Foundations of chemistry

Chapter 1

Key concepts in this unit

• The scientific method • The definition of chemistry • Matter and energy

– States of matter– Chemical and physical properties– Chemical and physical changes

• Measurements in chemistry– Units and SI system– Uncertainty in measurement: precision and accuracy– Using dimensional analysis– Mass percent– Density and specific gravity– Heat, temperature, specific heat

The Scientific Method

• The generally accepted approach to solving problems in the sciences.

• The pattern is used to generate rigorous, reliable, and repeatable research procedures in the discovery of new scientific concepts.

Steps in the scientific method

• An initial question usually starts the process…

• Experiments/observations-

• Law-• Hypothesis-

– Hypothesis may lead to ________

• Theory-

hypothesis

observations

law

Chemistry—A study of matter and energy

• Matter—– Mass—– D & C 131:7—spiritual things are also material– Since matter is everywhere, a basic understanding of

chemistry is essential.

• Energy—• Types of energy

– kinetic– potential

Laws of conservation

• Conservation of matter:

• Conservation of energy:

• Most chemical changes (reactions) observe these two laws.

• Nuclear reactions—changing matter into energyE=mc2

• Conservation of matter and energy:

– D & C 131:7

Classifying matter—states of matter

SOLID LIQUID GASShape

Density

Compressibility

• Other (exotic) states of matter– Plasma– Bose-Einstein condensate– Supercritical fluid– More?

Properties of matter

• Physical properties—

• Chemical properties—

• Which are physical? Chemical?Melting pointdensityflammabilityconductivityMatter states

Properties of matter

• Intensive properties—

• Extensive properties—

• Which are intensive? Extensive?massvolumedensitymelting pointboiling point

Changes in matter

• Physical changes—

• Chemical changes—

• Chemical changes also called chemical reactions

• Which changes are physical? Chemical?– Combustion– Evaporation– Dissolution– Fission

• Two types– Heterogeneous– Homogeneous. A homogeneous mixture also

called a ____________• Water and salt vs water and sand.

– A homogeneous mixture may have some physical properties differing from its components (such as melting point or boiling point)

– NO change in chemical properties.

Mixtures

• Mixtures may be separated by physical means. Examples:

• Distillation—

• Filtration—

• Chromatography—

Chromatography essentials

• Mobile phase• Stationary phase• Solvent front

Gas chromatography

Substances

• Substances include elements and compounds. They CANNOT be separated by physical means.

• Compounds: ____________________________________________________________________________

• Compounds follow law of constant composition

• Elements: ____________________________________________________________________________

System Internationale (SI)internationally accepted system of

measurement• SI units

– Mass – – Length – – Volume – – Temperature –

• Prefixes– 109 – giga (G) – 106 – mega (M)– 103 – kilo (k)– 10-2 – centi (c)– 10-3 – milli (m)– 10-6 – micro ()– 10-9 – nano (n)– 10-12 – pico (p)

Know all SI units

and prefixes on p 17 of text !!!

Uncertainty in measurement

• Two types of numbers:

–Exact numbers (counting or defined)

–Measured numbers

Accuracy and precision

• Accuracy— how close a single measurement is to a “true” value.

• Precision— how close a group of measurements are to each other

Precision vs. accuracy

Accurate and precise Precise, but not accurate

Accurate, but not preciseNeither accurate nor precise

Significant figures

• Used to illustrate how accurate and precise the measurement is.

• Measurements are reported where the last digit is the uncertain one.

• 5.0 g vs. 5.00 g. Which measurement is believed to be more accurate and precise?

Significant figure rules

1. Exact numbers have unlimited number of significant digits.

2. Nonzero digits are always significant.3. Zeros between nonzero digits are always

significant4. Zeros at the beginning of a number

(placeholders) are never significant5. Zeros at the end of a number after the decimal

point are always significant6. Zeros at the end of a number without a

decimal point are not very clear….

Scientific notation

• Two purposes for SN– Removing ambiguity of zeros– Handling very large or very small quantities.

number = N 10x

• N is a number between 1 and 10.• “x” is an exponent• Using a calculator, SN exponents entered with

the EXP or EE button.– 4.5 × 1014 entered as 4.5 EE 14

Significant figures in calculations

• Addition and subtraction—

• Multiplication and division—

• When carrying on several steps, retain extra digits from calculator in intermediate answers to avoid rounding errors. Round answer according to sig. fig. rules.

Dimensional analysis

• Any number multiplied by 1 is the same number – (a 1 = a)

• Conversion factor: a fraction expressing the same value in different units

multiplying any number by a conversion factor = multiplying number by 1

1 54.2

1

cm 54.2in 1

cm

in

• ALWAYS CARRY UNITS. They are essential in determining if a calculation was done correctly.

• Let’s try some examples…

Process for dimensional analysis

unitdesiredunitgiven

unitdesiredunitgiven _

_

__

Percent by mass

• Use any mass units, so long as you are consistent.

)(100

)(%

massrepartsmixtu

masspartsAA

Density

• Ratio of mass per unit volume• D = m/V• Density is an intensive property.

• Specific gravity is ratio of density of substance to density of water (1.00 g/mL @ room temp)

• Sp. Gr. = Dsub/Dwater

• Sp. Gr. is numerically equal to D, but it is unitless

• Examples…

Heat and temperature

• Temperature indicates _________________________________

• Heat flows in which direction?

• Temperature units• Celsius• Kelvin• Fahrenheit

• Conversions (just one or two)

Specific heat

• Amount of heat required to heat one gram of a substance one degree Celsius (or Kelvin) w/o changing phase.

• specific heat—C• Heat—q• Mass—m• Temperature change—

T• Is C an extensive or

intensive property?

TmqC /

Using specific heat

• Some examples…

1. Calculating specific heat of a substance

q = mC(Tf – Ti)

2. Transfer of heat from one substance to another

• qA = -qB