Chemical Foundations

Chapter 1

The Scientific MethodObservation

Hypothesis

Experiment

Theory (model)

Prediction

Experiment

TheoryModified

As needed

Law

Summary of observed

(measurable) behavior

Ex: law of conservation of

mass

A Theory (model) attempts to explain

why it happens

The Scientific MethodQualitative Quantitative

Overview:• Deals with descriptions• Data can be observed but not measured• Colors, textures, smells etc.•Qualitative -----Quality

Overview:• Deals with numbers• Data which can be measured• Length, Height, volume, weight, speed, time, temp• Quantitative-----Quantity

Example: Oil Painting• Blue & green paint• Gold frame• Masterful brush strokes

Example: Oil Painting• 10” x 14”• surface area 140 in2

• Weight: 8.5 pounds

Units of Measurement (1.3)

Physical Quantity Name of Unit Abbreviation

Mass Kilogram kg

Length Meter m

Time Second s

Temperature Kelvin k

Electric Current Ampere A

Amount of substance Mole mol

Luminous intensity Candela cd

SI System: based on the metric system and units derived from the metric system.

Units of Measurement (1.3)

Symbol Prefix Factor

G giga 109

M mega 106

k kilo 103

h hecto 102

da deka 101

BASE

d deci 10-1

c centi 10-2

m milli 10-3

μ micro 10-6

n nano 10-9

Units of Measurement (1.3)

Volume: is not a fundamental SI unit but is extremely important in chemistry. Volume can be derived from length.

Units of Measurement (1.3)

Mass vs. Weight

Remember MASS IS NOT THE SAME AS WEIGHT!

Mass is a measure of the resistance of an object to a change in its motion.

Weight is the response of mass to the force of gravity.

Uncertainty in Measurement (1.4)

Uncertainty: the uncertainty of measurement depends on the precision of the measuring device.Report any observed measurements by recording all the certain digits plus the first uncertain digit.

20.15 ml20.1 is certain 0.05 is uncertain

Precision and Accuracy (1.4)

Accuracy: agreement of a particular value with the accepted value.Precision: agreement among several measurements of the same quantity (reproducibility).

Precision and Accuracy (1.4)

Random Error: equal probability of being high or low.Systematic Error: error that occurs in the same direction each time.

Significant Figures & Calculations (1.5)

Scientific Notation

98,500,000 = ? 9.85 x 107

64,100,000,000 = ? 6.41 x 1010

0.0000000279 = ? 2.79 x 10-8

4,200,000 = ? 4.2 x 106

Significant Figures & Calculations (1.5)

Rules for counting Significant Figures:

1. Nonzero integers always count!2. Zeroes (3 classes):

a. Leading zeroes do not count (place holders)b. Captive zeroes do count

c. Trailing zeroes are if there is a decimal point

3. Exact numbers (counting or from definitions)

Significant Figures & Calculations (1.5)

Rules for Significant Figures in calculations:

1. For multiplication or division: the resultant is the same as the LEAST precise number in the calculation.2. For addition or subtraction: the resultant is the same number of decimal places as the least precise measurement in the calculation.

3. Rounding: DO NOT round until all calculations are completed. Use only the first number to the right of the last significant figure.

Significant Figures & Calculations (1.5)

Example:

12.1118.0

+ 1.01331.123

31.1

Dimensional Analysis (1.6)

Unit Factor Method/Dimensional Analysis: converting a given result from one system of units to another.

• Start with what value is known, proceed to the unknown.

• Draw the dimensional lines.• Insert the unit relationships.• Cancel the units.• Do the math, include units in answer.

Rules for Dimensional Analysis:

Notice that 1 kelvin = 1 degree Celsius

Boiling point of water

Freezing point of water

Celsius

100 ˚C

0 ˚C

100˚C

Kelvin

373 K

273 K

100 K

Fahrenheit

32 ˚F

212 ˚F

180˚F

Temperature (1.7)

Temperature (1.7)

Tf = Tc x 9oF/5oC + 32o F

Tc = 5oC/9oF(Tf – 32o F)

Tk = Tc + 273.15

Density (1.7)

Recall that you can measure either the volume or the mass of an object. Density is a property that describes the relationship between these two measurements.

Density (1.7)

Compound Density in g/cm3 at 20o C

Chloroform 1.492

Diethyl ether 0.714

Ethanol 0.789

Isopropyl alcohol 0.785

Toluene 0.867

A chemist has an unknown solution that he wants to identify. He measured out exactly 25.00 ml (cm3) of the substance and found that it has a mass of 19.735 g at 20 C.

Density = 19.735 g/25.00 cm3 = 0.794 g/cm3

Classifying Matter

A homogeneous mixture is the same throughout with visibly indistinguishable parts. (Solutions)

A heterogeneous mixture is one that has visibly distinguishable parts.

Mixtures (a variable composition)

Substances, on the other hand, cannot be separated into different kinds of matterby physical means such as sorting, filtering, heating, or cooling. (ex: Table salt)

Classifying Matter

Some substances, like silver, contain only one kind of matter. These substances are called elements.

Classifying Matter

Matter

Heterogeneous HomogenousPhysical Means

Pure Substances

Compounds ElementsChemical Means