Sunday, May 15, 2011

Final Exam Review #27

Final Exam Blog Response

pH and pOH:

 a)  What is the pH and pOH of a 0.0200M solution of Ca(OH)2?

b) What is the concentration of hydrogen and hydroxide ions in a solution of HCL with a pH of 3.24?

 c) A 50.0 mL solution contains has a pH of 1.007 before being diluted to a volume of 100.0 mL . What is the pOH of the final solution?

Useful equations pertaining to pH and pOH:

·      pH = -log(H+)
·      (H+) =10 –pH
·      pH = 14 – pOH

·      pOH = -log(OH-)
·      (OH-) = 10 –pOH
·      pOH = 14 – pH

-       Sig Figs: for pH, they only count after the decimal place
-       (H+) / (OH-) = molarity

 a) 0.0200 M of Ca(OH)2

- Ca(OH)2 is a base, so you are going to use pOH

You have to multiply the molarity by two since it is (OH)2
            0.0200 x 2 = 0.0400 M

Since you have the molarity of OH-, and you are looking for the pOH, use:
     pOH = -log(OH-)
     pOH = -log(0.0400)
     pOH = 1.398

*sig figs: using regular sig figs rules, the molarity has three sig figs. When finding the pH or pOH you only count sig figs after the decimal place. Therefore, the 1 in 1.398 doesn’t count as a significant figure, so you have to have three sig figs after the decimal, (.398)

     It is asking for the pH, and since you know the pOH you use:
     pH = 14 – pOH
     pH = 14 – 1.398
     pH = 12.602

b)  pH = 3.24; HCl; looking for (H+) and (OH-)

HCl is an acid, so you are going to use pH.

Since you are only given the pH, you have to use:
        (H+) =10 –pH
                        (H+) =10 -3.24
                        (H+) = 5.8 X 10-4 M

*sig figs: pH has two numbers after the decimal, therefore it has two sig figs. You do not count the three because it is before the decimal point. Since there is a total of two sig figs for pH, there is a total of two sig figs for (H+). You use the regular rule sig figs rule, so 5.8 = two sig figs.

You then need to find (OH-). Since you need the pOH first in order to find the (OH-), you use:
pOH = 14 – pH
pOH = 14 – 3.24
pOH = 10.76

Now that you know the pOH you can find the (OH-)          
            (OH-) = 10 –pOH
            (OH-) = 10 –10.76
            (OH-) = 1.7 X 10-11 M

*sig figs: same rule applies to this as it applied to find the (H+)

 c) Looking for pOH 
given information:
V1 = 50.0 mL = .0500L
pH = 1.007
V2 = 100.0 mL = .100 L

You will end up using the equation M1V1 = M2V2

First, you need to find the molarity of M1 (H+)
                (H+) =10 –pH
(H+) =10 -1.007
        (H+) = .0984 M

*sig figs: pH has three significant figures after decimal, so molarity will have a total of three sig figs

Now that you have all the necessary information for M1V1 = M2V2, you can solve for M2
V1 = 50.0 mL = .0500L            V2 = 100.0 mL = .100 L
                                    M1 = .0984 M                           M2 = ?

M1V1 = M2V2
M2 = M1V1/V2
M2 = (.0984 X .0500)/.1000
M2 = .0492 M
                                (H+) = .0492

             Now you have the (H+) for the final solution. Solve for the pH of this solution:
pH = -log(H+)
pH = -log(.0492)
pH = 1.308

Last step: solve for the pOH:
pOH = 14 – pH
pOH = 14 – 1.308
pOH = 12.692

a)    pH = 12.602
                  b)    (OH-) = 1.7 X 10-11 M
   c)    pOH = 12.692

Wednesday, April 6, 2011

Nuclear Reactors, Chernobyl, and Japan

Part 1: Nuclear Reactors:

What is a Nuclear Reactor?

A nuclear reactor is a device that triggers a nuclear chain reaction and controls and sustains them at a steady rate. Fission, the process used in nuclear reactors, takes place when bombarding a nucleus with another particle. It starts off with one neutron, which then produces more neutrons once it is bombarded with another particle, and so on as a chain reaction (1). Controlled fission is used in order to produce useful energy to use as electricity. Fission is a self-sustaining reaction, meaning it can keep itself going, and therefore is very good energy source that releases large amounts of energy in the form of heat. Although this is a very helpful aspect of fission, it can also be dangerous because it can get out of control very quickly and safety precautions need to be taken (3). Before being able to understand the disasters at Chernobyl and Japan and what went wrong to cause the disasters, it is first necessary to understand how a nuclear reactor works and the parts within it.

Parts of a Nuclear Reactor:
  • The core is where the radioactive material is stored. The most common type of fuel used in nuclear reactors is Uranium-235. (4)
  • The moderator is a material in the core that slows down neutrons without absorbing or reacting with them so that can continue the chain reaction and produce more fission. In most moderators water is used but in the moderator at Chernobyl grid graphite was used. (5)
  • Control rods are used to absorb neutrons. They can be inserted or withdrawn from the reactor core in order to control the rate of reaction. When the control rods are inserted into the core, they absorb a large amount of neutrons, therefore slowing the fission process down. When the rods are pulled out of the reactor core, fewer neutrons are absorbed, therefore speeding up the fission process. These rods are made of steel and contain a large amount of material that can absorb neutrons and are usually composed of boron. Fuel rods are narrow cylinders that contain small pellets of uranium fuel. (5)

  • The coolant is a material that passes through the core that is used to transfer heat from the fuel to a turbine. In more simple terms, the nuclear reaction produces heat, and the coolant carries the heat away. This also serves the function of keeping the reactor cool enough to prevent a meltdown. (1)
  • The steam generator is part of the cooling system. It is used to boil water and produce steam for the turbine. The turbine then transfers the heat from the coolant to produce electricity. (4)
  • Containment is the steel and concrete structure around the reactor core that separates the reactor from the environment to prevent radiation from escaping. (1)
  • Cooling towers release the excess heat that cannot be converted into energy. (1)

All of these components work together to produce useful energy in the form of electricity. Nuclear reactions in fuel rods heat water, and then the steam drives a generator to produce electricity. Cold water from the sea or rivers heat and converts steam back to water. The water cycles back to the core to be reheated and repeat the process. 

Part 2: Disaster at Chernobyl

What Happened at Chernobyl?

The disaster that took place at Chernobyl is considered to be the worst nuclear reactor disaster ever. Chernobyl is located in Ukraine near the capital city of Kiev. The nuclear reactor is a RMBK design, meaning that it has graphite as opposed to water in the moderator. On April 25, 1986, reactor 4 at Chernobyl was scheduled for routine maintenance and was shut down. It was decided that an additional test would also be performed in order to see how long turbines could supply power to keep the cooling system going in case of a power outage (2).
At 1:00 am on April 25, the operators at Chernobyl began to reduce power for the test, but the test was delayed for 9 hours due to the need of power in the nearby town, Kiev. This resulted in difficulties with the work shifts, leaving the unprepared night shift to run the test. On April 26, the operators carried on the power reduction of the reactor, but due to a mistake by an operator, the power drastically dropped and was too low to run the test. To try to increase the power to keep the test running, operators raised and removed all but six control rods from the core at 1:00 am. Yet again, this was a terrible mistake by the operator (2). The minimum safe operating number of control rods is 30, yet there were only 6 control rods in the reactor core at that time, making it very unstable (3). The operators did not think it was not ideal to shut down the reactor, so they disabled the automatic shutdown system to continue the test. The purpose of the test was to see how the reactor worked under low power, so it was necessary to shut down the automatic system. Once the reactor was considered stable enough, the engineers decided to continue the test (2).
At the time the test was continued, both turbines were shut down and there was a reduction in the water flow, causing power to rise. This caused the reactor to boil and overheat, and the water coolant started turning to steam. The power drastically increased. (2) At that moment the manual shutdown button was pushed and the control rods that were originally taken out to increase power, were inserted back into the core. Due to the design of the control rods and the way they were inserted, it relocated the coolant and drove all activity to the lower core. (3) This dramatically increased the power to 120 times its full power. At 1:23 am, two explosions occurred. (2)

Explosions and Evacuation:

The explosions were caused because the pressure from the excess steam, which was supposed to go to the turbines that had been shut down, broke pressure tubes. Fuel pellets in the core began to explode, causing the explosions. The roof of the reactor was blown off and radioactive contents and burning graphite exploded outwards. A large fire was started when air was sucked into the reactor and ignited flammable carbon monoxide. Firefighters were rushed to the scene of the large fire and were successful in putting out the large fire nine days later (2). The firefighters poured water on the fires and tried to stop them with sand, but it proved to be ineffective. They then resorted to stopping the fires with lead and nitrogen (6). Along with the large fire at the core, 30 additional small fires were started near the accident. The Soviet Union did not notify the people about this disaster until the day after it happened. The radiation level decreased for a short period of time and the Soviet Union tried to cover up the fact that this disaster ever happened. The radiation levels soon rose and evacuation was ordered two days after the explosion. Those that stayed in towns near the reactor were ordered to remain indoors so they would not be exposed to the radiation. There was a 30 km evacuation zone around the reactor and those near it had to be relocated. (2) 

How have they tried to fix the situation at Chernobyl?

One of the main problems at Chernobyl was that it didn’t have a containment, a steel or concrete structure around it to protect the environment from radioactive material. Once the explosions occurred, a large amount of radioactive debris escaped from the building and led to many long-lasting health effects. The Soviets decided in order to try to prevent radiation from escaping the reactor they would build a large shell around it to contain the radiation. The shell was made out of concrete and steel and would permanently cover the entire reactor. This is known as the Sarcophagus (2).


Health and Environment Effects:

The workers who helped in the clean up process were not equipped with proper protective gear and were exposed to high amounts of radiation. This led to sickness and many deaths among these workers who were some of the first to treat the reactor immediately after the accident. 31 people died immediately after the explosion, and it is predicted that more than 100,000 people have already died and as people continue to be exposed to radiation, that number will continue to increase (6). Chernobyl released as much as 100 times the radioactive contamination of the Hiroshima bomb (3). Over 300,000 people were resettled due to the disaster, yet millions still continue to live in the contaminated area. Rainfall and wind can also transport radiation to other countries. Radioactivity is still found in large amounts in Belarus, Ukraine, and Russia (3).
            Radiation puts people’s health into jeopardy by causing cancer and birth defects. Thyroid cancer is especially common among young children ages 0-14, and other cancers such as leukemia affect people exposed to radiation. Cesium-137 is a harmful substance from radiation that has a half-life of 30 years. Due to this long half-life, it is still found today in soils and foods in Europe. The contaminated soil cannot grow crops because it will contain radiation in foods and will harm people (7). Pripyat, a town very close to Chernobyl that housed plant workers is now a ghost town because everyone was ordered to evacuate from it (6). 


Part 3: Japan

What happened in Japan?

-       Explosions in reactors 1, 2, and 3.
-       Water was boiled down and exposed the rods. This caused the rods to overheat because there was no water to cool them. The extreme heat caused the explosion (9).
-       Now Japan is pumping cool seawater into the reactor to try to regulate the temperature and cool it down to prevent more explosions from occurring (9).
-       People are taking iodine pills to try to prevent the possibility of getting illnesses or cancer from the radiation. This helps protect the thyroid gland so it can’t absorb harmful iodine (8).  

Similarities between Fukushima and Chernobyl:

-       Evacuation was carried out in areas that were heavily impacted by radiation
-       Radiation entered the environment 
-    People reacted in fear 

Differences between Fukushima and Chernobyl:

            There are more differences than similarities:
-       Perhaps the main difference between the two is the reason each explosion occurred. The disaster as Chernobyl was caused when a new test was taking place and was due to careless mistakes by operators, whereas Fukushima was caused by a natural disaster – tsunami (9).
-       Another key difference between the two is the containment. Chernobyl released a much larger amount of radiation into the environment than Fukushima has. Fukushima has containment around it – heavy steel and concrete – to protect the environment from the radiation inside the core. Chernobyl on the other hand did not have one, so when it exploded the radiation was immediately released into the environment. The containment at Fukushima is keeping in a large amount of radiation (9).
-       The designs of the reactors were also different. Chernobyl used graphite in its moderator as opposed to water used in Fukushima. Graphite catches on fire easily, therefore causing a large explosion (8).
-       The Chernobyl plant was used to process plutonium weapons as well as supply electricity – Fukushima only to supply electricity (8).

Should we be worried?

-       No, the radiation is not as bad as Chernobyl and it will not spread to the U.S.
-       Fukushima has containment, so the radiation released into the environment is not as much.
-       Measures are being taken to control and watch the radiation.


Monday, January 31, 2011

Creative Chemistry Extra Credit


Covalent Compounds
Atoms are bonded
by sharing of electrons 
like a tug-of-war

Molecular Geometry

Linear: a highlighter 
Linear was very easy to find an example for. Anything straight will work!

Bent: scissors 
If you take away the sharp side at the top, this serves as an example of a bent object. As you can see, it is bent in the middle. 

Trigonal Planar: fan 
The three parts of the fan create a trigonal planar shape. 

Trigonal Pyramidal: Lamp 
Although it is not evident when you first look at it, the three lights are in the shape of a trigonal pyramidal. I found this very difficult to find an example for, so i bent the lights of a lamp in order to make the shape of a trigonal pyramidal. The light blue light is farthest away from us, the brown light is on the right side, and the dark blue light is on the left side of us. I tried to align the lamps to make the angles as correct as possible. 

Tetrahedral: music stand 
The three bottom feet of the music stand and the rod connecting the top to the bottom serve as a tetrahedral. The angles are not completely accurate, but the basic shape is represented. If the connecting rod was not present, the bottom legs would create a trigonal pyramidal! 

Saturday, December 11, 2010

If Your Cat Took Chemistry, Would She Eat This Stuff?

          For this blog, i decided to use a variety of products. I separated the products into three main categories. I tried to find a variety of items within each category in order to demonstrate that compounds are found in so many items. 


TLC Almay Longwear Makeup:
        1. zinc oxide  -   ZnO
Victoria Secret - Drenched in PINK: pretty and pure body lotion:
        2. sodium hydroxide  -   NaOH
Crest Whitening Dental Wraps:
        3. hydrogen peroxide  -  H2O2
Mary Kay Makeup Remover
        4. sodium chloride  -   NaCl
        5. potassium phosphate  -   K3PO4
Crest Whitening Toothpaste:
        6. sodium fluoride  -   NaF


Adora Calcium Supplement: 
        7. calcium carbonate  -  CaCO3
        8. magnesium oxide  -   MgO
Crystal Light Drink Mix - Raspberry Flavor:
        9. calcium phosphate  -   Ca3(PO4)2
Ramen Noodle Soup - Chicken Flavor
        10. potassium carbonate  -   K2CO3
        11. sodium phosphate  -   Na3PO4
        12. sodium carbonate -   Na2CO3
Slim Fast - French Vanilla: 
        13. magnesium phosphate  -   Mg3(PO4)2
        14. potassium iodide  -   KI
        15. chromium chloride:
                    - chromium (II) chloride  -   CrCl2
                    - chromium (III) chloride  -   CrCl3

Science Diet Sensitive Stomach Cat Food:
        16. potassium chloride  -   KCl
        17. copper sulfate:
                   - copper (I) sulfate  -   Cu2SO4
                   - copper (II) sulfate  -   CuSO4
        18. calcium iodate  -   Ca(IO3)2
        19. phosphoric acid  -   H3PO4
FortiDiet Hamster and Gerbil Food:
        20. cobalt carbonate
                   - cobalt (II) carbonate  -   Co2(CO3)3
                   - cobalt (III) carbonate  -   CoCO3
ProPlan Small Dog Biscuit:
        21. zinc sulfate  -   ZnSO4

Tuesday, November 9, 2010

Trimester 1 Exam Review Question #15

#15. Which would have the smallest radius: Na, I, and O? Explain your answer throughly.
                - Oxygen would have the smallest radius.


  Atomic radius is defined as one half of the distance between the nuclei of two atoms of the same element when the atoms are joined. The atomic radius decreases across periods because there are less electron shells to shield the attractive power of the nucleus. You add a proton each time you go across the period, making it have a more attractive power. The attractive power causes it to pull in the electron shells tighter, which decreases the radius. It increases down groups because each time you go down, a new energy level is added. This creates a new electron shell. The number of electrons outnumber the number of protons, which means the attractive force isn’t as great. This allows the shells to spread out more because it doesn't have the attractive force pulling it in, creating a larger radius. 

Oxygen would have the smallest radius because it has the smallest number of electron shells. This causes the positive charge to be greater and pull the electron shells closer, therefore decreasing the radius. Sodium has a larger radius than oxygen because it has more electron shells and a smaller attractive force, allowing the shells to spread out. This causes a larger radius. Iodine has a larger radius than oxygen because even though it has a very strong attractive force, the number of electron shells outnumbers the attractive force. This means the radius for iodine is larger because the all the shells spread out. 

Wednesday, October 6, 2010

Rutherford's Gold Foil Experiment


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                        Rutherford is best known for his gold foil experiment, which greatly contributed to the model of the atom as we know it today. His experiment introduced a new understanding about the atom, and proved his former teacher’s model incorrect. The gold foil experiment was conducted in 1909 at the University of Manchester by Geiger and Marsden, but his theory of the atom wasn’t complete until 1911 (4). 

Ernest Rutherford had the opportunity to study and research at a variety of colleges. At the colleges, he was able to make many discoveries that would assist him in his gold foil experiment. He studied radioactivity, which led him to discover alpha particles, the main focus in the gold foil experiment. Ernest Rutherford was born on August 30, 1871 in Spring Gold, New Zealand. He obtained his early education through government schools, and at the age of 16, he entered Nelson Collegiate School. In 1889 he was awarded a University scholarship to Canterbury College at the University of New Zealand. He graduated from Canterbury with a double major in mathematics as well as physical science. In the year 1849, he was awarded an 1851 Exhibition Science Scholarship that allowed him to study at Trinity College at the University of Cambridge as a research student. At Trinity College, he worked with J.J. Thomson in the Cavendish Laboratory, who would become a very important figure in the gold foil experiment (1). While working with Thomson, Rutherford studied radiation, which led to his interest in alpha particles. He was offered a job as a chemistry professor to be the Macdonald Chair of Physics at McGill University in Montreal. In 1898, he moved to Canada to take the job, where he continued to work with radioactivity. His research led him to discover that radioactivity was the "spontaneous disintegration of atoms" (2). Due to all the work he did at McGill University, he was awarded the Nobel Prize in Chemistry in 1908. In 1907, he succeeded Arthur Schuster at the University of Manchester, where he began an in-depth study of alpha particles (1). His research led him to discover that alpha particles cause a weak, but discrete flash when they strike a luminescent zinc sulfide screen (4). His research and findings about alpha particles would later prove to be very important in his gold foil experiment.

                                                      Ernest Rutherford (1)

Who was involved in the gold foil experiment?
Rutherford was credited for the gold foil experiment, but two other people played a important role in the experiment as well. Under the supervision of Rutherford, Geiger and Marsden performed the gold foil experiment. Hans Geiger, Rutherford’s partner, had worked with him at the University of Manchester since 1908, and Ernest Marsden was a student at the University of Manchester (4). Although J.J. Thomson wasn’t directly involved with the experiment, he played a key role, serving as the reason the experiment was performed. Rutherford was a former student of Thomson and highly looked up to him. The reason behind the gold foil experiment was to prove Thomson’s “plum pudding model” (5).  

                                                Rutherford and Geiger (2)

J.J Thomson’s “Plum Pudding Model”
The “plum pudding model” was J.J. Thomson’s theory of atomic structure that he developed in 1904 (3). His theory was that all the subatomic particles were spread evenly throughout the atom in one positively charged piece. In other words, negatively charged electrons were floating in a mass of positive charge (4).

Thomson believed the negative electron "plums" floated around in a large mass of positive         "pudding"  (3)

The experiment:
The gold foil experiment was ultimately performed in order to prove Thomson’s “plum pudding model”, although that was not the case. Just the opposite happened, proving the theory incorrect. The experiment consisted mostly of alpha particles and gold foil (5). An alpha particle is a helium nucleus released by radioactive substances (discovered when Rutherford was studying radioactivity). It is a fairly heavy, positively charged particle (6). To begin, polonium was put into a lead box that sent out alpha particles to a thin sheet of gold foil. The foil was then surrounded by a luminescent zinc sulfide screen that served as a backdrop for the alpha particles to appear on (4).  A microscope was placed above the screen so they could easily observe any contact made between the alpha particles and the screen. In order to see the light of the alpha rays more clearly, the experiment was performed in complete darkness. To begin the experiment, they aimed a beam of alpha particles at a piece of gold foil, and then observed the astonishing results (5).

A simple diagram of how the experiment was set up. (4)
            In order to prove Thomson’s “plum pudding model”, the alpha particles were supposed to go straight through the foil. Shockingly, although most alpha particles passed straight through the gold foil, some did not. A small amount of particles were deflected slightly from the straight path by only about one or two degrees. An even smaller amount of particles were reflected off the gold foil at very large angles, and some occasionally bounced directly back at the source (3). The fact that some particles bounced back at large angles was the most surprising factor of the whole experiment. They discovered that 1 in 20,000 particles would bounce back at approximately 90 degrees or more from the parent beam. Rutherford was so amazed by this outcome, he explained the result by saying, “It was as if you fired a 15-inch shell as a sheet of tissue paper and it came back to hit you.” (5).  

            Obviously, Thomson’s “plum pudding model” was proven incorrect. Thomson’s theory said that an atom was made up of empty space, but that couldn’t be correct if the particles had bounced back because they had to have hit something. Rutherford reasoned that the item that was hit must have been very small since the majority of the particles didn’t bounce off of it (5). Alpha particles are very heavy, and have a mass about 8,000 times that of an electron. The alpha particles were traveling at a very high speed when they hit the foil, so a strong force was necessary in order to redirect the alpha particles since they were already so heavy (6). The way and angles in which the alpha particles bounced off the foil indicated that the majority of the mass of an atom was concentrated in one small region, that Rutherford later called the nucleus (3). He reasoned that the nucleus held all the positive charge, while electrons occupied most of the atom’s space. In simpler terms, the atom was made up of mostly empty space, which was why the majority of the alpha particles passed through. The particles that were deflected must have hit something in order for it to bounce off. This item that the particles bounced off of was named the nucleus.

This model describes how some of the alpha particles passed straight through, and how others didn't. As seen in picture (b), some of the alpha rays hit the nucleus. Depending upon where the nucleus was hit, the angle from which it was deflected differed. (5)

1. An atom was much more than just empty space of scattered electrons. (as opposed to what the "plum pudding model" proposed)
2. An atom must have a positively charged center that contains most of its matter (5). 
                  - He called this dense, concentrated center the nucleus (4). 
3. The positively charged center (nucleus) was relatively small in reference to the total size of the atom (5). 

Importance/ Significance:
            Rutherford’s gold foil experiment proved the “plum pudding model” of the atom incorrect, which allowed for a more complete understanding of the atom. His discovery of the nucleus and atomic structure was refined by Niels Bohr. Niels Bohr designed a model of the atom based off of Rutherford’s experiment, which is often referred to as the Rutherford Bohr model. This is so important because this is the basic atomic model that is still being used toady (3). The discovery of the nucleus and atomic model also allowed for the development of nuclear physics (4). This highly contributed to discoveries of the atomic and nuclear bomb, as well as organizing the Manhattan Project (2). In conclusion, Rutherford’s gold foil experiment contributed to what is today’s atomic model, and there has yet to be another discovery to disprove it.

 (1) “Ernest Rutherford – Biography”. 5 Oct 2010 - bio.html
(2)  “Ernest Rutherford, first baron (1871 – 1937)”. October 5, 2010
(3) Pestka, Jessica. “About Rutherford’s Gold Foil Experiment”. October 5, 2010
(4) “An Overview of Rutherford’s Gold Foil Experiment”. October 5, 2010
(5)“The Gold Foil Experiment”. October 5, 2010