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The World of Chemistry
Chapter 1
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What Do Chemists Do?
• Solve Problems• Devise experiments • Analyze data• Draw conclusions• Develop products
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1.1. What Do Chemists Do?
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The Chemist’s Shorthand
• Matter:• Atoms:• Elements:• Molecules:• Compounds:
• Composition:
Chemistry is concerned with the systematic study of the matter of universeanything that has a mass and occupied space
the smallest identifying unit of an element
matter containing only one kind of atom element
two or more atoms bonded together
matter that contains different elements chemically bonded together
the relative proportions of the elements in a compound
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The Chemist’s Shorthand
• Matter:• Atoms:• Elements:• Molecules:• Compounds:
• Composition:
Chemistry is concerned with the systematic study of the matter of universeanything that has a mass and occupied space
the smallest identifying unit of an element
matter containing only one kind of atom element
two or more atoms bonded together
matter that contains different elements chemically bonded together
the relative proportions of the elements in a compound
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The Chemist’s Shorthand
compound
element
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The Chemist’s Shorthand
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The Chemist’s Shorthand
Pure substances
sucrose soln salt in sand
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The Chemist’s Shorthand
• Physical property: mp, bp, odor, color, etc• Physical change: change of physical properties
without changing chem. comp.• Chemical property : chemical reaction, combustion
• Chemical change: change in chemical comp.• Homogeneous mixture• Heterogeneous mixture
How can we tell the difference between the two substances ?
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The Chemist’s Shorthand
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The Chemist’s Shorthand
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Mixtures
• Homogeneous (solutions) vs. heterogeneous• homogeneous : uniform in composition• heterogeneous : Non-uniform in composition
• Separation by:• filtration : separating a heterogeneous solid-liquid
mixture• distillation : resolving a homogeneous solid-liquid
mixture
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The Scientific Method
Process of Science: asking questions and making careful observations.
science as a means of knowing;raising questions, designing experiments, gathering data, interpreting the data, drawing conclusions, raising more questions
: the structured way of knowing
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1.4. Units and Measurement
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Mass vs. weight
• Mass: a measure of the amount of matter
• Weight: a measure of downward force given by g.
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Prefixes
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Temperature Scales
Fahrenheit (German, 1714)Celsius (Swedish, 1742)
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Temperature Conversions
• KelvinTK = TC + 273
• CelsiusTC = (TF – 32)/1.8
• FahrenheitTF = 1.8(TC) + 32
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Sample Problem
The average human body temperature is 98.6o F. Express this temperature using the Celsius and Kelvin scales.
• TC = (TF – 32)/1.8TC = (98.6 – 32)/1.8 = 37.0o C
• TK = TC + 273TK = 37.0 + 273 = 310 K
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Derived Units
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Cubic meter, cubic centimeter
3
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Intensive & Extensive Properties
depends on how much quantity
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Density
massdensity = volume
Density reports the mass of a substance that is present in a given volume of the substance.
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Sample Problem
What is the density of a metal that has a mass of 61.5 g and a volume of 8.56 cm3?
=
=
3
3
massdensity = volume61.5 g
8.56 cm7.18 g/cm
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Conversion Factors
• One step conversions : a ratio, numerically equal to 1, by which
• a quantity can be converted from one set of units to another
• Multiple conversion factors
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1.5. Conversions and Dimensional Analysis
( ) =
39 lb 1 kg3 suitcases 53 kg1 suitcase 2.205 lb
• Use conversion factors to cancel unitsuntil the proper unit is in place.
• Three suitcases weigh 39 lbs each. How many kilograms is this?
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( ) =
4qt 0.946 L 1000 mL1 gal 3784 mL1 gal 1 qt 1 L
Sample Problem
How many milliliters are there in onegallon of soda?
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1.6. Uncertainty, Precision, Accuracy
• All measurements are made with some degree of uncertainty. To express uncertainty: 151±1 g.
• Exact numbers:a. Defined quantities such as a 1meter = 100
centimeters and items that are counted.• Precision:
a. Indicator of how close repeated measurements are to each other
• Accuracy: a. Indicator of how close a measurement is to its true
value
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Accuracy and Precision
Accuracy: How close we are to the true value. Precision: How close our measurements are to each other;
how consistent (or reproducible) our measurementsare.
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Significant Figures
: specific numbers in a measurement whose values we can trust325K / 3 = 108.33333333Are the endless decimal digits significant ?
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Sample Problem
a. 2012b. 0.0061c. 0.0130d. 6.02 x 1023
(four)(two)(three)(three)
How many significant figures are there in each of these numbers?
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Significant Figures in Calculations
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a. 13.42 – 2.9 =
Sample Problem
10.5
c. 5.5×102/(4.14 – 1.361) =b. (16)(0.0159) = 0.25
2.0×102
Report the answer to the correct number of significant figures.
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The Chemical Challenges of the Future
• Frontiers of medicine• New challenges in agriculture• Challenge of pollution• Global warming and pollution• Better materials• New ways to supply energy• Nanotechnology• Understanding life
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Career Opportunities in Chemistry