Abstract
The vapour pressures of six different elements – indium (ln), silver (Ag), gallium (Ga), copper (Cu), tin (Sn) and gold (Au) – were compared according to a quasi-static method of measuring vapour pressures. This study was undertaken to determine if these six metals have different chemical properties, which could affect the boiling point of a metal. Pressure was assessed by a U-tube manometer measuring the pressure in an open system. While measuring, there was a temperature range of 1952K to 2939K. The liquid state of matter of a metal was vaporized into its gaseous state. The results acquired in the research were compared to results from past experiments.
It was concluded that indium had the greatest volume of vaporized particles and thus greatest vapour pressure. gold had the lowest volume of vaporized particles, so the lowest vapour pressure. gold has the lowest volume of vapour pressure due to the strong intermolecular forces between the atoms, holding the bonds of the atom tightly packed. More energy is required to break the bonds. However, gold had the greatest ΔT_w(K). This implies that it has the greatest correction value and so should be viewed in greater detail.
The results and Nesmeyanov’s research (the past conducted experiment) have a high correlation between the temperature and the pressure of the metals (Nesmeyanov, 1964). This correlation is positive for temperatures above 2600K, but it also works for lower temperature. This indicates that this method is highly efficient in calculating vapour pressure of metals at high temperature.
Introduction
There are three very different and fundamental states of matter. All elements in the Periodic Table are able to change between those states; solid, liquid and gaseous, and gain different properties. The differences in properties arise from the different strengths of intermolecular forces, and this is due to the change in spaces between atoms. These distinct elements all react differently to their environment and surroundings (Yunhong R, 2012).
In the process called vaporization, heat is transferred through the element and the state changes from liquid to gaseous. Consequently, the distance between atoms increases and the atoms are free to move. This means that the entropy of the system increases, and becomes positive. Vaporization is said to be an endothermic process, heat is taken into the system, and thus ΔH is said to be positive.
Every process tries to decrease Gibbs free energy, and make it negative, this way a reaction occurs more spontaneously.
At one point the reactants will no longer react with the products, unless environmental factors are influencing the system, and an equilibrium has been established.
Le Chatelier’s Principle can also be applied to this phenomenon. By changing the different temperatures, the equilibrium of the reaction will shift towards the side that opposes the change. One can now imagine, that the equilibrium will move towards the side that favours the gaseous phase, as this state of matter contains most disorder. By looking at the Gibbs free energy formula, the higher the entropy of an element, the lower the Gibbs free energy.
The experiment proceeded in an open system. The vapor pressure is be said to be partial pressure as it is mixed with other molecules in the air. The point at which the vapor pressure is equal to the atmospheric pressure is said to be the boiling point of that specific element or molecule (Nave, n.d.).
The purpose of this paper is to see if there is a correlation between different temperatures and vapour pressures of all six elements. To do this, findings from this experiment were compared to the findings from outside. This is to see if there is a correlation between the intermolecular bonding and the corresponding volume of vapor pressure.
To gather the data of all six metals- indium (ln), silver (Ag), gallium (Ga), copper (Cu), tin (Sn) and gold (Au) -, a quasi-method of gathering vapour pressure was used. It will be discussed how we collected the data and calculated the vapour pressure. Conclusions will be drawn based on the outcomes, and any accuracy/reliability of the data will be questioned.
Method
Sampling:
To make the experiment as reliable as possible, random sampling was used to select five solid states of matter. The selection was randomized to make sure that all solid states of matter had an equal likelihood to be chosen. These five solid states of matter led to five different results of each metal per temperature. These five values were averaged to gain one final result.
Analysis
A simple quasi-static method was used to determine the vapour pressure. For this technique, a mercury manometer was used, also called a pressure gauge.
All metals, indium, silver, gallium, copper, tin and gold, were transformed from their solid to liquid state of matter. This was done using a Bunsen Burner. As all metals had the highest value of purity, 99.999%, the liquid itself was very pure before use.
A liquid state is needed as the metal needs to be able to travel through the pressure gauge, when the pressure inside the system is increased. The vapour pressure was determined after dynamic equilibrium was reached.
Mercury is placed inside the manometer and is equalled in level, due to the natural pressure of Mercury, in both sides of the U-tube. One side of the U-tube is attached to an empty flask, which is closed by a stopper. The other end of the U-tube is kept open to air.
The liquid state of matter of a metal is heated up to one of the temperatures (K), which is then added into the flask by using a syringe. The difference in vapour pressure was observed and recorded.
For further justification, the outcomes were checked against standard values from data gathered in previous experiments, which were checked using a vapor pressure analyser (n.d., 2016). The two results were compared and this way the errors were reduced, which made the research increase in reliability.
Hazards:
Proper handling of the metals and apparatus, including the mercury is required. Since the inhalation of mercury vapour can cause a damaging effect on the body systems; like nervous, digestive and immune.
Accuracy:
The measured gas pressure may be slightly different than the desired vapour pressure concluded from Nesmeyanov’s research (Nesmeyanov, 1964). This could be due to a number of reasons, but can be minimized by cautiously designing the experiment. The reasons for the difference between the results were:
o The wall of the flask has thermal resistance;
o Impurities of the liquid;
o Possible diffusion of an inert gas into the vapour.
o Correction used to stabilise heat loss to surroundings in an open system.
Analysis of Results
Raw data:
Fig.1. Vapour pressure-temperature data
This table, figure 1, demonstrates the raw data obtained. Every element, in liquid form, was tested at numerous high temperatures (in Kelvin) and then the vapor pressure was recorded (in bar). As seen on figure 1, for Au (gold) only vapor pressures were recorded at four high temperatures. This is due to the fact that Au does not react at lower temperatures for the reason that its structure is significantly stronger and heavily bonded. So, no vapor pressures were recorded as the element did not vaporize before it reached 2614K.
Processed data:
Fig.2. Vapour pressures of Indium, Silver, Gallium, Copper, Tin and Gold.
This graph in figure 2 displays how all the six elements reacted to the variety of high temperatures. Indium (ln) has the steepest gradient and reacts the most readily on the temperature, at lower degrees, and so evaporated the most. This implies that the vapor pressure is the highest. It was also concluded that ln has the weakest bonding and needs less heat to decompose. This element was the only one with outliers, which are displayed above the line of silver (Ag). The graph for ln in figure 3 also displays these outliers.
Fig.3. Vapour pressures of Indium, Silver, Gallium, Copper, Tin and Gold.
The graphs in figure 3 are all individual graphs. There is a positive correlation observed between pressure and temperature. In conclusion, all elements react with temperature to produce vapor pressure, which can be seen by looking at both fig.2. and fig.3. However they all vaporize at different temperatures.
ln Ag Ga Cu Sn Au
Temperature (K) 2678 2614 2600 2593 2605 2614
P (Bar) 3.20 2.40 1.60 0.30 0.30 0.10
ΔT_w (K) 18.0 16.0 23.0 15.0 18.0 20.5
Figure 4 presents all data assessed at temperatures around 2600K. The observation made here corresponds to the graphs above. ln has the greatest vapor pressure, at around 2600K, whereas Au has the lowest. The other elements are then displayed in order from greatest volume to the lowest volume of vapor pressure.
Mean: ln Ag Ga Cu Sn Au
Temperature (K) 2354.5 2437.0 2391.9 2709.6 2638.1 2754.8
P (Bar) 1.7166 1.3260 0.70593 0.61227 0.40714 0.24375
ΔT_w (K) 14.889 11.880 16.357 20.091 19.143 21.250
Figure 5 demonstrates the averages of the entire research. Once more, the same outcome is displayed. ln has the greatest volume and Au has the lowest volume of vapor pressure. It is also displayed that Au has the greatest ΔT_w (K).
Analysis and evaluation
The vapour pressure is defined as the volume of gas particles when vaporization occurs between the solid to the liquid state of matter, when the system is at dynamic equilibrium. Consequently, the greater the volume of gas particles at equilibrium, the greater the vapour pressure of the metal.
This is due to the intermolecular forces and bonding in the metallic structure and between metals. Particular metals, like Au as shown in figure 5, contain strong intermolecular forces, and so more energy, in the form of heat, is required to disrupt the bonds and make the metal vaporize.
London Dispersion interaction, also called Van der Waals forces, is weaker than the ion pair interaction. To make this clearer, the molecule with no ion pair or dipole-dipole interactions and only London dispersion forces, will have a greater volume of vapor pressure as less heat energy is required to break the bonds (N, 2016).
The most known intermolecular forces ordered by strength are:
London Dispersion (Van der Waals), Dipole-Dipole interactions, Hydrogen (H)-bonding, Ion-Dipole interactions, Ion Pair forces (N, 2016).
Not all these intermolecular forces are present in the metals. For example, Hydrogen bonding is not present as the hydrogen atom is not present in the molecules used in this experiment. They are only present in molecules that bond to Fluorine (F), Nitrogen (N) and Oxygen (O), elements which were not used in this particular research.
Conclusion
In summary, we can draw the conclusion that if an atom has stronger intermolecular bonding and/or forces, the overall vapour pressure will be lower. Due to that stronger bonding requires more heat to break and so has a higher boiling point. Therefore, the substance will not vaporize as easily. This implies that the intermolecular bonding indeed affects the vaporization process, and the corresponding volume of vapour pressure. The data obtained is in good agreement to the referenced data.
This correlation will be of great value in further research, as scientists are now able to work with certain/more accurate values for vapour pressure of metals. Furthermore, it is relevant as scientist can now know what temperature a metal can withstand before vaporizing, which can be useful for industrial work.
Moreover, there is a significant correlation, between temperature above 2600K and pressure, between the results and Nesmeyanov’s research (Nesmeyanov, 1964). This implies that the correction made did not significantly affect the results. Indicating that this method is highly efficient in calculating vapour pressure of metals at high temperature.
...(download the rest of the essay above)