Scratch

Purpose
    The purposes of this laboratory were to: 
1) make observations while watching materials interact and undergo change,  and
2) record these observations as qualitative or quantitative.

Materials and Methods
    The procedures were followed exactly as written for Experiment 2A on pages 10-11 of Essential Experiments by Morrison and Scodellaro, with the following exceptions:
1) one beaker was used instead of three; and
2) one test tube was used instead of two.

Observations
    When the mossy zinc was put into the water for Part I of this experiment, no reaction occurred.

Table 1.  Summary qualitative and quantitative observations when mossy zinc was dropped into a beaker filled with water.
Qualitative Observations
Quantitative Observations (if any)
No reaction occurred.
N/A


    On the contrary, when the calcium metal was dropped into the water, it immediately started to produce gas.  This was proved by removing the test tube and lighting a flame above the open end of the tube.  There was an audible pop, signifying that the gas was hydrogen gas.  Also, a white precipitate was formed in the water.  This solution was basic because the pH of the final result was above 8.1 as seen when tested with the use of phenolphthalein because it turned bright red.

Table 2.  Summary of qualitative and quantitative observations when calcium metal was dropped into a beaker filled with water with a test tube covering the metal.

Qualitative Observations
Quantitative Observations (if any)
Solution was basic
pH was above 8.1
Produced gas
Produced more than 50 mL 
Metal dissolved in water
N/A
Gas popped when exposed to flame
N/A
Solution turned cloudy
N/A


    After placing the roll of aluminum into the copper chloride solution,  many reactions occurred.  The aluminum began to decompose into a bright red substance, and heat was produced.  The thermometer read 61°C, rising from 20 degrees. when the mixture was at the highest temperature.  The solution turned from blue to dark green, and a purple gray precipitate began to form at the bottom of the beaker.

Table 3.  Summary of qualitative and quantitative observations when a roll of aluminum was dropped into a beaker filled with copper chloride solution.

Qualitative Observations
Quantitative Observations (if any)
Produced heat
61°C at highest
Solution turned from blue to green
N/A
Aluminum decomposed
N/A
White precipitate formed
N/A
Smelled bitter
N/A
Gas rose from beaker
N/A





Results
    There was no reaction between the zinc and water in Part I of this experiment.  The equation for the reaction is shown below.

Zn + H2O →  no reaction

The zinc was not 

    The reaction between the calcium metal and the water in Part I of this experiment is explained by the equation

Ca(s) + 2 H2O → H2 + Ca(OH)2

where the gas produced was H2, and the white precipitate that formed in the water was Ca(OH)2.  The two molecules of water broke up into two hydrogen anions which combined to form hydrogen, and one hydroxyl which bonded with the calcium metal.
    The reaction between the copper(II) chloride solution and the aluminum metal in part II of this experiment can be represented by the equation

3 CuCl(aq) + 2 Al → 2 AlCl3 + 3 Cu

This formed the copper that colored the solution.  The chlorine atoms detached from the copper, and reacted with aluminum to form aluminum chloride, leaving the copper to be unbonded.  Before the aluminum reacted with the chlorine, it became molten aluminum.  This explained the exothermic increase in temperature, where the energy gained from the transfer of electrons became heat.  This copper reacted with hydroxide ions in the water to form copper hydroxide:

Cu + (OH) → Cu(OH)

 The copper hydroxide was an aqueous solution, and, as the Cu(OH) settled, a white precipitate formed at the bottom of the beaker.  After a few hours, the copper hydroxide would completely sink, leaving the solution to be clear, with a white precipitate at the bottom.  By taking extra hydroxide ions from water, the solution became acidic.
    The aluminum chloride reacted with water:

AlCl3 (aq) + 3 H2O → Al(OH)3 + 3 HCl

producing aluminum hydroxide and hydrochloric acid.  

Conclusion
    During this lab, it was noted that zinc did not react with water, the calcium dissolved in water to produce hydrogen gas, and the aluminum melted in the copper chloride to form many chemicals including aluminum chloride and copper hydroxide.  These observations were classified into quantitative and qualitative categories.

Questions
1. To figure out the amount of gas produced in a chemical reaction, an inverted container filled with liquid could be placed over the reaction, and by measuring the amount of liquid that was displaced, the amount of gas produced could be found.

2. Phenolphthalein is a compound which changes color depending on the acidity of the material that it touches.  When its pH is above 8.1, it turns bright red, otherwise, it is colorless.  It is commonly used for testing pH levels; however, it is not very accurate, since it can only tell if the substance is acidic or basic – but not the specific pH of the substance.