Emergent topics on chemistry education [experimental teaching]
The concept of sublimation iodine as an example
Marina Stojanovska,* Vladimir M. Petruševski,* Bojan Šoptrajanov**
* Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Ss Cyril & Methodius University, Skopje, Republic of Macedonia.
** Macedonian Academy of Sciences and Arts, Skopje, Republic of Macedonia. E-mail: email@example.com
Sublimation is a process that is defined unequally in different textbooks and in various chemistry sources. Inexactness in defining basic concepts in chemistry can lead to alternative meanings for different people. Inconsistent explanations, then, can serve as a basis for developing misconceptions and preconceptions in latter students' education. Thus, the notion that upon heating iodine only sublimes, but does not melt is present in many chemistry textbooks, teachers lectures and, therefore, in students minds and may be considered as one of the widespread misconceptions in chemistry teaching. In this paper we offer a lecture demonstration showing the existence of all three states of iodine, supported by a short video-clip, hoping to give a contribution to the correction of misbelieves about the process of sublimation and the examples of subliming substances.
Keywords: sublimation, misconceptions, textbooks, experiments, iodine, chemistry teaching.
La sublimación es un proceso que ha sido definido de varias maneras en diferentes libros y otras fuentes. Las definiciones inexactas de los conceptos básicos de la química puede conducir a significados alternativos para diversas personas, a explicaciones inconsistentes y, entonces, pueden ser una base para el desarrollo de ideas previas en alumnos que están por tomar sus cursos de química. Por tanto, la noción de que al calentarse el iodo sublima, pero no funde, está presente en muchos libros de texto, profesores, lecciones y, por ende, en la mente de los estudiantes, como una concepción alternativa más difundida en la enseñanza de la química. En este artículo se ofrece una lección con demostración que muestra la existencia de los tres estados de agregación en el iodo, apoyada por un pequeño video, con la intención de contribuir a la corrección de las ideas estudiantiles acerca del proceso de sublimación y los ejemplos de las substancias que subliman.
Palabras clave: sublimación, concepciones alternativas, libros de texto, experimentos, iodo, enseñanza de la química.
(1) Misbelieves and misconceptions
There are several terms that refer to students' misbelieves. Some authors use the word "misconception" to define erroneous notions and others use "preconceptions" that are related to previous knowledge or arise during the course of instructions. The expression "alternative conceptions" is considered by some authors as some kind of compromise or agreement that incorporates students' faulty views during science teaching (Horton, 2004, p. 5).
The misconceptions (incorrect notions) are powerful, extremely persistent and hard to change, creating obstacles to further learning (Pabuçcu & Geban, 2006). The process of previous learning plays an important role in students' understanding and the quality of the subsequently learned concepts (Roschelle, 1995). A large number of students (and some teachers, too) believe that their established concepts are correct because they make sense, meaning that they correspond to their understanding of the phenomenon in question. Consequently, when students face new information which, unlike their alternative conceptions, does not fit their previously established mental framework, they may ignore it or reject it because it seems wrong (Horton, 2004, p. 1). They attempt to solve problems in chemistry courses without real understanding of a process or a phenomenon connecting them with their previous information and concepts, which, however, may not be scientifically correct. Students can be very successful and intelligent; they may have high grades, but still retain certain misconceptions. Identifying the weaknesses in the concept-building is especially important during the students' first exposure to chemistry. The misconceptions they build in the early stages of their development are the most resistant to change during the subsequent instruction, the students constructing the new knowledge on a faulty basis and rearranging the new information and ideas to fit the framework of ideas they believe are correct. Thus, it is of utmost importance to identify, confront and correct different misconceptions that students have. The knowledge of students' misconceptions is helpful in deciding where to start and how to continue teaching.
(2) Subliming substances
It is interesting (but also disturbing) that some of the basic concepts and terms used in the chemistry education from the earliest stages up to the university level are not properly, precisely and unequivocally defined and seem to have different meanings for different people. Rather surprisingly, the concepts of sublimation and subliming substance seem to fall into this category.
The IUPAC terminology compendium (McNaught & Wilkinson, 1997) defines sublimation as "the direct transition of a solid to a vapor without passing through a liquid phase. Example: The transition of solid CO2 to CO2 vapor." If this is the complete definition of it and has no limitations, its microscopic meaning would simply be passing of molecules from a solid substance to the gaseous state of that substance. Thus it would be completely analogous to evaporation passing of molecules from the liquid state/phase of the substance to its gaseous state. It would be applicable to any solid, at any pressure or any temperature above 0 K, the possible differences being only quantitative and dependent on the vapor pressure of the solid in question. Indeed, such a broad (and loose) definition of sublimation is widely found in textbooks and other sources of chemical information. For example, the definition in a standard science textbook (Trefil & Hazen, 2000) is that "some solids may transform directly to the gaseous state by sublimation", the term "solid" clearly implying a substance and this makes the things to become more complicated.1
When examples of subliming substances are considered, the most usually quoted ones are dry ice (solid carbon dioxide), iodine and naphthalene. Thus, in a classical chemistry textbook (Choppin & Jaffe, 1965) it is stated that: "The transition directly from solid to gas is known as sublimation. Carbon dioxide is an example of a substance that sublimes (and) ... iodine is another example." In the Chang's book Chemistry (Chang, 1990) naphthalene and iodine are given as examples of volatile solids which may be in equilibrium with their vapors and, by implication, can be considered as subliming substances.
On the other hand, many articles can be found (Wisconsin State Journal, 2010; Habby, 2011; Wikipedia, 2011; Silberberg, 2006), about the process of sublimation of snow and ice which sublime, albeit slowly, below the melting-point temperature. This phenomenon is operative for example when linen are hung wet outdoors in freezing weather to be retrieved dry at a later time. The loss of snow from a snowfield during a cold spell is often caused by sunshine acting directly on the outer layers of the snow. Ablation is a process which includes sublimation and erosive wear of glacier ice. The snow sublimes through a process that is similar to evaporation. In fact, whenever there is an interface of air and water (either liquid or solid), the H2O molecules will have some tendency, more or less pronounced, to leave the condensed phase and the processes of water evaporation and sublimation are observable at any temperature. Clearly, this is nothing new or spectacular but we do not think of water as a typical example of a subliming substance since ordinarily ice first melts and then vaporizes.
In fact, depending on the properties of a given solid in question, only a few substances will readily sublime under ordinary laboratory conditions without ever passing through the liquid state. Solid carbon dioxide (dry ice), with its triple point in the phase diagram lying above 1 bar, is the typical example of such a behavior. At ordinary atmospheric pressure (i.e. at atmospheric pressure close to 1 bar) dry ice can not be melted. Another (albeit somewhat exotic, radioactive and very poisonous) substance with analogous properties is uranium hexafluoride with its triple point being ≈337 K and 1.5 bar.
Other solid substances, especially if they are highly volatile (characterized by their high vapor pressure), may sublime at room temperature but if the temperature is carefully increased, it is possible to melt them. Iodine, for example, at ordinary pressures can exist in the liquid state at temperatures in the interval from 113.6 to 184.4 °C (Petrucci, 2001). Our relatively simple experiment (described below) provides an impressive demonstration for this. It should be noted that the triple point of iodine is found below 1 bar (113.5ºC; 12.07 kPa) and such is also the case with naphthalene (80.25ºC; 1.0 kPa) or camphor (180.1ºC; 51.44 kPa), the latter compound being sometimes quoted, together with carbon dioxide, iodine and naphthalene, as a typical substance that sublimes.
The examples given above lead to the necessity to set up a more restrictive meaning of the concept of sublimation with a view to the definition of a subliming substance.2 In our view, sublimation (in the restrictive mining of the term) would be a process where a solid substance on heating, at ordinary atmospheric pressure, undergoes a solid → gas transition directly, without first melting, i.e. without the appearance of a liquid phase. The typical example obeying such a restrictive definition would be solid CO2 but not iodine, naphthalene or camphor. We believe that at the high-school level only this restrictive definition is suitable (perhaps sometimes accompanied by a warning that a more precise definition exists). It is the latter definition that is dealt with in the present paper and this (in our view, as already pointed out), should be used in the general pedagogical practice.
Unfortunately, the broad rather than the restrictive definition is firmly entrenched in the minds of students, teachers, textbook authors and practicing chemists. Thus, if asked to name a subliming substance, iodine is very likely to appear as one of the preferred examples.
The problem: a lasting misconception
One of the widely spread misconceptions is that about the sublimation of iodine. There are too many people (Chemical forums, 2005; Trach, 2003) believing that, even at standard pressure, iodine can only sublime and not be melted, and such notions are indeed found in many books, including several textbooks that are in use in Macedonia. Thus, at two instances (Aleksovska & Stojanovski, 2005; Doneva-Atanasoska, Aleksovska & Malinkova, 2002) the authors say that upon heating iodine transforms directly from a solid to a gaseous state ("without being liquefied"), while in a textbook for the 1st year of reformed gymnasium (Cvetković, 2002) the definition and the examples given are similar, but heating is not mentioned explicitly.
Consequently, many teachers honestly believe that iodine is a typical example of a substance that, irrespective of the experimental conditions, sublimes without being melted, being ignorant, consciously or subconsciously, of the incompleteness in their understanding of the meaning of the term. Thus, in their lectures instructors loosely use the term "sublimation" and the imprecise definition of sublimation is instilled in the student's minds as a truism. The notion is strengthened by the fact that students could have seen the demonstration in which iodine crystals are heated to release violet vapor and it has been explained in terms of sublimation (Kotz, Treichel & Townsend, 2009). In such a case, they have a false impression that a liquid is not produced since the deep color of the iodine vapor that is quickly released often masks the appearance of the liquid phase (Yahoo answers, 2009). In fact, iodine vapor can be seen even without heating. If, namely, iodine crystals are put in a test tube (or better, sealed into a larger vessel), not very intense violet vapor can be observed inside the ampoule almost instantaneously (Figure 1) this being indeed associated with the sublimation of solid iodine due to its relatively high vapour pressure.
Unfortunately, the combined effect of the instructor's teaching and the student's personal experience (imprecise and incomplete as it turns out to be) forms a basis for a misconception that is readily accepted by the students. They "know" that solid iodine can only sublime and can not be first melted and in their mind this is final.
However, as mentioned above, it is a known fact that at atmospheric pressure iodine is liquid in the interval from 113.5 to 184.4°C meaning that iodine first melts and then vaporizes rather than "skipping" the liquid phase (Wikipedia, 2011; Heilman, 2004). Indeed, as discussed below, it is possible to obtain liquid iodine at atmospheric pressure by controlling the temperature at just above the melting point of iodine and see the melt. This is not new at all. There are at least two offered demonstrations (Summerlin, Borgford & Ealy, 1987; Najdoski & Petruševski, 2002) in the literature devoted to chemical lecture experiments and demonstrations where the authors offered suitable experiments to demonstrate the existence of liquid iodine at atmospheric pressure. Now we try to strengthen the notion by including a short video clip. In the latter decision, we were governed by the common saying that "a picture substitutes a thousand words". Consequently a video clip can indeed substitute (even literally) a thousand pictures, although the effect of live experiments is beyond doubt even stronger. It is a pity that all too many instructors rely heavily on available video material prepared by others instead of performing real experiments (Petruševski, Stojanovska & Šoptrajanov, 2009) but that is a fact. Therefore, if the material we offer here helps in fighting the misconception about iodine only subliming, but not melting upon heating, then it will completely serve its purpose.
Confronting the misconception: the offered experiment and video clip
The most effective chemistry tool among numerous teaching strategies and techniques used to reduce misconceptions in science teaching is an experiment or a demonstration. Using demonstration (or experiment), one can, more or less, easily test his/hers assumptions and confirm the correctness (or falseness) of the proposed hypothesis. Demonstrations/experiments are an inextricable component of chemistry teaching and, if properly preformed, lead to a development of an active and creative thinking.
As a means for fighting the discussed misconception, a laboratory demonstration was devised,3 in which appropriate apparatus and careful control of the temperature just above the melting point of iodine is employed.
The experimental setup (Figure 2) for this experiment includes a beaker filled with glycerol, a thermometer, a heater and a narrow test tube containing iodine crystals. The test tube may be sealed (for safer work), but this is not a necessary precondition for performing the demonstration. Glycerol has been chosen for this purpose because, on one hand, its boiling point (290 ºC) is much higher than the melting point of iodine (113.5 ºC), and on the other, glycerol is a colorless liquid unlike oil that has previously been used (Summerlin, Borgford & Ealy, 1987). The glycerol bath is heated to approximately 140 ºC. As temperature passes over the melting point of iodine, it can be clearly seen that iodine crystals begin to melt and, after some time, flow along the test tube inner walls when the tube is tilted (Figure 3). The process of iodine melting can be easily noticed on the video clip prepared for this demonstration. The first part of the clip shows the behavior of iodine crystals in a test tube and is to be compared with the behavior of the liquid iodine (obtained a few minutes later).
The result of the experiment (or, for that matter, the video clip) shows very clearly and beyond any doubt that iodine can be liquid under atmospheric pressure. This is only one example of the fact that experiments (carried out either by teachers or students) are very powerful tool in chemistry teaching. They can be used as an introductory or as a conclusion of the lesson, to verify or to explore phenomena, as well as to serve as a concept building and correcting existent misunderstandings and misconceptions students may have. Another aspect that has to be addressed at this point is caution while reading experimental procedures and performing the experiments. There are cases (one of them is dealt with in this paper) when the result of the experiment does not correspond to the summary or the explanation offered.
If no demonstration is performed, a lot of efforts might be needed to convince the students to abandon the previously learned concepts and to finally accept the new knowledge as valid and correct. Nevertheless, we should continue the search for suitable (novel or existent) ways to persuade the students and eliminate the effect of this misconception.
The authors would like to express their sincere thanks to M. Sc. Robert Jankuloski, assistant professor at the University of Audiovisual Arts European Film and Theatre Academy ESRA ParisSkopjeNew York, Photography Department, and to Mr. Vančo Mirakovski, Quasar Film Skopje, for preparing and supplying us with the video clip and the photograph for Figure 3.
Liquid_iodine?.mpg (video clip, available at the URL http://bit.ly/A6F1GS).
Aleksovska, S., Stojanoski, K., Chemistry for the 4th year of the reformed gymnasium education, Skopje, Prosvetno delo, 2005, p. 239 (in Macedonian). [Links]
Chang, R., Chemistry, 4th edition, Blacklick, Ohio, McGraw-Hill, 1990, p. 484. [Links]
Chemical forums, 2005. Consulted in the URL http://www.chemicalforums.com/index.php?action=printpage;topic=3946.0 (accessed on November 1st, 2011). [Links]
Choppin, G. R., Jaffe, B., Chemistry: Science of Matter, Energy and Change, Morristown, New Jersey, Silver Burdett Company, 1965, p. 13. [Links]
Cvetković, S., Chemisty for the 1st year of the reformed gymnasium education. Skopje, Prosvetno delo, 2002, p. 23 (in Macedonian). [Links]
Doneva-Atanasoska, G., Aleksovska, S., Malinkova, B., Chemisty for 7th grade. Skopje: Prosvetno delo, 2002, p. 30 (in Macedonian). [Links]
Haby J. Consulted in the URL http://www.theweatherprediction.com/habyhints2/369/ (accessed on November 1st, 2011).
Heilman, C., 2004. Consulted in the URL http://radioweblogs.com/0101365/2004/06/04.html (accessed November 1st, 2011).
Horton, C. (with other members of the Modeling Instruction in High School Chemistry Action Research Teams at Arizona State University), Student Alternative Conceptions in Chemistry, Worcester, MA, 2004. [Links]
Kotz, J. C., Treichel, P. M., Townsend, J. R., Chemistry & Chemical Reactivity, 7th edition, Thomson Brooks/Cole, 2009, p. 606. [Links]
McNaught, A. D., Wilkinson, A., Compendium of Chemical Terminology, 2nd edition, IUPAC, Oxford, Blackwell Science Ltd., 1997, p. 401. [Links]
Najdoski, M., Petruševski, V. M., The Experiment in the Teaching of Chemistry II, Skopje, Magor, 2002, pp. 356357 (in Macedonian). [Links]
Trach, B., 2003. Iodine crystal formation. Consulted it the URL http://www.newton.dep.anl.gov/askasci/chem03/chem03117.htm (accessed on November 1st, 2011). [Links]
Pabuçcu & Geban, Remediating misconceptions concerning chemical bonding through conceptual change text, H.U. Journal of Education, 30, 184192, 2006. [Links]
Petrucci, R., Harwood, W., Herring, G., General Chemistry: Principles and Modern Application, 8th edition, New Jersey, Prentice-Hall, Inc., 2001. Consulted in the URL http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/FG13_18.JPG (accessed on November 1st 2011). [Links]
Petruševski, V. M., Stojanovska, M., Šoptrajanov, B., "Modernization" of the chemistry education process. Do people still perform real experiments?, Educ. quím., 20, 466470, 2009. [Links]
Roschelle, J., 1995. Public Institutions for Personal Learning: Establishing a Research Agenda. Consulted in the URL http://www.exploratorium.edu/ifi/resources/museum-education/priorknowledge.html (accessed on November 1st 2011). [Links]
Silberberg, M., Chemistry: The Molecular Nature of Matter and Change, 4th edition, New York, McGraw-Hill, 2006, p. 436. [Links]
Summerlin, L. R., Borgford, C. L., Ealy, J. B., Chemical Demonstrations: A Sourcebook for Teachers, Vol. 2. Washington DC, American Chemical Society, 1987, p. 66. [Links]
Trefil, J., Hazen, R., The Sciences, 2nd edition, New York, John Wiley & Sons, 2000, p. 217. [Links]
Wikipedia, Sublimation. Consulted in the URL http://en.wikipedia.org/wiki/Sublimation_%28phase_transition%29 (accessed on November 1st, 2011). [Links]
Wisconsin State Journal, February, 2010. Consulted in the URL http://host.madison.com/wsj/news/local/article_bd20cdbb-a044-5f8b-9817-de7baa27f9d4.html (accessed on November 1st, 2011). [Links]
Yahoo answers, 2009. Consulted in the URL http://uk.answers.yahoo.com/question/index?qid=20091214091324AAjQsVx (accessed on November 1st, 2011).
1 The definition of evaporation (McNaught & Wilkinson, 1997) is "The physical process by which a liquid substance is converted to a gas or vapour" where there is an explicit mention of "a ... substance".
2 An alternative would be to coin a new term for the special type of sublimation that is analogous to boiling rather than to evaporation. This will be discussed in one of our forthcoming contributions.
Iodine is a substance which is present in a crystalline form. When this iodine is heated, it converts it into a gaseous form. The sublimation of iodine takes place in the presence of air or oxygen, the particles overcome the force of attraction between them and therefore sublimation takes place.Why does sublimation occur in iodine? ›
Van der Waals forces that link iodine molecules together in a crystal are relatively weak. That is why iodine usually sublimes very easily (that is, passes directly from the solid to the gaseous state) without going through the liquid state.What happens when iodine sublimes? ›
A crystal of iodine sublimes from its solid state to its gaseous state without turning into a liquid. Iodine forms a molecular covalent crystal.Is iodine an example of sublimable substance? ›
Iodine is a sublimable substance.What kind of change is sublimation of iodine? ›
In sublimation of iodine, a change of state occurs from solid to gas without converting to liquid. It is a physical change which happens quickly, and is reversible too.What is the sublimation Give 5 example? ›
sublimation, in physics, conversion of a substance from the solid to the gaseous state without its becoming liquid. An example is the vaporization of frozen carbon dioxide (dry ice) at ordinary atmospheric pressure and temperature.Why does iodine sublime and not melt? ›
The iodine atoms within one molecule are pulled closely to each other by a covalent bond. Between the molecules, there exist weak van der waals forces. When Iodine crystals are heated, the van der waals are easily overcome and the molecule breaks into gas phase. They sublime and form a purple colored dense vapor.Which Colour is formed in sublimation of iodine? ›
Solid iodine on sublimation gives violet vapours of iodine.How iodine is purified by sublimation? ›
Iodine is solid at room temperature. In the laboratory, solid iodine is kept in sublimation apparatus and is heated under vacuum. Because of the reduced pressure, the non-volatile impurities remain behind. Pure iodine volatilizes and settles on a cool surface by condensation.What does iodine look like after sublimation? ›
Place the flask on a hot plate, and turn on the hot plate so the flask is heated slowly. Purple Iodine vapor will be formed, and solid Iodine crystals should form on the bottom of the watch glass.
Just as water evaporates slowly at room temperature and quickly at its boiling point, iodine only sublimes quickly when heated up to near its sublimation point (more than 100 °C).Does iodine undergo sublimation when heated? ›
When iodine is heated sublimation can be readily observed. Iodine's vapor is a distinctive purple color and has a very strong scent, making it easy to detect. The video below shows the sublimation and deposition of iodine.What is iodine and example? ›
Also called iodide, iodine is a type of mineral that's naturally found in the earth's soil and ocean waters. Many salt water and plant-based foods contain iodine, and this mineral is most-widely available in iodized salt. It's important to get enough iodine in the diet.Can we separate iodine by sublimation? ›
Iodine-salt mixture can be separated through sublimation. Iodine will sublime whereas salt will be left behind. Sublimation is a technique that helps chemists to purify.What is sublimation method? ›
Sublimation consists of the evaporation of a solid from a hot surface and subsequent condensation on another surface at a lower temperature. Depending on the nature of the solid, sublimation can occur at atmospheric pressure or vacuum.What is an example of sublimation phase change? ›
The best example of sublimation is dry ice which is a frozen form of carbon dioxide. When dry ice gets exposed to air, dry ice directly changes its phase from solid-state to gaseous state which is visible as fog. Frozen carbon dioxide in its gaseous state is more stable than in its solid-state.Is sublimation an example of a chemical change? ›
Sublimation is classified as a physical change.Is iodine an example of deposition? ›
Deposition is the transition of a substance directly from the gas to the solid state on cooling, without passing through the liquid state. Examples: Camphor, Iodine, Ammonium Chloride, Naphthalene, etc.What is sublimation write 2 Example? ›
Sublimation is the change of the gaseous state directly into the solid state, without going through the liquid state, and vice versa. Examples of sublimation:- dry ice, moth balls or napthalene balls, camphor (kapur).What is sublimation explain with example and diagram? ›
SUBLIMATION: The change of the solid state of the matter directly on heating to vapor state (without becoming liquid) is called sublimation. The substance is dry ice, Naphthalene balls (mothballs, Iodine, Ammonium chloride, etc.)
Iodine on heating forms a purple vapour which turns back to grey iodine crystals when it cools. There is no change because all of the iodine vapour turns back to solid iodine crystals.Why does iodine solution stop changing Colour? ›
A sample is removed from the test tubes every 10 seconds to test for the presence of starch. Iodine solution will turn a blue/black colour when starch is present, so when all the starch is broken down, a blue-black colour is no longer produced. The iodine solution will remain orange-brown.Is iodine sublimated element? ›
Only Iodine is a halogen that sublimates, or converts directly into a gaseous form without melting.Why does iodine turn blue and black? ›
Iodine is a common indicator to test for the presence of starch. The light orange-brown colour Iodine solution turns blue-black in colour when it reacts with starch. This indicates the presence of carbohydrates in the food item to which iodine solution was added.How does sublimation occur? ›
Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. For those of us interested in the water cycle, sublimation is most often used to describe the process of snow and ice changing into water vapor (gas) in the air without first melting into water.What happens when iodine is added to water? ›
Iodine occurs naturally in water in the form of iodide. When added to water, elemental iodine hydrolyses in a pH-dependent manner to form hypoiodous acid and iodide. Iodine is an essential dietary element for mammals.What is the reaction of iodine with water? ›
Iodine, I2, like chlorine and bromine, does not react with oxygen, O2, or nitrogen, N2. It does, however, react with ozone, O3, forming the unstable compound, I4O9, which has a yellow colour. Iodine, I2, reacts with water, forming the compound of hypoiodite, IO–.What happens when iodine touches water? ›
Iodine may also occur as I3-(aq), HIO(aq), IO-(aq) en HIO3(aq). Iodine can bind to many different substances, for example other halogens. The compounds that are form behave differently when they come in contact with water. When iodine ends up in surface waters, it may escape as iodine gas.What is the main function of iodine? ›
Iodine is needed to make the thyroid hormones thyroxine and triiodothyronine, which assist with the creation of proteins and enzyme activity, as well as regulating normal metabolism.What is iodine and how does it work? ›
Iodine is a mineral found in some foods. The body needs iodine to make thyroid hormones. These hormones control the body's metabolism and many other important functions. The body also needs thyroid hormones for proper bone and brain development during pregnancy and infancy.
Iodine is a nonmetallic, nearly black solid at room temperature and has a glittering crystalline appearance.Which technique is used to separate iodine? ›
Thus, to separate salt and iodine we can use the sublimation technique.What is sublimation in chemistry? ›
Sublimation: The process in which a solid transforms into a gas phase without first melting to form a liquid phase. (Sublimation is not synonymous with evaporation; evaporation is a liquid-to-gas phase change.)Which process is used to separate iodine from? ›
This process is called sublimation. On cooling, the vapour changes back to solid directly. Iodine is a solid that sublimes. When a mixture of iodine and sand is heated in a beaker, the iodine changes from solid to vapour directly.Why sublimation process is used? ›
Sublimation is a technique used by chemists to purify compounds. A solid is typically placed in a sublimation apparatus and heated under vacuum. Under this reduced pressure, the solid volatilizes and condenses as a purified compound on a cooled surface (cold finger), leaving a non-volatile residue of impurities behind.What are the uses of sublimation? ›
There are practical applications of sublimation in forensic sciences. To purify the volatile compounds, the purification method in use by chemists is sublimation. One important use of sublimation is in the frozen food industry which is called freeze-drying.How iodine is an example of deposition? ›
When solid iodine is warmed, the solid sublimes and a vivid purple vapor forms (Figure 11.6. 6). The reverse of sublimation is called deposition, a process in which gaseous substances condense directly into the solid state, bypassing the liquid state. The formation of frost is an example of deposition.Can iodine be separated by sublimation? ›
No worries!What is sublimation process? ›
Sublimation is the transition of a substance directly from the solid phase to the gas phase without passing through the intermediate liquid phase (Table 4.8, Fig. 4.2). Sublimation is an endothermic phase transition that occurs at temperatures and pressures below the triple point of a chemical in the phase diagram.What is sublimation explain with diagram and example? ›
Sublimation is a phenomenon by which Solids directly get converted into Gas without conversion into Liquid State. Eg. Naphthalene balls get converted from solid to gaseous state without being converted into Liquid state.