Purpose: The purpose of this lab is for students to observe various changes that take place in a chemical laboratory, both physical and chemical. Students will determine if a given change is physical or chemical and will write the chemical reaction for the observations that they make.
Introduction: According to Dalton, a chemical change is the combination, separation, or rearrangement of atoms. However, when a reaction is observed, individual atoms cannot be seen. Therefore, we need some sensible guidelines to determine whether a change is chemical or physical. A change is usually chemical if properties of the system change. For example, if a solution changes color, if a solid (precipitate) forms, if a temperature change occurs, if a gas is formed, then the change is probably chemical. This is because in a chemical change, new substances are formed. A physical change produces no new substances. Therefore when a substance melts, freezes, condenses, vaporizes, sublimates, deposits, changes shape, as long as it is the same substance before and after the change, it is undergoing a physical change.
Review the appropriate concepts in your text book before performing this lab.
Types of chemical reactions
In this lab you will observe many changes and you will determine if each change is a physical or chemical change. If the change is chemical, you will show the chemical reaction that is taking place. If the change is physical, you will show the phase change as a reaction as well. As seen below in the examples, the chemical reactions show the reactants on the left side of the arrow, and the products on the right side of the arrow. The reactants are the substances that we start with, the products are what are formed after the change.
Ex. The chemical change of the hydrolysis of water
H2O (l) --> H2 (g) + O2 (g)
Ex. The physical change of the evaporation of ethanol
C2H5OH (l) ---> C2H5OH (g)
1. Zinc and copper (II) sulfate vs copper and zinc sulfate
In this experiment, a piece of solid zinc metal is placed in a container with a solution of copper (II) sulfate. In a separate container, a piece of copper metal is placed with a solution of zinc sulfate. Only one of these systems will react (you will learn more about this in the redox chapter.) Note the appearance of the reactants before and after the process for both systems. Determine which system reacts and write the equation for the reaction that occurs.
Zinc metal + copper(II) sulfate ---> copper metal + zinc sulfate
Copper metal + zinc sulfate ---> zinc metal + copper(II) sulfate
2. Heating of sodium chloride
In this experiment, solid sodium chloride is heated past its melting point. Note its appearance and state before and after and determine the change it undergoes.
Sodium Chloride ---> Sodium Chloride
3. Heating of copper(II)sulfate pentahydrate
In this experiment, solid copper(II)sulfate pentahydrate is heated until the color changes. After heating, water is added to the substance. Note its appearance before heating, after heating, and after the addition of water to the heated product, and determine the change the substance undergoes.
Copper(II)suflate pentahydrate ---> Copper (II) sulfate + water
Copper (II) sulfate + water ---> copper (III) sulfate pentahydrate
4. Ignition of magnesium metal
In this experiment a ribbon of solid magnesium metal is set on fire. Note its appearance before and after it burns, and determine the change it undergoes. Also, based on your life experience, do you anticipate that this process is exothermic (heat energy is
eleased in the process) or endothermic (heat energy is absorbed in the process.)
Magnesium metal + oxygen ---> magnesium oxide
5. Magnesium with hydrochloric acid
In this experiment, magnesium metal is reacted with hydrochloric acid. Note appearance of reactants and products at the beginning and at the end of the reaction, and note what happens during the reaction. Determine the change it undergoes and google this reaction to see if it is endothermic or exothermic. What would you expect the reaction container to feel like once the reaction is complete?
Magnesium metal + hydrochloric acid ---> magnesium chloride + hydrogen
6. Copper (II) sulfate with sodium carbonate
In this experiment, a copper (II) sulfate solution is mixed with a sodium carbonate solution. Note the appearance of the solutions before the reaction and after. Determine the type of change that occurred.
Copper (II) sulfate + sodium carbonate ---> copper (II) carbonate + sodium sulfate
7. Heating and cooling of iodine
In this experiment, solid iodine is heated until it sublimates and then the gas undergoes deposition when it comes in contact with the cold flask. Note observations through the processes. Determine the changes that occurred.
Iodine ----> Iodine
Iodine ----> Iodine
This material may consist of step-by-step explanations on how to solve a problem or examples of proper writing, including the use of citations, references, bibliographies, and formatting. This material is made available for the sole purpose of studying and learning - misuse is strictly forbidden.Table of Reactions and Observations:
Reaction 1: Zinc and copper (II) sulfate vs. copper and zinc sulfate
• Observations of zinc in copper (II) sulfate (before/during/after):
Before the reaction, CuSO4 solution is blue and zinc is shiny-silvery colored. During the reaction, the color of the solution gets paler as reaction goes on and the metal piece starts to change its color to black. After the reaction is complete, the solution was colorless and some reddish-brown solid formed on the surface of the metal piece.
• Observations of copper in zinc sulfate (before/during/after):
At the beginning, the solution is...