isat test 2 ch. 5 (chemistry & composition of water)

properties of water

• high boiling point

• high freezing point

• high specific heat capcity

• less dense as solid than it is as liquid

• excellent solvent (universal)

how is water a “universal solvent”?

many diferent substances can easily dissolve in water

• great carrier of essential minerals

• never “pure”

solution

homogeneous mixture of uniform composition

solvent

substance, often liquid, capable of dissolving one+ pure susbtances

what is created when water is the solvent?

AQUEOUS SOLUTION

heat of vaporization

heat that must be absorbed to change liquid into vapor = 2250 J/g for H2O

polar covalent bond

covalent bond which electrons aren’t equally shared, but displaced toward more electronegative atom

o-atom

attracts electrons in bonds more than H-atoms

• due to electronegativity

electronegativity

how strongly an atom attracts electrons in a chemical bond to itself

differences of electronegativity

• O has large electronegativity

• H has small electronegativity

hydrogen bonds

electrostatic attraction between a hydrogen atom with partial positive charge in one molecule & an atom bearing a partial negative charge in another molecule

high boiling point

extra energy needed to break hydrogen bonds

high freezing point

hydrogen bonds give water regular shape (structure), so freezing can occur more easily

high specific heat capacity

takes energy to increase molecular movement since hydrogen bonds provide a stable structure

freezing water expands

hydrogen bonding provides structure that’s less dense & has “open space”

excellent solvents

polar charge can attract & dissociate other charged particles (ions)

ionic bonds

electrons aren’t shared, but given from one atom to other

polyatomic ions

ions composed of a group of atoms with covalent bonds & overall charge

• can form ionic bonds with other ions to make a neutral compound

lewis structures for polyatomic ions

one+ more electrons are lost/gained to complete octet rule

• gain of electrons give a negative charge

• loss of electrons give a positive charge

what does it mean when “like dissolves like”?

• polar compound (ethanol) will dissolve in a polar solvent (water)

• nonpolar compound (oil) will dissolve in a nonpolar solvent (gas)

• polar compound (water) will NOT dissolve in a nonpolar solvent (oil) & vice versa

why can’t we drink seawater?

saltier than cells of our body

• through osmosis, water leaves cell of body to dilute saltwater that we drank = dehydration

• cells shrivel up

where does the most useable water come from?

surface water (lakes, rivers, groundwater)

how is water used?

• domestic

  • public supply

  • private wells

• agricultural

• industrial

  • mostly for cooling

• in-stream

  • hydroelectric power

  • recreation

  • navigation

filtration & disinfection

most important things to clean water we drink

what is the leading cause of death globally among children <5?

waterborne disease

what are the biggest uses when using water?

thermoelectric power & agriculture

primary steps of water treatment

• flocculation: sticking particles together

• sedimentation: removing large particles

• filtration: removing smaller particles

• disinfection: killing harmful microbes

types of desalination

1. distillation

2. membrane filtration (reverse osmosis)

point source

comes from a pipe

• industrial

• wastewater treatment plant

non-point source

comes from general land use in the watershed

• atmospheric

• urban

• agricultural

• residential

• all precipitation

• runoff of cars (rainbow liquid), salt on roads on waterways, soil erosion from crops & fertilizers, construction sites (sediment)

watershed

area of land that drains to a common point/waterbody

• in nutrition: you are what you eat

• in water quality: river’s health reflects the watershed

• streams in forested watersheds have much lower nitrate levels than suburban/agricultural watershed (use of fertilizers)

what are the water quality indicators measured in lab?

• temperature

• conductivity

• pH

• dissolved oxygen

• nutrients (phosphorus & nitrogen)

• turbidity

• e coli

effect of temperature (water quality)

lower temperatures generally increase biological diversity

effect of nutrient

nutrient enrichment → community composition change → algal blooms → low DO

conductivity

measure of sum of ions dissolved in water

what do ions conduct for water quality?

electrical current

• measuring how conductive water is provides indirect measure of ions

sources of conductivity (water quality

• urban runoff

• agricultural runoff

• point sources

• mining

turbidity

measure of water clarity & light refraction

• high levels (>~10) indicate high suspended solids

sources of turbidity (water quality)

• urban runoff

• agricultural runoff

• construction runoff

• instream erosion

dissolved oxygen (water quality)

necessary for aquatic life

• when biodegradable organic matter is present in water, microorganisms will degrade material & consume oxygen

• low oxygen can cause death in ocean

function of dissolved oxygen (water quality)

• mixing (aeration)

• biodegradable organic matter

pH

measure of acidity, refers to concentration of H+ ions in water

• defined as pH = -log([H+])

source of pH

• atmospheric acid deposition

• mine drainage (oxidation of pyrite)

• anaerobic decomposition of organic matter (swamps)

what is labeled for a pH LESS than 7?

acidic

what is labeled for a pH MORE than 7?

basic

acids

release hydrogen ions in aqueous solution

• hydrogen ion has no electron & one proton

bases

release hydroxide ions (OH-) in aqueous solution

what happens when there’s too much H2O compared to H+ & OH-

H+ & OH- will form H2O

what happens when there’s too less H2O compared to H+ & OH-

H2O will form H+ & OH-

effects of excess solids

healthy aquatic community requires clean stream bottom with space between rocks & gravels (interstitial space)