no slide title - mister chemistry problem 3 a metal cube has a mass of 20 g and a volume of 5 cm3....
TRANSCRIPT
Measurement
International System of Units (SI)
• revised metric system proposed in 1960
• widely used in science
• 7 base units
SI Base Units
Length Meter mMass Kilogram kgTime Second sElectrical current Ampere ATemperature Kelvin KAmount of Substance Mole molLuminous intensity Candela cd
SI Prefixes
Tera- T 1012 Deci- d 10–1
Giga- G 109 Centi- c 10–2
Mega- M 106 Milli- m 10–3
Kilo- k 103 Micro- µ 10–6
Nano- n 10–9
Pico- p 10–12
Derived units in SI
measured in terms of one or more base units
= 1000 (dm3 )
1dm3 = 1 liter ( L)
= (m3)volumem x m x m
= (g/cm3) = (g/ml)mass/volumedensity
= (kg/dm3)
Density
The mass of a substance that occupies one unit of volume
massvolume
Density =kg
dm3=
g
cm3=
g
ml=
Example
What is the density of a piece of concrete that has a mass of 8.76 g and a volume of 3.07 cm3
massvolume
Density =8.76g
3.07 cm3= = 2.85g/cm3
practice problem 1
A piece of metal with a mass of 147 g is placed ina graduated cylinder. The water level rises from 20 ml to 41 ml. what is the density of the metal.
mass
volumeDensity =146 g
21 ml= = 6.95 g/ml
20 ml41 ml =- 21 ml
practice problem 2
What is the volume of a sample that has a mass of 20 g and a density of 4 g/ml
= 5 ml20 g 4 g
mlx
Practice problem 3
A metal cube has a mass of 20 g and a volume of 5 cm3. Is the cube made of pure aluminum?
mass
volumeDensity =20 g
5 cm3= = 4 g/ml
density of Aluminum is 2.7 g/ml
Temperature
There are three systems for measuring temperature that are widely used:
Kelvin scale
Celsius scale
Fahrenheit scale
K = C˚ + 273.15
C˚ = K - 273.15
F˚ = C˚ (9/5) +32
C˚ = ( F˚ - 32) 5/9Used mainly in engineering
TemperatureKelvin scale Celsius scale Fahrenheit scale
373.15
273.15
233.15
100˚C
0˚C
- 40˚C
212˚F
32˚F
-40˚F
Handling Numbers
In chemistry we deal with very large and very small numbers
Scientific Notation
is a way of dealing with numbers that are either extremely large or extremely small
N x 10n
where N is a number between 1 and 10 and n is an exponent that can be a positive or negative integer
Exponents
0.001 = = 10-3
10 1
10 1
10 1
x x
10 x 10 = 102100 =
0.1 =10 1
= 10-1
Example
Express 568.762 in scientific notation.
568.762 = 5.68762 x 102
note that the decimal point moved to the left by two places and n = 2.
Example
Express 0.00000772 in scientific notation.
0.00000772 = 7.72 x 10–6
note that the decimal point moved to the right by six places and n = –6.
practice problem 12
Express the following quantities in scientific notation.
c. 4500000 m
d. 685000000000 m
.
.
= 4.5 x 106
= 6.85 x 1011
practice problem 12
Express the following quantities in scientific notation.
e. 0.0054 kg
f. 0.00000687 kg
.
.
= 5.4 x 10-3
= 6.87 x 10-6
Scientific Notation
To add or subtract using scientific notation, first write each quantity with the same exponent n. Then add or subtract the N parts of the numbers; the exponent parts remain the same.
practice problem 14e
(1.26 x 104 kg) + (2.5 x 103 kg)
= 1.51 x 104 kg
= (1.26 x 104 kg) + (0.25 x 104 kg)
practice problem 14f
(7.06 x 10-3 kg) + (1.2 x 10-4 kg)
= 7.18 x 10-3 kg
= (7.06 x 10-3 kg) + (0.12 x 10-3 kg)
Scientific Notation
To multiply numbers expressed in scientific notation, multiply the N parts of the numbers in the usual way, but add the exponent n’s together.
practice problem 15a - 15b
(4 x 102 cm) (1 x 108 cm)
= 4 x 1010 cm2
(2 x 10-4 cm) (3 x 10-2 cm)
= 6 x 10-6 cm2
Scientific Notation
To divide numbers expressed in scientific notation, divide the N parts of the numbers in the usual way, but subtract the exponent n’s together.
practice problem 16a - 16c
6 x 102 g / 1 x 108 cm3
= 3 x 101 g/cm3
= 3 x 106 g/cm3
9 x 105 g / 3 x 10-1 cm3
The Unit-Factor Method ofSolving Problems
also called “dimensional analysis”
it is a good idea to carry units in a calculation to ensure that the answer to the problem has the correct units
The Unit-Factor Method
2.54cm = 1 in dividing both sides of the equation by 2.54cm2.54cm2.54cm
1 in2.54cm
=1 we create an expression called a unit-factor
1 in
2.54cm=1 also called a
conversion factor
Example
What is the length of a 2.85cm pin in inches?
2.85 cm = 1.12 in1in2.54cmx
practice problem 17a
= 3.6 x 105 ms360 s 1 s
1000 msx
convert 360 s to ms
practice problem 17b
= 4.8 kg4800g 1000g
1 kgx
convert 4800 g to kg
550 m
1 s
Example 2 - 4
what is a speed of 550 meters per second in kilometers per minute
1 min
60 sx
1000 m
1 kmx
1 min
33 km=
60 min
1 hrx
How many seconds are there in 24 hours ?
24 hr1 min
60 sx = 8.64 x 104 s
practice problem 19
the density of gold is 19.3 g/mL.What is the gold’s density in decigrams per liter ?
practice problem 20
19.3 g
1 mL 1 L
1000 mLx
1 g
0.1 dgx
1 L
1930 dg=
Example
Where were you a billion seconds ago ?
1x109 sec24 hours
1 dayx
60 min
1 hourx
365 days
1 yearx = 31.7 years
1 min
60 secx