dr. lucio gelmini room 5-132a gelminil@macewan.ca 497 …academic.macewan.ca/gelminil/intro.pdfyour...

Chemistry 101Dr. Lucio Gelmini

Room 5-132AGelminiL@macewan.ca

497-5813http://academic.macewan.ca/gelminil

Welcome to CHEM 101Grant MacEwan University

September 2011

Welcome to Day One!

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Chemical Principles 6ed, Student solutions manual & OWL access code w/ ebook, $144.95

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•Room 7-143 Friday, September

9 10:30 AM-12:30 PM•Room 5-206 Tuesday, September

13

11:00

AM

1:00

PM

Thank You Have a Great Semester!

Goals for this class and beyond•

To develop chemical intuition and curiosity

•

To acquire the knowledge and know- how for solving chemistry problems

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To learn how to learn, particularly in a science classroom

–Definitions

–Scientific problem solving

–Math review

–Uncertainty in measurement and significant figures

Review topics

What is chemistry?•

Chemistry is the science of matter and its transformations

•

Goals:–

to better understand the nature of matter

–

to predict and control its behavior–

to develop new combinations, processes, and applications

Scientific method•

Observations–

Qualitative, quantitative, or semi-quantitative

•

Hypothesis–

Initial opinion or guess

•

Experiments–

Rational, repeatable investigations

•

Verification/communication–

Further investigation

–

Formulation of laws, theories, and/or models

Thinking chemically•

Problem solving: repetition, practice, and experience

•

Educated guessing

•

Trial and error

Central idea in chemistry•

Macroscopic properties and behavior result from submicroscopic properties

•

Observable changes ↔

Unobservable causes

Definitions•

Matter:

has mass and volume

•

Properties: characteristics that give each substance a unique identity

–

Physical: shows these by itself withoutinteracting with another substance color, state (s, l, g), density, …

–

Chemical: substance shows these as it interacts with or transforms into other substances reactivity, flammability, …

Physical vs. chemical change

•

Physical change

Chemical Change•

Ice (solid water) → liquid water

Water

→ hydrogen + oxygen

Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Physical states of matter

Example physical & chemical properties of copper

Shiny

Reddish

Malleable

Conductive

d = 8.95 g/cm3

melts at 1083°C

boils at 2570°C

slowly reacts in moist air

reacts with nitric acid

slowly forms a deep-blue solution in aqueous ammonia

Conceptual chemical reactionA + B ↔ C + D

“Reactants”

→ “Products”

“Forward”

and “reverse”

direction

•

Depending on the process or reaction:–

Energy can be absorbed or released

–

Energy change can be large or small

Examples•Chemical reaction:

Methane (natural gas) combustion releases heatCH4

(g) + 2 O2

(g) → CO2

(g) + 2 H2

O(g)

•Physical transformation:

Water boiling to form steam requires energy

H2

O(l) →

H2

O(g)

Problem Solving– Identify problem

•

Given and desired values

– Plan•

Find known relationships

– Set up•

Conversion/unit cancellation

– Calculate solution•

Number and units

Quantitative science•

Values:–

number + unit

•

Units:–

chemistry uses SI units (International System of Units) –

the metric system

•

Math:–

go through appendix 1 (math review) and 2 (units/calculations)

Exact vs. inexact numbers•

Exact:–

defined or counted

–

have as many sig.figs. as needed–

no uncertainty

–

do not limit #sig.figs. in answer

•

Inexact:–

come from measurements

–

have associated uncertainty (from measurement)–

may limit #sig.figs. in answer

Precision vs. accuracy•

Precision–

how close repeated measurements are to each other →

reproducibility

•

Accuracy–

how close measurements are to actual (real) value →

correctness

•

Precise•

Not Accurate•

Better Accuracy•

Not Precise•

Precise•

Accurate

Mass of Water

9.80

9.90

10.00

10.10

10.20

1 2 3 4 5

Trial

Mas

s (g)

Precision vs. accuracySystematic error

–

measured values are all above or below real value

–

can be corrected for (in theory)

•

Random error–

measured values are scattered above and below real value

–

can only be minimized through more precise measurement/equipment

Mass of Water

9.90

10.00

10.10

10.20

10.30

1 2 3 4 5

Trial

Mas

s (g

)

Calculations and meaning – Significant Figures

•

Number of decimal places in a reported value:–

should reflect the precision of the measurement

–

depend on scale/divisions on measuring device

1.4 cm ±

0.1 cm

to 1/10 of a cm0 1 2

1.38 cm ±

0.01 cm

to 1/100 of a cm0 1 2

Rules for Determining Significance•

All non-zero digits are significant

•

Zeroes may or may not be significant–

Leading: NOT significant 0.0023 g has 2 sig.figs.

–

Buried:

ARE significant

0.00203 g has 3 sig.figs.

–

Trailing: depends on if a decimal point is presentwith “.”

–

significant 0.00230 g has 3 sig.figs.

without “.”–

who knows? 230 g has 2 or 3 sig.figs.Choice – express/convince yourself

Examples•

3400000 mL

•

0.0004050 g•

4.050 ×

10-4

g

•

43001 s•

0.1044 km

•

15.0 cm3

•

Scientific notation removes any ambiguity:•

Example:

1000 m

–

1.000 ×

103

m

4 sig.figs.

to ±1 m

–

1.00 ×

103

m

3 sig.figs.

to ±10 m

–

1.0 ×

103

m

2 sig.figs.

to ±100 m

Calculations and significant figures•

Addition & subtraction:–

Round answer to least precise decimal place

•

Multiplication & division:–

Round answer to least number of sig.figs.

106.78 mL = 106.8

mL

83.5

mL+ 23.28 mL

863.0879 mL = 863.1

mL

865.9 mL

-

2.8121 mL

= 23.4225 cm3

=

23

cm39.2

cm ×

6.80 cm ×

0.3744 cm

Rounding•

Round at the end of all steps in a calculation–

If the digit removed is more than 5, the preceding number increases by 1, hence, 1.347 g→1.35 g

–

If the digit removed is less than 5, the preceding number is unchanged, hence,1.343 g → 1.34 g

–

If the digit removed is 5, the preceding number increases by 1 if it is odd and remains unchanged if it is even.1.345 g → 1.34 g 1.335 g → 1.34 g

Example 1

=−cm

cmcm085.7

448.13521.16 22

cmcmcm

cmcmcm 104.2

085.7904.14

085.7448.13521.16 222

==−

•

All measured #s•

Units are kept or cancelled

mmcm

mcm 02104.010104.2100

1104.2 2 =×=× −

•

Defined relationship

Example 2( )

=××

31000

14

55.111080.4

cmmg mg

g

( )316.4

55.110.48

55.111080.4

331000

14

cmgmg

g

cmg

cmmg

==××

•

Measured #s •

Defined relationship

SI Base Units

•

First 5 –

most important in this class

Base quantity Name Symbollength meter m mass kilogram kg time second s

temperature kelvin K amount of substance mole mol luminous intensity candela cd

electric current ampere A

Derived units•

Combination of base units

•

Examples:

–

Area: two dimensional “length”

m × m = m2

–

Volume: three dimensional “length”m×m×m = m3

–

Speed: length”and

time →

m / s–

Work/energy:

mass, length, acceleration

kg × m × m/s2 = = J

And so on…

Prefixes

•

Bigger than base

Smaller than base

Exponential Name Symbol1×1024 yotta Y 1×1021 zetta Z 1×1018 exa E 1×1015 peta P 1×1012 tera T 1×109 giga G 1×106 mega M 1×103 kilo k 1×102 hecto h 1×101 deka da

Exponential Name Symbol1×10-1 deci d 1×10-2 centi c 1×10-3 milli m 1×10-6 micro µ 1×10-9 nano n 1×10-12 pico p 1×10-15 femto f 1×10-18 atto a 1×10-21 zepto z 1×10-24 yocto y

•

Express huge range of values in more manageable ways

Using prefixes•

Exponential replaces prefix and vice versa

•

More coming on conversion problems

gkg 31011 ×=

mnm 91011.411.4 −×=

Using relationships in conversion problems

•

What is the price of 325 cm of copper wire that sells for $0.15/ft?

•

Find desired –

look for words like “what is”, “calculate”, “find”, …–

Target:

price ($)

•

To what is target compared –

look at other end of the “question”–

Given:

325 cm wire

•

Set up problem to cancel units –

Price:

in $

Length: in cm

–

Length-price relationship: in $ and feet

•

Find conversion factors (may need to look up)(Given on test)–

1 in = 2.54 cm (exactly)

–

1 ft = 12 in (exactly)–

1 ft = $0.15(exactly)

•

Set up problem to cancel units•

Perform math –

check value and units

60.1$ft115.0$

in12ft1

cm54.2in1cm325 =×××

More•

How many sodium atoms would it take to form a line 1 foot long (1 foot = 0.3048 m) if the diameter of a sodium atom is about 186 picometers?

•

The symbol for sodium is Na.–

Target: # Na atoms Given:1 foot

–

Conversion factors:

1 foot = 0.3048 m1 pm = 1 ×

10-12

m

1 Na atom = 186 pm–

Calculation:

912

0.3048 1 11 1.64 101 1 10 186

m pm Na atomft Na atomsft m pm−× × × = ×

×

Density –

mass and volume•

Density:

ratio of mass to volume

•

Units: g/mL, g cm3, g/L, …•

Densities of common substances:

vmdor

volumemassdensity ==

Substance Physical State Density (g/cm3)Hydrogen Gas 0.0000899Oxygen Gas 0.00133

Grain alcohol Liquid 0. 789Water Liquid 0.998

Table salt Solid 2.16Aluminum Solid 2.70

Lead Solid 11.3Gold Solid 19.3

*At room temperature(200C) and normal atmospheric pressure(1atm).

Freezing and boiling points of water

MOST COMMON CONVERSIONS IN CHEMISTRY

g A ↔ mol A ↔ mol B ↔ g B

g CO to mol CO or mol CO to g CO(periodic table converts mass ↔ to moles)1 mol CO = 28.0103 g CO

How about mol A ↔ mol B?

Mol A ↔ Mol B

•

A few ways of doing this1.Chemical formula

H2

O says that for every mole of H2

O there are two moles H or one mol O1 mol H2

O = 2 mol H = 1 mol O

How about CuSO4

•5 H2

O Conversion factors?

Mol A ↔ Mol B

•

A few ways of doing this2.Chemical reaction (balanced)

2 Al(s) + 6 H+(aq) → 2 Al3+(aq) + 3 H2

(g) 3 mol H2

= 6 mol H+

= 2 mol Al = 2 mol Al3+

USE COEFFICIENTS IN BALANCE REACTION