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Effects of Concentration and Temperature on Equilibrium: Lab

The purpose of this experiment was to study the effects of concentration and temperature changes on the position of equilibrium in a chemical system and to observe the common-ion effect on a dynamic equilibrium (Beran, 2009). LeChatelier’s Principle states that if and external stress is applied to a system in a state of dynamic equilibrium, the equilibrium shifts in the direction that minimizes the effect of that stress (Beran, 2009). Dynamic equilibrium can be defined as the condition in which a chemical system has reached a state where the reactants combine to form the products at a rate equal to that of the products re-forming the reactants (Tro, 2010). Most chemical reactions do not produce 100% yield of product because of the chemical characteristics of the reaction. After a certain period of time, the concentrations of the reactants and products stop changing (Beran, 2009). This indicates the chemical reaction is in equilibrium and when a reactant is added, and then it shifts the solution either left or right as an attempt to relieve stress and compensate for the change. In this experiment, the solution was brought out of equilibrium indicated by either a color change or precipitate formation.
In part A of the experiment, concentrations of the reactants and products were changed to indicate the change of colors when drops of concentrated NH3 were added to 0.1 M of CuSO4, shifting the solution to the right, forming ammonia-complex ions. When the strong acid HCl is added, this removes the ammonia from the equilibria and the reactions shift left to relieve the stress. The net ionic equation can be represented as
[Cu(H2O)4]2 (aq) 4NH3 (aq) ïƒŸïƒ [Cu(NH3)4]2 (aq) 4H2O (l)
In part B of the experiment, silver ions such as carbonate, chloride, iodide, and sulfide are used in this experiment as they form precipitates, dissolve precipitates, and form gaseous substances. Nitric acid is added to silver carbonate in order to shift the equilibrium to the right. The addition of NH3 removes the silver ion, shifting the equilibrium to the left, causing AgCl to dissolve. Next, adding H reforms solid silver chloride, shifting the equilibrium right again. Then, adding the iodide ion to the equilibrium results in the formation of the precipitate of solid silver iodide, shifting the equilibrium to the left again. The net ionic equation for the reaction is represented as:
Ag2CO3 (s) ïƒŸïƒ 2Ag CO32- (aq)
The changes in concentrations affect the equilibrium, significantly. If the concentration of a reactant was increased, to reduce the concentration, the system shifts to the left or towards the reactant, to make it as the product. This increase in concentration can occur to any species of the equilibrium reaction and the system would shift towards the increased concentration (Beran, 2009). The concentration can be chemically increased with additions of aqueous substances that can react with the equilibrium reaction. However, the same is not true for acids and bases. When an acid concentration is increased, the system tends to the opposite and thus flows towards the base, to increase its concentration (Beran, 2009). To prevent any changes in the acid-base pH, buffers are mainly used to sustain the equilibrium. Buffers have to consist of a weak or strong acid or base and its conjugate species (Tro, 2010).
As for parts D and E, the common ion effect and the temperature effect are tested. By adding drops of HCl to 1.0 mL of CoCl2 and by comparing the color change to that of 1.0 mL of CoCl2 placed in a hot water bath. The ionic equation for the reactions can be represented by:
4Cl- Co(H2O)62 Heat ïƒŸïƒ CoCl42- 6H2O
Materials and Procedures: Please refer to Experiment 16 on pages 201-212 of Laboratory Manual for Principles of General Chemistry by J.A. Beran. Note that part C of the experiment was not performed.
Data and Results: Table 1: Metal-Ammonia Ions
CuSO4
[Cu(NH3)4]2
HCl Addition
Color
Light Blue
Dark Blue
Light Blue
Table 1 shows the colors that the solution changed to as reactants were added.
Table 2: Multiple Equilibria with the Silver Ion
Observation of Na2CO3 combine with
AgNO3 and net ionic equation
Ag2CO3(g) ↔ 2Ag (aq) CO32- (aq)
Turned brown
HNO3 was add to solution
The solution turned colorless and shifted to the right with the formation of water and carbon dioxide
HCl addition and net ionic equation
Ag (aq) Cl-(aq) ↔ AgCl(g)
Cloudy Solution and shifts right
NH3 addition
Ag (aq) Cl-(aq) ↔ AgCl(g)
Clear Solution and shifts left
HNO3 addition
Cloudy and shifts to the right
Excess NH3 addition again
Clear again and shifts to the left
KI added
Turned to off white and shifts left
Na2S addition and net ionic equation
Ag2S(s) ↔ S2-(aq) Ag(aq)
Turned dirty brown
Table 2 shows the changes in the solution as reactants were added.
Table 3: A Buffer System
Bronstead acid equation
CH3COOH(aq) H2O(l) ↔ H3O (aq)
CH3CO2-(aq)
Color of universal indicator with CH3COOH
Red with pH~4
Color of universal indicator with NaCH3CO2
Light Red with pH~2
Shift to the left
Color of universal indicator in H2O
Orange with pH~6
After HCl was added
Well A1 with buffer, pH~4 (red), ΔpH~2
Well B1 with water, pH~3 (light red) ΔpH~3
After NaOH was added
Well A2 with buffer, pH=5 (red), ΔpH~3
Well B2 with water, pH=12 (blue), ΔpH~6
Table 3 shows the effect on equilibrium with the change in pH and the containment of a buffer system.
Table 4: Equilibrium (Common-Ion Effect)
Color of CoCl2(aq)
Light red
HCl addition and net ionic equation
4Cl-(aq) [Co(H2O)6]2 (aq) ↔ [CoCl4]2-(aq) 6H2O(l)
Turns purple. Shifts to the left.
Water added to solution
Turns light red again
Table 4 shows the change in equilibrium due to the common-ion effect.
Table 5: Equilibrium (Temperature Effect)
Color at room temperature
Red
Color when heated
Purple
Table 5 shows color change due to the temperature effect on equilibrium.
Discussion: In Table 1, the solution CuSO4 was in equilibrium in a light blue color until the equilibrium shifted to the right as drops of NH3 were added, forming the product. When the acid HCl was added, the equilibrium shifted left again, turning the color of the solution light blue again. This was because the H ions equalized the Cu(NH3)42 that formed. Because this chemical system was in a state of dynamic equilibrium, the color of the solution was able to turn light blue again as the products can reform the reactants.
In Table 2, 1/2 mL 0.01 M AgNO3 1/2 mL 0.1M Na2CO3 formed a precipitate. When HNO3 was added, this showed a change in equilibrium by dissolving the precipitate, forming a clear solution. The action was reversed again as HCl was added and a precipitate was formed again, supporting the dynamic equilibrium. Also supporting the dynamic equilibrium, by showing the reverse chemical reaction, the addition of concentrated NH3 then dissolved the precipitate that was formed. Once the second of addition of HNO3 was added, a white gas formed because there was too much concentration of HNO3. When NH3 was added after that, more white gas formed because there was too much concentration of HNO3. When NH3 was added after that, more white gas formed because the concentration of the product was now also in excess. The addition of KI formed a white foggy gas on top of the solution, which was probably a result of the iodide ion and excess concentration of the reactant. Not only did the equilibrium change, but a physical change occurred as well. The gas was less dense than the solution. The addition of Na2S turned the solution partially brown. This was because of an excess concentration of the product. In the test tube, there was a white has from the potassium iodide, a brown later between the white has and the clear liquid from the sulfide, and the clear liquid from the normal concentrations of the solution of silver, chloride, and nitric acid.
In part C with the buffer systems. The Bronstead acid equation was used to obtain the initial pH values. Table 3 shows the initial pH values with the color indicators. As HCl was added the reaction shifted to the left to balance the acid and increased the base. The effect of buffers on the equilibrium can be seen. As the strong acid HCl was added, the change in pH of the water system was higher than the change in the buffer system. Most importantly, as the strong base NaOH was added, the change in the water system increased significantly to 12. However, the buffer system stayed within its range. Thus, the useful property of buffers is accepted as they contain the high changes in the pH.
Tables 4 and 5 show the color changes using the common ion effect and temperature change. Both the addition of the concentration of HCl into CoCl2 and the placement of CoCl2 into a hot water bath both changed the equilibrium of the solution by turning it purple. The equilibrium shifted back to red when water was added again or the temperature was back to normal room temperature.
Conclusion: The systems under states of dynamic equilibrium shifted in directions to minimize the effect of the stress that was placed upon the system. In this experiment, the effects of stress were caused by changes in concentration and temperature. LeChatlier’s Principle was supported based on the experiments conducted where colors of the solutions were reversed and precipitates could be dissolved and formed again without the concentrations being in excess. Based on the experiment, the hypothesis stated if the equilibrium of a system in a state of dynamic equilibrium shifted left or right, then LeChatlier’s Principle would be supported. The hypothesis and LeChatlier’s Principle were both supported.
There are many improvements that can be done to this experiment. One of them is that there can be more tests done to see how the equilibrium is affected in the metal ammonia ions. Another improvement that can be made to the experiment is comparing to the pH chart to infer and analyze the color changes. A third improvement is further studying the effect of temperature in the equilibrium changes. This would give a better idea on its effects.
Post Lab Questions: Predict what would appear in the solution if NaOH were been added to
CuSO4 solution instead of NH3?
More of a bluer color would be observed with increase in formation of Cu and Ni ions.
HNO3, a strong acid is added to shift the Ag2CO3 equilibrium to the right. Why does this shift occur?
The removal of the CO32- ions means that have to be replace so a shift to the right is necessary.
Predict what would happen if .1M NaBr had been added to solution in part
B.3 instead of the Na2S solution. Explain?
It would probably combine with Br ion to form silver bromide due that the NaBr is more soluble, and thus is more able to remove the iodide ion from the AgI formed from the last equation when KI was added.
Write an equation that shows the pH dependence on the chromate, dichromate equilibrium system.
CrO42- ↔ Cr2- 4O
Cr2O72- ↔ 2Cr2- 7O
When 5 drops of .10 M HCl is added to 20 drops of a buffer solution that is .10 M CH3COOH and .10 M CH3CO2- only a very small change in pH occurs. Explain?
The CH3CO2- equaling the amount of moles in the acid and ends up absorbing all the acid and cause of this there is a decrease in CH3CO2- and an increase of CH3COOH which is where the small change in pH occurs.
Literature Cited
Beran, J.A. (2009). Pages 201-212. Laboratory Manual for Principles of General Chemistry. Hoboken: John Wiley

Microwave Bridge to Measure Absorption

More accurate methods of measuring microwave attenuation and phase are constantly being sought, particularly for such applications as plasma diagnostics. The microwave bridge technique described here was developed for the study of a quiescent plasma having an electron density of 1015 to 1018 m−3 corresponding to a plasma frequency of 3 Ã- 108 to 1010 Hz, and an electron collision frequency of 1010 to 1011 s−1. The plasma had a broad dimension of 0·3 m. For such a plasma a probing frequency of 10 GHz was considered to be the most suitable; at this frequency the attenuation α and phase shift δβ expected were 0·1 < α< 50 dB and 1° < δβ < 1000° respectively.
A balanced microwave bridge was used measure the absorption. Five-mm power was obtained from the second harmonic generated in a non-linear silicon crystal driven by a 1-cm reflex klystron oscillator. A block diagram of the apparatus is shown in Fig. 1.
The 5-mm radiation was then divided between two nearly identical wave guides and recombined in a bridge T-junction. One output arm of the T fed a matched load and the other fed a harmonic converter. The converter mixed the incoming 5-mm radiation with the second harmonic of another 1-cm local oscillator, and the heterodyne signal current was fed to a 24-Mc/sec. amplifier.
Provisions were made for inserting a step-attenuator pad in the amplifier cascade after three stages of amplification. Both the signal oscillator and local oscillator were frequency-stabilized to a high mode of a 3-cm cavity using a Pound4 and, later, a Zaffarano5 circuit. The frequency of the signal-generator fundamental was measured with the M.I.T. frequency standard.6.
The signal-generator fundamental was amplitude-modulated with a rotating attenuator at 30 cycles/sec. The detected output from the receiver could then be filtered for the 30-cycle modulations. This modulation was amplified and converted to D.C. with a phase detector.
The signal was read on a milliammeter and the 30-cycle modulation merely provided a convenient monitoring current to amplify after filtering. In operation, the sample arm of the bridge was filled with tank oxygen at 80 cm Hg, and the bridge balanced for no receiver output by means of the r-f phase shifter and attenuator in the sample arm.
The sample was then pumped out and the bridge rebalanced as well as possible by slowly admitting tank argon into the sample arm to an appropriate pressure. The final minimum was achieved with readjustment of the r-f phase shifter. The use of argon for rebalancing allowed the bridge to work under constant impedance conditions.
This procedure proved necessary for accuracy. Argon was chosen because its dielectric constant is similar to that of oxygen. Since argon is monatomic, it has no absorption in the region of these measurements
Check measurements on nitrogen using argon as a balancing agent disclosed no absorption greater than 1 db/km. The minimum signal current was noted and the phase shifter was readjusted to give a maximum output; the 24-Mc/sec. step attenuator was then introduced, and the current-output reading was made as nearly equal to that observed at minimum balance as was possible. The attenuator had a minimum change of 1 db and the readings were taken to 0.5 db by interpolation. The attenuator reading then gave the value of the maximum to minimum power ratio as: db = 101og (Pmax/Pmin). It can be shown that the attenuation in the gas may be calculated as: where AP = power absorbed, P = incident power on sample, a = Pmax/Pmin.
APPLICATION OF MICROWAVE BRIDGES COMPACT MICROWAVE ELECTRON SPIN RESONANCE SPECTROMETER ESR-1000
ESR spectrometer is an ideal instrument for on- and off-line ESR testing under laboratory and plant conditions. When using additional and software means the spectrometer becomes not only for routine measurements, but also a research instrument for develop.
METER USING A MICROWAVE BRIDGE DETECTOR FOR MEASURING FLUID MIXTURES
A meter comprising a waveguide through which a substance to be measured can flow; a transmitting antenna in the waveguide; a detecting antenna in the waveguide spaced a predetermined distance from the transmitting antenna along the flow path of the waveguide; a microwave bridge having a power input port, a transmitting output port connected to the transmitting antenna, a detecting output port connected to the detecting antenna, and a bridge output port which measures the difference in the power to the two antennas; a microwave generator connected to the input of the microwave bridge;
A phase sensitive detection system connected to the bridge output port for providing an output of a frequency characteristic of microwave propagation within the waveguide; and a switch connected to each of the ports of the microwave bridge for switching the microwave bridge out of the circuit and connecting the transmitting antenna to the microwave generator and the detecting antenna to the phase sensitive detection system.
INVESTIGATION OF STEP-EDGE MICROBRIDGES FOR APPLICATION AS MICROWAVE DETECTORS
Step-edge micro bridges of Y-Ba-Cu-O are investigated for use as microwave detectors at 35 GHz. The superconducting thin films is laser deposited upon a defined substrate step-edge, which is formed by wet chemical etching of an SrTiO3 layer, which again was laser deposited on an LaAlO3 substrate. The voltage response of the device is directly proportional to the power of the microwave signals within a dynamic range of 50 dB and exhibits an NEP of 3.2*10-9 W/Hz1/2 at 74 K.
STATIC AND DYNAMIC TESTING OF BRIDGES THROUGH MICROWAVE INTERFEROMETRY
A novel microwave sensor capable of remote detection of structural displacements is experimented as geotechnical instrument for static and dynamic testing of bridges. The sensor is based on an interferometric radar providing range imaging capability and sub-millimetric accuracy range displacement measurement.
Dynamic monitoring calls for sampling rate high enough for transient analysis, while static monitoring requires long-term stability. The instrument has been designed in order to provide both these features. The results of a validation campaign on a railway bridge during the final test before going into service are reported.
UNLOCKING FREE RADICALS WITH MICRO ELECTRON SPIN RESONANCE
Free radicals are highly reactive chemical species that govern many fundamental chemical processes in nature, most notably combustion and oxidation. Until now, direct measurement of the composition and concentration of free radicals has represented a challenge for chemists due to the complexity and expense of the necessary equipment.
An innovation in sensor design, the Micro Electron Spin Resonance spectrometer (Micro-ESR), measures free radicals with a compact, low-cost and ruggedized device.
The spectrometer enables new low-cost applications such as online measurement of lubricant breakdown in engines and machinery, online airborne particulates monitoring in diesel engine exhaust and even spin immunoassay medical diagnostics.
PHASE-LOCK MICROWAVE BRIDGES FREQUENCY STABILIZERS TO ELECTRON PARAMAGNETIC RESONANCE SPECTROMETERS
Several electronic systems are described which lock the frequency of the microwave power source to the resonant frequency of the sample cavity in an electron paramagnetic resonance spectrometer while retaining the spectral purity obtainable when the microwave power source is phase-locked to a high stability (MHz) crystal oscillator.
A SIMPLE AND STABLE MICROWAVE SQUID A new, simple and stable type of microwave SQUID has been developed successfully at 10 GHz by using a bridge type junction which can be fabricated very easily. In consequence of adopting a junction of this type, the microwave SQUID has the merit of being free from adjustment and endures several heating cycles between room and liquid He temperatures. This type of SQUID has a slightly poorer S/N ratio, to be improved in future, but has the same characteristics as previously reported SQUIDs with a point contact junction
INTEGRATED DIRECTIONAL MICROWAVE BRIDGE With the advent of electronic equipment, radio frequency (“RF”), microwave, and millimeter wave circuits are common. As telecommunication systems continue to advance, there is a constant need to increase the bandwidth, speed, efficiency, and miniaturization of new telecommunication devices while constantly increasing the quality of the telecommunication devices and reducing the manufacturing costs.
Typically, telecommunication devices, and electronic equipment in general, include numerous types of electronic components and circuits including directional couplers and directional bridges. Generally, directional couplers and directional bridges are electronic devices utilized in RF, microwave, and millimeter wave signal routing for isolating, separating or combining signals. Typically, directional couplers are utilized as impedance bridges for microwave and millimeter wave measurements and for power monitoring.
Directional couplers and directional bridges (generally known as “directional circuits”) are usually three-port or four-port devices/circuits that have a signal input port (from a source) and a signal output port (to a load) and at least one coupled port whose output is proportional to either the incident wave (from the source) or the reflected wave (from the load). It is appreciated by those skilled in the art that it is common practice in RF, microwave, and millimeter wave engineering to consider an electrical signal in an electronic circuit/device as the sum of an incident and a reflected travelling wave to and from a source and load, respectively, relative to a characteristic impedance Z.sub.0 of the electronic circuit/device (typically about 50 ohms). A directional circuit generally separates a transmitted signal into the detection circuit or coupled port based on the direction of the signal propagation. There are many uses for these directional circuits including network analysis and monitoring the output signal levels of a travelling wave incident on a load.
At present, there are numerous approaches to implementing a directional circuit. One example is to implement a directional coupler as a device that has a physical length over which two transmission lines couple together electromagnetically or that utilizes the phase shift along a length of transmission line. Another example approach (known as a directional bridge) may utilize lumped elements that may include transformers and resistors.
Examples of an implementation of known directional couplers 100 are shown. The directional coupler 100 may include three ports such as a signal input port (“port A 102”), a signal output port (“port B 104”), and at least one coupled port (“port C 106”). The directional coupler 100 may be in signal communication with a signal source 108 via signal source impedance (“Z.sub.source”) 110, and a load having load impedance (“Z.sub.load”) 112. As an example of operation, the directional coupler 100 may be utilized to unequally split the signal 114 flowing in from the load at port B 104 while simultaneously fully passing the signal 116 flowing in from the opposite direction from the source 108 into port A 102. Ideally the signal 114 flowing in from the load at port B 104 will pass to the coupled port C 106 and appear as coupled signal 118. Similarly, an input signal 120 at port C 106 would pass to port B 104. However, port A 102 and port C 106 are isolated in that any signal 116 flowing into port A 102 will not appear at port C 106 but will propagate through to port B 104. Additionally, port B 104 is isolated from port A 102 because any signal 114 from port B 104 will flow to port C 106 not port A 102. An example of an implementation of the known directional coupler 100 is shown utilizing two transformers T1 and T2 and a resistor R.
Unfortunately, directional couplers have the disadvantage that they are typically too large to be practical for an integrated circuit (“IC”) except at very high frequencies because at low frequencies approaching direct current (“DC”) they are typically too large to be practical for many electronic instruments. As an example, directional couplers are usually limited by size limitations to low frequency operation of about 10 megahertz (“MHz”) in most electronic devices.
REFERENCES (1) http://webcache.googleusercontent.com/search?q=cache:dUhPu_0QV0gJ:www.ee.tsinghua.edu.cn/mzy/images/TheMicrowaveAbsorptionSpectrumofOxygen.pdf working of microwave bridges

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