Chemistry Flashcards
What 3 parts make up an atom?
- Protons
- Neutrons
- electrons
Where are electrons found?
In orbitals going around the nucleus
How many can electrons can each electron hold?
- 2 in the first
- 8 in all thereafter
How does the periodic table arrange atoms?
by the number of protons, also arranges them by properties
What is the ratio of protons to electrons in an uncharged atom?
1:1
What are the valence electrons?
the ones in the outermost shell of the atom
Why are valence electrons important?
They determine how an atom interacts with others
What makes an atom to be in it’s most stable state?
full outer shell
What is the name for the process which causes an atom to lose electrons?
oxidation - forms a cation
What is the name of the process which causes an atom to gain electrons?
reduction - forms anions
What is a molecule?
A group of atoms held together in a stable assoication
What is a compound?
A molecule containing more than one type of element
What allows an ionic bond to form?
Large difference in electrongegativity, (different charge)
What makes a covalent bond stronger?
the number of bonds
single < double < triple…
What is a true covalent bond?
A covalent bond with no difference in electronegativity
What does an electronegativity difference of >1.8 mean for bonding?
Ionic bonding
What does an electronegativity difference of 1.8>x>0.4 mean for bonding?
Polar covalent bond
What does an electronegativity difference of <0.4 mean?
nonpolar covalent bond
What limits chemical reactions?
- temperature
- concentration
- catalyst
- free energy
What kind of bonding is present in water?
polar covalent and hydrogen
What happens in hydrogen bonding?
A very high electronegativity difference causes the molecules to form greater inter-particle interactions with other molecules
What are the physical properties of water?
- high specific heat capacity
- high heat of vaporization
- high specific latent heat
- high surface tension
What do the terms hydrophillic and hydrophobic mean?
Hydrophillic - bonds readily with water
Hydrophobic - does not bond with water - is imiscible with it
Is water better at dissolving charged (ionic) or non-charged molecules?
ionic
What is solubility?
A measure of how much solut can be dissolved in a solvent
What effects solubility?
Temperature and pressure
How does temperature effect solubility?
solubility of most gases decrease with increasing temperature
solubility of solids increase with increasing temperature
What is Henry’s law?
The amount of dissolved gas is proportional to its partial pressure above the liquid
X(aq) = K*Px
How can solubility be related to an equilibrium reaction?
- salt is put into water and begins dissolving
- salt continues to dissolve; however dissolved ions will also precipitate. Because the salt dissolves faster than its ions precipitate, the net movement is towards dissolution
- the rate of dissolution will eventually equal te rate of preciptiation. Solution is in equilibrium - ions will continue to dissolve and precipitate
What is the equation for molarity?
= [moles of solute/ litres of solution]
What does a mole show?
The number of molecules in a given mass
n = m/gfm
What does GFM stand for?
gram formula mass
What is the equation for normality?
N = equivalent of solute/1L of solution
What is the equilibrium constant?
The equilibrium expression for a reaction of constant temperature
Keq = [C]^c[D]^d/[A]^a[B]^b
the objects in [] represent the molar concentration, molarity, moles per litre
Products over reactants, each to the power of their coefficients
Precicts the predominant direction of the reaction
What does the equilibrium equation relate?
The concentration of reactants and products
What is Le Chatelier’s principle?
“When an equilibrium system is subjected to a change in temperature, pressure or concentration of a reacting species, the system reacts in a way that partially offsets the change while reaching a new state of equilibrium”
What doe Le Chatelier’s principle mean?
Any stress placed on a system in equilibrium will cause the system to shift to minimise the effect of the stress
What defines the amount of a gas in liquid?
Henry’s law
What is the unit of K if the gas concentration is in Moles/ Litre?
Mole/ litre/ atm
What is biochemical oxygen demand?
a measure of water pollution
What does biological oxygen demand measure?
How much dissolved oxygen is consumed as microbes/ bacteria break down organic matter
What does high BOD indicate?
that levels of dissolved oxygen will fall, with potentiall dangerous implications for biodiversity
What causes high BOD?
high levels of organic pollution
Microbial activity uses up O2
What is an acid?
A chemical that releases H^+1 ions
What is a base/ alklai?
a chemical that accepts H^+1
What is a buffer?
A chemical that accepts/ releases H^+1 ions as necessary to keep pH constant
What is the definition of an acid?
Anything that produces hydrogen ions in a water solution
What is the definition of a base?
Anything that produces hydroxide ions in a water solution (OH^-)
What are some common acids?
- Citrus fruits
- Aspirin
- Vitamin C
- Vinegar
- hydrochloric acid
What are some common bases?
- detergents
- ammonia based cleaners
- sodium hydroxide
What can the strength of an acid be expressed by and what does it mean?
equilibrium - the equilibrium constant can be found
K <1 is a weak acid
What does a buffer solution usually consist of?
A weak acid and a salt that releases additional A^- ions
A salt procides a high cocentraion of A^- ions
What is the usual equation for a weak acid?
HA + H2O –> H3O^+ + A^-
How do you remove metal ions from a solution?
precipitate them as a metal hydroxide
How do we precipitate metals?
- Raise pH with a common alklaine material
- metals bcome insoluble
- precipitate them
What is the drinking water standard for alkilinity?
there isn’t one
What is alkalinity?
The capacity to neutralise an acid, hence why there is no drinking water standard
What is hard water?
The concentration of calcium carbonate
How is the contents of hard water precipitated?
As a result of le Chatelier’s principle, it can have hug costs and loss of energy
What causes hard water?
Ca^2+, Mg^2+, Fe^2+, Mn^+
What reacts with hard water to form insolutble calcium and magnesium stearates?
sodium stearate (soap)
What were the common water pollutants prior to the 1970s, and their consequences?
waterborne diseases
fish kills and river fires
What are common water pollutants since the 1970s?
Nurients, nitrogen and phosphorous
- carcinogens and other toxins
What are the latest water pollution concerns?
- emerging compounds
- carbon-footprint and energy consumption
What do we need to monitor to try and mitigate the pollutants in water?
- for diseases heavy metal and pathoges
- fish kill - temperature, pH, dissolved oxygen
- algal blooms - N,P
- other parameters - colour, odor, trubidity, voaltile suspended solids (VSS), total suspendie solids (TSS)
What is the equation for reaction free energy and stoichiometry?
delta Gr^o = delta Ga^o’ - deltaGd^o’
delta Ga^o’ = the electron acceptor half reaction
delta Gd^o’ = electron donor half-reaction
standard free energy
If delta Gr^o’ is negative, what does this mean?
THe reaction is spontaneous - exogenic, as written
If delta Gr^o’ is positive, what does theis mean?
The reaction is not spontaneous as written (endergonic)
What is a microbial redox reaction?
When organics in sewage are used as the energy source (sulfate to sulfide)
Then sulfide goes towards hydrogen sulfide equilibirum
Henry’s law applies
gasuous hydrogen sulfide dissolves into water to condense at the crown of the pipe and used as an electron source by sulfide oxidizer
this produces acid and dissolves concrete
What kind of redox reaction causes the corrosion of concrete pipes?
microbial
What happens in the during the corrosion of steel?
- Iron acts as an electron donor, oxygen as an excepttor
- current flows from anode to cathode
- this makes an electrochemical reaction
What is the conventional waste heirarchy?
- (smallest) waste reduction
- recycling
- anerobic composting
- aerobic composting
- waste-to-energy
- modern landfill recovery and using CH4
- modern landfill recovering and flaring CH4
- Pre-regulation landfill (waste dump) (largest)
What are the key features of an engineered landfill site?
- a gas extraction pipe
- an impermeable clay cap
- a synthetic membrane liner
- leachate collection and rainage system
- compacted low permeability clay
- leachate drain
- leachate collection sump
Under what conditions does degredation initially occur in landfills?
aerobic
After a short amount of time what happens to the conditions of degredation?
anerobic
What is the end product of landfill degredation?
Inert materials, glass, metals, plastics and ‘others’
What are the main types of carbohydrate molecules produced by photosynthesis?
Hemicellulose and cellulose
What is the main building block of cellulose?
Glucose
- a mono sccharide
- it’s a simple sugar with the functional group C=O
What is the process for the fomation of cyclic monosaccharides?
Aldehyde + alcohol –> hemiacetal
Leanr form of glucose and other monosaccharides can bend c=o functional group reacts with OH group on carbon 5
This makes the cyclic of the monosaccharide
How are disaccharides formed?
two glycosidic linkages aloha and beta are formed
The same reation an link many monosaccharide units together
What is cellulose?
A polysacccharide made up of many glucose monosaccharides formed by beta - glycosidic bonds
Forms fibres and sheets
This also allows hydrogen bonding between chains
alpha linkages give starch and glycogen
What is hemicellulose?
Also a polysaccharide but contains only 5 and 6 membered rings
More complicated structure than cellulose
The two most common monosaccharides are glucose and xylose
How are proteins made?
By linking together amino acids (alpha-amino acids)
These contain bth an acid and a basi part
Each amino acid has an R group, or functional group
There are 20 amino acids with different R groups
What are the amino acids with hydrophobic side groups?
- Valine
- Leucine
- Isoleucine
- Methionine
- Phenylanine
What are the amino acids with hydrophobic side groups?
- Asparagine
- Glutamic acid
- Glutamine
- Histidine
- Lysine
- Arginine
- Aspartic acid
What are the amino acids that are neither hydro phobic or phillic?
Glycine Alanine Serine Threonine Tyrosine Tryptophan - Cysteine - Proline
How do amino acids link together?
Peptide bonds
C- OH bonds with H-N
This forms a N-C peptide bond and releases water
What kind of organic compunds are fats and oils?
Triacylglycerols
What does saturated mean in fats and oils?
containing only single bonds
What does unsaturated mean in fats and oils?
containing double bonds
Are oils or fats unsaturated or saturated?
oils - unsaturated
fats - saturated
What is the main landfill degredation process?
INputs: liquids (waste, rain etc.), Solids (wastes - inert and biodegradable), gases - air in void spaces
Processes: microbial activity, solution/ precipitation reactions, volatislisation, Sorption, Filtration
Outputs: Landfill leachate, Ladfill gas, residual solids
What are the main landfill biodegredation phases?
1 Hydrolysis/ aerobic
- Hydrolysis and anerobic (fermentation)
- Acetogenesis
- Methanogenesis
- Oxidation
What happens in phase 1 of landfill decomposition?
Aerobic:
bacteria metabolise waste to produce CO2, H20, and heat (up to 90 C)
Limiting factor is the avaiabilit of oxygen
What happens in phase 2 of landfill degredation?
Anerobic:
Different micro-organsims become dominant
Carbohydrates and proteins break down to give sugars. CO2, H2, NH3 and organic acids
Temperature falls to between 30 and 50 C
LFG consists of 80% CO2 and 20% H2
What happens in phase 3 of landfill degredation?
Organic acids converted to acetic acid
CO2 and H2 so low pH (4)
acidic conditions promote metal solubility and leaching
Methanogenic bacteria become dominant
What happens in phase 4 of landfill degredation?
Composition of LFG ~60% methand 20% CO2
Slow reactions
Low temperatures
acids are degraded so pH increases to 7-8
LFG is generated for between 15 and 30 yeaers, low levels for up to 100
What happens in phase 5 of landfill degredation
all reactions end, residual soils are in equilibrium
What is the Ideal gas law?
PV = nRT n = number of moles R = universal content of all gases (1 mole at 1 atm pressure occupies 22.414 L at 273 K)
R = 0.082 L-atm/ mol-K
What is thermodynamics?
The study of the effects of work, heat and energy on a system
What are the three laws?
1: work, heat and energy
2 - entropy
3 - free energy
What is thermodynamics used for?
to calculate the generation of heat
to define the direction of spontaneous change
What is enthalpy?
the heat of the reaction = the sum of the standard entthalpy of the products - the sum of the standard enthalpy of the reactants
- the values must be multiplied by the number of moles entering into the reaction
What is the gibbs free energy?
G = H -TS H = Enthalpy T = absolute temperature S = entropy (J/K)
How do we find the activation energy of a reaction?
The difference between the energy of the reactants and the highest point on the graph
What is the effect of an enzyme of the activation energy?
reduces it
What happens to the liquid formed within a landfill?
They percolate downwards through the waste and potentially down into the soil below, this can have disastrous effects
What is landfill leachate?
The liquid formed within a landfill from the liquids that enter the site combined with material that is leachd from the wastes as the infliltrating liquids percolate downwards through the waste
What is BOD5?
The BOD over a 5 day period
What is the total organic carbon?
The total mass of organic carbon per litre of sample
What is COD?
The chemical oxygen demand uses a strong chemical oxidising agent to measure the amount of oxidisable organic matter. It determines the amount of oxygen needed to chemically oxidise the organics in a wastewater
What are the fundamental reactions for rapid chemical oxidation?
organic waste –> CO2 + heat + by-products
Inorganic waste –> solid ash residue
What do we need for waste combustion?
Time
Temperature
Turbulence
Why is TTT important?
Time: combustion gases must remain at high temperature >2 seconds at the correct temperature
Turbulence - contact, oxygen and temperature
What are the advantages of getting energy from waste
- No methane production
- incineration close to wher waste is generated/ collected
- No long term liabilities
- Produces an ash (IBA) with:
1/10 of the volume and
1/3 of the total weight - emissions are controlled
- energy can be extracted
- ash can be used as an aggregate
What are the disadvantages from energy from waste?
- Generates CO2
- not popular with the public
- high costs and long pay back periods
- long-term waste disposal contraacts
- sometimes seen as not compatible
- needs high calorific value wastes (paper and plastics)
- dioxins and furans produced (not fully understood)
What are some of the effects of exposure to dioxins and furans?
Acne Digestive disorders Muscle and joint pain Neurological disorders - memory loss, depprssion, heart complaints and cancers
How is bottom ash recycled?
Aged raw ash –>
Magnet extracts ferrous and non-errous metals
–> screen splits >20mm (~15%) used as coarse aggregate
<8mm (~45%) used as fines (can be problematic)
the rest 8«20 is used in cement and bound bituminous asphalt
What is produced from APC (AIr pollution control) measures?
lime, fly ash and carbon
produced from cleaning the gaseous emissions from waste incineration
How do we dispose of APC molecules?
- hazardous waste landfill
- solidifaciation/ stabilisation
- long-term storage in a salt mine
- chemical treatment - mixing/ reacting with waste acid
- thermal treatment - vitrification
What is the composition of the gases in the atmosphere?
- clean air
- GHG
- gaseous pollutants
- volatile air compounds
- particulate matter
What is the composition of ‘clean air’?
78% nitrogen, 21% oxygen 1% other
What are primary pollutants?
Pollutants that are directly emited from cars, industry….
What are secondary pollutants?
Pollutants that are a result of reactions in the atmosphere - ozone
What is plancks law?
E(lambda,T) = C1/[lamda^(5e^C2/lamdaT) - 1]
E = therotetical radiation intensity (blackbody) per surface area and is subject to a wavelength T = absolute temperature (K) lambda = wavelength (micro m) C1 = 3.74*10^8 C2 = 1.44*10^4
What does plancks law tell us?
The spectral radiation intensity with various temperatures plotted against the wavelength
What is the surface temperature of the sun, where we take the theoretical radiation from?
5800K
What does Wien’s displacement rule show?
The wavelength at which maximum power is related
What is Wien’s displacement rule?
lambda max = 2898/T
lambda max in microns
What is the equation for the energy of the photons?
E = h*f h = 6.26*10^-34
f can be rewritten c/lambda
What doe we use to measure the concentration of particles in air?
~moles of X/ mole of air
This allows it to remain constant when air density changes
How high is the earth’s atmosphere?
560km
what are the four layers of verticle temperature?
- troposphere
- stratosphere
- mesosphere
- thermosphere
- We only need to know the top 2
Why does CO2 and other GHG cause global warming?
Sun inputs shorter wacelength energy, earth reflects back longer wavelength energy, this becomes trapped by the layer of GHGs
What ozone layer absorbs ultraviolet radiation?
between 20 and 30 km
this happends in the stratosphere
O2 + UV sunlight = O + O
O + O2 = O3
What part of the atmosphere does global warming occur in?
Troposphere - between 0 and 15 km
CO or VOC + NOx + sunlight –> O3
What does the troposhere reaction count for in global warming?
It is a major component of photochemical smog, causes damage to humn health and plants
How do bonds get broken in the earth’s atmosphere?
Photons are incident upon the atoms, light at a specific wavelength (E = hf) has the energy to displace an electron from the outer shell
O2 + hf –> 2O+
What is the average lifetime of an ozone molecule in the upper atmosphere?
30 minutes at 30km
What is the ozone concentration at sea level?
0.01 ppm
What are free radicals?
Atoms or molecules containing an odd number of electrons, such as OH(dot) O(dot)
Why are free radicals dangerous?
usually very reactive- these react with particles in the atmosphere and stop the ozone layer from forming, makes an ozone layer hole
This means that more UV gets to us, can be very dangerous
What is the troposphere?
- The site and source of weather, water vapor and clouds
- pollutants are removed from the troposphere withing days
- pollutants at the very top can last for days
What trace gases are present in the troposphere?
CO, NO, halogens, radon, SO2, HS and VOCs
Why is smog dangerous?
It converts pollutants to ozone particles which can cause extreme health problems
What were the consequences of London smog in the 50s?
1952 a week of intense fog and smoke in london resulted in 4000 deaths
4 day period in donora (PA) in 1948 (14000 population) caused 20 deaths and 6000 illnesss
What caused smog in london?
High SO2 from burning high sulphur coals
liquid aerosols/ foggy conditions
presence of significatn fine particulate matter
What happens to the pollutants in the troposphere?
React with free radicals (OH) - initiates the oxidation of all gases other than HCl
Why should we care about aerosols?
They can travel deeply into the respiratory tract
- short-term effects: eye, nose, throat and lung irritation, coughing sneezing, runny nose and shortness of breath
- long term: lung misfunction and worsened medical conditions, such as asthma, increased rates of chronic bronchitis, increased rate of mortality from lung and heart disease
What aer some natural sources and sinks of atmosphereic aerosols?
from both natural and human sources:
- primary particlses
- chemcial particles
Sinks:
- wet depsition (rain out)
- dry deposition
What causes acid rain?
<4.5 pH
result of the emission of sulphur dioxide and nitrogen oxides
What are the dangers of acid rain?
Causes problems to trees, aquatic life, buildings and public health
