1. Analysis of alum

2. objectives
To determine the percentage of water in alum hydrate To develop the laboratory skills for analyzing a hydrate

3. discussion
What is a hydrate ? An operational definition for a hydrate is a compound that has a fixed number of water molecules. The number of water molecules is referenced as water of crystallization or water of hydration. An example according to your lab is barium chloride dihydrate , BaCl2.2H2O.

4. discussion
This lab is about the decomposition of alum, a compound used in styptic pencils to stop bleeding of minor cuts. Reaction: KAl(SO4)2.12H2O (s)---- (heat) KAl(SO4)2(s) + 12 H2O (g) Alum hydrate delta anhydrous compound water of crystallization

5. discussion
Calculation: Example Exercise 1 – Theoretical % of water in Alum 1 K = g 1 Al = g 2 (SO4) x g = g 12 (H2O) x g = g g (Total) g/ g x 100% = 45.58% water

6. discussion
Calculation (2): According to lab example A sample of alum has a mass of g and loses g of water when decomposed by heating. Calculate the experimental percentage of water . Mass of water/mass of hydrate x 100% = % water g/1.150 g x 100% = 45.5% water

7. Equipment and chemicals
Wire gauze alum, Kal(SO4)2.12 H2O 250-mL beaker watchglass

8. Procedure Percentage of Water in Alum Hydrate
Weigh a clean, dry, 250-mLbeaker covered with a watchglass. Add about
g alum hydrate into the beaker, and reweigh accurately.
2. Support the beaker and watchglass on a ring stand using a wire gauze ( Figure 1).
Heat the hydrate gently, and you should observe moisture on the sides of the beaker and bottom of the watchglass. Continue heating until all the moisture is evaporated.
When the hydrate is completely decomposed, it will change from crystalline to powder.

9. p