Decomposition

12/09/96

Purpose: In this lab we will observe the products of decomposition of potassium
perchlorate (KClO4). We will then predict from our results the correct chemical
reaction equation.

Procedure: 1. Weigh out about 4.0g of KClO4 in a test tube. Record the
accurate weight below. Product Weight Before Weight After Mass of Test tube +
KClO4 41.5g 39.8g Mass of Test tube 37.5g 37.5 Mass of KClO4
4.0g 2.3g 2. Set up the apparatus shown below.

3. Gently heat the test tube containing the potassium perchlorate. Gas should
begin to collect in the collection bottle. Record all observation. 4. Once the
reaction is complete, no more gas give off, allow the test tube to cool. While
the test tube is cooling test the gas in the collection bottle with glowing
splint. Caution: Do not leave the rubber tubing down in the water trough during
cooling or you will experience back-up. 5. After the test tube has
cooled weigh it on a balance. What is the change in mass?

Observations: Oxygen flowed from the test tube into the bottle of water, forcing
the water out. Burning ember re-ignited when placed into the bottle of O2.

Calculations: 1. The number of moles of KClO4 that we began with is .03 moles.
4.0g ¸ 138.6g/mol = .03 moles 2. The number of moles of O2 that were present in
our sample of KClO4 was .06 moles. 1.9g ¸ 32g/mole = .06 moles 3. The number of
moles of O2 lost is .02 moles. 1.7g ¸ 32g/mol = .05 moles 4. KClO4 à KCl + 202
4.0g ¸ 138.6g/mol = .03 moles ´ 202 ¸ KClO4 = .06 moles ´ 32g = 1.9g 5 Percent
Yield: 89% O2 lost 1.7g ¸ O2 Expected 1.9g

Category: Science