Lab 9 Determination of a Chemical Formula PDF

Preview

Summary

Lab 9 Determination of a Chemical Formula...

Description

Jade Boyd

Chem 111 Lab 11/26/16

Determination of a Chemical Formula

The objective of this experiment was to find the formula of a chemical compound. To find the formula we find the mass of each of the elements in a weighed sample of that compound. We then take the mass of each of the elements and use them to make a ratio of each of the elements to each other and use that to form the compound. In this experiment, we used these principles to find the formula of the compound with the general formula Cu x Cl y * z H2O

First we placed one gram of hydrated copper chloride in a clean, dry crucible. We placed the crucible on a clay triangle supported by an iron ring and lit the bunsen burner. We heated the crucible by moving the bunsen burner back and forth. As the sampled warmed, we saw the green crystals begin to change to brown around the edges. We continued heating until all the crystals changed to the anhydrous brown form. 2 minutes after the crystals were all brown, we removed the burner and we covered the crucible to minimize rehydration and let it cool for 15 minutes. Then we weighed the crucible and its contents and transferred the brown crystals into a beaker and added 5-7 mL of water to rinse the crystals off the crucible. The crystals turned green as they rehydrated. We then formed a .25 g of aluminum wire into a spiral and immersed the coil completely in the solution. The coil began to bubble because of the release of hydrogen gas and began to look fuzzy and red because of the formation of copper metal. The solution began to fade in color. Within 30 minutes the reaction was complete. The solution was almost clear. We added 6 M Hal to dissolve any insoluble aluminum salts. After removing and cleaning the wire, we used a Buchner funnel to separate the copper from the solution. After the solution and copper were separated we dried the copper and funnel paper in a heat lamp and accurately weighed them. The following is a chart with all our data.

Atomic Mass of Copper

63.546 g

Atomic Mass of Chlorine

35.45 g

Atomic Mass of Hydrogen

1.008 g

Atomic Mass of Oxygen

15.99 g

Mass of Crucible

62.021 g

Mass of Crucible and Hydrated Sampled

63.045 g

Mass of Hydrated Sample

1.024 g

Mass of Crucible and Dehydrated Sample

62.835 g

Mass of Dehydrated Sample

.814 g

Mass of Filter Paper

.177 g

Mass of Filter Paper and Copper

.523 g

Mass of Copper

.346 g

No. Moles of Copper

.00544 moles

Mass of Water Evolved

.445 g

No. Moles of Water

.024713 moles

Mass of Chlorine in sample

.468 g

No. Moles of Chlorine

.01320 moles

Mole Ratio, Chlorine:Copper in Sample

2:1

Mole Ratio, Water:Copper in Hydrated sample

2:1

Formula of Dehydrated Sample

CuCl2

Formula of Hydrated Sample

CuCl2 * H2O

The following are the formulas used in this experiment.

To find the mass of the hydrated sample: (Mass of hydrated sample and crucible)-(mass of crucible) To find the mass of the dehydrated sample: (mass of crucible and hydrated sample)-(mass of crucible) To find the mass of copper (Mass of filter paper and copper)-(mass of filter paper) To find the # of moles of copper: Mass of copper/atomic mass To find the mass of water evolved: (mass of hydrated sampled)-(mass of dehydrated sample) To find the # moles H2O: Moles of H2O/ Atomic mass To find the mass of chlorine in the sample: (mass of dehydrated sample)-(Mass of copper)

This experiment taught me how to find the formulas of the chemical compounds we have been working with all semester in our lab. It went smoothly but I can see that mistakes could be made if people weren't precise in their measurements or calculations....