Transcript what is chemistry - Maria Regina High School

WHAT IS
CHEMISTRY?
Demo: Let’s make slime!
Chemistry – the study of matter
and its reactions
Matter - anything that has
mass and volume
- Includes living and
non-living things
AREAS OF STUDY
Organic Chemistry – C compounds
Inorganic Chemistry – non-C compounds
Biochemistry – study of living matter
Analytical Chem. – composition of matter
Physical Chem. – mechanisms, rate and
energy transfer
THINKING LIKE A SCIENTIST
1.
2.
3.
The Scientific Method
Analyze - identify the known
- find the unknown
Calculate - make conversions
- solve for the unknown
Evaluate - does the answer make sense
Theory – a well tested explanation for a set of
observations
Law – concise statement that summarizes
a set of results
MATHEMATICAL CALCULATIONS
I Scientific Notation (Exponential form) – used
to express very large and very small numbers
coefficient X 10 to a power
↓
↓
> 1 < 10
the # of times the coefficient
is multiplied by 10 to equal
the standard number
Standard Form
Exponential Form
25,000
=
2.5 x 104
DETERMINING EXPONENTIAL FORM
For Numbers > 10
Exponent = the number of times the decimal
point is moved to the left to produce a
coefficient between 1 and 10
Ex. 8,200,000
6 places = 8.2 x 106 , or, 8.2 is
multiplied by 10 - 6 times
to equal 8,200,000
2,250
=
For numbers < 1
The exponent is negative
* Indicates the number of times the
coefficient is divided by 10 to get to the
standard
To convert from the standard – count the
number of times the decimal must be
moved to get to the coefficient
Ex. 0.00075 =
4 places = 7.5 x 10-4 or, 7.5 divided by
10, 4 times
CONVERTING FROM SCIENTIFIC
NOTATION TO STANDARD FORM
1.
2.
For + exponents → move the decimal to
the right
For (–) exponents → move the decimal
point to the left
Ex. 3.3 x 10-6 =
______________
1.5 x 103 =
______________
MULTIPLYING AND DIVIDING
Multiplying
1. Multiply the coefficients
2. ADD the exponents
3. Re-configure if necessary
Ex. (2 x 102) x (4 x 106) = ___________
(3.1 x 104) x (5 x 10-7) = ___________
Dividing
1.
2.
3.
DIVIDE the coefficients
SUBTRACT the exponents
Re-configure if necessary
Ex. 3.0 x 105 = ______________
6.0 x 102
3.0 x 105
6.0 x 10-3
= ______________
ADDING AND SUBTRACTING
1.
2.
3.
4.
Both exponents MUST be the same
Convert one number if necessary
Add (or subtract) the coefficients
Re-configure if necessary
Ex. 8.0 x 102 + 5.4 x 103 =
8.0 x 102 + 54 x 102 = _____________
II SIGNIFICANT FIGURES
Those digits (of a measurement) known
with certainty plus the right most digit that
is estimated.
Ex.
Counting Sig Figs
1. Every non-zero digit is significant
2. Zeros in the middle of a # are significant
ex. 605 = 3 sig figs
3. Zeros at the beginning of a number are NOT
significant = placeholders
ex. .0025 = 2 sig figs
4. Zeros at the end of a number are only significant if
they follow a decimal
ex. 7500 = 2 sig figs
ex. 75.00 = 4 sig figs
5. Counted numbers = unlimited sig figs
The Atlantic and Pacific Rule
(Easy way to count sig figs)
Does the number have a decimal point?
Decimal point Absent - Atlantic Ocean
Decimal point Present - Pacific Ocean


source
Decimal point present:
•Start on Pacific (left) side of number
•
Start counting with first non-zero
digit and count until the end of the
number
2545.300 g
has 7 sig figs
0.004530 km
has 4 sig figs
Decimal point absent:
•
Start on Atlantic (right) side of number
•Start counting with first non-zero digit
and count until the end of the number
5400 m
5431 m
has 2 sig figs
has 4 sig figs
Calculations with sig figs
Multiplication and Division
The answer can have only as many
significant figures as the number
with the least number of sig figs
Calculations are Rounded Off
24.56 cm X 14 cm =
a)
343.84 cm2
b)
343.8 cm2
c)
343 cm2
d)
340 cm2
EXAMPLE
2.2 X 104
X 3.12 X 106
Answer = 6.9 x 1010
Addition and Subtraction
The answer can have only as many
decimal places as the number with
the least number of decimal places
Calculations are Rounded Off
422.63 cm
29.472 cm
+________________
115.9 cm
a)
568.002 cm
b)
568.00 cm
c)
568.0 cm
d)
568 cm
MEASUREMENTS
Accuracy – a measure of how close a
measurement comes to the true value of
whatever is being measured
To evaluate – compare the measured value to
the true value
Precision – a measure of how close a series of
measurements are to one another
To evaluate – compare the values of 2 or
more repeated measurements
ACCURACY AND PRECISION
III CALCULATING ERROR
Error – difference between the accepted value
and the experimental value
may be + (greater) or – (less)
Calculated by % = Percent Error
% Error = Exp Value – Accepted Value x 100
Accepted Value
EXAMPLE
A student measured a sample of NaCl to be 22.75
grams. The true value of the sample was 22.50
grams. Calculate the % error
Known: Measured sample = 22.75 g
True mass = 22.50 g
Unknown: % error
Solve: 22.75 g – 22.50 g x 100 =
22.50 g
0.25 x 100 = 1.1 %
22.50
HW – PG 72 #’s 13-15
Measured value = 124.1o C
Actual value = 125.7o C
Unknown = % Error
Solve
124.1o C – 125.7o C x 100 = - 1.6o C =
125.7o C
125.7o C
0.0127287 x 100 = 1.272 %
13.
14.
11 soccer players
10, 800 m
0.070020 m
5.00 m3
note: counted items
have unlimited sig figs
15.
a)
b)
(5.3 x 104) + (1.3 x 104) = 6.6 x 104
(7.2 x 10-4) / (1.8 x 103) = 4.0 x 10-7
c.
104 x 10-3 x 106 = 107
d.
(9.12 x 10-1) – (4.7 x 10-2) =
(9.12 x 10-1) – (.47 x 10-1) = 8.7 x 10-1
e.
(5.4 x 104) x (3.5 x 109) = 18.9 x 1013 =
1.89 x 1014 = 1.9 x 1014
International System of Units
1790 – French Academy of Sciences
created the metric system
Based on 3 Requirements
Basic Standard = Earth
1.
The unit of length was to be a
portion of the Earth's
circumference
Internal Consistency
2.
Units for capacity (volume or space)
and mass related to the unit of length
Ease of Use - Calculations
3.
Larger and smaller units are created
by multiplying or dividing the basic
units by factors of 10
Smaller & Larger Units
►1/10
of a meter = decimeter
►1/100 of a meter = centimeter
►1/1000 of a meter = millimeter
►10
meters = dekameter
►100 meters = hectometer
►1000 meters = kilometer
Prototype kilogram in
France
Systeme International (SI)
►Based
on the metric system, invented
in 1790*
 Originally, earth-based standards
 Volume & mass linked to length
 Larger & smaller multiples of each unit
related by powers of 10
*updated in 1960
What is a meter?
1790: 1/10,000,000 th
of the distance from
the North pole to the
equator
1983: the distance light
travels in a vacuum in
1/299,792,458 th of a
second
What is a Liter?
• defined as a cube measuring 10
centimeters on each side, or
1000 cm3
10 cm
• based on the meter, which is
based on the Earth
10 cm
What is a kilogram?
mass of 1 Liter of water at 4°C
10 cm
Why water?
10 cm
So… the kilogram is based
on the liter, which is really
based on the meter, which is
really based on the Earth
What is a second?
The second was originally
defined as 1/86,400th of the
average solar day
Now: defined in terms of
electron transitions in Cs-133
7 Fundamental Quantities of SI
Quantity
Length
Mass
Name
Abbreviation
meter
kilogram
m
kg
Time
second
s
Temperature
kelvin
K
Amount of
Substance
Mole
mol
Luminous
Intensity
candela
cd
Electric Current
ampere
A
Derived Units
► Combinations
of fundamental units
► Many, many derived units
► Examples:




Speed or distance/time = m/sec
Area or Length X Width = cm2
Volume or Length X Width X Height = cm3
Density or Mass / Volume = g/ml
What is a kelvin?
The kelvin is defined in terms
of water & absolute zero
0 K = Absolute zero
bp of H2O = 100C = 373 K
mp of H2O = 0C = 273 K
What is a mole?
►The
amount of substance which has as
many elementary particles as there are
atoms in 0.012 kilogram (12 grams) of
carbon-12
METRIC MEASUREMENTS
MEASUREMENT
1.
2.
3.
4.
5.
Length
Mass
Volume
Temperature
Time
DEFINITION
STANDARD UNIT
Prefixes in the SI System
Prefix
Symbol
Value
Power
Use
Giga
G
1,000,000,000
109
Gigabyte
Mega
M
1,000,000
106
Megamillion
Kilo
k
1,000
103
kilometer
deci
d
0.1
10-1
decimeter
centi
c
0.01
10-2
centimeter
milli
m
0.001
10-3
millimeter
micro

0.000001
10-6
micrometer
nano
n
0.000000001
10-9
nanometer
Prefixes
►The
prefixes can be used with all 7
fundamental units!
 Kilometer
 Milliliter
 Centigram
 Microsecond
 Nanokelvin
IV METRIC CONVERSIONS
1.
Temperature Conversions
K = oC + 273
oC = K – 273
ex. BP of H2O is 100o C
BP of H2O in K =
ex. FP of H2O = - 273o K
FP of H2O in o C =
CONVERSIONS
2.
Metric Conversions – used to measure quantities in
different ways
Ex. 1 meter = 10 decimeters = 100 cm = 1000 mm
Conversion Factor – a ratio of equivalent measurements
- used to change one unit to another unit
- the value of the numeral will change (in multiples of 10)
- actual size and quantity stays the same
ex. 1 m = conversion factor
100 cm
=
100 cm
1m
Conversion Factors
Write the conversion factors for the following:
l to ml
=
Kg to g
=
cm to mm
=
l to μl
=
Conversion Problems
► Convert 3.5
kg to g
► Known: 1000 g = 1 kg
► Unknown: # g
► Calculate
► 3.5
kg x 1000 g = 3,500 g
►
1 kg
► Note: conversion factor must be written to
cancel all units except the unknown unit.
V EQUATIONS
Density = Mass / Volume
How would you find mass if you are given
the density and the volume?
Solve for M
M=DxV
Solve for V
V = M/D
TO MODIFY AN EQUATION
Change Sides……..Change Signs
D = M
V
V=M
D
M = VD
EXAMPLE
P1 x V1 = P2 x V2
SOLVE FOR P2
P2 = P1 x V1
V2
CALCULATIONS WITH UNITS
Density = g/cm3
Mass = g
Volume = cm3
Mass = Density x volume
g = g
cm3
x
cm3
CALCULATIONS WITH UNITS
P2 = P1 x V1
V2
atm = atm x ml
ml
P in atm
V in ml