Lab Report

Topics: Water, Hydrate, Water of crystallization Pages: 5 (1100 words) Published: November 26, 2012
Chemistry Lab Report

Water Hydration


A hydrated crystal or hydrated occurs when water becomes tightly attracted to a metal salt base on it’s polarity. The water molecules maintain integrity as molecules, however they are considered to be part of the formula of the hydrate. When the hydrate metal salt crystal is heated, the attractions to the water are broken by the heat energy and the water escape from the crystal. After heating the salt crystal is called as anhydrous, which means without water. Many of the salt contain transition metals such as cobalt that is colorful (purple). Often the color of transition metal like cobalt’s color will change as a function of how many waters it is attracted to. Compounds containing water (H2O) of hydrated are written with water separate by a dot (.). This (.) means for hydrated metal salt there are how many number of moles of water bound to each mole of that metal salt.

Research Question:

The aim of this experiment is to calculate the number of moles of water bounded to each mole of cobalt chloride ( CoCl2. H2O). This cobalt chloride hydrated may be monohydrate with 1 mole of water attracted to cobalt chloride. It may be dihydrate, trihydrate, tetrahydrate or pentahydrate; your task is to determine which one you are given.


If cobalt chloride were heated until there is no further lose in weight, 6 moles of water would be lost from 1 mole of salt. Therefore it is predicted that there are 6 moles of water in this reaction.

Materials (Apparatus):

1. 3 gram of cobalt chloride
2. Evaporating dish
3. Tongs to hold the evaporating dish
4. Ring stand
5. Iron ring
6. Clamp
7. Bunsen burner
8. Matches
9. 40.20 g size of the crucible
10. Digital balance/ g 0.01
11. Clay triangle
12. Gloss rod

1. Place an empty crucible on digital balance by uncertainty of 0.01g 2. Measure the size of the crucible without salt
3. Add 3 gram of cobalt chloride to the crucible
4. Measure the total size of crucible containing cobalt chloride 5. Take the crucible containing salt, place it on the Bunsen burner by tongs. Place crucible on a clay triangle and iron ring to protect the crucible from falling. 6. Gently heat the crucible by Bunsen burner

7. Use a gloss rod to give a movement to cobalt chloride to crystalized. 8. Record time for salt crystallization
9. Stop heating when cobalt chloride crystalized
10. Wait for few second for crucible to cool down
11. Place and Measure the anhydrous crucible by digital balance 12. Using calculation find the number of moles in this reaction.

CoCl2 .nH2O CoCl2 + nH2

Data Collection and Processing:

Process| Observation during the experiment |
Changes in color | As we started heating the crucible containing CoCl2. H2O , the color of the CoCl2 started to change from violet purple to dark purple and the blue in 6 minutes and it is because of water evaporation. | Appearance of the salt during heating | After 3 to 5 minutes, as water was evaporating and reaching its melting and boiling point, salt began to bubble. At the beginning of heating it was powdery solid then it changed to liquid and at last solid again. Volume of salt decreases because of lost of molecules. We waited for 10 minutes until it cooled down. |


Raw data collected

Mass| Grams | Uncertainty /g ±0.01|
Crucible| 42.20 g| 0.02 %|
Pure H2O | 1.36 g| 0.73 %|
Pure CoCl2| 1.66 g | 0.60 %|
| | Total uncertainty |
| | 0.08 %|

Find the masses:

Crucible + CoCl2.H2O = 45. 23 g

Anhydrous = 43.86 g

Mass of pure H2O = 45.23 – 43.28 = 1.36 g

Mass of pure CoCl2 = 3.02 – 1.36 = 1.66 g

Find the uncertainty:

CoCl2 = 1.66 = 0.01 = 0.60 %
100 x

H2O = 1.36 = 0.01 = 0.73 %
100 x

Crucible = 42.20 = 0.01...
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