Part C: Identification of hydrates In this section you will try to determine through the testing of a series of compounds, which ones are true hydrates. Heat the test tube and note any condensation that may appear at the mouth of the test tube as evidence of dehydration, note the color of the residue.
Note the color of the dissolved residue. Part D: Determination of the formula of a hydrate In this section we will determine the number of moles of water present per mole of anhydrous solid in a given hydrate. Using crucible tongs, clean a porcelain crucible and its cover using concentrated nitric acid 6 M. Pour the used nitric acid in the waste container provided. Rinse the crucible and its cover with distilled water.
Set the crucible with its cover slightly open on a clay triangle and heat strongly for at least 10 minutes. Allow the crucible to cool down to room temperature do not set the hot crucible on the bench top. Weigh the crucible with its cover to the nearest 0. Making sure to handle the crucible and its cover with clean tongs, add about 1 g weighed to the nearest 0. Record the mass of the crucible, cover and sample. Heat the content of the crucible with its cover slightly open to allow the water of hydration to escape, first gently about 10 minutes , then strongly about 5 minutes.
Weigh and record the mass of the cooled crucible with its cover and content anhydrous residue. Save the residue and perform your calculations. If the results of your calculations suggest that you have some water left in the residue, reheat your sample for an additional 5 minutes, allow it to cool down and weigh it again. Pre-laboratory Assignment: Properties of Hydrates A student trying to determine if a white solid is a true hydrate heats the sample and finds that there is evolution of water, that the residue obtained is soluble in water and that the solution is colorless.
Is this a true hydrate? He weighs a clean and dry crucible with its cover and records a mass of He then weighs the sample in the crucible and cover and obtains a mass of He heats the sample, allows it to cool to room temperature and reweighs it to obtain a mass of What color would you expect to see when this student dissolves the blue residue in water at the end of the experiment?
Part B: Hygroscopic and Efflorescent Solids Substance Initial mass of container and sample Final mass of container and sample Change in mass Observations on structure, texture , wetness, etc. How will the weight be affected by placing a warm beaker on the balance? Some compounds like carbohydrates release water upon heating by decomposition of the compound rather than by loss of the water of hydration.
These compounds are not considered true hydrates as the hydration process is not reversible. A hydrate is a substance that contains water. In inorganic chemistry, it refers to salts or ionic compounds that have molecules of water incorporated into their crystal structure. Some hydrates change color when they are heated. Since water vapor is released and the solid changes color, this should be considered as a chemical reaction, not a physical change. By heating copper II sulfate pentahydrate until it was white and contained no more water, you undergo a chemical change.
Basically, if you have a substance which gives off water when heated and yet does not contain hydrogen in its formula, you have a HYDRATE!!! Is it possible to use the appearance of hydrates to determine if there is moisture in a room? Yes, it is possible in some cases. For example, CoCl2 is blue in the unhydrated form and pink in the hydrated form. Why do hydrates easily lose and regain water?
The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained. To lose water of hydration; the process occurs when the hydrate has a vapor pressure higher than that of water vapor in the air. There are three main types of dehydration: hypotonic primarily a loss of electrolytes , hypertonic primarily loss of water , and isotonic equal loss of water and electrolytes.
The most commonly seen in humans is isotonic. Hydrates are formed when water and light end natural gases come into contact at certain temperature and pressure conditions. Examples of hydrates are gypsum commonly used in the manufacturing of wallboard, cement and plaster of Paris , Borax used in many cosmetic, cleaning and laundry products and epsom salt used as a natural remedy and exfoliant.
Hydrates are often used in skin care products to infuse moisture into the body. Most hydrated salts melt with decomposition as temperature increases, forming water and a lower hydrated salt. Likewise, water that has been removed can be replaced, and the results of the hydration reaction will be the same every time the experiment is conducted. Certain heat reactions cause water extraction through decomposition of the compound rather than the loss of water. For example, although carbohydrates release water when heated, they are not true hydrates, because the carbohydrates are decomposing to produce energy that is expended.
Therefore, the hydration process is not reversible in the reaction because the energy produced cannot be replaced. Every hydrate possesses a crystalline structure that contains a fixed number of water molecules.
A hydrate will often seek water molecules from the atmosphere to fill an incomplete crystal, but too many water molecules surrounding a hydrate will lead to dissolution or clumping with other hydrates possessing similar properties. Most salts are hydrates, and many salt structures will remain dissolved in water at any temperature. As a result, these crystals are used in a variety of sports beverages, such as Gatorade, to provide essential hydration to athletes during practice and game performance.
Adelaide Tresor has been a technical writer and book editor since Tresor holds a bachelor's degree in journalism and is also a certified teacher with experience in English, mathematics, chemistry, and environmental science. She currently teaches AP Physics.
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