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I. Aim: To determine the formula of the hydrate of copper (II) sulfate.
Hydrates are ionic compounds that have a definite amount of water as part of their structure. The water is chemically combined with the salt in a definite ratio. Ratios vary in different hydrates but are specific for any given hydrate.
In this experiment, the hydrate of copper sulfate has the formula CuSO4.xH20. When it is heated, the water is released as vapor and we can describe the reaction as below:
Hydrate Anhydrous salt + Salt
CuSO4.xH20 CuSO4 + xH20
The amount of water in the hydrate is determined by taking the difference between the mass of the hydrate before and after heated. Then, the percentage composition of water can be calculated basing on its mass. According to usual theory, hydrated copper sulfate has the following formula CuSO4.5H2O. Therefore, the result collected from the experiment should be x = 5.
* 1 x Evaporating dish
* 1 x Pipe-clay triangle
* Some crucible tongs
* 1 x Pressed fiber pad
* 1 x Digital balance (uncertainty: ï¿½0.001g)
* 1 x Spatula
* 1 x Glass stirring rod
* 1 x Bunsen burner
* 1 x Tripod stand
2. Chemical: Hydrated copper (II) sulfate
* Independent: the mass of hydrated salt.
* Dependent: the percentage composition of water in the hydrate.
* Control: room temperature, capacity of fire gas, standard equipment.
1. Clean and dry evaporating dish.
2. Set up a Bunsen burner under a tripod stand with a pipe-clay triangle on top.
3. Place the empty evaporating dish on the clay triangle and heat the dish with the hottest flame for 3 minutes. This is done to be sure that the dish is absolutely dry.
4. Use tongs to remove the dish from the clay triangle and then place it on a pressed fiber pad so that it can cool for several minutes.
5. Use a digital balance to determine the mass of the cooled evaporating dish. Record this mass to the same number of decimal places as the uncertainty of the balance (ï¿½0.001g), in other words, the measured mass will have 3 decimal places. Remember not to weigh the dish when it is hot because heat waves tend to be circular and upward, which tends to make objects appear to weigh less.
6. With the dish on the balance, put into it a specific amount of hydrated copper sulfate; make sure that the amount of hydrated copper sulfate is less than half full of the dish. Be sure the spatula is very clean to avoid contamination. Record the mass of the dish with the hydrate to the same number of decimal places as the uncertainty of the balance.
7. Place the dish on the clay triangle. Gently heat the dish by moving the burner bark and forth around the base. Increase the heat gradually. Avoid any popping and spattering.
8. Heat strongly for 5 minutes or until all of the blue color has disappeared. During the heating, a glass stirring rod should be used to spread the solid and break up larger portions of the hydrate. Be sure not to pick up any of the solid on the stirring rod. If the edges of the solid appear to be turning brown, remove the heat momentarily and resume heating with a cooler flame.
9. Allow the dish to cool for 2 minutes. Immediately find the mass of the dish with the anhydrous salt, and record the mass to the same number of decimal places as the uncertainty of the balance. The dish must be weighed before the compound reabsorbs water from the atmosphere.
10. Calculate the initial amount of hydrated copper sulfate before heated. Record the answer to the same number of decimal places as its calculated uncertainty.
11. Determine the amount of vaporized water. Record the answer to the same number of decimal places as its calculated uncertainty.
12. Then, the value of x can be found basing on the formula ratio.
13. When finish, the anhydrous salt can be thrown into the waste container and the evaporating dish washed.