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how-does-the-magnitude-of-upper-critical-solution-temperature.pdf

<span class="correct" data-content="Excellent personal engagement shown through the student's connection of everyday observations with scientific inquiry. This demonstrates genuine curiosity and introspection about chemical phenomena, establishing a strong foundation for the research process.">I feel that the most interesting part of studying experimental science is the way it connects real life observations and phenomenon with facts and principles we study in a text book. The genesis of this essay begins from an anecdote along the same idea, which I made much before I was introduced to the term &ndash; Extended Essay in the IB Diploma Program. Having passion for cooking, I observed something that really intrigued me; when I took oil in the pan and then added water to it, it did not mix and separated clearly into two distinct layers. But after heating it for some time, it existed as a single layer. In contrast, I have also observed that sometimes if either the amount of oil or water is too less in comparison to the other, they mix with each other at room temperature only. This observation immediately popped certain questions in my mind - Does the miscibility of a pair of liquids depend on the ratio of the mass/volume in which they are mixed or the temperature? What if I add something else in this mixture; will that affect the miscibility in any way?

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To satiate the inquirer hidden inside, I explored more. After an effective search with the help of my supervisor, I came across few credible journals and research articles which taught me about something called &lsquo;smart polymers&rsquo;. The aforementioned are basically preparing polymers that are partially miscible with water and exhibit either LCST or UCST.

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These polymers are mainly used in the field of pharmacy and metal extractions, detection of carcinogenic metal ions in foods and so on. What intrigued me the most was the fact that the properties of this partially miscible polymer-water system can be altered by adding various ionic electrolytes or organic compound to make them more effective and useful.

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<span class="correct" data-content="The research question demonstrates exceptional focus and clarity, specifically addressing the chemical principles of phase separation and solubility. The use of precise chemical terminology (UCST, phenol-aqueous NaCl system) and quantitative parameters shows sophisticated understanding of the chemistry involved.">This urged me to explore more on how the mutual solubility of two liquids could be affected by addition of impurities. Further academic reading and consultation with my supervisor introduced me to the system of phenol and water as a common example of partially miscible liquids whose mutual solubility largely depends on temperature as well as the presence of external impurities. To make the discussion more specific and concise, I decided to conduct my Extended Essay in Chemistry based on the following research question -&nbsp;How does the magnitude of upper critical solution temperature (UCST) of phenol(hydroxy benzene)-aqueous NaCl system depend on the molar concentration(moldm-3) of theaqueous solution of NaCl added to it, determined using mutual solubility curve?

<span class="correct" data-content="This section demonstrates good knowledge and understanding of liquid-liquid systems with clear categorization and appropriate examples. The student effectively explains the differences between immiscible, miscible, and partially miscible systems in a structured manner.">Liquid-liquid system (mixture of two liquids) can be categorized into three types based on their miscibility (solubility of one of the liquid into the other).

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Immiscible &ndash;&nbsp;If liquid A and liquid B when mixed together at room temperature form two distinct layers, the two liquids are considered to be completely immiscible with each other.

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Example - pentane and ethanoic acid.

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Miscible &ndash;&nbsp;If the two liquids A and B when mixed with each other at room temperature form one single layer, the &nbsp;liquids are considered to be completely miscible with each other.

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Example - water and ethanol.

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<span class="correct" data-content="The explanation of partially miscible liquids shows excellent understanding of how temperature and composition affect solubility. The student effectively communicates the complexity of these systems and provides a relevant example with phenol and water that will likely be central to their investigation.">Partially miscible &ndash; There are certain liquid pairs whose mutual solubility depends on the composition of the mixture and the temperature of the mixture. In this case, when the two liquids are mixed, they might form two distinct layers or one single layer depending on the temperature at which they are mixed and the ratio of volume in which they are mixed. Even if they form two distinct layers, the volume of the individual layers after mixing is either greater or smaller than the volume of the individual liquids before mixing. Such kind of liquid pairs are considered to be partially miscible.

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A system of phenol and water is one such example of partially miscible liquids.

<span class="correct" data-content="The student demonstrates good knowledge and understanding of chemical concepts by accurately explaining the Upper Critical Solution Temperature (UCST) as it applies to the phenol-water system. This shows alignment with the research question and indicates a strong grasp of the underlying chemistry principles relevant to the investigation.">For any pair of liquids there exists a temperature, above which they are completely miscible with each other/form a clear single layer solution irrespective of the proportion in which they are mixed. This temperature is called Upper critical solution temperature (UCST). The phenol-water system exhibits Upper critical solution temperature.

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<span class="incorrect" data-content="While the student appropriately refers to appendix content, this section would benefit from briefly explaining the significance of LCST (Lower Critical Solution Temperature) in the main text to maintain flow and completeness of understanding. Cross-referencing is good practice, but core concepts should be introduced in the main text before directing to appendices.">Refer appendix A.1. for definition of LCST

<span class="correct" data-content="The methodology for determining UCST is explained clearly, showing good understanding of the chemical principles involved. The student has effectively articulated the systematic approach to data collection required for this investigation.">In order to determine UCST of a partially miscible pair of liquids, I would have to record the temperature points at two instances &ndash;

<ul>
	<li>When the turbidity of the solution disappears i.e. completely mixes into a clear layer due to gradual heating.- t1</li>
	<li>&nbsp;When the turbidity re-appears due to cooling - t2</li>
</ul>

<span class="correct" data-content="Strong critical thinking is demonstrated in the explanation of how to process the collected data. The student shows good understanding of how to transform raw data into useful information through averaging temperatures and plotting against concentration to determine UCST.">The average miscibility temperature would be hence given by finding the average of the two temperatures t1&nbsp;and t2.&nbsp;The average miscibility temperature is plotted against mass percentage of any one of the liquid to obtain the mutual solubility curve and the UCST is calculated from the maxima of the curve,

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<span class="incorrect" data-content="While the student mentions a 'predicted graph,' no actual graph is included in this section. For stronger presentation, the student should include the referenced visual representation of the UCST curve to enhance communication of the expected results.">The following is a predicted graph of how the UCST value will be plotted &ndash;

ucst.svg

<span class="correct" data-content="Good understanding of physical chemistry concepts related to miscibility of liquids at different temperatures. The explanation accurately describes the relationship between temperature and miscibility states, which demonstrates knowledge and understanding of the chemistry principles underlying your research.">Above t1,&nbsp;the pair of liquids are completely miscible, whereas below t2,&nbsp;the pair of liquids are completely immiscible irrespective of the proportion or ratio in which they are mixed with each other. Therefore, in between t1&nbsp;and t2&nbsp;the pair of liquids are partially miscible. The midpoint of this region would indicate the temperature at which the liquids are completely miscible.

<span class="correct" data-content="Excellent explanation of the relationship between UCST and mutual solubility. This demonstrates strong knowledge and understanding of the chemical principles being investigated. The clear articulation of how UCST values relate to solubility provides important context for interpreting your results.">The value of UCST showcase the extent of mutual solubility for any pair of liquids. As the UCST increases, it indicates that the mutual solubility for the pair of liquids is decreasing. Hence, as a pair of liquids become more soluble into each other, the value of UCST should decrease.

<span class="correct" data-content="The methodology is well-described with appropriate detail of the experimental procedure. The student clearly outlines the approach for studying phenol's behavior with varying NaCl concentrations, showing good understanding of practical chemistry techniques. The explanation of measuring both the disappearance and reappearance of turbidity demonstrates thoughtful experimental design.">Definite mass (5.00 &plusmn; 0.01g) of phenol was taken in a test tube and the volume of aqueous NaCl &nbsp;added to it was varied to vary the mass percentage of phenol. Subsequently, different concentration of NaCl solutions were added to the test tube as an impurity. The test tube was then heated in a water bath to record the temperature (t1) at which the turbidity disappears i.e. a single layer in formed. It is then allowed to cool down to record the temperature(t2) at which turbidity re-appears (separation into two distinct layers). <span class="incorrect" data-content="While the statement about the method being 'easy and convenient' is valid, the student should provide more justification for this methodological choice in relation to the research question. Consider explaining why this approach was selected over alternatives and how it specifically addresses the research objectives.">This method is chosen as it is easy and convenient to perform in a school laboratory.

<span class="correct" data-content="Good critical thinking is demonstrated here as the student evaluates alternative methods for determining UCST and explains why they couldn't implement this approach. This shows awareness of multiple methodologies and limitations in their research context, which is important for a chemistry extended essay.">The UCST of a pair of liquids can also be determined by studying the variation of the morphology of the molecules in the mixture using SEM(Scanning electron microscopy) and dynamic light scattering method. The pair of liquids has to be heated and at various temperature, the morphology of the mixture has to be investigated. At UCST, both the liquids will undergo a significant change in their morphology and behave as an emulsion. This method was not viable for me as it involve the use of high end apparatus which are not available in a school laboratory.

Intermolecular interactions between phenol.svg

<span class="correct" data-content="Good scientific explanation of intermolecular hydrogen bonding. The student demonstrates strong knowledge and understanding of chemical principles by accurately explaining how hydrogen bonding affects solubility between phenol and water.">Both phenol and water has inter molecular H bonding in the pure state due to the presence of polar O-H bonds in them. On mixing, these molecules will break the H bonds within their own system and form inter molecular H bonds with each other to become mutually soluble. The formation of inter molecular H bonds between them depends on two factors. -&nbsp;

<ul>
	<li><span class="correct" data-content="Excellent conceptual understanding of concentration effects on solubility. The student shows critical thinking by explaining how component ratios affect the hydrogen bonding and solubility properties, which demonstrates a thorough grasp of the chemical principles relevant to the research.">If the amount of one component in the system is significantly lesser than the other, they will form the H bond easily and become soluble with each other even at a low temperature.</li>
	<li>&nbsp;In case, both the components are present in nearly equal proportion, the temperature of the system has to increase to provide more kinetic energy to the molecules and break the H bond within their own system to form H bond with each other. Thus, as the ratio of the components in the mixture approaches towards 1:1, they become mutually soluble only above a particular temperature which is considered as the UCST value of that system.&nbsp;</li>
</ul>

<span class="incorrect" data-content="While the explanation of treating the system as binary is reasonable, the student should provide a more detailed justification for this simplification and discuss potential limitations of this approach to demonstrate stronger critical analysis.">The current investigation deals with a phenol-aqueous NaCl system which is actually a ternary system phenol, water and NaCl but it may be looked upon as a binary system of phenol and water with NaCl as an impurity in it, as the solutions of NaCl used are dilute.

<span class="correct" data-content="The student demonstrates excellent critical thinking by comprehensively explaining the chemical principles behind UCST behavior in the phenol-water system with NaCl. This explanation shows strong knowledge and understanding of intermolecular forces and solubility concepts, effectively applying chemical principles to support their argument.">The UCST of a pair of liquids decreases as we add an impurity which is soluble in both the liquids while it increases as we add an impurity, soluble in one of the liquids and insoluble in other. NaCl is an ionic compound which is soluble in water but not in phenol. Hence, presence of NaCl in a phenol-water system would increase the value of UCST. As we add NaCl, more water molecules are engaged in hydrating the Na+ and Cl- ions formed from disassociation of NaCl. Thus, amount of H2O molecules available to hydrate phenol molecule decreases and hence the mutual solubility of phenol and water decreases, which in turn increases the UCST.

<span class="correct" data-content="The student demonstrates strong methodological planning by clearly identifying the independent variable and establishing a good range of concentrations including a control. This shows careful experimental design aligned with the research question.">The molar concentration of NaCl (aq) added to phenol is the independent variable. The solutions used are of concentration &ndash; 0.0 moldm-3 (only distilled water; used as control), 0.5 moldm-3, 0.7 moldm-3, 0.9 moldm-3, 1.1 moldm-3 and 1.3 moldm-3. All these solutions were prepared by adding requisite mass of NaCl weighed in an electronic mass balance in a 100cm3 volumetric flask. A graduated measuring cylinder was used to measure the volume of water added.

<span class="correct" data-content="This paragraph effectively explains the experimental methodology for determining UCST in the phenol-NaCl system. The student clearly describes the temperature measurement process, the equipment used, and how the average miscibility temperature was calculated. The approach shows good understanding of the principles involved in creating a mutual solubility curve.">The temperature at which turbidity disappears (formation of one single layer) and reappears (separation into two distinct layers) of the phenol-NaCl(aq) system was noted down by taking the mixture in a test tube, heating it in a water bath and allow it to cool down after that. A stainless steel temperature probe coupled with a Lab Quest was used to record the temperature. The average of these two temperature values was used as average miscibility temperature and plotted against the mass percentage of phenol used to determine the UCST from the mutual solubility curve. In this way, the UCST value of the phenol-NaCl(aq) system was determined as the dependent variable for all values of concentration of NaCl(aq).

<ul>
	<li><span class="correct" data-content="Excellent detail in presenting the controlled variables with precise measurements and uncertainty values. This demonstrates strong understanding of experimental design principles and supports the reliability of your data collection process.">Mass of phenol added &ndash; 5.00 &plusmn; 0.01 g</li>
	<li>Apparatus used to record temperature-stainless steel temperature probe</li>
	<li>Surface area &ndash; same test tube (20 cm3, hard glass) was used in all trials.</li>
	<li>Apparatus used to record mass &ndash; electronic mass balance.</li>
	<li><span class="correct" data-content="Your attention to controlled variables such as reagent purity and consistent materials shows methodical planning. Cross-referencing to your appendix for detailed methodology demonstrates excellent organization and thorough documentation of your experimental approach.">Percentage purity of reagents &ndash; both phenol and NaCl used were from the same reagent bottle.</li>
</ul>

Refer to Appendix A.2.- for the significance and method of controlling these variables.

<span class="incorrect" data-content="This conclusion statement lacks supporting evidence from data analysis. You need to reference specific statistical analysis results that demonstrate the absence of correlation. Include p-values, correlation coefficients, or other quantitative measures that justify this claim about the relationship between UCST and NaCl concentration.">There is no correlation between the UCST of phenol-aqueous NaCl system and the molar concentration of aqueous NaCl used.

<span class="correct" data-content="Your statement of a positive correlation between UCST and NaCl concentration demonstrates good analytical thinking and shows you have identified a clear relationship from your data, which effectively supports your research question.">There is a positive correlation between the UCST &nbsp;of phenol-aqueous NaCl system and the molar concentration of aqueous NaCl used.

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<span class="incorrect" data-content="While you mention regression analysis, this statement is too brief. Consider expanding this to explain which regression model you'll use, the specific hypotheses being tested, your confidence level, and how this statistical approach specifically helps answer your research question.">Regression analysis will be done to test the hypotheses to be accepted.

<span class="incorrect" data-content="This brief reference to an appendix provides insufficient information for the reader. It would be more effective to briefly describe what Appendix A.3 contains and explain its relevance to the main argument. Without this context, the reader must interrupt their reading flow to check the appendix, potentially disrupting understanding of your analysis.">Refer to Appendix A.3.

<span class="incorrect" data-content="This reference to an appendix lacks sufficient context and explanation within the main body of the essay. According to presentation criteria, when appendices are used, the essay should include a clear summary or explanation in the main text to help readers understand what information they'll find in the appendix and why it's relevant to the research question. Consider adding a brief description of what Appendix A.4 contains and its significance to your investigation.">Refer to Appendix A.4.

<ul>
	<li><span class="correct" data-content="Excellent attention to safety considerations when handling phenol. You've properly identified its corrosive nature and potential hazards, demonstrating good laboratory practice and ethical research conduct. This shows engagement with the experimental process and awareness of safety protocols essential for IB Chemistry practical work.">Wear protective glasses, gloves and a lab coat at all times in order as phenol is a very corrosive compound and can cause extreme burns and blindness.</li>
	<li>The procedure should be carried out in a well ventilated environment so as to minimize any sort of inhalation caused due to heating of phenol.</li>
	<li>The phenol should be stored in a cool environment and disposal of phenol waste must be carried out judiciously, should be placed in a labeled glass bottle with a tightly secured lid.</li>
</ul>

<span class="correct" data-content="This shows good awareness of safety procedures and environmental responsibility in chemistry experimentation. The student demonstrates understanding of the proper disposal of phenol waste and laboratory cleaning protocols, which reflects solid knowledge of laboratory practice.">Phenol has widespread harmful environmental effects. All phenol waste were diluted and disposed off safely into a waste chemical bin. All glass apparatus used were washed with chromic acid before reuse.

How Does The Magnitude Of Upper Critical Solution Temperature (Ucst) Of Phenol (Hydroxy Benzene) - aqueous NaCl System Depend On The Molar Concentration (mol dm-3) Of The Aqueous Solution Of NaCl Added To It, Determined Using Mutual Solubility Curve?

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