Chapter 5 - Water Flashcards
What happens to water when it freezes?
it expands
What is specific heat? Is it high or low for water?
how much energy it takes to raise 1 gram of a substance 1 degree celsius
high for water (1 cal/(g x degrees celsius)
What is heat of fusion? Is it high or low for water?
the amount of energy it takes to change a substance from solid to liquid
high for water
What is heat of vaporization? Is it high or low for water?
the amount of energy it takes to change a substance from liquid to gas
high for water
What are the properties of water?
standard for celsius
18.02 g/mol
boiling point 100 degrees celsius
What is the structure of water?
H-O-H
- bent
- two O-H bonds (covalent, shared electrons)
- -> electrons not shared equally, more time spent around oxygen atoms
What is electronegativity (EN)?
how attractive an atom is to electrons (ex. O is more electronegative than H)
Properties of electronegativity
- atoms further right on PT have stronger electron pull
- going down the PT has less electron pull
(exception: noble gases don’t want more electrons or to have to give them up - all substances want to be like noble gases)
Electronegativity Scale
H: 2.1 F: 4 Cl: 3 go left and drop .5 each atom from F go right from Na and add .3, right from P add .4
Water’s O-H bonds
O: 3.5, H: 2.1
more electrons around O –> O has partial negative charge, H has partial positive charge (polar covalent bond: opposite partial charge at either end of molecule)
What are hydrogen bonds?
attraction between two different molecules
- weak bonds: covalent are 10 times stronger
- result of bonds: H2O sticks together
- -> liquid, high boiling/melting temp, etc because H-bonds take energy to break
What molecules create hydrogen bonds?
N-H
O-H
H-F (only hydrofluoric acid)
Why does water expand when freezing?
- hydrogen bonds: freeze–>crystal structure
- atoms can’t get close due to bonds
- -> result: ice, less dense than water
What is density?
measurement of how much matter is in a certain volume
- mass per unit volume (kg/m^3, g/L, g/cm^3)
- -> water: 1 g/cm^3, ice: .92 g/cm^3 (however, solid is usually denser)
Division of Earth’s water
fresh water = 2.6% (.01% ground/surface water, 2.59% glaciers/ice caps)
salt water = 97.4%
surface water: oceans, lakes, rivers, glaciers (often contaminated)
ground water: wells, rural (contaminant-free, ground filters water)
Water Consumption
drinking: 1.5 gal/day
washing/flushing: 40 gal/day
typical westerner: 100x body mass/day
Water Use
80% power plants, irrigation/agriculture
20% other uses (cooking, cleaning, sewage, drinking)
What is an aquifer?
water trapped in sand/gravel
- if this gets contaminated = very bad
- depleting quickly because farmers are taking too much
- -> we use 48 in/yr, replenished by rainfall by 2 in/yr
What is a solvent?
dissolves other compounds
What is a solute?
stuff being dissolved
What is a solution?
solvent + solute
What is an aqueous solution?
water is the solvent
ex. saline solution: solvent is water, solute is salt
What are ions?
charged particles
What is concentration?
the amount of solute per volume of solvent
“[…..]”: “concentration of”
How do you measure concentration?
- percent by mass
- parts per million (grams/million grams, mg/L)
- parts per billion (grams/billion grams, micrograms/L)
What is molarity? How do you find it?
moles per liter
- convert g to mol
- convert volume to L
- divide mol by L
What are electrolytes?
substances that conduct electricity when dissolved in water
Ex.
-pure distilled water (non-conducting)
-sugar dissolved in water (non-conducting –> non-electrolyte)
-NaCl dissolved in water (conducting –> electrolyte)
Conductivity is due to ____ in a solution
ions
- more ions = better conduction
- electrolyte = ionized
What is an ionic compound made of?
cations and anions
What are polyatomic ions?
where an ion has a different number of protons or electrons because they are filling and octet
*know name, formula, and charge for test (CHEAT SHEET)
What are ionic bonds?
bonds that hold ionic compounds together
-opposite charges attract (cations and anions)
How can you tell is something is an ionic compound?
cation: metal or ammonium (NH4+)
anion: nonmetals and polyatomic anions
1. metal + nonmetal
2. metal + polyatomic ion
3. ammonium + nonmetal
4. ammonium + polyatomic ion
How to name ionic compounds
- name cation as element
- name anion, add “ide” to element name
- name the polyatomic ion of it applies (don’t mess with ending)
Periodic Table charges
metals: 1A: +1, 2A: +2, 3A: +3, 4A: +4
nonmetals: 4A: -4, 5A: -3, 6A: -2, 7A: -1
Know these: Ag: +1, Cd: +2, Zn: +2
What is formula for Sodium Chloride?
NaCl
What is formula for Magnesium Bromide?
MgBr2
What is the formula for Calcium Oxide?
CaO
What is the name for BaCl2?
Barium chloride
What is the name for K2O?
potassium oxide
What is the name for Mg(OH)2?
magnesium hydroxide
What is the name for KNO3?
potassium nitrate
How do you label for charges?
roman numerals
what is the name of FeCl2?
2 Cl = -2, so Fe = +2
iron (II) chloride
what is the name of FeCl3?
3 Cl = -3, so Fe = +3
iron (III) chloride
what is the name of Cr2S3?
3 S (-2) = -6, so 2 Cr = +6 chromium (III) sulfide
what is the symbolic name of Manganese (IV) oxide?
Mn = +4, O = -2
Mn2O4
Dissolving sodium chloride in water
- partial charges in H20 will still be attracted to full formal charges of other molecules
- created energy through hydrogen bonds makes up for the bonds are broken in NaCl
What are insoluble ionics?
ion attraction that is too great for H2O to break therefore won’t dissolve (much)
What are solvable covalents?
ex. sugar, ethanol (covalent compounds, soluble, non-electrolytes)
- have O-H groups (hydroxyl), hydrogen bond with water
Consumption of pollutants
polar: go into bloodstream (polar environment) are are filtered through kidneys
non-polar: go to fat cells (non-polar environment) and will build up because they are not filtered out
–> less of these
What are some mineral concerns of water?
Ca: nutrient that makes water hard
Nitrates: agricultural runoff, cause “blue baby” syndrome (soluble, hard to get out of water)
Lead, Chlorine: toxic
Na: cause high blood pressure
How to make potable water?
- Screen: large objects
- Al(OH)3: sticks to dirt/clay (insoluble)
- Chlorination: kill bacteria/virus, bad taste/smell, toxic by-products (Cl is toxic but not on a drastic level)
What is distillation?
liquid solution is heated, vapors are condensed and collected (expensive because you have to use solar panels to heat water)
What is desalinization?
a process that removes ions from salt water
What is osmosis?
water goes through a semipermeable membrane (wall with holes that only H2O molecules can pass through) from a solution that is LESS concentrated to a solution that is MORE concentrated
What is reverse osmosis?
forcing water through a semipermeable membrane from a solution that is MORE concentrated to a solution that is LESS concentrated (expensive because you must use high pressure pump to do this)
