Monday, May 2 nd : “A” Day Tuesday, May 3 rd : “B” Day Agenda Check lab write-ups Pre-lab Discussion Lab: “Percent Composition of Hydrates” Lab will be due next time… Looking Ahead Next time: Lab Calculations/Movie
Lab Write-Up “Percent Composition of Hydrates” Many ionic compounds include individual water molecules as part of their crystalline structure. If heated, the water molecules are driven off, leaving the pure anhydrous form of the compound. The number of moles of water driven off per mole of anhydrous compound should be a simple whole-number ratio. This information can be used to determine the formula of the hydrate.
Lab Write-Up “Percent Composition of Hydrates” In this lab, you will determine the following: 1.The empirical formula of the hydrate, including its water of crystallization. 2.If the compound is useful as an indicator when it changes from the hydrated to the anhydrous form. 3.The mass of water absorbed by 25g of the anhydrous compound.
Lab: “Percent Composition of Hydrates” 1. What chemical is being used in this lab? Copper (II) Sulfate, CuSO 4 Hydrated crystals 2.How much of it do you use? 5 grams
Lab: “Percent Composition of Hydrates” 3.What is a hydrate? A compound that has individual water molecules as part of its crystalline structure. 4.Why is the copper sulfate heated? To drive off the water.
Lab: “Percent Composition of Hydrates” 5.Why do you heat the copper sulfate more than once? To make sure that all of the water is gone. 6.What does anhydrous mean? “With all water removed”, especially water of crystallization.
Lab: “Percent Composition of Hydrates” 7. What do you need to do with the crucible before placing it on the balance? Cool it in the desiccator. 8.Why is a desiccator used to cool the sample? The hot sample will absorb water from the air if not placed in the desiccator.
Safety Guidelines 1.We are using bunsen burners: your hair must be tied back! 2.Be careful with the crucible/cover. They are extremely hot and tipsy. If you drop it…DO NOT try to catch it…let it fall. It’s easier to clean up a spill than to treat a burn or a cut. 3.Be sure to cool the crucible/cover before placing it on the balance…hot crucibles WILL damage the balances!
Lab: “Percent Composition of Hydrates” Make sure your data has the correct units. Using complete sentences, complete the “observations” section on page 79 and answer Analysis questions #1 and #2 on page 80. We’ll do the rest of the calculations together next time. Be careful and have fun!