Suggestion on note taking

Lab manual

Ch 1. Matter, Measurement, and Problem Solving

What is chemistry?

Matter and Mind

a specific matter — substance

Chemistry is the science of substances ― their

structure, their properties, and the reactions that

change them into other substances.

Linus Pauling

Substances are composed of extremely small particles called atoms.

If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.

Richard Feynman

Substances are composed of extremely small particles called atoms.

Atoms combine together and form a particlecalled molecule.

More details later.

hydrogen atom oxygen atom

hydrogen molecule oxygen molecule water molecule

Chemistry is the science of substances ― their

structure, their properties, and the reactions that

change them into other substances.

Linus Pauling

Mercury and Iodine Combine to Form Mercury (II) Iodide

Chemical Change = Chemical Reaction new substances produced

Chemistry is the science of substances ― their

structure, their properties, and the reactions that

change them into other substances.

Linus Pauling

Chemistry is a discipline of science that stronglydepends on experiments.

Experiments Measurements

Every physical quantity consists of a numberAND a unit.

Results of measurements: physical quantities

e.g.: length, temperature, voltage …

Two Systems for Units

English System

Metric System SI System

We use SI System for measurements

My height: 1.74 m

San Francisco to Barnesville: 4100000 m

Thickness of paper: 0.0002 m

Try to remember them.

My height: 1.74 m

San Francisco to Barnesville: 4100000 m

Thickness of paper: 0.0002 m

= 4100 km

= 0.2 mm

Scientific Notation

a x 10n

1 ≤ |a| < 10, n is an integer

Negative exponent:

33

110 0.001

10 5

5

110 0.00001

10

Express the following numbers in scientific notation

25 −1700 0.38 −0.0000990

Read Appendix I: A

a x 10n

1 ≤ |a| < 10, n is an integer

Units are involved in calculations just as numbers.

Your calculator does not deal with units.You must work on it!

Unit Calculations

Never drop units!

A physical quantity can be viewed asa product of a number and its unit.

a x

number unit

5 m

A B

AB = 15 m

C

AC = 10 m

CB = ?

CB = AB − AC = 15 m − 10 m = (15 − 10) m = 5 m

a x − b x = (a − b) x

H = 3 cm

W = 6 cm

Area = W x H = 6 cm x 3 cm = 18 cm2

a x • b x = ab x2

V = L3 = (5 cm)3 = 53 (cm)3 = 125 cm3

(a x)3 = a3 x3

What is the volume of a cube with edgelength 5 cm?

L = 5 cm

How many times is AB compared to CD in length?

AB 15m1.5

CD 10m

a a=

b

x

x b

A B15 m

C10 m

D

A B15 m

Time consumed to move from A to B is 5 s.What is the average speed?

153 3

5

Distance m mSpeed m/s

Time s s

meters per second

a a=

b b

xx/y

y

We use SI System for measurements

Mass is a measure of the quantity of material in anobject.

Weight is the force that gravity exerts on an object.

F = ma

G = mg

Unit: kg

Unit: N

Mass ≠ Weight

Chemistry is a discipline of science that stronglydepends on experiments.

Experiments Measurements

Some basic concepts related to measurements

Reliability of Measurements

Accuracy refers to the agreement of a particularmeasurement with the true value.

absolute error = experimental value − true value

To quantify accuracy, define:

experimental value (m) absolute error (m)

52 2

50 0

51 1

48 −2

True value = 50 m

sign of absolute error: direction|error|: size

relative error = absolute error / true value

= absolute error / theoretical

relative error is often given in percentage:

| |: to make % error a positive number

unknown

experimental value theoretical value% error = x 100%

theoretical value

theoretical: from calculation or provided by experts

experimental value (m) absolute error (m)

52 2

50 0

51 1

48 −2

True or theoretical value = 50 m

experimental value theoretical value% error = x 100%

theoretical value

What are the percent errors for the measurementslisted in the table?

1. Random Error: from imperfection of measurements. random, cannot avoid. can take average of multiple measurements to reduce it to certain degree.

Types of error based on sources

true value

2. Systematic Error:

usually from the measuring tool same direction could fix

Types of error based on sources

true value

Random error and systematic error.

Reliability of Measurements

Accuracy refers to the agreement of a particularmeasurement with the true value.

Precision is the degree of agreement among severalmeasurements.

Accuracy ≠ Precision

The Results of Several Dart Throws Show the Difference Between Precise and Accurate

No class on WednesdayLecture tomorrowMeet in classroom IC 420

Section E: 10:00 am

Section F: 1:00 pm

How to report a measurement?

mL

We report a measurement by recording

ALL the certain digits + ONE uncertain digit

Significant Figures

(except leading zeros. more details in a minute.)

Sig figs carry the information you know abouta physical quantity from your measurement.

Rules for counting sig figs

1. Nonzero digits always count.

2. Zeros a) Leading zeros do not count.

b) Zeros between nonzero digits always count.

c) Zeros at the end count only if the number contains a decimal point.

Special case: Exact numbers have infinite number of sig figs.Determined by counting, theory, or conversion.

Or conversions involving prefixes:

Rules for counting sig figs

1. Nonzero digits always count.

2. Zeros a) Leading zeros do not count.

b) Zeros between nonzero digits always count.

c) Zeros at the end count only if the number contains a decimal point.

Special case: Exact numbers have infinite number of sig figs.Determined by counting, theory, or conversion.

Examples: questions 77 and 78 on p 40

Note: Scientific expression does not change the number of sig figs.

a x 10n

1 ≤ |a| < 10, n is an integer

Only need to count sig figs in “a”

Rules for sig figs in calculations

1. For multiplication and division, the result has the samenumber of sig figs as the measurement with the fewestsig figs. (e.g. Q 83, practice on Q 84)

2. For addition and subtraction, the result has the samenumber of decimal places as the measurement with the

fewest decimal places. (e.g. Q 85, practice on Q 86)

Round properly

3. For calculations including two types, follow the two rulesin each step but round off at the end. (e.g. Q 87, practice on Q 88)

(made to preserve the information carried by the sig figs)

Or conversions involving prefixes:

Conversion factor # desired unit

# given unit

#: copy from the relation between two units.

= 1

Physical quantity with given unit x Conversion factor

= Physical quantity with desired unit

5.0 in = ? cm

5.000 in = ? cm

19.21 cm = ? in

6.81 cm2 = ? in2

66 km/h = ? m/s

5.000 in = ? m

3.2 m = ? mm

3.2 cm = ? mm

7.8 g/cm3 = ? kg/m3

Three Basic Physical Quantities

Volume

Density

Temperature

1 m = 10 dm = 100 cm

(1 m)3 = (10 dm)3 = (100 cm)3

1 m3 = 103 dm3 = 106 cm3

For liquid or gas, define: 1 L = 1 dm3

Then: 1 mL = 1 cm3

Volume and its units

How much room an object occupiesin space.

Density: mass of a substance per unit volume of the substance.

V

md ,

Volume

MassDensity

Unit: kg/m3, g/cm3, g/mL

Density is a property of substances. It is determined by thesubstance’s identity and external conditions, not by thesubstance’s mass or volume.

A metal has a mass of 35.5 g and volume 4.55 cm3.

a) What is the density of this metal?

b) What is the volume of the same kind of metal with mass 101 g?

c) What is this metal likely to be?

V

md ,

Volume

MassDensity

How to find density?

How to find mass? balance

How to find volume?

• Liquid: graduated cylinder, beaker, buret, pipet…

• Solid

Regular shape: Measure dimensions, then calculate

Irregular shape: water displacement

First lab, Experiment 2

• Gas: Chapter 5

Second lab, Experiment 3

Temperature scales

TC, Celsius scale, °C

TF, Fahrenheit scale, °F

TK, Kelvin scale, K (not °K)

Temperature: a measure of hotness or coldness of an object.

Temperature conversions

K C o

KT T 273 K

C

F23C5

F9TT o

o

o

CF

Normal body temperature is 98.6 °F. Convert this temperature tothe Celsius and Kelvin scales.

Problem Set 1