Chemical Reactions

Introduction/ Background

The purpose of this lab is to observe the different reaction types and the macroscopic events they caused. These reactions include decomposition, synthesis, single replacement, double replacement, and combustion. Synthesis is where two or more substances combine to form a single product, in a decomposition reaction a compound breaks down to form two or more simpler substances, in single replacement one element takes the place of another compound metal takes place of a metal, in double replacement the positive and negative portions of two ionic compounds interchange two metals are replaced by two metals, and in a combustion reaction a substance rapidly reacts with oxygen to form one or more oxides and releases energy. Through this experiment we were able to observe three of these reactions which we will identify further on.

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We began by obtaining 3 test tubes, a test tube rack, a test tube holder, a bunsen burner, and other needed the materials. We then put on our safety equipment and began the experiment!

We added approximately 1/2 ml. of CuSO4 to one of the beakers. A small amount of Zinc was added to the solution and was closely observed. Bubbles were almost immediately visible and that the zinc was changing a dark rust color and later on seemed to begin breaking down. We tested for hydrogen gas and were assured none was being released. This leads us to assuming that this reaction represents the equation Zn+CUSO4 -> ZNSO4+CU and is a single displacement reaction type. In this it is obvious that the SO4 stays in place from start to finish with the only change being the switch between the copper and zinc ions and referring back to the top a single displacement reaction is when one element takes the place of another which is what we see in this reaction.

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For the next mixture we will be using approximately 1/2 ml. Ba(NO3)2 and 1/2 mL of CuSO4. After mixing them together we noticed immediately the formation of a white foam separating itself from the darker blue solution. Our hypothesis was that the equation of this reaction is CuSO4 + Ba(NO3)2 --> BaSO4 + Cu(NO3)2 and the reaction type is the double displacement reaction type. As you can see the Cu and Ba ions replace each other on the SO4 and (NO3)2 ions. Double displacement is two ionic compounds interchanging two metals thus our reasoning.

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In the third experiment we placed some magnesium in about 1/2 mL of HCL solution. This proved to be a very interesting mixture and immediately bubbles were noticeable. We tested for hydrogen gas and found that there was indeed hydrogen gas being released from the still active bubbles. The most fascinating part of this experiment was the heat produced by the mixture and was the major source of our hypothesis. The equation for this is Mg2+HCl= Mg+HCl2 and is a combustion reaction due to the energy produced creating the heat we observed.

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The last experiment we conducted used H2O2 mixed with MnO2. As soon as the two were mixed the otherwise clear H2O2 turned to gray then to a black color within a few seconds. The bubbles were very intense and if heated to quickly it would bubble out of control as some individuals discovered. The chemical equation of this is 4H2O2+MnO2 → 2O2 + 4H2O+MnO2 and we know this to be a Decomposition reaction. As you can see on the right side of the equation H2O2 has lost one oxygen creating H2O and producing O2. Just as the decomposition reaction is defined as a compound breaking down to form two or more simple compounds so does H2O2 break down to form the simpler compounds O2 and H2O.

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Conclusion

As you can see each of the five reaction types has specific characteristics in what happens when one mixes two compounds together. This is what allowed us to determine what type of reactions each one was and what its chemical equation turned out to be.

Please click for clearer image of the data table.