Chemistry, the Scientific Method, and the

SI System of Units

Chemistry is the study of matter

and the transformations it can undergo…

Chemistry is the study of matter

and the transformations it can undergo…

Chemistry Is All Around Us

…Matter is anything that occupies space.…Matter is anything that occupies space.

Parts of the Scientific Method

• Identify an unknown.• Make a hypothesis

(a testable prediction).• Experiment to test

the hypothesis.• Draw a valid conclusion.

Using the scientific method requires that one be a good observer.

observation inference

involves a judgmentor assumption

uses the fivesenses

DataObservations are also called data.

There are two types of data.

qualitative data quantitative data

descriptions; measurements; no numbers must have numbers

and UNITS

A Scientific Experiment

procedure

the order of events

in an experiment;

the “recipe”

Experiments must be controlled; they

must have two set-ups that must differ

by only one variable.

The conclusion must be based on the data.

variable

any factor that

could influence

the result

Make observationMake observation

Ask questionAsk question

Develophypothesis

Develophypothesis

Test hypothesis with an

experiment

Test hypothesis with an

experiment

Analyze dataand draw

conclusions

Analyze dataand draw

conclusions

Hypothesis IS

supported

Hypothesis IS

supported

Hypothesis is NOT

supported

Hypothesis is NOT

supported

Developtheory

Developtheory

Test hypothesis with furtherexperiments

Test hypothesis with furtherexperiments

Revisehypothesis

Revisehypothesis

Scientific Method

A Common System for Trade

In 1790, the French government appointed a committee of scientists to develop a universal measuring system.

English system of measurement originated in 1215 with the signing of the Magna Carta. It attempted to bring uniform measurements to world trade.

It took ~10 years, and they unveiled the Metric system.

length meter mmass gram gvolume liter Ltime second s

The SI International System of Units

Length meter m

Mass kilogram kg

Time second s

Amount of substance mole mol

Thermodynamic temperatureKelvin K

Electric current amperes amps

Luminous intensity candela cd

Quantity Name Symbol

Using only these 7 units, all other units of measurement can be derived. For example, area is meters squared. Another example

is electric charge which is amps multiplied by seconds.

Derived Units Commonly Used in Chemistry

Area square meter m2

Volume cubic meter m3

Force newton N

Pressure pascal Pa

Energy joule J

Power watt W

Voltage volt V

Frequency hertz Hz

Electric charge coulomb C

Quantity Name Symbol

Prefixes in the SI System

Power of 10 for Prefix Symbol Meaning Scientific Notation_______________________________________________________________________

mega- M 1,000,000 106

kilo- k 1,000 103

deci- d 0.1 10-1

centi- c 0.01 10-2

milli- m 0.001 10-3

micro- m 0.000001 10-6

nano- n 0.000000001 10-9

The Commonly Used Prefixes in the SI System

Area and Volume: Derived Units

Area = length x width

= 5.0 m x 3.0 m

= 15 ( m x m)

= 15 m2

Volume = length x width x height

= 5.0 m x 3.0 m x 4.0 m

= 60 ( m x m x m)

= 60 m3

Significant Figures, Precision, and Accuracy

Significant Figures• Significant figures are numbers that

mean something when reporting a value.

• Just because your calculator gives out the value 0.5384615 when 7.00 is divided by 13.0, to a scientist not all of the numbers in 0.5384615 have meaning.

• Significant figures reflect the significance of the measurements upon which the scientific calculation is based.

Rules for Counting Significant Figures -

DetailsNonzero integers always count as significant figures.

3456 has 4 sig figs.

Rules for Counting Significant Figures -

DetailsZeros

Leading zeros do not count as

significant figures.

0.0486 has 3 sig figs.

Rules for CountingSignificant Figures -

Details

Zeros Captive zeros

always count as significant figures.

16.07 has 4 sig figs.

Rules for CountingSignificant Figures -

DetailsZeros Trailing zeros are significant only if the number contains a decimal point.

9.300 has 4 sig figs.

Rules for CountingSignificant Figures -

Details

• Exact numbers (such as those in conversion factors) have an infinite number of significant figures.

1 inch = 2.54 cm, exactly

Sig Fig Practice #1How many significant figures in each of the following?

1.0070 m

17.10 kg

100,890 L

3.29 x 103 s

0.0054 cm

3,200,000

Use the Rounding Poem to Round Numbers CorrectlyFind your numberLook right next door4 or less, just ignore5 or greater add one more!

Round 4.167 to the closest hundredths4.167 Find your

numberLook right next door4.17

Rules for Significant Figures in Mathematical

Operations

Multiplication and Division: the # of sig. figs. in the result equals the number in the least precise measurement (lowest # of sig. figs.) used in the calculation.

6.38 x 2.0 = 12.76 13 (2 sig figs)

Sig Fig Practice #2

3.24 m x 7.0 m

Calculation Calculator says: Answer:

22.68 m2 m2

100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 g/cm3

0.02 cm x 2.371 cm 0.04742 cm2 cm2

710 m ÷ 3.0 s 236.6666667 m/s m/s

1818.2 lb x 3.23 ft 5872.786 lb·ft lb·ft

1.030 g ÷ 2.87 mL 2.9561 g/mL g/mL

Precision and AccuracyAccuracy refers to the agreement of a particular value with the true value. If the true value were 5.00 and three measured values 2.0, 6.0, and 7.0 average out to 5.0 (as they do), then that set of measurements would be accurate.

Precision refers to the degree of agreement among several measurements made in the same manner.

Neither accurate nor

precise

Precise but not accurate

Precise AND accurate

Reporting Measurements

• This is where significant figures come from: actual measurements obtained in the laboratory.

• Report what is known with certainty

• Add ONE digit of uncertainty (estimate it!)

Practice Measuring

cm0 1 2 3 4 5

cm0 1 2 3 4 5

cm0 1 2 3 4 5

Avoid Parallax Errors When Measuring

Parallax errors arise when a meniscus or needle is viewed from an angle rather than from straight-on at eye level.

Correct: Viewing the meniscus

at eye level

Incorrect: viewing the meniscus

from an angle

Measuring Volume

Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level.

Read the volume using all certain digits and one uncertain digit.

Certain digits are determined from the calibration marks on the cylinder.

The uncertain digit (the last digit of the reading) is estimated.

Use the graduations to find all certain digits

There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are…

52 mL.

Estimate the uncertain digit and take a reading

The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is .

The volume in the graduated cylinder is

0.8 mL

52.8 mL.

10 mL GraduateWhat is the volume of liquid in the graduate?

_ . _ _ mL6 _6

25mL graduated cylinder What is the volume of liquid in the graduate?

_ _ . _ mL1 1

Self TestExamine the meniscus below and determine the volume of liquid contained in the graduated cylinder.

The cylinder contains:

_ _ . _ mL

Reading the ThermometerDetermine the readings as shown below on Celsius thermometers:

_ _ . _ C _ _ . _ C

Using the Balance• Use the On/Off Zero button to zero

the balance.• Use the Cal/Unit button to change

the units: g is grams, oz is ounces, ozt is troy ounces, and dwt is pennyweights.

Reporting Measurements: Once Again

• Report the digit for the unit that is known with certainty

• Add ONE digit of uncertainty (estimation)

• Even if the uncertain digit is 0, it still must be reported.