In association with Nuffield Foundation. The practical activity takes around minutes, depending on the competence of the class. Students should all be standing and should wear eye protection. Students with long hair should tie it back.
It is a good idea for students to practice lifting the lid on and off the crucible and the crucible off the pipe clay triangle before they start. This has the added bonus of checking that all the tongs are functioning correctly. To enable students to light their Bunsen burners they will need access to matches or lighters. The most significant hazard in this experiment is the hot apparatus. Warn students that it will take some time to cool down. For classes with shorter attention spans, the final step of heating to constant mass could be omitted.
Fresh, clean magnesium is best for this experiment. If the magnesium is tarnished then emery or sand paper will be required to clean it. If it is looking tarnished or black then clean it using the emery paper. Twist it into a loose coil. Place the crucible containing the magnesium in the pipe clay triangle and put the lid on. It is best to start with a gentle blue flame, but you will need to use a roaring flame with the air hole fully open to get the reaction to go.
You may see the magnesium begin to flare up. If the lid is off for too long then the magnesium oxide product will begin to escape. At this point, remove the lid and heat for another couple of minutes. Replace the lid if it appears that you are losing some product.
Repeat this step until the mass readings are consistent. This should allow them to calculate the mass of the mass of the magnesium mass 2 - mass 1 and the mass of the product mass 3 - mass 1. They could also calculate the increase in mass mass 3 - mass 2which corresponds to the mass of oxygen. Students sometimes get unconvincing results to this experiment. It is worth evaluating what they have done as there are several reasons why their results may be disappointing:.
METHOD 1 To find the formula of magnesium oxide, students will need the mass of the magnesium and the mass of the oxygen. They will also require the relative atomic masses. Magnesium is 24 and oxygen is They should divide mass by the atomic mass for each element. The gives the number of moles of each. Having done this for both elements, they should find the ratio between the two by dividing them both by the smallest number.
You will need a copy of the graph below for the class. All students plot their masses of magnesium and oxygen onto the graph. This helps to show clearly any anomolous results and should help to convince students who are disappointed by a This collection of over practical activities demonstrates a wide range of chemical concepts and processes.
Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures.
Challenge the misconception that metals and non-metals are completely opposite in their properties with this activity.If we can't tunnel through the Earth, how do we know what's at its center?
All Rights Reserved. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply. Hottest Questions. Previously Viewed. Unanswered Questions. Why the empty crucible should be heated before starting the experiment? Wiki User It should be heated to rid it of any and all foreign material that might add to the weight when you place you sample in it.
Related Questions Asked in Science Experiments Why empty crucible should be heated before experiment? The scope is to eliminate any impurities from the crucible, up to constant weight. Asked in Chemistry Why are crucible heated before weighed? Because it must be heated.
Asked in Science Experiments Why should you heat an uncovered crucible in a chemistry lab experiment? A crucible is a heat-resistant container in which materials can be heated to very high temperatures. If you heat with the cover on, it could produce an overflow of the material. Asked in Chemistry What is a crucible and cover? A crucible is a small refractory container used in laboratories to contain a sample to be heated. A crucible is used to contain chemical compounds when heated to extremely high temperatures.
The clay triangle is used to hold a crucible while the crucible is heated. Asked in Chemistry What is clay triangle how it is use?As part of the procedure for the determination of the sulfate content of an unknown sample it will be necessary to accurately determine the empty weights of a set of crucibles.
This is accomplished by first cleaning the crucible and then heating them in the flame of a Tirrel burner. They are then cooled and weighed. This process of heating and cooling is repeated until successive weighings agree to within 0. The procedure will, in addition, acquaint the student with the use of the analytical balance and the proper use of the desiccator.
Be sure that you read the appendix section dealing with the use of desiccator. Wash and rinse four 10 ml crucibles and their lids. Identify each of the crucibles by means of existing visual differences. Carefully note in your lab notebook what these identifying marks are and assign a number to each crucible.
Do not use marking pens or pencils to mark your crucibles. The high heat which will be used to take them to constant weight will obliterate such markings and more importantly will affect their weight in an unpredictable manner. The lids to the crucibles do not need to be taken to constant weight, however, they should be clean.
Place a Tirrel burner under the crucible and adjust the flame of the burner to give a non-luminous flame with a full gas supply. The tip of the flame cone should be just below but not touching the crucible. Heat the crucible at red heat in this manner for minutes.
Allow it to cool for a few minutes and then place it in the desiccator. Reheat and reweigh it until successive weighings agree to within 0. Your first exercise teaches you some skills on the proper use of the laboratory burner in this case called a Tirill Burnerthe adjustment of the flame and the proper placement of a crucible which is to be heated to constant weight. You ought to make sure at the outset that the crucibles you use have indelible identifying marks on them.
Sometimes there are indentations left during the manufacture of a crucible which will allow you to distinguish one from another. More likely, there will be a letter or number written into the side by a former student, such as the one shown at the left. Note the "A" scratched into the glossy surface. This can be done with the diamond pencil available in the lab, as shown at the right. The hottest part of the flame is at the top of the bright cone of oxidation.
The zone beneath the sharp point of the cone is filled with a rising mixture of cool gases not yet in the process of combustion. Although the rim around this zone is quite hot, the gases inside are essentially at room temperature. See that placement on the left. Such a placement is not recommended Note the correct placement of the crucible in the photograph at the right. The crucible may be placed right side up, as in the left photo, or on its side, as in the right photo.
Heating it on its side is preferred because the overall strain on the ceramic material at the high temperatures used is somewhat less. The crucible ought to be heated to incandescence for minutes left. At the end of this time, remove the flame and allow the crucible to cool on the iron triangle for a few minutes right.
When transferring a crucible to the dessicator tongs must be used. If the crucible has been allowed to cool, you may use bare tongs leftbut if you must transfer a hot crucible, make sure that you cover the ends of the tongs with aluminum foil right as the paint on the tongs might melt onto the crucible and change its weight. Make sure you grab the crucible on the edge as shown. Don't try to pick up a crucible by squeezing the tongs on the outer rim both because the crucible may slip from your grip owing to its slick walls.A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures.
While crucibles historically were usually made from clay,  they can be made from any material that withstands temperatures high enough to melt or otherwise alter its contents.
The form of the crucibles has varied through time, with designs reflecting the process for which they are used, as well as regional variation. Crucibles used for copper smelting were generally wide shallow vessels made from clay that lacks refractory properties which is similar to the types of clay used in other ceramics of the time.
Early examples of this practice can be seen in Feinan, Jordan. The main purpose of the crucible during this period was to keep the ore in the area where the heat was concentrated to separate it from impurities before shaping. The use of crucibles in the Iron Age remains very similar to that of the Bronze Age with copper and tin smelting being used to produce bronze. The Iron Age crucible designs remain the same as the Bronze Age.
The Roman period shows technical innovations, with crucibles for new methods used to produce new alloys. The smelting and melting process also changed with both the heating technique and the crucible design. The crucible changed into rounded or pointed bottom vessels with a more conical shape; these were heated from below, unlike prehistoric types which were irregular in shape and were heated from above. These crucibles in some cases have thinner walls and have more refractory properties Tylecote p During the Roman period a new process of metalworking started, cementationused in the production of brass.
This process involves the combination of a metal and a gas to produce an alloy Zwicker et al. Brass is made by mixing solid copper metal with zinc oxide or carbonate which comes in the form of calamine or smithsonite Rehren p This reaction has to take place in a part-closed or closed container otherwise the zinc vapour would escape before it can react with the copper.
Cementation crucibles therefore have a lid or cap which limits the amount of gas loss from the crucible. The crucible design is similar to the smelting and melting crucibles of the period utilizing the same material as the smelting and melting crucibles.
The conical shape and small mouth allowed the lid to be added. Cementation vessels are mass-produced due to crucibles having to be broken open to remove the brass once the reaction has finished as in most cases the lid would have baked hard to the vessel or the brass might have adhered to the vessel walls. Smelting and melting of copper and its alloys such as leaded bronze were smelted in crucibles similar to those of the Roman period which have thinner walls and flat bases to sit within the furnaces.
The technology for this type of smelting started to change at the end of the Medieval period with the introduction of new tempering material for the ceramic crucibles.
Some of these copper alloy crucibles were used in the making of bells. These later medieval crucibles were a more mass-produced product. The cementation process, which was lost from the end of the Roman to the early Medieval period, continued in the same way with brass. Brass production increased during the medieval period due to a better understanding of the technology behind it.Burning of Magnesium Ribbon Experiment - #aumsum
Furthermore, the process for carrying out cementation for brass did not change greatly until the 19th century. However, during this period a vast and highly important technological innovation happened using the cementation process, the production of crucible steel. Steel production using iron and carbon works similarly to brass, with the iron metal being mixed with carbon to produce steel. The first examples of cementation steel is wootz steel from India Craddock pwhere the crucibles were filled with the good quality low-carbon wrought iron and carbon in the form of organics such as leaves, wood etc.
However, no charcoal was used within the crucible. These early crucibles would only produce a small amount of steel as they would have to be broken once the process has finished.
By the late Medieval period steel production had moved from India to modern-day Uzbekistan where new materials were being used in the production of steel crucibles, for example Mullite crucibles were introduced.
Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. It only takes a minute to sign up. After we heated the crucible we were to cool it down using a Desiccator.
Then this question came to my mind: Why must we cool it down? By doing researches in the Net I were only able to come up with these suggestions, but none seem very applicable for me:. Anyone sane, and with regards to the value the balance has in the lab, would give slightest chances that the hot container would harm the surface of the balance and therefore, damage it.
Using Einstein's formula:
But chances are that I'm wrong too. So, why must we cool the crucible in order to measure the mass of the sample in it using a balance? A container that is not at ambient temperature will generate air currents around it.
If you place such a non-ambient container in a balance, air currents will develop around the container as it heats or cools to ambient. These air currents will cause the balance to read incorrectly. The other two answers here are fine; it's true that as the hot object you're trying to weigh warms the air around it, the air will rise, creating air currents that will give you an unsteady reading.
The balance pan will heat up, too, causing metal parts in the balance to expand. This will also contribute to an error in your reading, and as the metal cools, the reading will change. Another contribution to the error is that the density of a hot sample is less than the density of a cold sample, so its buoyancy is different.
The object will appear to gain a tiny amount of weight as it cools! And a fourth thing: if you put a hot object into an air-tight dessicator, the air inside will contract as the object coolsand you might have some trouble getting the lid off again!
Your gut feeling is right: Very hot crucibles can cause damage to the balance. However, this isn't the main reason for why chemists cool their samples down before measurement. We are all familiar with convection currents : When air is heated the molecules will collide more than its previous state; resulting in an increase in either volume or pressure depending on the "flexibility" of the environment of effect.
Thus, the density of hot air decreases, and it goes up and "replaces" the cold air. If the process of heating the air continues, hot air will continuously go up in what we call a "convection current". The system of the crucible is thermodynamically open, so in contact with air it will lose some of its heat to its surrounding gas, which is normally atmosphere air. If we put the hot crucible for measuring its mass, convection currents will occur around the crucible, where it's in contact with the surrounding air.
The motion of the hot air upwards forces your crucible upwards, but in small amounts. The balance has to be precise enough to detect these differences, though. Most balances in the labs can measure up to 0. Since you usually need or are made to write exact measurement results up to 1 miligram, these differences are going to be irking pests in measurement. This is a very useful source from which the answer came from. It also has useful recommendations on practical problems in the lab.All compounds consist of elements chemically combined in fixed proportions — they obey the Law of Constant Composition.
One way to express the proportion each of element in a compound is as a percentage by mass, or mass percent. In Part A of this lab, a sample of potassium chlorate will be experimentally analyzed in order to determine the mass percent of elemental oxygen present in it. Students will perform a quantitative analysis of the reactants and products of this reaction, measuring the initial mass of solid potassium chlorate used before heatingand the mass of the solid potassium chloride product, or residue, remaining after heating.
Applying the Law of Mass Conservation, the difference in these measured masses is the mass of oxygen released from the original potassium chlorate sample. From this data, the experimental mass percent of oxygen in potassium chlorate will be determined:.
Mass percentages of elements in compounds can also be theoretically calculated using molar masses, along with the known chemical formula of the compound. Thus, the theoretical mass percent of oxygen in potassium chlorate would be calculated using the expression:. Students can therefore evaluate their accuracy in this experiment by comparing their experimental results to the true theoretical value, and by calculating their percent error.
In Part B of this lab, the residue left after heating will be qualitatively analyzed in order to demonstrate that it is chemically different from the initial potassium chlorate sample.
Specifically, the residue will be tested for the presence of chloride ions by the addition of nitric acid and aqueous silver nitrate.
A positive test is indicated by the formation of a white precipitate. The actual identity of the residue will then be conclusively verified by comparing this result to those obtained for identical tests on known samples of potassium chlorate and potassium chloride.
Be especially careful when using the Bunsen burner and handling hot equipment. Remember that most items look exactly the same whether they are hot or cold. Heat the potassium chlorate sample slowly to avoid any splattering. Be aware that silver nitrate may stain the skin and nitric acid may burn the skin. If a spill of either chemical occurs, rinse under running water and report the accident to your instructor.
Nitric acid spills may also be neutralized using the sodium bicarbonate solution by the sinks. Show your work clearly for each step in the table below. Show your work clearly. Observations after the addition of both nitric acid and silver nitrate. Explain how your observations in the table above verify that the residue in your crucible after heating is potassium chloride.
Are there any other observations that you have made during this experiment not those in the table above that would suggest that the potassium chlorate was converted to a new substance upon heating?
Which of the following sources of error could be used to explain this discrepancy circle one? Explain your choice. Your response should include an analysis of the formulas of the compounds involved. To qualitatively demonstrate that the residue resulting from the decomposition of potassium chlorate is potassium chloride. Safety Be especially careful when using the Bunsen burner and handling hot equipment. Part A: Mass Percent of Oxygen in Potassium Chlorate The following steps should be carried out for two separate samples of potassium chlorate.
Clean both crucibles and their lids obtained from the stockroom by thoroughly rinsing with distilled water then drying as completely as possible with a paper towel. Weigh the first crucible and lid on an electronic balance and record this mass on your report form.
Add approximately 1 gram of potassium chlorate to the crucible. Do not do this over the balance! Then weigh and record the mass of the crucible, lid and potassium chlorate sample. Fetch a stand and ring clamp from the back of the lab. As shown in the figure and photo on the following page, place your clay triangle on the ring, and then place the crucible containing the sample onto the triangle.
Cover the crucible with the lid.
5: The Composition of Potassium Chlorate (Experiment)
Using a Bunsen burner, heat the crucible and sample for a total of 12 minutes.If we can't tunnel through the Earth, how do we know what's at its center? All Rights Reserved. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply.
Hottest Questions. Previously Viewed. Unanswered Questions. Why do you need to heat the clean crucible before using it? Wiki User If you are using the crucible for any type of gravimetric analysis observing changes in mass upon the heating of a compoundthen before you add your sample you need to bake the crucible in order to drive off any adsorbed materialsnamely water.
If you do not do this, then the initial mass of your compound will be artificially high, and so when all that adsorbed stuff is baked off, your change in mass will be high. After the crucible absorbed the direct heat it alowed the mixture to cook evenly. Asked in The Crucible play Why must the crucible be cooled before weighing? There are a few reasons: Safety, so individual does not get burned; a hot crucible could damage the scale; hot crucible could alter the substance being weighed; a hot crucible as the heat is released into surrounding air, it causes convection air currents when using an electronic scale than measures to multiple decimal places can give a miss reading and give the individual a larger error percentage in their experiment.
Asked in Science Experiments Why should you heat an uncovered crucible in a chemistry lab experiment? A crucible is a heat-resistant container in which materials can be heated to very high temperatures. If you heat with the cover on, it could produce an overflow of the material.
Asked in Cleaning What is the right way to clean retainers? I clean my retainer with my toothbrush and Listerine. There are tablets you can buy that you put in water and they dissolve and clean the retainers. Using heat can misshapen your retainers! Asked in Chemistry, Bunsen Burners What items is used to distribute heat from a Bunsen burner when heating the bottom of a crucible?
A crucible is placed in a pipestem triangle placed on an iron ring while being heated.
This supports the crucible while allowing the bottom of the crucible to be directly exposed to the flame of the Bunsen burner. There is no item that is used to distribute heat from a Bunsen burner when heating the bottom of a crucible. The bottom of the crucible is intended to be exposed to the direct flame of the Bunsen burner. Asked in Science What is used to heat small amounts of solids? Crucible and lid. It is called a Crucible. Asked in Chemistry Why are the empty crucible and cover fired to red heat?
To drive off any volatile materials that might alter the mass of crucible and cover. It is necessary to cover the crucible when it is being heated for two basic reasons: primarily, it maintains a higher temperature inside the crucible.
Without the lid, the heat simply escapes. Secondly, it keeps the material inside the crucible from splashing out. Crucibles are porcelain-like containers used in chemistry to heat substances to very high temperatures. Crucible tongs are large pincers made of welded steel that are used to grasp and take a hot crucible out of a fire or furnace, or to move a crucible from one location to another.
Asked in Physics, Energy What should be used to heat a solid in the presence of air? Asked in Physics, Energy Which of these items should be used to heat a solid in the presence of air? Asked in Physics, Nuclear Energy How do you harness nuclear energy? Nuclear energy is produced by the release of heat from unstable elements such as Uranium. The energy is harnessed by using the energy to heat water.