Purpose:

The purpose of today's lab is to completely separate a mixture into its components using only physical means.  Your mixture will contain three components:  (NH₄)₂CO₃ (ammonium carbonate), NaCl (sodium chloride or salt), and colored sand.  Two of the components:  ammonium carbonate and sodium chloride are white powders and would be difficult to separate using say a pair of tweezers and a magnifying lens.  However, the other component, colored sand, could probably be separated this way (but that is a story for another day).

You will be using a combination of physical properties to quantitatively separate these components. To remove the ammonium carbonate, you will take advantage of the fact that it sublimes at a very low temperature.  You will heat the entire mixture and the ammonium carbonate will turn into a gas leaving the salt and sand behind.  Next, you will use the fact that salt is very water soluble, but the sand is not.  You will add water to the salt and sand that remains and this will dissolve the salt leaving the sand behind.  You will then  'decant' the water leaving the sand behind.  After you dry the sand, you will determine its mass.

Constructing an aluminum weigh boat:

1. You will want to carry out the ammonium carbonate sublimation in an aluminum boat.  But we are VolState, so you will have to make your own.
   
2. Obtain a pre-cut piece of heavy gauge aluminum foil.
3. Use  your 250 mL beaker as a mold and fold the aluminum foil around the base until you obtain something like the figure below (use a pair of scissors to trim your boat).  Make sure the bottom is flat and that the sides are as smooth as possible to make it water tight.   (Note:  the photo below shows two types  of commercially (i.e., more money than we want to spend) available weigh boats....I don't expect yours will look quite this finished, but they do give you the idea of what you are after).
   

1. Accurately weigh your aluminum boat to the nearest 0.001 g.  (Note:  ALWAYS report every digit from the balance).
   
2. On the back bench, you will find four containers labeled A, B, C, and D.  Pick one and shake it vigorously for 10-20 seconds to make sure it is evenly mixed (homogeneous).
3. Accurately weigh (0.001 g) about 5 grams on one of your mixture into your aluminum boat and reweigh.  (Note: ALWAYS remove the boat from the balance before adding or removing mixture; then put the boat back onto the balance).
   
4. Place your boat and mixture on your hotplate and crank the temperature up to about half way.  Adjust the snorkel hood so it is about a foot above the hot plate.  This will remove any toxic vapors as the ammonium carbonate sublimes.
   
5. You may or may not see any vapor as the ammonium carbonate sublimes, but keep heating for about five to ten minutes.  However, if you start to see any tan color forming in the boat, then stop heating and remove the aluminum boat and let it cool.
   
6. Use your crucible tongs to remove the aluminum boat and allow it to cool to room temperature.
7. Weight the boat to the nearest 0.001 g.
8. If you subtract this weight from the weight is Step #2, you will have the mass of ammonium carbonate in your mixture.  Q.E.D.
   

1. Now your boat contains salt and colored sand.  You will separate them by dissolving the salt with water, leaving the sand behind.
2. Carefully add about 5 mL of distilled water to your 'boat' and use a disposable pipette to stir it around.
3. Use the disposable pipette to remove as much as the water as you can.  (Note:  be very careful that you do not remove any of the sand!)
   
4. Add another 5 mL of distilled water and rinse the boat again to make sure all of the salt has been removed.
5. Repeat Steps #2 through #4 as necessary until all of the salt has been removed.
   
6. Remove as much as the water as you can with the disposable pipette.
7. Now heat your boat on your hotplate for about 15 minutes to remove any traces of water.  (Note:  if you see any white spots appear, that means you did not remove all of the salt).
8. Let your boat cool to room temperature and weigh it.  (Note:  it is VERY important that an object is at room temperature before you weigh it!)
   
9. At this point, we are not sure that all of the water has been removed, so we will heat it again on the hotplate for another 10 minutes.
10. Let your boat cool to room temperature and weigh it.
11. If the weight from Step #10 and Step #8 are within 0.01g of each other, you are done heating.  If not, you will need to heat your boat a third time.
12. Now the mass of sand is the mass from Step #1 minus the mass in Step #10.  Q.E.D.
13. Believe it or not, the colored sand is fairly expensive, so your instructor will be collecting it so we can use it again.
    

1. There are a number of chemical means to independently determine the amount of sodium chloride in your mixture.  However, due to safety and time constraints, you will determine the amount of sodium chloride by difference.
2. From the above procedures, you know the weight of the original mixture.  You also know the weight of the ammonium carbonate in the mixture, and the weight of the sand in the mixture.  Therefore, the amount of sodium chloride is simply the weight of the mixture minus the weight of the ammonium carbonate and the weight of the sand.
3. Note:  if you made mistakes in the amount of ammonium carbonate, or the sand, this will cause an error in your amount of salt.
   

OK, let's work through an EXAMPLE (your numbers will be different!!) assuming that you obtained the following data:

So, what is the % of each component?

First we need to calculate the mass of the original mixture:

Likewise, we can calculate the mass of the sand:

mass of sand  =  [E]  -  [A]  =  5.300 g  -  5.000 g  =  0.300 g

We can then determine the mass of the salt, by subtracting the mass of the ammonium carbonate and the mass of the salt from the original mass of the the mixture:

mass of salt  =  original mass of mixture  -  mass of ammonium carbonate  -  mass of sand

mass of salt  =  1.500 g  -  0.400 g  -  0.300 g  =  0.800 g

Now that we have the mass of each component, we simply divide each by the total mass of the mixture and multiple by 100 to get the percent::