0.3 Going green with al  (Page 2/3)

Experimental Procedure

Wear safety goggles at all times during this lab.

Wear gloves when using concentrated acid and base.

For this experiment there are two samples of aluminum that will be used. Some of the steps will be the same for both cans, but some will be different so it is essential that you keep track of the samples. The best way to ensure there is no confusion is for Group A to do the experiment with sample #1 and Group B to do the experiment with sample #2. However, it is still important to understand what your other group is doing so try to be as involved as possible as you are carrying out your part.

Sample #1 (Group A)

Part 1: Preparation of Alum

1. Cut a 5cm x 5cm square piece of aluminum from a scrap aluminum can and sand the paint off using steel wool.
2. Cut this piece into smaller pieces (about 0.5 cm long) and weigh out ~0.5 g. Record the weight to 3 decimal places.
3. Place the aluminum in a 400-mL beaker and add 25 mL of 4 M KOH.
4. Place beaker on the heating mantle and heat gently.

CAUTION - H 2 GAS (VERY EXPLOSIVE) IS PRODUCED.ENSURE THAT YOU ONLY HEAT THE BOTTOM OF THE BEAKER

1. When the bubbles have stopped, remove from the heat.
2. Vacuum filter the solution. This is done by taking a filter funnel, placing a piece of wet filter paper in it, placing the funnel in a vacuum flask, and attaching the flask to the vacuum line, labeled “vac” on the outlet taps . Save the filtrate (the liquid inside the filter flask). You may dispose of the solid in the marked waste beaker.
3. Clean the 400 mL beaker you used before and pour the filtrate into it.
4. Carefully, rinse your 100 mL graduated cylinder. Dispense 15 mL of 3 M H ₂ SO ₄ into it, which you will then add to the filtrate.

CAUTION - H 2 SO 4 IS A STRONG ACID AND DEHYDRATOR.  SEE TA IMMEDIATELY IF YOU SPILL ANY! 

USE EXTREME CAUTION WHEN CLEANING YOUR GRADUATED CYLINDER AFTER IT HAS COME INTO CONTACT WITH THE SULFURIC ACID. BE SURE TO WEAR GLOVES WHILE HANDLING IT AT ALL TIMES!!

1. A white powder of Al(OH) ₃ should form.
2. Vacuum filter this solution, using a clean piece of weighing paper, and save the solid Al(OH) ₃ .

Part 2: Qualitative Analysis of Alum

1. Use a spatula to transfer a few of the Al(OH) ₃ crystals (about 5 mg) to a watch glass. Add 3 drops of water to the crystals. Stir gently until the crystals dissolve.
2. Use a small piece of indicator paper to see whether the solution is acidic, basic, or neutral.
3. Now add 1 drop of 0.5 M BaCl ₂ (barium chloride) to the solution. Record your observations.
4. As you now know, a really good test for the presence of potassium is a flame test. Using the hot grips, hold a spatula in the flame of a Bunsen burner to volatilize impurities from the spatula.
5. When one end of the spatula is red hot, remove it, and quickly touch it to a small cluster of crystals. Several should stick.
6. Slowly bring the spatula (plus crystals) toward the flame and watch carefully. Hold the crystals in the flame for at least 5 seconds (until the solid glows). Record your observations.
7. Dispose of the Al(OH) ₃ and related compounds in the marked waste beaker.