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Multimedia Chemistry I & II (1996-9-11) [English].img
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à 1.2èScientific Notation
ä Express ê followïg numbers or calculations ï scientific notation with ê specified
or proper number ç significant figures.
â Express 306000 ï scientific notation ë four significant figures
èèèè306000 = 3.060x10É
The decimal poït moves five places ë ê left ë show only one digit
before ê decimal poït; å, consequently, ê power ç ten is 5.
éS In chemistry å many oêr areas as well, we frequently work
with very small å very large numbers.èHålïg êse numbers becomes
easier when êy are expressed ï an exponential form known as scientific
notation.èTry enterïg one ç ê fundamental constants ç chemistry å
physics, 0.000000000000000000000013806, ïë your calculaër.èYour
calculaër may accept this number, but ê number certaïly is ëo long
for ê calculaër display. In scientific notation this number is
1.3806x10úìÄ.èWhich way would you prefer ë write this number?
Hopefully you answered, "Usïg scientific notation".
The general form ç a number ï scientific notation is Nx10¡, where
N is normally a number with one place before ê decimal poït å "m" is
an ïteger.èTo write a number ï scientific notation, you count ê
number ç places that ê decimal poït must be moved from its origïal
location so as ë leave one nonzero figure before ê decimal poït.èIf
you move ê decimal poït ë ê left, ên ê exponent (power ç ten)
is positive.èWe usually omit ê plus sign ç a positive exponent.èIf
you move ê decimal poït ë ê right, ên ê exponent is a negative
ïteger.
Examples:è24000000 = 2.4x10Æèåè0.000018 = 1.8x10úÉ
It is helpful ë remember that a positive exponent means that ê number
is greater than one.èA negative exponent means that ê number is less
than one.
You need ë pay particular attention when addïg å subtractïg numbers
expressed ï scientific notation.èThe numbers must be expressed so that
ê powers ç ten are ê same.
èè 3.6x10æ + 5.761x10ô = 0.036x10ô + 5.761x10ô
èè 3.6x10æ + 5.761x10ô = 5.797x10ô
To represent 3.6x10æ so that ê power ç 10 is 8, we need ë move ê
decimal poït two places ë ê left.èMovïg ê decimal poït ë ê
left ïcreases ê value ç ê exponent.èOf course, your calculaër is
smart enough ë do this auëmatically; but if you want ë check your
results, you must be able ë do êse calculations without your calcu-
laër.
Durïg multiplication å division, we obey ê normal rules for hålïg
exponents.èIn multiplication, ê exponents are added.
èèèè10ⁿ x 10¡ = 10Ñⁿó¡ª
èèèè1.2x10É x 6.0x10Å = 7.2x10ö
èèèè5.9x10É x 7.4x10Å = 43.66x10ö, but we round ë 4.4x10îò
because êre are only two significant figures å we only want ë show
one place before ê decimal poït.
In division, ê exponent ç ê denomïaër is subtracted from ê
exponent ç ê numeraër.
èèèè10ⁿ / 10¡ = 10Ñⁿú¡ª
èèèè3.2x10Ä / 8.9x10úîì = 0.36x10ÑÄúÑúî쪪 = 0.36x10îÉ
èèèè3.2x10Ä / 8.9x10úîì = 3.6x10îÅ
To show one place before ê decimal poït, we moved ê decimal poït ï
0.36 one place ë ê right.èMovïg ê decimal poït ë ê right
decreases ê exponent.
Fïdïg powers å roots ç numbers raised ë a power is anoêr applica-
tion ç ê rule for addition.èTo fïd 10ⁿ ë ê "m"th power means that
10ⁿ is multiplied times itself "m" times.èSïce we add exponents, "n"
will be added "m" times, which is ê same as ê product ç n x m.
Symbolically, (10ⁿ)¡ = 10ⁿñ¡.è
To fïd ê "m"th root ç a number, we divide ê exponent by "m"
(or multiply by 1/m).
èèèèèèèmí─────
Symbolically,èá(10ⁿ)è= 10ⁿ¼¡.
Once agaï, your calculaër will håle êse operations but you should
be able ë check your results.èOccasionally, we encounter numbers that
exceed ê range ç normal calculaërs.èWhen takïg roots, ê exponent
must be evenly divisible by ê root.
What is ê cube root ç 8.8x10ìÄ?èThe power "23" is not evenly
divisible by 3.èBoth 21 å 24 are divisible by 3.èIf we make ê
exponent 21, ên ê number before ê 10ìî will be greater than 1 å
it should be relatively easy ë guess ê approximate cube root.
èè (8.8x10ìÄ)î¼Ä = (880x10ìî)î¼Ä
èèèèèèèèè = (880)î¼Ä x (10ìî)î¼Ä
èèèèèèèèè = 9.6x10Æ
1èExpress 4208000 ï scientific notation ë 3 significant
èèèèè figures.
è A) 4.208x10æèè B) 4.21x10æèè C) 4.20x10Åèè D) 4.21x10Å
üèTo express this number ï scientific notation, we must move ê
decimal poït 6 places ë ê left such that only ê 4 is left ç ê
decimal poït.èRoundïg 4.208000x10æ ë three significant figures
ïcreases ê zero ë 1 because 8 is greater than 5.
Ç B
2èExpress 70225600 ï scientific notation ë 4 significant
èèèèè figures.
èèèèè A) 7023x10Åèèèèè B) 7.0226x10Æ
èèèèè C) 0.7022x10ôèèèè D) 7.023x10Æ
üèTo express this number ï scientific notation, we must move ê
decimal poït 7 places ë ê left such that only ê 7 is left ç ê
decimal poït.èRoundïg 7.0225600x10Æ ë four significant figures
yields 7.023x10Æ because ê zero is significant.
Ç D
3èExpress 0.0006850 ï scientific notation ë 2 significant
èèèèè figures.
è A) 6.9x10úÅèè B) 68x10úÉèè C) 6.9x10úÉèè D) 6.8x10úÅ
üèWe must move ê decimal poït 4 places ë ê right such that
only ê 6 is left ç ê decimal poït.èConsequently ê power ç
ten is -4.èWhen roundïg ë two significant figures, we drop ê 50.
Roundïg even means that ê 8 remaïs unchanged.èThe fïal result is
6.8x10úÅ.
Ç D
4èExpress 0.000000083039 ï scientific notation ë 3 significant
èèèèè figures.
è A) 8.304x10úô B) 830x10úîò
è C) 8.30x10úô D) 8.304x10úÆ
üèWe must move ê decimal poït 8 places ë ê right such that
only ê 8 is left ç ê decimal poït.èConsequently ê power ç
ten is -8.èWhen roundïg ë three significant figures, we drop ê 39.
The fïal result is 8.30x10úô.
Ç C
5èComplete ê followïg calculation å express ê answer ë
ê proper number ç significant figures.
èèèèèèèèèèèèèèèèèèèèèèèèè 5.1x10îì
èèèèèèèèèèèèèèèèèèèèèè───────────────────── = ?
èèèèèèèèèèèèèèèèèèèèèè7.12x10îæ x 2.892x10Å
èèè A) 2.5x10úöèè B) 0.25x10úôèè C) 2.1èè D) 2.48x10úö
üèThe result ç this calculation should be reported ë two signifi-
cant figures because we are multiplyïg å dividïg numbers å 5.1x10îì
only has two significant figures.èApproximatïg ê answer, we would
round 5.1 ë 5, 7.12 ë 7, å 2.892 ë 3.èPerformïg ê operations
before ê powers ç ten, you obtaï 5/(7x3) = 0.24.èThe power ç ten ï
ê answer is 12 - 16 - 4 = -8.èSo our approximate answer is 0.24x10úô,
which we convert ë 2.4x10úö.èThe decimal poït was moved one place ë
ê right so we decreased ê exponent by one from -8 ë -9.èThe fïal
result is 2.5x10úö.
Ç A
6èComplete ê followïg calculation å express ê answer ë
ê proper number ç significant figures.
èèèèèèèèèèèèèèèèèèèèèèèè 4.221x10Ä
èèèèèèèèèèèèèèèèèèèèèè────────────────────── = ?
èèèèèèèèèèèèèèèèèèèèèè3.090x10ì x 8.011x10úæ
èA) 1.71x10Äèè B) 1.094x10úÅèè C) 1.705x10æèè D) 1.7051797x10æ
üèThe result ç this calculation should be reported ë four signif-
icant figures because we are multiplyïg å dividïg numbers each ç ê
numbers has four significant figures.èApproximatïg ê answer, we would
round 4.211 ë 4, 3.090 ë 3, å 8.011 ë 8.èPerformïg ê operations
before ê powers ç ten, you obtaï 4/(3x8) = 0.17.èThe power ç ten ï
ê answer is 3 - 2 - (-6) = 7.èSo our approximate answer is 0.17x10Æ,
which we convert ë 1.7x10æ.èThe decimal poït was moved one place ë
ê right so we decreased ê exponent by one from +7 ë +6.èThe fïal
result is 1.705x10æ.
Ç C
7èComplete ê followïg calculation å express ê answer ë
ê proper number ç significant figures.
èèèèè 1.38x10Ä + 2.77x10Å + 6.44x10ì = ?
è A) 2.97x10Åèè B) 1.059x10Éèè C) 3.552x10Åèè D) 2.9724x10Å
ü When addïg or subtractïg numbers that are expressed ï scien-
tific notation, we must first express ê numbers ë ê same power ç
ten.èSïce we are addïg êse numbers, ê sum must have a power ç ten
greater or equal ë ê largest number.èThe largest number has a power
ç ten equal ë 4.èRewritïg ê numbers so that êy are expressed as
ten ë ê fourth power leads ë
èèèèèèè 0.138x10Å + 2.77x10Å + 0.0644x10Å.
Remember that when we move ê decimal poït ë ê left, we ïcrease ê
power ç ten.èLookïg at ê numbers before ê tens, we have 0.138,
2.77, å 0.0644.èThe 2.77 is uncertaï ï ê hundredths place å
êrefore ê result ç ê sum 2.9724 is rounded ë ê hundredths
place.èThe fïal result is 2.97x10Å.
Ç A
8èComplete ê followïg calculation å express ê answer ë
ê proper number ç significant figures.
èèèèè 4.17x10úÅ + 8.826x10úÄ - 4.53x10úÉ = ?
èA) 9.1977x10úÄèè B) 8.466x10úÄèè C) 9.20x10úÄèè D) 9.198x10úÄ
ü When addïg or subtractïg numbers that are expressed ï scien-
tific notation, we must first express ê numbers ë ê same power ç
ten.èRewritïg ê numbers so that êy are expressed as ten ë ê -3
power leads ë (you could choose anoêr power ç ten)
èèèèèèè 0.417x10úÄ + 8.826x10úÄ - 0.0453x10úÄ.
Remember that when we move ê decimal poït ë ê left, we ïcrease ê
power ç ten.èLookïg at ê numbers before ê tens, we have 0.417,
8.826, å 0.0453.èThe 0.417 å 8.826 are uncertaï ï ê thousåths
place.èThe 0.0453 is uncertaï ï ê ten-thousåths place. Therefore,
ê result ç 9.1977 is rounded ë ê thousåths place, 9.198.èThe
fïal answer is 9.198x10úÄ.
Ç D
9èComplete ê followïg calculation å express ê answer ë
ê proper number ç significant figures.
èèèèè 7.112x10úÉ
èèèèè ────────── - 6.641x10úÄ = ?
èèèèè 2.56x10úì
è A) -0.257èè B) -3.86x10úÄèè C) 1.840x10úìèè D) -6.6407x10úÄ
üèWhen 7.112x10úÉ is divided by 2.56x10úì, ê result is
2.778125x10úÄ.èThis result has three significant figures å, êrefore,
is uncertaï ï ê hundredths place ç ê number before ê power ç
ten.èThe 6.641x10úÄ is uncertaï ï ê thousåths place ç ê number
before ê power ç ten.èThe difference must be uncertaï ï ê largest
valued place which is ê hundredths place ç ê number before 10úÄ.
The fïal answer is -3.86x10úÄ.
Ç B
10èComplete ê followïg calculation å express ê answer ë
ê proper number ç significant figures.
èèèèèè3.81x10Å + 9.73x10Å
èèèèèè─────────────────── = ?
èèèèèèèè5.6814x10É
èè A) 2.3832x10öèè B) 4.196èè C) 0.2383èè D) 6.53x10Ä
üèAddïg 3.81x10Å å 9.73x10Å, we obtaï 13.54x10Å or 1.354x10É.
This result has four significant figures.èWe are dividïg by a number
with five significant figures, so ê result can not have more than four
significant figures.èThe end result is 0.2383.
Ç C