintyUncertainty

RecallRecall: in chemistry (or any science) we deal : in chemistry (or any science) we deal with a lot of uncertainty. Scientists have to be with a lot of uncertainty. Scientists have to be skeptical of their measurements and skeptical of their measurements and explanations – but how skeptical?explanations – but how skeptical?

QuestionQuestion: how do we handle uncertainty?: how do we handle uncertainty? AnswerAnswer: Calculations like : Calculations like percent errorpercent error and and

significant digitssignificant digits allow scientist to see how far allow scientist to see how far off they may be.off they may be.

UncertaintyUncertaintyPercent ErrorPercent Error: is calculated as seen below: is calculated as seen below

Percent Error = Percent Error = experimental value – theoretical valueexperimental value – theoretical value X 100 X 100theoretical valuetheoretical value

Because absolute value is used % error will always be a positive Because absolute value is used % error will always be a positive number.number.

Ex: what is the % error of an experiment where a student produces 43 Ex: what is the % error of an experiment where a student produces 43 g of sodium sulfite from the reaction including sodium, sulfur and g of sodium sulfite from the reaction including sodium, sulfur and oxygen? The theoretical mass of sodium sulfite was 49.2 g.oxygen? The theoretical mass of sodium sulfite was 49.2 g.

Ex: what is the % error of an experiment where a student observed that Ex: what is the % error of an experiment where a student observed that the time a certain reaction lasted was 15.24 s? The theoretical time that the time a certain reaction lasted was 15.24 s? The theoretical time that was calculated was 15.01 s.was calculated was 15.01 s.

UncertaintyUncertainty

Significant FiguresSignificant Figures

Question:Question: Which of the following Which of the following measurements is the most precise?measurements is the most precise? 12.000 m12.000 m 12 m12 m

UncertaintyUncertainty Answer:Answer: 12.000 m is more precise because 12.000 m is more precise because

what is being said is that this measurement was what is being said is that this measurement was to the closest 0.001 m opposed to being to the closest 0.001 m opposed to being measured to the closest meter. measured to the closest meter.

These numbers are not saying the same thing.These numbers are not saying the same thing. 12.000 is saying the measurement is between 11.999 12.000 is saying the measurement is between 11.999

m and 12.001m m and 12.001m 12 is saying the measurement is between 11 m and 12 is saying the measurement is between 11 m and

13 m 13 m 12.000 contains 5 significant digits whereas 12 only 12.000 contains 5 significant digits whereas 12 only

contains 2contains 2 All numbers but the last ones are certain.All numbers but the last ones are certain.

UncertaintyUncertainty

Determining Significant digits:Determining Significant digits: All non-zero numbers are significantAll non-zero numbers are significant

95.32 95.32 4 sig figs 4 sig figs Zeros after decimal points are significantZeros after decimal points are significant

54.100 54.100 5 sig figs 5 sig figs Zeros between non-zero numbers are significantZeros between non-zero numbers are significant

120.0000001 120.0000001 10 sig figs 10 sig figs Zeros that are place holders are Zeros that are place holders are notnot significant significant

0.000045 0.000045 2 sig figs 2 sig figs 0.001000 0.001000 4 sig figs 4 sig figs

SummarySummary

What questions do you still have?What questions do you still have? What was unclear?What was unclear?