Analysis of Alum
* In this lab we performed several tests to determine if our crystals were actually aluminum potassium sulfate. * Procedures:
* Aluminum potassium sulfate, 2.5 g
* Equipment – Part 1:
* 150 mL beaker
* Bunsen burner
* 2 capillary tubes
* Mortar and pestle
* Notched stopper to hold thermometer
* Ring stand
* Rubber band
* Universal clamp
* Equipment – Part 2:
* Balance, .001 g precision
* Bunsen burner
* Crucible and cover
* Crucible tongs
* Ring stand, ring support
* Wire gauze
* Procedure - Part 1. Melting Point Determination of Alum: * Pulverize 0.5 g of dry alum.
* Pack alum in capillary tube. Push open end of capillary tube into pile of alum. * Turn tube so the open end is up, and bounce the bottom of the tube on the desktop several times. * Fasten tube to thermometer with rubber band.
* Use thermometer clamp and notched cork stopper to fasten the thermometer to ring stand. * Immerse bottom of capillary and thermometer in beaker of water and heat. * Record temperature range at which alum melts in data table. * Repeat melting point determination, using new sample of alum and new capillary tube.
* Procedure – Part 2. Determination of the Water of Hydration in Alum Crystals * Set up Bunsen burner on ring stand beneath a ring clamp holding a clay pipe stem triangle. * Adjust height of ring clamp so that bottom of crucible sitting in clay triangle is 1 cm above burner. * Place crucible with cover in clay triangle and heat over burner flame until crucible is red hot. * Turn off gas and remove burner.
* Using crucible tongs, remove crucible cover and place it on wire gauze on tabletop. Using tongs, remove crucible from clay triangle and place it on wire gauze. * Allow crucible to cool for 10 minutes.
* Use analytical balance to find mass. Handle with tongs to avoid getting finger prints on crucible and lid. * Record mass in data table.
* Add 2 g of alum crystals to crucible. Weigh crucible, cover, and crystals and record mass in data table. * Set crucible at angle in triangle held in ring on ring stand. Cover crucible loosely with crucible cover, and heat gently. Alum will melt, and water of hydration will evaporate. * After bubbling has stopped, heat sample more strongly for five minutes. * Turn off gas and remove burner.
* Using tongs, remove crucible cover and place it on wire gauze on tabletop. With tongs, remove crucible from clay triangle and place it on wire gauze. * Allow crucible to cool for 10 minutes.
* Measure and record mass of crucible, cover, and anhydrous alum. * Repeat procedure until constant mass is obtained. * Record final mass of crucible, cover, and anhydrous alum in data table. * Dispose of anhydrous alum. Clean crucible and cover. * Procedure – Part 4. Flame test for the K+ Ion
* Crush small sample of alum crystal.
* Heat flame loop red hot in Bunsen burner flame and then plunge loop in 0.5 M HCl. Repeat. Heat loop to red hot one more time. * Pick up small sample of crushed alum on the hot loop and move it slowly from outer edge to the hottest part of the Bunsen burner flame. * Observe and record the resulting color of the flame test. * Data Collection:
* Part 1 Data Table:
| Trial #1
Measured melting point
| 92.5 ℃
Literature melting point
| 92.5 ℃
* Part 2 Data Table:
Mass of crucible and cover
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