These are background information provided by students in previous semesters. This is the absolute minimum that should be included in a lab report. The more detailed the report, the higher the grade. Also note that none of them provide a bibliography.
386 - Determining the Empirical Formula of Copper
Chloride
I. Purpose- To determine the empirical formula of a compound
containing only copper and chlorine.
II. Background- The simplest whole-number ratio in which kinds
of atoms combine to form a compound is called the empirical
formula of that compound.
The laws of chemical combination were formulated in the early part of the 19th century. They are a result of the first use of quantitative measurement in chemistry.
In 1799, Joseph Proust proposed the law of definite proportions (also called the law of constant composition). The law states that compounds contain elements in certain fixed proportions and in no other combinations, regardless of the method of preparation. Thus, chalk, or calcium carbonate, is always 40% calcium, 12% carbon, and 48% oxygen, by weight.
If the stoichiometric formula of a pure compound is known, its percentage composition may easily be calculated. To establish the empirical formula of an unknown but pure chemical compound when the weight percentages of its constituent elements are determined (such as by chemical analysis). Whereas a stoichiometric compound has a definite, fixed composition, a mixture can have an infinitely variable composition.
Most compounds are stoichiometric; that is, they have a fixed composition. A few solid inorganic compounds do not have constant, integral ratios of atoms, however, and mixtures have infinitely variable compositions.
III. Cautions-Wear approved eye protection while in the
lab. Copper chloride solution is toxic and irritant. 10% Hydrochloric
acid solution is toxic and corrosive. Aqueous copper chloride is a
toxic, irritating solution. Avoid contact with your eyes, skin, and
clothing. Avoid ingesting the solution. The reaction between Zn metal
and copper chloride solution is quite exothermic. Hence, the beaker
and the solution may become quite warm or even hot. Avoid burning
your hands while handling the beaker. Wash your hands thoroughly with
soap or detergent before leaving the laboratory.
Lab #396: Introducing the Qualitative Analysis of a Group of
Cations
I. Purpose- The experiment will help develop a procedure using chemical reactions to detect the presence of barium, lead (II), and iron (Ill) ions in a solution.
II. Background- Chemists often need to know what specific
ions and of what concentration they exist in a sample of an unknown
inorganic compound. To determine the specific ions in a sample
chemists rely on qualitative analysis. To determine how much ions are
in the given solution a quantitative analysis is also needed.
Qualitative analysis often uses a visible characteristics~olor, but
mostly uses characteristics pertaining to chemical reactions. These
precise chemical reactions help to reveal chemical characteristics
such as the formation of insoluble substances or soluble complex
ions, This particular experiment will use a sequence of reactions to
separate and identify three metal cations - barium ion, lead (II)
ion, and iron (III) ion.
Before doing this experiment a basic understanding of new terms and
concepts must be made. Qualitative analysis - analysis of chemical
data to determine chemicals present in a solution. Quantitative
analysis-uses exact amounts of ions present by using stoichiometry of
the reactions involved in the qualitative analysis. Molecular
equation - the equation for the reaction that shows all species in
their undissociated forms. Complete ionic equation or ionic equation
- shows all of the ions from the dissociated substances, as will as
the undissociated substances. Spectator ion - any ion that does not
appear to be directly involved in the reaction. Net ionic equation -
the equation that focuses only on those ions and compounds that are
directly involved in the reaction.
III. Cautions- As with all labs safety goggles should be
worn at all times to help reduce risk of serious injury. Chemicals
used in this lab present dangers; barium nitrate is toxic and an
oxidant, hydrochloric acid is toxic and corrosive, iron (III) nitrate
is irritant and an oxidant, lead (II) nitrate is toxic irritant and
an oxidant, potassium thiocyanate is toxic, and sodium sulfate is
irritant. This lab requires mixing substances in an open test-tube. A
lab student should never put fingers or thumbs over the mouth of a
test-tube while mixing solutions. The lab instructor will provide
examples of proper procedures of mixing substances in test-tubes. As
always, listening to instructions, familiarizing one's self with the
lab, and using proper lab procedures will help reduce risk of injury
in the lab.
#389 Single Replacement Reactions and Relative
Reactivity
I. Purpose- Lab number 389 deals with determining the relative reactivity of aluminum, iron, and copper. The lab also demonstrates how single replacement reactions occur and under what conditions they will occur. It will also be determined as to the order from observations of chemical changes occurring when single replacement reactions of these metals and their metallic ions are carried out. This lab module first begins the experiment by making observations concerning metals and their metallic salts. The next part of this experiment involves reacting metals with dilute Hydrochloric Acid, next metals and solutions of metallic salts are reacted. The final stage of the experiment involves the processing of all data to determine what types of equations are needed to show the various types of reactions.
II. Background- In order to fully understand the lab a complete review of terminology is necessary. Single replacement reaction - a reaction where one element displaces another. Activity - term for an element who can loose electrons easily. Total ionic equation - an equation where all aqueous substances are assumed to have dissociated into ions in the solution. Dissolution - the term for a dissociated metallic salt dissolved in water. Spectator ion - any ion that does not change, or is not effected by the chemical reaction. Net ionic equation - the final equation showing the total chemical reaction. Relative reactivity - the determination that some elements are more or less reactive in relationship to one another.
III. Cautions-This lab requires the use of three potentially hazardous substances; Copper (II) sulfate, hydrochloric acid, and iron (II) sulfate. Copper (II) sulfate is toxic and an irritant therefore the student should avoid contact with skin, eyes, and avoid inhaling vapors of this substance. Hydrochloric acid is toxic and corrosive, which can cause sever burns. Lab students should avoid contact with clothing, eyes, mouth, and avoid inhaling toxic vapors of this acid. Iron (II) sulfate is a toxic solution requiring careful handling to prevent spillage. As always, safety goggles should be worn at all times during the lab.