| Now filter the salt water/calcium phosphate mixture using the gooch crucible and a filter flask. | The sodium chloride should dissolve in the water to form saltwater, but the calcium chloride will not.
Movie: Add 10Ml of Water
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Do you think this mixture is heterogeneous or homogeneous? Why? Record your answer supported by appropriate observations on your data sheet.
Movie: Stirring the Mixture
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| Put the gooch crucible in the rubber adapter on the filter
flask. Hook the rubber hose to the sidearm of the flask and the aspirator on the faucet. Turn on the faucet to the aspirator to pull a vacuum in the flask. You may need to press gently down on the gooch crucible to seal it against the rubber adapter in order to establish a vacuum in the flask.
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With a vacuum in the flask, pour the saltwater/calcium phosphate mixture into the gooch crucible. Let all of the salt water pass into the flask, Repeat this next step three times: add 2-3mL of distilled water to the 100mL beaker and swirl it around to pick up any white residue on the sides. Pour this into the gooch crucible and let the vacuum suck it through the filter.
Movie: Separating the Mixture
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Now that the mixture has been filtered, the gooch crucible needs to be heated under the heat lamp. First the gooch crucible must be removed from the filter flask. Attention: Break the vacuum in the flask by tilting the gooch crucible up, then turn off the faucet. (Warning: If you turn off the faucet first, tap water will be sucked back into your flask!) Dry the calcium phosphate by placing the gooch crucible underneath the heat lamp, and turning the lamp on. Watch the movie to the left to see how to adjust the heat lamp. |
| Warning:
the lamp and crucible will be very hot at first when the heating is complete.
Make sure you do not pick up the crucible with your bare hands. Instead use the forceps in your drawer.
Also, the lamp will be very hot when heating is complete, it may be a good
idea to unplug the lamp first instead of trying to turn the switch off. The calcium phosphate must be thoroughly dry before weighing. To test for dryness use the forceps to pick up the crucible and weigh it. Record the mass of the crucible/calcium phosphate. Then put the crucible back under the heat lamp. Let the crucible heat for a few more minutes. Place the crucible back onto the balance, weigh it record the mass. If the masses have not significantly changed, then the all the water has been removed. |
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Pour the salt water from the vacuum flask into the casserole. Do the next three times total. Rinse the vacuum flask thoroughly with 2-3 mL of distilled water and pour the rinse water into the casserole. |
| Heat the salt water in the casserole over a bunsen burner keeping the liquid at a constant, gentle boil. Don't let the water boil over the sides. The liquid will start to spatter once some of the water is boiled off, be careful not to let too much spatter over the side. (Some of it will it just can't be helped.) |  |
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The end result should look something like this (picture on the left). You should let it cool for a bit, weigh it heat it then again for a few more minutes and then weigh it again. If the massess have changed radically, then there is still a significant amount of water left and should be heat longer in order to drive off the remainder of the water. |
