intensive chemistry day 2: properties of matter katy johanesen ph.d. candidate, usc department of...

Intensive ChemistryDay 2: Properties of Matter

Katy JohanesenPh.D. Candidate, USC Department of

Earth Sciences

This talk has two basic parts:

Properties of Matter Physical Reactions

Properties of matter

• All matter has mass, volume, density, and certain physical and chemical properties

• Dictated by the atomic or molecular structure

• Matter can be malleable, ductile, sectile, magnetic, conduct heat or electricity, react with water or oxygen…

• Color, phase at room temperature, and hardness are also properties

Properties of compounds

• A compound does not have the same properties as the elements that make it up.

• Table salt (NaCl) is edible and dissolves in water• Sodium (Na) and Chlorine (Cl) are both poisonous• Na metal reacts strongly with water

(our bodies are full of water)• Cl2 was used as a poison gas in WWI

• http://www.youtube.com/watch?v=9bAhCHedVB4

Density

• Density = mass/volume• Atomic mass of elements in the compound (mass)• Phase/crystal structure of the compound (volume)

• CAUTION: weight ≠ mass!• Weight is a force• weight = mass times acceleration due to gravity

• Two minerals… use density and the periodic table to determine which is which.

• Formulas: PbS and FeS2

Phases of matter

• Phase = a volume of space where all physical and chemical properties are uniform

• Solid, liquid, gas, plasma• Supercritical fluids and degenerate gases are other strange phases

of matter that do not naturally exist on Earth’s surface

• Form of matter depends on space between molecules and energy of the system

• Energy = heat

Common phases of matter• Solid = molecules are close together and ordered in a

crystal; energy of the system is the lowest

• Liquid = molecules are close together but are able to move and switch places; energy in the system is higher than in solid

• Gas = molecules are widely separated, move around freely, move at high speeds; energy in the system is the highest of all three– Ideal gas law: PV=NkT

• http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=25

Definitions modified from http://www.enchantedlearning.com/physics/Phasesofmatter.shtml

Not so common phases of matter• Plasma = gas composed of positively charged ions +

electrons; energy is so high matter becomes ionized; makes up 99.9% mass of the solar system

• Ex: the sun, stars, fluorescent lamps, arc welding, lightning, plasma TV

• Supercritical fluid = when a liquid or a gas is compressed and heated enough, their densities become equal; no distinction between liquid and gas beyond this pressure and temperature

• Found: deep within Earth, other planets

• Degenerate gas = gas compressed so hard that atoms are touching; behaves like a solid

• Ex: white dwarf stars, neutron stars, metallic hydrogen (Jupiter, Saturn)

Definitions modified from http://www.enchantedlearning.com/physics/Phasesofmatter.shtml; background from dailymail.co.uk

Solids: crystal structure

• Atoms or molecules organize into regular, repeating structures

• NaCl is ionically bonded• CaCO3 contains ionic and covalent bonds

(CO32- is a covalently bonded ionic compound)

• Graphite and Diamond are both covalently bonded, but have different properties due to the crystal structure

– Color– Hardness– Crystal shape

Solids: crystal structure

• Metals and Alloys: + ions bonded by delocalized valence electrons

• Ductile: can be drawn into a wire (Cu, Au, Ag)• Malleable: can be hammered into a sheet (Au, Pb, Al)• Sectile: can be cut with a knife (Na, Au, Paper)• Electric conductivity- electrons are free to move

through the material

Physical Reactions

• Reversible• Change in state or phase• Change in shape or crystal structure• Mixture of two or more substances which can

be separated again

• What are some physical reactions you can think of?

Phase transitions• Matter can change

between phases with enough change in energy or pressure

• Each element (and compound) can have a different boiling point (ptable.com)

Figures modified from Wikipedia

Phase Diagram

Ping-pong ball model of matter

• Balls represent atoms or molecules

• Shaking the container represents energy (heat)

• What would happen if the same number of molecules occupied a larger container?

Solutions• Solutions are homogeneous mixtures

composed of one phase• Solutes are dissolved in solvents• Solutes and solvents can be any forms of

matter– Gas in gas (air, O2 in N2)– Liquid in liquid (vodka)– Solid in solid (steel)– Gas in liquid (soda)– Solid in liquid (salt water)– Liquid in gas (water vapor)– etc.

Source: http://commons.wikimedia.org/wiki/File:SaltInWaterSolutionLiquid.jpg

Solutions

• Solutions are physical, not chemical reactions; can be separated to their constituent parts– Can boil (or freeze!) seawater to remove water

from salt– Can let soda go flat to remove carbon dioxide from

soda water– Can boil amalgam to remove mercury from gold

(used in CA gold rush!)

Source: http://commons.wikimedia.org/wiki/File:SaltInWaterSolutionLiquid.jpg

Solutions: Acids and bases

• Acids and bases are ionic compounds that dissolve and break apart in water to form excess H+ or OH- ions– The strength is based on the concentration of ions

• Acids are in lemons, vinegar, coffee, milk… • Bases are in peppers, seawater, bleach, soap…• Acids and bases can be solids, liquids, or gases

• most acids and bases we know are solutions in water

Brønsted-Lowry theory of Acids and bases

• Acids are H+ donors; bases are H+ acceptors– Recall that: H2O = H+ + OH-

– Another way of representing this is:• H2O + H2O = H3O+ + OH-

• Example: Add HCl (gas, acid) to water:– HCl + H2O = H3O+ + Cl-

• In this case, HCl is an acid because it donates the H+ to the water molecule, creating H3O+

Brønsted-Lowry theory of Acids and bases

• Example: Add NH3 (gas, base) to water:– NH3 + H2O = NH4

+ + OH-

• In this case, NH3 is a base because it accepts the H+ from the water (leaving extra OH- in solution)

pH

• One way to quantify the strength of acids and bases is the pH scale

• pH = potential of Hydrogen

• is a scale from 0-14• Pure water (neutral) is pH = 7• Acids are < 7• Bases are >7

pH indicators• Indicators can tell us the pH of a

solution by changing colors when added

• Litmus paper turns red in acid, blue in base

• Phenolphthalein solution turns purple when in a base, colorless in an acid/neutral

• pH paper strips can accurately measure pH from 0-14

pH

• Water breaks up to form a very tiny percentage of H+ and OH- ions; most stay as bonded H2O

• H2O = [H+] + [OH-]

• Scale is a mathematical representation of the concentration of H+ ions

Introduction to Scientific Notation

• Scientific notation is used to represent very large or very small numbers as exponents

• Often chemistry uses 10 as a base number• 10,000,000 = 107 or 10×10×10×10×10×10×10• 0.0000001 = 10-7 or 10/10/10/10/10/10/10

pH

• Normally when pure water breaks into ions, it forms a ratio of 10-7 H+ and 10-7 OH- ions for every water molecule– Based on the last slide, that

means for every ten million liters of water, there is one gram of H+ (and OH-)

pH• pH is a exponential scale based on

the strength of H+ ions– pH 0 (acid) = [H+] = 100 or 1

• 1 gram of H+ per every 1 L of water– pH 7 (neutral) = [H+] = 10-7

• 1 gram of H+ per every 10,000,000 L of water

– pH 14 (base) = [H+] = 10-14

• 1 gram of H+ per every 100,000,000,000,000 L of water

• The higher the pH, the less H+ in solution

Acids and Bases are useful

• Stomach acids break down our food (digestion)

• Geologists use acids to digest rocks in the lab• HF digests silica• HCl digests iron

• Bases are great for cleaning (lye, bleach, ammonia, soaps)