Color or odor alone will not indicate whether a substance is ionic or molecular. Oxidation with Oxygen Combustion. Place a small amount, about the size of half a pea, of each unknown on the end of a spatula and place this in the flame of a Bunsen burner that is near or under a snorkel. Be careful not to melt the snorkel hood.
Record whether or not the unknown burns. Data and Results. Minimum Amount of Water Needed to dissolve 0. List of Possible Unknowns. Ionic Compounds. Molecular Compounds. If the reference is an internet site, the complete URL to the specific webpage that has the information you provided must be given. Post-laboratory Questions. Discuss in detail how you would classify each unknown based on the overall set of data for each unknown. Based on the literature values for some physical and chemical properties of the unknown possibilities, discuss how you determined the identity each unknown.
Physical and Chemical Properties Objectives The main objective of this experiment is to experimentally determine several chemical and physical properties of two unknown compounds and based on the set of properties identify each substance as either ionic or molecular.
Introduction All substances can be characterized by their unique sets of physical and chemical properties. Special Safety Precautions Be careful not to burn yourself with either the Bunsen burner or the melting point apparatus. Protocol Obtain 2 unknowns from your instructor and record the code numbers of your unknowns in your record book. Solubility in Water For each unknown determine the solubility in water as follows: Place 0. Aqueous Reactions. Search for:.
Key Points Solubility is the relative ability of a solute to dissolve into a solvent. Several factors affect the solubility of a given solute in a given solvent. Temperature often plays the largest role, although pressure can have a significant effect for gases. Show Sources Boundless vets and curates high-quality, openly licensed content from around the Internet. Licenses and Attributions. Tell students that one contains salt, one contains sugar, and the other contains either salt, sugar, or something else.
Explain that the class will design a dissolving test to try to figure out what substance is in which cup. Students will record their observations and answer questions about the activity on the activity sheet. Have a discussion with students about the best way to design a dissolving test to see if there is a difference between salt and sugar.
Note: A solubility test is normally measured by the mass of a substance that dissolves in a given volume of water. In middle school, students can weigh the solutes for a solubility test that uses equal masses.
Discuss with students how they should test the substances in cups A, B, and C. Students should understand that they need to test them the same way they tested the sugar and salt so they can compare them to what they saw before.
The substance in cup B dissolved completely and the fastest. It was like the sugar. The substance in cup C dissolved more slowly than the sugar and did not dissolve completely.
It was like the salt. It was not like sugar or salt. Show the animation Dissolving Different Substances. Note: The animation uses two types of models. For the salt, the model shows the sodium and chloride ions as individual spheres with their respective charges. For the sugar and alum, no individual atoms are represented. The structures of these molecules are complicated and made up of many atoms bonded together in complex ways.
Therefore, simple shapes of hexagons and diamonds with positive and negative charges are used to represent the molecules of these substances. Explain that since the atoms and molecules that make up sugar, salt, and alum are different, and have different charges, each substance has a different structure. They also, as a result, interact differently with water molecules.
Because each substance is made from different atoms in different arrangements, they dissolve differently. Alum has an interesting property that is different from many other substances. One way to tell the difference between salt, sugar, and alum is to do a water cleaning test. The water in the container with the alum should look clearer than the water with the salt or sugar. It should only take 10 - 15 minutes to see a noticeable difference. This test shows that alum has a characteristic property of being able to make dirty water clearer.
When might you come into contact with unknown chemicals in the real world? Simple tests you can do. Chromatographic methods. Spectroscopic methods. X-Ray crystallography a.
X-ray diffraction, or XRD Mass spectrometry. A solution that cannot dissolve any more solute under the given conditions. To measure concentration, you compare the amount of solute to the total amount of solution.
Why is solubility useful in identifying substances? You can identify a substance by its solubility because it is a characteristic property of matter. Solubility indicates the maximum amount of a substance that can be dissolved in a solvent at a given temperature.
Such a solution is called saturated. Solubility is the property of a solid, liquid, or gas, called a solute, to dissolve in a liquid solvent to form a homogeneous solution. The solubility of a substance in a solvent changes as the temperature of the solution changes. As temperature rises, typically the solubility of solids in liquids becomes higher.
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