Types of Chemical Reactions

Purpose: This lab will demonstrate several different types of chemical reactions. The five chemical reactions that we are currently studying in chemistry are: combination reactions, which are two or more substances combining to form a new substance; decomposition reactions, which are a substance breaking down into two or more different substances or elements; single-replacement reactions, which involve a metallic ion replacing a different metallic ion from an ionic compound; double-replacement reactions, which involve the swapping of metal ions from ionic compounds; and combustion reactions, which involve the presence of heat and oxygen to burn a substance and create new substances. In this lab, we will be engaging in several experiments do demonstrate many of these types of reactions to ourselves.

Data and Calculations:

Reaction	Observation	Reaction Type
Fe + CuSO4	Iron becomes rust-coloured, liquid loses blue color, turns more clear to greenish.	Single-replacement
Pb(NO3)2 + KI	Liquid turns bright yellow, dazzling yellow powdered precipitate can be seen sinking to the bottom of the tube.	Double-replacement
Mg + HCl	Magnesium dissolves in the acid very quickly. Bubbles form, and after they are collected in a large test tube and ignited, a loud “pop” can be heard.	Single-replacement
Electrolysis of H2­O	The negative side of the U-shaped tube with electrodes at each end produces much more gas than the positive side.	Decomposition

Analysis:

2) The following are the equations for each of the reactions.

a) Fe(s) + CuSO₄(aq) → Cu(s) + FeSO₄(aq)

b) Pb(NO₃)₂(aq) + KI(aq) → K₂(NO₃)(aq) + PbI_4­(s)

Pb(NO₃)_2­(aq) + 4KI(aq) → 2K₂(NO₃)(aq) + PbI_4­(s)

c) Mg(s) + HCl(aq) → MgCl₂(aq) + H₂↑

Mg(s) + 2HCl(aq) → MgCl₂(aq)_­ + H₂↑

d) H₂O(l) → O₂(g) + H₂(g)

2H₂O(l) → O₂(g) + 2H₂(g)

5) Please refer to my purpose for my explanations. Here’s more:

There are five types of reactions: combination, decomposition, single-replacement, double-replacement, and combustion reactions. I will start from the top. A combination reaction is one in which two or more elements or substances come together to create a new substance. An example of this is when oxygen and hydrogen combine to form water. A decomposition reaction is when a substance breaks down into two or more substances that used to make up that substance. A great example of this type of reaction is when sugar (C₆H­₁₂O₆) breaks down into carbon (C) and water (H₂O). A single replacement reaction happens when an ionized metal, such as lithium, replaces another cation, such as magnesium, from an ionic compound dissolved in water, such as magnesium chloride. A double-replacement reaction happens when two aqueous ionic compounds, such as sodium cyanide and sulfuric acid, swap their cations, becoming hydrogen cyanide gas, and sodium sulfate. Finally, a combustion reaction is when an element or compound such as magnesium, and oxygen gas are heated together, and create one or more new substances, such as magnesium oxide, and emit heat in the process.

Results/Discussion: This lab was very useful to me in demonstrating all the different types of chemical reactions, so that I could witness them, and see that they actually do work. This visualization of abstract topics that we are studying was a tremendous help in showing me how they work. In the iron and copper sulfate experiment, I could clearly see the solid becoming red, and the blue tint leaving the liquid, which was proof that the copper was being replaced by the iron in the ionic compound. The experiment that formed the yellow precipitate was a bit puzzling, since I did not really know which product was the solid, and which was the liquid. The electrolysis decomposition experiment immediately showed how water decomposes into oxygen and hydrogen, since gas bubbles started rising instantly after the experiment is started. One side produces much more gas than the other, and I think that the greater gas produced is hydrogen, because in the balanced equation (2H₂O(l) → O₂(g) + 2H₂(g)), two hydrogen molecules are produced from water, compared with only one oxygen molecule. Some potential errors that may have occurred during the course of the lab is mixing the wrong chemicals together, or waiting too long to capture the hydrogen from the magnesium and HCl experiment, resulting in the failure to notice the hydrogen gas being formed.