Environmental Chemistry Test Questions – Flashcards
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Unlock answers| What is the nucleus composed of |
| protons and neutrons |
| how big is the nucleus compared to the atom as a whole? |
the nucleus is a very small volume compared to the volume of the atom but it holds almost all of the atom's mass ; very dense |
| What is the relative mass of the subatomic particles? |
Proton: 1.00727 amu Neutron: 1.00866 amu Electron: 0.00054858 amu |
| What is the notation for isotopes? |
AX ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Z ; ;X = the atomic symbol of the element A = mass number; A= Z+N Z = atomic number (the number of protons in the nucleus) N= number of neutrons in the nucleus |
| aside from zAX, what is an alternative notation for isotopes? |
element-A ; A=the mass number |
| How do you find the number of protons, neutrons, and electrons, given the symbol of an isotope? |
Use AZX ; Z = the number of protons If there is no charge, the number of protons = the number of electrons A-Z = N so subtract A from Z to get neutrons if you don't know X you can use A and Z to get the number of protons and neutrons, then use a periodic table to find X |
| How do you calculate the mass number of an element? |
use ZAX
A is the mass number
Mass Number (A) = #protons (Z) + # neutrongs (N) A = Z+N
eg. Nitrogen-14 (14N) and Nitrogen-15 (15N) have mass numbers of 14 and 15 we could also write Nitrogen-14 with both the mass number (14) and the atomic number (7) ie. 147N |
True or false: isotopes are chemicall different |
False
isotopes are chemically identical |
True or False:
Isotopes have the same masses |
False
Isotopes have different masses |
| What are five processes for radioactive decay? |
Alpha Decay
Beta Decay
Gamma Emission
Positron Emission
Electron Capture |
| Describe alpha decay, what happens to atomic number and mass number as a result of alpha decay, and give an example of a nuclear equation for this process |
when an alpha particle (2 neutrons and 2 protons, essentially a He nucleus) is lost
atomic number decreases by 2 mass number decreases by 4
22288Ra -> 42He + 21886Rn
|
| Describe beta decay, what happens to atomic number and mass number as a result of beta decay, and give an example of a nuclear equation for this process |
when a beta particle (fast moving electron found in the nucleus) is lost
atomic number increases by one atomic mass stays the same
***different from electron capture because e- on right*** neutron changes to a proton 23490Th -> 0-1e + 23491 Pa |
| Describe gamma emission, what gamma rays are, what happens to atomic number and mass number as a result of gamma emission, and give an example of a nuclear equation for this process |
when the nucleus rearranges, occurs whenever nucleus undergoes some other type of decay (alpha beta, positron emission, electron capture) gamma rays are high energy photons
no loss of particles from nucleus no change in composition of nuceus (same atomic # and mass #)
AZX -> AZX
|
| Describe positron emission, what postirons are, what happens to atomic number and mass number as a result of postiron emission, and give an example of a nuclear equation for this process |
when an atom loses a positron in the nucleus
a positron is basically an anti-electron with a charge of +1 and a negligible mass
mass number stays the same atomic number decreases by one
positrons result from protons changing into neutrons
2211Na -> 0+1e + 2210Ne |
| Describe electron capture, what happens to atomic number and mass number as a result of electron capture, and give an example of a nuclear equation for this process |
when an inner orbital e- is pulled into the nucleus ***anti-beta decay*** ***e- on the left of equation*** no particle emission, but the atom changes *same result as positron emission* proton combines with e- to make a neutron
mass number is the same atomic number decreases by one
20080Hg + 0-1e -> 20079Ag
|
| What are the approximate contributions of various sources of radiation to our overall exposure? |
man made and natural sources
82% - natural sources (Radon gas from the ground) 11%- inside the human body (Carbon-14) 8% - rocks and soil (uranium) 8% - cosmic rays from space (supernovas, higher up more exposure) 11% - medical x-rays 4% - nuclear medication 3% - consumer products 1% - other (phosphorus in fertilizer etc) |
| How does ionizing radiation affect bonds? |
it knocks electrons from atoms or molecules can generate highly reactive free radicals |
| how does radiation damage DNA? |
| it produces free radicals that are reactive and can alter the structure of the DNA which leads to mutations in the DNA th. these mutations affect cell replication that can lead to cancer, or if the mutations occur in gametes it can be passed on to offspring. Because DNA produces RNA which produces protiens, it can also lead to problems in protien production which can cause overall health problems. |
| How does wavelength relate to energy? |
energy is inversely proportional to wavelength
electromagnetic radiation with shorter wavelength (gamma rays, X-rays, UV rays) are more energetic and thus more ionizing |
| How do alpha, beta, and gamma radiation compare in terms of penetration power? |
alpha particles are the larges and can't penetrate through a piece of paper or skin. won't cause problems unless inhaled/injested
beta particles can penetrate more than alpha and can go through paper, plastic, and skin
gamma rays can penetrate the most and cause more diffuse radiation sickness. they can go through paper, plastic, skin, steel, and lead so it takes a lot to stop gamma rays from getting through. |
| is alpha, beta, or gamma radiation the most destructive? |
alpha radiation is the most destructive because it is the most ionizing
due to its large particles/low penetration it does not transmit through skin, however if it is injested or inhaled it can be harmful (Radon gas = problem b/c we can inhale it) |
| what is a half-life? |
the length of time it takes one-half the radionuclides to decay
|
| how do you calculate the time to get a fraction of an isotope or the fraction of an isotope given the time? |
the fraction of the orginal isotope that remains after a given number of half lives is 1/(2n) where n is the number of half lives
ex problems: 1. Radium-223 has a half life of 12 days. How long will it take for a 1.00 mol sample of 223Ra to contain only 0.25 moles of 223Ra?
.25mol÷1mol = 1/4 (1/2n) so n= 2 half lives 12 days x 2 = 24 days
2. what fraction of a 100mg sample of 99Tc remains after 2.0 days if 99Tc has a half life of 6 hours?
n= 2 days=((24x2hours)/6hours)=8hours 1/28=1/256=(1/256)x100mg=0.39mg remaining |
| How can the half-life of carbon-14 and tritium be used to date materials and what is the approximate half-life of each? |
c-14 has a half life of 5730 years tritium has a half life of 12.26 years
C-14: works by comparing the amount of C-14 to C-12 b/c C-14 is radioactive with a half-life of 5730 years while living, the C-14/C-12 ratio is kept constant by the CO2 in the air being respired through the body but once dead the C-14 to C-12 ratio decreases, this can help with dating for things up to 50,000 years old
tritium can be used for more recent objects (up to 100 years) and works in much the same way where delicate instruments look for traces of tritum and compare with the amount in lving/current things to see how old it is. |
| How does nuclear transmutation generate new elements? |
it uses a particle accelerator to bombard elements with small nuclei, protons, or neutrons, if the catch on it can cause a new element to be formed
this is how many of the obnoxious elements like Americum are formed |
| How are radioisotopes used? |
food sterilizers - kill bacteria and don't do harm to body tracers in physical, chemical, and biological systems (medical tracers) * certain organs absorb most or all of a particular element so we can measure the amount absorbed by using tagged isotopes of the element and a Geiger counter. they use radioisotopes with short half-lives and use low ionizing radioisotopes (beta or gamma) |
| Why is radiation therapy used to treat cancer? |
| radiation is most lethal to dividing cells |
| How does radiation therapy target tissue? |
| with direct x-ray beams, implanted radioisotopes, or tracers |
| How does fission work? |
| it works because some nuclei are so unstable that if their nucleus is hit just right by a neutron the large nucleus splits into two smaller nuclei |
| How does fusion work? |
| it works by accelerating small nuclei to such a degree that they overcome their charge repulsion and are smashed together to make a large nucleus |
| How much energy do fission and fusion produce? |
| Huge amounts of energy by E=mc2 |
| How does a fission chain reaction work? |
it occurs when a reactant is also a product (in the fission process it's the neutrons)
basically, one element undergoes fission, producing new elements and neutrons, the neutrons hit other elements and cause fission, which releases more neutrons which hit more elements which causes more fission etc
it's like a game of marbles where if you hit it just right they bounce out of the ring ; ; |
| what is the critical mass? |
| the minimum amount of fissionable isotopes needed to sustain the fission chain reaction |
| what are fissionable isotopes used as fuel in reactors or nuclear weapons? |
| uranium-235 and plutonium-239 |
| What is the natural isotope for uranium and what must be done to make it useable in a reactor or for a bomb? |
it is naturally uranium-238 but it must be enriched to uranium-235 to be used in reactors and bombs ; ; |
| How does a nuclear power plant generate heat and control the nuclear reaction? |
they use fission of U-235 or P-240 to make heat ; the fission reaction takes place in the reactor core ; fissionable material is stored in long tubes arranged in a matrix called fuel rods (subcritical) ; between the fuel rods are control rods made of neutron absorbing material (B and/or Cd) neutrons needed to sustain the chain reaction ; the rods are placed in a material called a moderator used to slow down the ejected neutrons (allows chain reaction to occur below the critical mass) |
| What happened at Chernobyl? |
| In 1986 in Ukraine, during a safety test the cooling water supply stopped causing the temperature of the reactor to rise quickly. There were too few control rods and they could not insert them fast enough. The water and graphite produced hydrogen gas that exploded. It was not a nuclear explosion but radioactive fission products were released into the atmosphere |
| What are the different ways of handling nuclear waste and the benefits/problems of each? |
It is typically stored near reactors which requires constant monitoring to ensure the integrity of the storage Long term storage in ground, but must take care to avoid groundwater contamination, can also bring up environmental justice issues b/c of where they want to bury the waste (Yucca Mountain) Isotopes may be used as fuel to produce lighter more stable elements (transmutation of waste) - this is currently not practical for volume and type of waste generated by reactors Launching into space -dangerous due to risk of accident during launch (and expensive) |
| What is a breeder reactor? |
breeder reactors produce fissionable fuel 233U or 239Pu from non-fissionable isotopes 232Th or 238U ; they produce more fuel than they can use, this excess fuel can be used for energy, bombs, or power plants |
| What are the conditions for nuclear fusion? |
| high temperatures and large amounts of energy required to initiate, but should continue if you can get it started - currently impractical for energy production but used in bombs (thermonuclear devices) |
| Where does the sun's energy come from? |
| the fusion of hydrogen to helium |
| Which releases more energy: fusion or fission? |
| fusion |
| What kinds of bombs were used to bomb Hiroshima and Nagasaki? |
| fission bombs aka atomic bombs |
| What are thermonuclear (hydrogen) bombs and how nuclear are they? |
they are the most nuclear weapons available currently
they use fissionable material to initiate a fusion reaction between 2H and 3H much of the energy released is still derived from the fission reaction they are 1000x more powerful than the bombs dropped in Japan |
| What is the aftermath of a nuclear accident or bomb? |
the radioactive materials in the bomb or the nuclear reactor are released into the atmosphere and can rain down for days and weeks over thousands of miles
the fission of these atoms can produce many products, most of which are also radioactive and some have long half lives
neutrons released can act on atmosphere to produce C-14, H-3 etc
the breakdown of U-235 can produce Sr-90, I-131, and Cs-37 which are all dangerous isotopes |
| why are Sr-90, I-131, and Cs-137 dangerous? |
Sr is close to Ca on the periodic table and when injested it gets into bones however it only has a half life of 28.5 years so you will probably still be alive when it undergoes decay (and it will still be in your bones)
I-131 is dangerous because it tends to concentrate in the thyroid and in high concentrations can cause cancer. Its half life is 8 days (chernobyl decendents/survivors have high rates of thyroid cancer)
Cesium-137 has a half life of 30 years and can be distributed throughout the body, it is toxic in small amounts |
