These salts, when they have absorbed water, are called The ions in some salts attract and form strong bonds with water Negatively charged parts within each molecule. Water has a polar structure: it has positively and Some chemical compounds, especially inorganic salts, incorporate water into theirĬrystalline structures. Hydrated salt of known formula but unknown water content. Of known formula ( CuSO 4♵H 2O) and finding the formula of a The lab portion of this work conists in confirming the formula of a hydrate Nomenclature, and the molar mass of hydrates. ![]() Students willīe introduced to the concept of hydrated salts, anhydrous salts, hydrate This lab activity combines in-class problem-solving with lab work. The lab work has two objectives: first, confirm the formula of a hydrate with known formula and second, find the formula of a hydrate in which the salt formula is known but not the molar amount of water. If your results are not within 0.03 grams of your previous heating, reheat, cool, and weigh until it does! (This may take several heatings).Note for Teachers: Give out this lab handout at least one dayīefore doing this lab and assign the problems for homework. If your results come within 0.03 g of the mass of the previous heating, begin your calculations. After allowing it to cool again (with the lid completely on), reweigh the crucible and its contents. In order to ensure that all the water was driven off from the hydrate, reheat the crucible, its contents, and its lid.When the crucible has cooled, weigh the crucible, lid, and the contents.Turn off the burner and allow the crucible to cool for at least five minutes with the cover closed completely. Maintain this temperature for five minutes. Adjust the cover until there is a 0.5 cm opening between it and theopening. Gradually increase the flame until the crucible bottom is at most a dull red. Place the crucible, with its lid only slightly askew, on the triangle and heat it very gently so as to avoid spattering. ![]() Record the number or letter of your unknown in your lab manual. Record the mass of the crucible, lid, and unknown hydrate. Weigh the crucible and its contents with the lid. Add hydrate crystals to the crucible until it is 1/4-1/3 full (about 1 to 5 g).Record the mass of the empty crucible and lid. Do not weigh the crucible while it is still hot! After you have allowed it to cool for a few minutes, use crucible tongs to transfer the crucible and the lid to your balance. Heat with a Bunsen burner for 2-3 minutes to clean and dry the crucible. Leave the cover askew so that any water in the crucible can easily escape. Place a dry, clean crucible with a lid in a clay triangle mounted on an iron ring.Finally, you can determine the number of moles of water that are in your sample, and use this to determine theformula of the hydrate. You can then use this to determine its molar mass and use this information to determine the number of moles of anhydrous salt that are in your sample. At the end of the experiment, your teacher will give you the formula for the anhydrous salt of your unknown. You will determine the mass of water driven off by heating and the amount of anhydrous salt that remains behind. In this experiment, you will be given a hydrate whose formula is unknown. ![]() ![]() The dot between the CuSO4 and the 5H2O indicates that the water molecules are loosely attached to the other formula units. Yet, each mole of hydrate contains five moles of water. One example is the hydrate copper sulfate. The ratio of moles of water present per moles of anhydrous (dry) salt is usually a whole number. This suggests that water was present as part of the crystal structure. The crystals change form, even color sometimes, as the water is driven off. Many salts that have been crystallized from a water solution appear to be perfectly dry, yet when heated they yield large quantities of water. AP Chemistry – Lab 02: Formula of a Hydrate
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