Laboratory #3 Report

Alpha, Beta, and Gamma Rays

In this experiment, the penetrating abilities of three types of radioactivity: alpha, beta, and gamma were examined. A Geiger-Mueller counter and computer software was used to detect the levels of radioactivity direct from the source and through certain barriers.  It was found that the least penetrating particles were alpha, beta particles were the second, and gamma were the most penetrating.

Dana Edwards

Sarah Jane Slater

10/18/06

I. Introduction

There are several reasons why someone would conduct this experiment. The information the results provide could possibly be used in medicine and science. This lab helped distinguish between radioactivity and electromagnetic radiation. Electromagnetic radiation is energy that is emitted in waves traveling at 300,000 kilometers per second, that take the form of visible light, radio waves, or X-rays, depending on their frequency. Radioactivity is the spontaneous emission of radiation from the nucleus of an unstable atom. It is caused by the imbalance between nuclear forces holding the nucleus together. Electromagnetic radiation requires an input force to be emitted, where as radioactivity is completely spontaneous. Radiation can be found in certain elements, but electromagnetic radiation cannot exist inside matter. Radioactive decay can be found in the form of matter and energy, but electromagnetic radiation is only found in energy.

An element is radioactive if it has an unstable nucleus. Certain isotopes of an element can be radioactive, while others are not. Alpha radiation is matter in the form of two protons and two neutrons, bound together into a particle identical to a helium nucleus. They can barely penetrate a sheet of paper, but are harmful if inside the body. Beta radiation is also matter, but in the form of high-energy electrons. It is negatively charged, and its penetration is moderate. Gamma radiation is energy in the form of high-frequency electromagnetic waves. It has no charge, no mass, and is highly penetrating.

There are four different ways in which radiation can interact with cells. First, it can pass right through the cells without inflicting any damage. Second, the radiation can go through a cell, and destroy it in the process, by replacing the cell with radiation. Third, it can go into a cell and rearrange its DNA. However, the DNA can sometimes reconstruct itself afterwards. Lastly, the radiation can enter the cell and harm the reproductive portion of the DNA. This is the most harmful of the four scenarios, and by hurting the reproductive system of the cell; it multiplies rapidly, forming more mutated cells, with nothing regulating the rate of reproduction. These mutated cells are commonly known as cancerous cells. If they are not found and removed within a person, they will multiply beyond control, becoming possibly fatal. 

Gamma rays are the most dangerous type of radiation to a living organism. They are not only extremely penetrating, but they have a very high frequency and energy level. Because of its ability to penetrate, it can easily pass through an organism and harm its cells. Out of alpha, beta, and gamma radiation, gamma is the only one that can pass through a barrier such as the human body, enabling it to inflict great damage. This was discovered by observing its ability to maintain a stable level of radiation through different thicknesses of plastic and lead. The radioactivity level of alpha and beta particles, however, was decreased through the assorted obstructions.

II. Results

1. Data (see attached)

B.  Calculations

There were a few different types of calculations that were conducted during the lab. Firstly, the background radiation in the room was recorded. It was done twice, getting 8 counts in thirty seconds each time, which was doubled to get 16 counts per minute (8∙2=16cpm). To find the average of the two trials of background radiation, they were added together, (16+16=32cpm), and than divided by two (32÷2=16cpm), to get an average of 16 counts per minute for our background radiation.

The radiation levels (in counts per 30 seconds) of alpha, beta and gamma radiation were then recorded. After getting the number of counts per 30 seconds, the number was doubled, to get the number of counts per minute. (ex. 234∙2=468cpm). After getting the total counts per minute, the average of the background radiation (16cpm) was subtracted from this number. (ex.468-16=452cpm) to get the counts per minute due to source.

III. Discussion

Several trials were conducted with the three types of radiation to find their penetration levels through certain objects. First, the source was placed under the Geiger-Mueller counter unobstructed, allowing for the full amount of radiation emitted from the source to be recorded. Next, paper was placed in between the source and the counter, blocking a significant amount of radiation only with alpha particles. This showed that alpha particles are the least penetrating of the three types of radiation, because a thin barrier of a single piece of paper reduced the detected radiation levels from 452cpm to 56cpm, by a factor of 7. Next, two pieces of thin plastic were placed in between the source and the counter. The radiation from the alpha particles was again decreased significantly, down to 16cpm. The beta radiation took its first major plummet when obstructed by the thin plastic, decreasing from 11,344cpm with the paper barrier to 2,424cpm. The gamma radiation was not decreased at all. The amount of plastic used to obstruct the source was then doubled, from two thin pieces of plastic to four. The alpha radiation became undetectable through the thick plastic, with the Geiger-Mueller counter registering only the 16cpm of background radiation that was originally recorded. The beta radiation again decreased significantly, from 2,424cpm from the thin plastic to 130cpm with the thick plastic, by a factor of 17. Once again, the gamma radiation remained relatively unaffected. Next, two pieces of thin lead were placed blocking the source. The alpha radiation was again undetectable, and the beta radiation decreased to 16cpm from 130cpm with thick plastic. Lastly, four pieces of lead were placed between the source and the counter. Alpha and beta radiation were again very low, (20cpm and 24cpm respectively) and gamma took its first noteworthy fall, from 1,414cpm with thin lead to 1,010cpm with the thick lead.

The results of this lab showed clearly the order of penetration capabilities of the three kinds of radiation. Alpha particles were the least penetrating, because a single piece of paper decreased the emitted alpha radiation by a factor of 7. Beta was the second most penetrating type of radiation examined, decreasing incrementally due to the paper and plastic, and reaching its threshold when the lead was added. Gamma radiation was by far the most penetrating type of radiation. It remained constant (1,414cpm-1,596cpm) throughout all the trials but the last, the thick lead, when it decreased from to 1,010cpm, a small drop in radiation compared to those of the alpha and beta particles.

Some of the results recorded were surprising. Specifically, more radiation was recorded from alpha and beta particles when the thick lead was blocking the sources than when the thin lead was. The alpha radiation went up from 0cpm with the thin lead to 20cpm, and the beta went up from 16cpm to 24cpm. The conclusions drawn from this experiment do not allow alpha and beta particles to have more detectable radiation through thicker barriers. Therefore, this must be a phenomenon.

IV. Conclusion

The knowledge we gained from the results of this laboratory experiment can be applied in many beneficial ways. We now understand better the different kinds of radiation that exist. We found that some forms of radiation are not very penetrating, where as others are. From this information, we now understand the safety hazards in dealing with different kinds of radiation. Alpha particles are externally not very dangerous to us, because they can barely penetrate a piece of paper. If ingested, they pose a potential health risk, which is, however, much lower than the danger of ingesting beta and gamma radiation. If I were to introduce a radioactive element into a patient’s body, I would use alpha particles. The particles could diagnose a particular illness, with a relatively low risk to the patient. I would definitely not choose gamma radiation to be ingested by my patient. Gamma rays are very penetrating, making them much more harmful to the human body. They have the potential to destroy cells, or mutate them to form cancerous cells.

When the body is receiving X-rays, a special blanket must be worn to protect the body from excess radiation. Based on the knowledge we gained from this experiment, we believe that the blanket should contain lead. It is a very dense substance, and it shielded the most radiation in all of our trials. Lead walls should also be placed around the core of nuclear power plants to protect workers and civilians from the high levels of radiation. 

Dana Edwards 11/15/06

Chemistry- Doctor Musser

Lab #6 Questions

Periodic Law

1. There are several trends that are made within the columns and rows of the periodic table. Within each column or group, the oxidation numbers tend to be uniform. For instance, in group 1, all the elements have a +1 oxidation state, except for hydrogen, which has a +1 or -1 oxidation state, because it is a gas and allows both oxidation and reduction. In group 14, all the elements have a +4 oxidation state, although some include others, such as Sn (+2, +4). The oxidation numbers represent how many electrons an element has to lose or gain in order to become a stable ion, with all its energy levels full. An element can have two or more oxidation numbers because it can end up with either the s or the p energy levels complete. In the case of Sn (+2, +4), it can lose two electrons to complete the 5s sublevel ((KR) 5s2), or it can lose four electrons, getting rid of the 5s electrons and completing the 4p sublevel (Kr). Another (quite obvious) trend is that the atomic numbers increase as you go down the period table, from left to right. The atomic number represents the number of protons in an atom. As it increases from left to right, so do the oxidation numbers of the elements. However, at the end of each row, the next element skips down to the next row, and the oxidation numbers are reset to 1. So, the atomic number and oxidation numbers are related, although the oxidation numbers repeat periodically. The Densities of the elements appear to increase along the rows from left to right, resetting periodically at the beginning of each row. The melting point of each element does not appear to follow a general trend, although the melting points of the gasses and liquids are all very low temperatures, below 0 degrees Celsius. The atomic radii of the elements increase as they go down the columns. This is because the farther down the columns the elements are, the farther away from the nucleus the electrons become, making the distance from the nucleus to the outside of the electron cloud greater, and therefore the atomic radius bigger.  Lastly, the gases and liquids are all on the right side of the periodic table, to the right of the staircase of metalloids.

2. There are exceptions to the trends listed above. First of all, the oxidation numbers are not completely constant in each row. For instance, in group 15, the pnictogens, the general oxidation number is +3. All of the elements in group 15 have a +3 oxidation state, because they can all lose 3 electrons and end up with a full s energy level. However, some have other oxidation states, such as Sb, which also has a +5 state. This is so because it can end up with a full s energy level or a full p energy level. Another factor that allows for these exceptions in oxidation levels is the state of the matte of the element. If it is a metal, it can only lose electrons or oxidize, making a positive ion. If it is a nonmetal, it can only gain electrons or redact, making a negative ion, and if it is a metalloid it can both oxidize and redact. Next, there is an exception to the densities of elements in the periodic table. They do increase from left to right in the rows, however the gasses all have very low densities, regardless of their position on the table. There is one exception to the trend of atomic radii. Aluminum has a bigger atomic radius than gallium, although it is above it in group 13. There is a single exception to the position of the metalloids, metals and nonmetals in the periodic table. Aluminum (Al) is a metal, however it is on the staircase and therefore should be a metalloid.

3. Metals and nonmetals have very different properties.  Metals are malleable and shiny, while nonmetals are brittle and dull. Metals can only perform oxidation, and nonmetals can only perform reduction. This is because metals have a low affinity for electrons, while nonmetals have a high affinity for electrons. 

1. There exists a relationship between oxidation number and electron configuration for main group elements. Generally, the higher the number of valance electrons in the electron configuration, the higher the positive oxidation number. This is because the more valance electrons an atom has, the more electrons it has to lose before it has complete sublevels. However, this does not apply to every group. Group 18 has the highest number of valance electrons (8), but its elements do not oxidize or redact at all, due to the fact that their sublevels are all full. In addition, most nonmetals do not oxidize, so their oxidation numbers do not follow the trend; instead they redact by gaining electrons. An atom’s electron configuration can easily be figured out by its location in the periodic table. In order to identify its electron configuration, one simply counts the sublevels starting from the first element, hydrogen, at 1s1. For example, the electron configuration of Sodium would be 1s2 2s2 2p6 3s1. It can also be written shorthand, by finding the preceding noble gas, showing it in parentheses, and then identifying the rest of the configuration following the noble gas. The electron configuration of sodium, written in shorthand, would be (Ne) 3s1.

To Be or Not To Be Salty: That is the Question

Laboratory #7 Report 

Distillation of Saltwater

In this experiment, the process of salt-water distillation was examined, and the resulting distillate was compared with the original saltwater. A simple distillation apparatus, including a Bunsen burner, a boiling flask, a thermometer, a condenser, and a beaker was used in the laboratory. It was found that the condensate was free of salt, clearer and less conductive than the original salt water.

Dana Edwards

12/03/06

I. Introduction

One would conduct this experiment in order to see if the process of distilling water changes it in any way. As the results portray, the process does, in fact, alter the constitution of a salt-water solution. It removes all traceable amounts of salt from the mixture. This is a powerful discovery because it leads to the capability of humans to extract fresh water from the vast salty oceans and seas covering the planet. Distillation, or some other form of water desalinization, will become increasingly important as our water consumption exceeds the rate at which the planet’s fresh water sources replenish. 

Fresh water is vital to human survival, and a fundamental part of their lives. It has been ranked second only to oxygen as essential for life. The adult human body is about 75 percent water, and one must drink about two and a half quarts daily to remain fully healthy. It is the key to all bodily functions. It aids digestion, regulates body temperature and blood circulation, carries oxygen and nutrients to cells throughout the body, and removes toxins and wastes. In addition to its essential purposes, it serves as a means of maintaining bodily hygiene, such as in showers.

Fresh water, or water with an ionic content of less than 0.5 parts per thousand, makes up about 2.5 percent of the earth’s water. 69 percent of this fresh water exists in icecaps and glaciers, and another 30 percent in ground water. Theoretically, all of that fresh water is usable, but practically very little is obtainable. It would be very difficult to use ice caps as a water source because of their remoteness from inhabited areas, and because they are in a solid form and are therefore difficult to transport and require melting to become usable.  Similarly, most ground water is much too deep to be able to harness as a source. That leaves less than one percent of all fresh water as easily accessible surface water, such as lakes and rivers. Most of the fresh water that humans use comes from lakes and rivers that comprise only 0.2 percent of all fresh water. Another source of fresh water that humans use is the atmosphere. It holds a substantial amount of fresh water in the form of water vapor. However, in order to utilize the water in the sky, humans must be in an area with regular precipitation.

Different areas throughout the planet have different amounts of available fresh water for usage. Climate and location are two factors that influence the availability of fresh water for a local population. An area with heavy rainfall, for instance, generally has plenty of fresh water for consumption and other uses. Conversely, a dry area must rely on other sources, such as lakes. 

Cate School does not have a “water shortage”. The Santa Barbara area, Carpinteria included, gets its water from an array of sources. They include Gibraltar Reservoir, Lake Cachuma, recycled water, ground water, and desalinization. The sources are bountiful enough to provide for the roughly 400,000 people in Santa Barbara County. Although there is a relatively low yield of yearly rainfall in the area, most of the sources are renewable. For instance, Lake Cachuma is fed by the Santa Ynez river, constantly flowing, filled by rainfall up in the mountains, and desalinization is an essentially boundless source, limited only by the energy it takes to desalinate the ocean water.

The water cycle is the description of the continuous movement of water, on, above, and below earth’s surface. Because it is a continuous cycle, there is no beginning or end, so one must pick an arbitrary point at which to begin explaining it: Water is stored in the oceans and in freshwater lakes. Due to evaporation from the sun, some of the water on the surface of oceans and lakes is taken up into the atmosphere, in the form of water vapor. In addition to evaporation, transpiration and sublimation add to the water vapor in the atmosphere. Transpiration is the process in which water escapes the leaves of a plant through their stomata. It is a side effect of plants opening their stomata to obtain carbon dioxide. Sublimation occurs in the water cycle when water vapor is obtained directly from snow or ice, without stopping at the intermediate liquid stage. 

With all this water stored in the atmosphere from evaporation, transpiration, and sublimation, the clouds drain their water supply through the process of precipitation. However, in order for that to take place, condensation must first occur, during which the water vapor turns back into either a liquid or a solid and condenses in clouds, due to a drop in temperature. So, precipitation can occur as rain, hail, or snow. If the temperature is cold enough, snow or ice will remain for periods of time, storing water. Rain and snowmelt form runoffs that feed streams. The streams will either feed into a lake or river, or in to the ocean. In addition to runoffs, snowmelt and rain goes underground through the process of infiltration. It seeps through the soil, and is either stored underground in aquifers as ground water, comes up to the surface in springs, or empties in to freshwater sources or the oceans. The water cycle is nature’s own water purification system. In it, water is constantly changing forms, and impurities are removed through the many processes, such as in evaporation from the oceans, where salt is left behind and fresh water is stored in the atmosphere.

Distillation is a way of separating a substance into its component fractions through the application of heat. It works upon the principle that all substances have different boiling points. For distillation to work properly, the boiling points of the substances must be significantly different. For instance, in the case of saltwater, the boiling point of sodium chloride is much higher than that of water, so when the water boils and evaporates, the salt is left behind in a solid state. If the boiling points of the substances trying to be separated are too similar, however, both substances will be evaporated and the condensate will be similar to the original mixture. Distillation also occurs in nature. When saltwater evaporates from the oceans due to heat from the sun, the salt is left behind and fresh water rises up into the atmosphere as water vapor. When the water condenses in the clouds, and finally precipitates, it is devoid of sodium chloride. This is nature’s way of producing fresh water from the salty oceans.

 Distilled water is not a very good conductor of electricity. In its purest form, water has a conductivity of about .00001 siemens per meter (s/m). The number of ions a solution holds determines its conductivity, therefore the more impurities water has, the more conductive it is. Hence, regular undistilled drinking water has a conductivity of about .05 s/m, higher than that of pure water. Following the same trend, seawater is much more conductive than freshwater. It has many more dissolved substances, primarily sodium chloride. Due to its abundance of ions, it has a conductivity of about 5 s/m, much more than that of distilled and undistilled fresh water.

II. Results

1. Data (see attached)

2. Calculations

There were no real calculations in this laboratory. However, there were some recorded measurements and observations that will be reviewed in the following discussion section.

III. Discussion

Only one trial of saltwater distillation was recorded in this laboratory. Before the experiment commenced, the simple distillation apparatus was assembled. A metal arm with a clamp held the boiling flask full of saltwater. Glass tubing was inserted into the beaker, and a thermometer was placed at the top of the apparatus, with the tip slightly above the water surface. A Bunsen burner was placed below the beaker. Connected to the beaker through glass tubing was a condenser, held up by another arm and clamp. Two tubes ran out of it: an in-tube supplying cold water and an out-tube emptying out the water. The water was necessary in order to cool the condenser so condensation could take place. Finally, attached to the end of the condenser was a beaker for collecting the condensate.

Prior to the heating process, the saltwater was observed and its conductivity was tested. The saltwater appeared colorless and slightly cloudy. If carefully examined, tiny particles were visible within the solution. Its conductivity was taken with a two-pronged device. It registered a conductivity level of high-3. Next, the saltwater was placed in the boiling flask, the Bunsen burner was lit, and the water for the condenser was turned on. Nothing eventful took place until the thermometer registered 35 degrees Celsius (C.). At that point, tiny bubbles began rising from the bottom of the flask and popping on the surface. At 50 degrees C., the bubbles increased in size and speed, and by 55 degrees C., there were large bubbles rising very quickly to the surface of the solution. However, there was still not a drop of condensate. At 60 degrees C., the saltwater came to a full boil, and the temperature quickly rose from 60 to 100 degrees C.

Soon after the water began boiling and the temperature reached 100 degrees C., the first drop of condensate formed and slid down the condenser into the collecting beaker. From that point on, about every 6 seconds a droplet of condensate would form and drop into the beaker. It seemed odd that there was not a continuous stream of condensate, but incremental droplets. Perhaps it took a certain amount of vapor to build up in order for condensation to occur. Anyways, this 6-second-condensate-droplet-formation continued throughout the rest of the heating process. The only other observation recorded was that the temperature rose gradually from 100 to 105 degrees C.

After the desired 50 milliliters of condensate was collected, the heating process was stopped. The distilled condensate was than examined. It was colorless, like the original saltwater; however, it appeared completely clear, with no visible particles inside. Its conductivity was recorded at low-9, much lower than the high-3 level recorded for the original saltwater. Finally, the remaining saltwater in the boiling flask was examined. A ring of salt was visible at the original water level, and splotches of salt existed all around the inside of the flask. It was colorless, and it appeared to be even cloudier than before the heating process. This is due to a greater concentration of salt in the water, because the salt remained while most of the water evaporated and re-condensed into the collecting beaker. It registered a conductivity of high-5, higher than that of the original saltwater and the condensate.

Earlier in this report, it was stated that the more ionic particles a solution contains, the more conductive it is. This is perfectly demonstrated by the results of this laboratory. The solution with the highest concentration of salt (the remaining saltwater in the flask) registered the highest conductivity of all three liquids examined. Next, with the second most amount of sodium chloride was the original saltwater solution, and lastly the distilled water, registering the lowest conductivity.

The highest temperature the vapors reached was 105 degrees Celsius. This seemed surprising because at first thought, one thinks that water cannot reach a temperature of over 100 degrees C., its boiling point. However, after consideration, one realizes that it was not the temperature of the water being recorded, but the temperature of the water vapors. Water vapor is the gas form of water, and therefore it can reach temperatures exceeding 100 degrees Celsius. 

So although the 105-degree temperature was unexpected, it makes sense in retrospect. As water is heated, it boils when it reaches 100 degrees Celsius. It then begins evaporating into water vapor. If the water vapor were to remain at a constant 100 degrees C. throughout the rest of the experiment, where would the heat from the Bunsen burner go? Due to the law of the conservation of energy, the energy from the Bunsen burner must heat something. So, the Bunsen burner continues to heat the water vapor to higher temperatures, while the boiling water is not physically capable of surpassing 100 degrees C., and therefore remains at that temperature, boiling, until it has all evaporated.

In order to improve this experiment, one might conduct other tests to further examine the differences between distilled and un-distilled saltwater. For instance, besides measuring the conductivity of the substances, one might measure the ph-levels, to see if the process of distillation effects acidity. In addition, one could test for substances other than sodium chloride, to see if the boiling points differ enough to allow for separation within the solution. Finally, one could conduct several trials, and take more careful measurements of temperature and other factors, in order to provide a broader spectrum of data.

IV. Conclusion

Tap water contains many impurities. These impurities are in the form of dissolved minerals. The existence of these minerals allows for tap water to conduct electricity fairly well. This is because the more ions dissolved in water, the more free electrons the solution holds. With more free electrons, charge can pass through a substance with greater ease, the definition of conductivity.

These minerals exist in tap water because of the circulation of water through the water cycle. When precipitation and snowmelt form runoffs, they pass over the surface, picking up minerals and particles. If the runoffs lead to a freshwater source such as a lake, they carry more minerals than they originally started with, depositing them in the lake. In this manner, the mineral content of a lake gradually builds over time, as runoff leaves particles in the lake that are left behind as the water evaporates from the surface. However, most lakes have an outlet, allowing some of the mineral-enriched water to flow out to another source, ultimately the ocean. So, since much of tap water is taken from lakes and other deposits of freshwater, it contains many minerals and impurities that have built up over time in the source.

Humans do not need “pure” water to live. In fact, water containing minerals is good for one’s health. Minerals such as calcium, manganese and strontium, found in tap water, are important in order to remain healthy. Purifying water to the extent that it contains no minerals would simply be a waste of energy. However, humans cannot drink water with too many impurities. Seawater, for example, contains far too many dissolved salts (primarily sodium chloride) to be fit for human consumption.

Lakes such as the Great Salt Lake and the Salton Sea have a very high salt content because they have no means of emptying themselves. The mineral content, including sodium chloride, builds up over time due to surface runoff that picks up particles that accumulate in the lake. The reason these lakes have a much higher salt content than most is that they have no outlet, or means of emptying their salty water. As time goes on, the minerals continue to accumulate. Therefore, there is currently more salt in these lakes than there was in the past, and the amount will continue to increase in the future.

Distillation is an effective way of separating salts from water because of the large differences in boiling points of the two substances. Water boils at 100 degrees C., and sodium chloride, as most ionic compounds, boils at a very high temperature. When water boils and evaporates at 100 degrees C., salt is left behind in its solid state. 

Substances with boiling points similar to that of water are not effectively separated through distillation. For example, methyl tert-butyl ether (MTBE), a gasoline additive with a boiling point of 55.2 degrees C., would not be completely separated from water through simple distillation. If an aqueous solution including MTBE were placed over heat, it would boil before the water does, and when the water evaporates and condenses, it would have already done so, and the resulting condensate would be contaminated with the pesticide. In the same fashion, methyl bromide would not be effectively separated from water through distillation. However, since methyl bromide has a boiling point almost 100 degrees less than that of water, separation will occur, but there will still be some contamination. Generally, the closer together the boiling points of substances are, the more contaminated the condensate will be.

Since distillation only works well with substances of significantly different boiling points, not all impurities are removed from water through distillation. There can be many different types of particles within water, all with different boiling points. Therefore, it is extremely difficult to precisely separate water from its multitude of contaminants with similar boiling points. Due to this, distillation is not usually done on a large scale as a public source of clean water.

Another reason why distillation is not widely used for obtaining clean water is that it is uneconomic. It takes an enormous amount of energy to boil water on a large scale. Only countries with cheep sources of energy and no alternative sources of fresh water use distillation as a large public water source. One such country is Saudi Arabia, which produces 16 percent of the world’s desalinated water through an advanced distillation process. It has an enormous amount of oil as a cheep energy source, and virtually no alternative natural sources of fresh water.

The human population is currently rising at a fast pace. As the population increases, so does the need for fresh water, as it is essential for survival. Even today, many areas on the planet face a serious lack of water. These areas generally have low rainfall and no near sources of stored fresh water, or are simply too poor to be able to harness a water source. In the future, humans will have to find a way to bring fresh water from areas of abundance to areas with a serious lack. 

In addition to the growing need for water due to a rise in population, global warming is decreasing the amount of available freshwater sources. Firstly, as the global temperature rises, the icecaps and glaciers begin melting. Although humans have not yet figured out an effective way to use the icecaps as a freshwater source, they could possibly in the future. However, if the icecaps continue melting due to global warming, they will cease to be an option. As a result of the icecaps melting, the water level of the oceans is beginning to rise. If it continues to rise at the current rate, low freshwater sources near the coast will become submerged under the ocean.

 Desalinization, through distillation or some other method, may become a vital technique in the future. Because, though lakes and rivers hold a limited amount of water for human usage, the oceans hold a boundless amount of water, simply in need of purification to become fit for consumption. Perhaps more efficient methods of water desalinization will be developed in the future, or perhaps humans will be forced to compensate in some other fashion. The water usage per capita of the United States is much greater than that of any other nation. Americans must learn to be more conservative of water: by taking shorter showers, turning the faucet off while brushing their teeth, and reducing their participation in water-consuming activities such as golf.

Laboratory #9 Report

Metal Reactivities

In this experiment, the relative reactivities of copper, magnesium, zinc, and silver metals were examined. Thin strips of three of the metals (copper, magnesium, and zinc) were placed in nitrate salt solutions of all four elements, and the ensuing chemical reactions (or lack there of) were observed and recorded on the data sheet. The results concluded an order (from most to least reactive) to the four metals: magnesium, zinc, copper, silver.

Dana Edwards

02/07/07

1. Introduction

Metals, alone in their elemental form, are stable and will not undergo chemical reactions. In order to react, a metal must encounter another metal, anion, or compound. If in contact with another metal, electrons will be transferred from the metal with the lower electron affinity to the one with the higher electron affinity. After losing one or more electrons, the metal will become a positive ion, or anion. If in contact with an anion, a metal can give its electrons to the ion, forming an ionic compound. If introduced to a compound, the metal may undergo a single displacement reaction and give its electrons to the element previously bonded to the compound. This kind of reaction took place during this laboratory.

What determines the reactivity of a given metal is its ability to lose electrons easily, or with the least amount of energy. Ionization energy is closely related to the reactivity of a metal; it is the energy it takes to strip an element of its outer electrons, causing it to react and form a cation. Therefore, the two are essentially inversely related; the lower the ionization energy of a metal, the more reactive it is.

Electronegativity is also related to both reactivity and ionization energy. It is similar to electron affinity; it is the ability of an element to attract electrons. Generally, the higher the electronegativity of a metal, the less reactive the metal is. The subtle difference in relationship between electronegativity and the other two chemical characteristics is that electronegativity is the ability to attract electrons in the context of a chemical bond. If the electronegativity levels of two elements do not differ significantly enough, electron transferal from the less electronegative atom to the more electronegative atom (forming an ionic bond) will not occur; instead a covalent bond can form where one or more of the electrons is shared. This can only occur between two nonmetals. Furthermore, if one element within a covalent bond pulls on the shared electron(s) slightly more than the other, a polar-covalent bond will form. Because of the difference in nature of assigning electronegativity levels and reactivity levels, the two do not always inversely correspond. For instance, barium is less electronegative than lithium, however it is also less reactive. If the two were in a perfect inverse relationship, the less electronegative element would have to be more reactive than the more electronegative element. However, generally, for metals, reactivity is inversely related to ionization energy, electron affinity, and electronegativity.

The periodic table is arranged in a way that elements with similar characteristics are grouped together. Reactivity is one such property. Generally, the further down the table one looks, the more reactive metals are. This is because elements in lower rows in the table usually have larger atomic radii. Since the reactivity of a metal is given by its ability to lose electrons, a metal with a larger atomic radius will be more reactive; its outer electrons will be freer to leave because of their great distance from the nucleus and therefore weaker force binding them to the center of the atom. Conversely, the least reactive metals are towards the top of the periodic table. Their atomic radii are smaller, and therefore their nuclei pull harder on their outer electrons, prohibiting the transferal of electrons from occurring as easily as with more reactive metals further down on the periodic table.

Highly reactive metals will readily form cations when placed in contact with less reactive metals. Francium, for instance, the most reactive metal, will always give its electron away to another metal. There are various uses for reactive metals. Gunpowder, for example, undergoes radical combustion when it is lit. This is due largely to the reactive metals in its composition, such as potassium and sometimes sodium. Reactive metals are also used in batteries, where metals in the anode oxidize to form cations and free electrons, which travel to the cathode and are then cycled back into the battery. The flow of electrons through the battery contains current that can power electrical devices, a very useful application of reactive metals and the reactions they undergo.

Very non-reactive metals do not serve many practical functions, such as producing energy, however they are used because of their sheer non-reactivity, in such applications as jewelry and dentistry. Gold and silver, both very non-reactive metals, are used in jewelry because they do not oxidize or corrode over time, as do many reactive metals. Therefore, they can remain shiny and beautiful, serving their purpose as being aesthetically pleasing. In dentistry, similar non-reactive metals are used. Gold crowns are common, because one does not want one’s dental caps to corrode. It is especially important to use a non-reactive metal, such as gold, in dentistry, because people consume many different things that come into contact with their teeth, and a more reactive metal could possibly oxidize or react with traces of metals or other elements found in the food we eat or the air we breathe.

The selection of appropriate metals is quite important in such fields as the construction business. It would be helpful to know the reactivity of metals if constructing large buildings. For instance, it would be a bad idea to use very reactive metals for the structure or support. Over time, the reactive metals would oxidize and become instable, putting the building and its inhabitants at risk. Less reactive metals would be safer to use for the foundations of large buildings. A metal used often in constructing buildings is iron. Iron is a smart choice because it is not very reactive, and because of its abundance in the earth’s crust, making it an economical choice. In addition to reactivity and availability, knowing the physical properties of metals should also be involved in an architect’s plans for building. If one was to build a very large building, the structure would have to be quite strong, to prevent it from toppling, particularly in abnormal conditions such as earthquakes. If the building were near the San Andreas Fault Line, where earthquakes are relatively common, it would be even more vital to use a strong metal for the core support of the building. Perhaps not a pure element should be used, but rather a metal alloy, such as steel, to provide maximum strength.

Such are a few of the ways the information gained from this lab can be applied. The knowledge can be used to better understand the importance of metal reactivities, in such fields as jewelry, dentistry, and the construction business. The purpose of this laboratory was simply to spark the interest of its participants in the field of chemistry in yet another way, particularly to help them better understand how metals react with one another, through observing simple reactions between four different metals. Similar single displacement oxidation reactions, as were observed in this lab, exist within batteries. Perhaps a purpose of this laboratory was to demonstrate the great sources of energy that can come of these simple reactions between metals. One can achieve the purpose of the lab by further researching the many applications of metal reactivities, and by continuing to pay attention in chemistry class by fully engaging oneself and listening attentively to the wise words of Doctor Musser.

      II. Results

1. Data (see attached)

2. Calculations

There were no real calculations done in this laboratory. However, there were some recorded observations that will be discussed in the following discussion section.

3. Discussion

The procedure of this laboratory was relatively simple and straightforward.  In preparation, thin strips of copper, magnesium, and zinc were cleaned by rubbing them vigorously with metal filings. This was to ensure that they contained no traces of other metals from previous trials, which would skew the results of the experiment. Three strips of the three elements were placed in small plastic wells. Then, nitrate solutions containing all four metals were placed in contact with each of the strips (five drops in each well), one by one, and the observations were recorded.

One of two things would take place when a nitrate solution was introduced to one of the metal strips. Either no visible reaction would occur, or the strip would immediately change color where in contact with the solution. In most cases, the strip would turn a dark color, blackened as if from smoke. However, in the case of copper when it reacted with silver nitrate, it turned a dull, grey color, rather than a dark, smokey color. This is probably because copper has a lighter appearance than zinc and magnesium. In addition to the change of color that occurred in all the cases where the metals reacted, dust or particles of the metal strip usually accumulated on the bottom of the solution after a few minutes. Also, in some cases, tiny bubbles formed in the solution.

After all the solutions were introduced to the strips, it was possible to then examine the results and consider the relative reactivities of the four metals. Once again, reactivity is the ability of a metal to lose its outer electrons to a less reactive metal, ion or compound, and either form a cation or enter an ionic bond. In this laboratory, the metals in their elemental form were reacting with ionic compounds containing other metals, and either undergoing no reaction or undergoing a single displacement reaction. Therefore, it is relatively simple to discern the relative reactivities of the four metals. One simply has to see how many reactions occurred for each metal, out of a possible three, the encounters with the three different solutions. Magnesium underwent a reaction with copper nitrate, zinc nitrate, and silver nitrate; therefore it is the most reactive of the four metals. Zinc reacted with two of the solutions, copper nitrate and silver nitrate, but not with magnesium nitrate, furthering the theory that magnesium is the most reactive. Copper reacted only with the silver nitrate solution, and silver, although it was not tested, apparently reacted with none of the three solutions.

As is demonstrated by the results, the most reactive metal (magnesium), in its elemental form, reacted with all the solutions it encountered. Conversely when the magnesium nitrate solution was introduced to copper, zinc, and silver, no visible reaction took place. This is because those three metals were not reactive enough to give their electron to the magnesium in the nitrate solution, and cause a single displacement reaction. Magnesium was able to displace all three of the solutions. Here is the balanced equation and half reactions that magnesium underwent when reacting with silver nitrate. Similar single displacement reactions occurred in all the instances when a visible chemical reaction was observed.

IV. Conclusion

According to the introduction to this lab in the Laboratory Manual, an activity series is a ranking of metals based on their relative chemical reactivities, or their willingness to give up electrons. The activity series of the four metals involved in this lab was unknowingly provided in the abstract to this report. However, here it is again, from most to least reactive: Magnesium, Zinc, Copper, and Silver. 

From this laboratory, it was possible to find the relative reactivities of the four elements, in other words, their reactivities in relation to one another. This was done, as stated in the discussion section, simply by observing how many reactions each metal underwent; the most reactions indicated the most reactive metal and the least indicated the least reactive metal. However, it would be very difficult to find the actual reactivities of the metals, it would probably involve equipment and knowledge beyond the level of our chemistry class.

The Statue of Liberty was made of copper instead of zinc simply because copper is less reactive than zinc. As it states in the introduction, it is safer and sturdier to use metals of lower reactivity for constructing large buildings. Because the Statue of Liberty is made of copper, a metal with a low reactivity even when compared in an activity series with all other metals, it will not oxidize and corrode as quickly as it would if it were made of zinc or some other metal with a higher reactivity. However, there are a few other metals which would have been better to use because of their lower reactivities. Silver, which was recorded in this lab as being the least reactive of the four metals, would have worked well as the material for the statue. In addition to silver, there are three other metals with lower reactivities than copper: mercury, platinum and gold. Silver, platinum, and gold were not used to build the statue because they are rare and it would have been enormously expensive. Mercury was obviously not used because it is a liquid under normal temperatures. Therefore, it makes quite a lot of sense that the French chose copper as their metal of choice when constructing the Statue of Liberty, their gift to the United States for inspiring the French Revolution. 

The relative reactivities of a given metal are determined by which other metals it reacts with, and which it does not. Those the metal does not react with are more reactive than it, and it is more reactive than those it does react with. Using this simple rule, it is possible to determine the relative reactivities of metals by conducting straightforward experiments such as in this laboratory, and ordering the metals from ones that reacted the most to ones that reacted the least, forming an activity series.

It is most likely that very non-reactive metals will be found in a free state in nature. Highly reactive metals, such as potassium, lithium, and sodium would be hard to find in their pure, elemental form, because they are so quick to give away an electron or two to any nearby compound, ion, or element. There is evidence of this in the natural world. Gold, silver, and platinum, very non-reactive metals, exist on their own in nature. Mining for the three precious metals is a large industry, because they are valuable and it is possible to find large clumps of them in their elemental form, such as gold nuggets. Sodium, on the other hand, is rarely found in an uncombined state. Most of the earth’s sodium exists within ionic compounds, such as NaCl.