Experiment 4 Determination of Empirical Formulas Lab Report I need an lab report in general for lab chimstry a P ? EXPERIMENT #4: DETERMINATION OF EMPIRICA

Experiment 4 Determination of Empirical Formulas Lab Report I need an lab report in general for lab chimstry a
P ?
EXPERIMENT #4: DETERMINATION OF EMPIRICAL FORMULAS
Individual Pre-lab
1. The main goal/purpose of the experiment is (what are you trying to discover in this lab):
2. The hypothesis(es) we seek to test in this experiment is(are) (what is the basis of your
experiment, see chapters on chemical compounds and empirical formula in your text):
3. The key question the experiment seeks to answer is (what problem are you addressing?):
4. The controls involved in this experiment are (a control is used to minimize the unintended
influence of other variables on the same system):
5. The key concept(s) or theory(ies) behind the experiment is(are) (define terms like Constant
Composition, Conservation of Mass, empirical formulas, mole ratio, combustion reactions, etc.
can you explain the relevant theory):
6. The important technique(s) used in this experiment is(are)
Please describe:
7. The experiment is based on the following assumptions (identify your assumptions and determine
if they are justifiable):
8. The data that will be collected in the experiment are (what do you plan to record in your
notebook)
9. The potential consequences of the experiment are:
10. The point of view behind the experiment is (make sure it’s scientific).
11. What special safety precautions do you need to be aware of for this experiment?
This content has been modified from The Foundation of Critical Thinking’s Mini Guide to Scientific
Thinking (www.criticalthinking.org).
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EXPERIMENT #4: DETERMINATION OF EMPIRICAL FORMULAS
Group Experimental Design Pre-lab
Write a detailed experimental procedure for perform the combustion of magnesium in air. This
procedure should be written stepwise with the initials of the student who is performing that step in
the procedure. Here is an example:
1. Weigh substance- AW (these are the initials of student performing task)
2. Get the volume of substance – EE
3. etc.
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EXPERIMENT #4: DETERMINATION OF EMPIRICAL FORMULAS
Project:
Most metals form metal oxide with oxygen where the oxygen ion is -2 charged. Some reactive metals,
such as Li, Na and K, can form peroxide with oxygen. In these peroxides, Li Oz, Na2O2, oxygen is -1. An
amateur scientist claims that magnesium (Mg), a relatively reactive metal, also forms peroxide when
burned in air. Your team is called upon to solve this mystery. Specifically, you will:
1. perform the combustion of magnesium in air and determine the empirical formula of the
magnesium-oxygen compound;
2. based on the empirical formula, determine if the compound is an oxide, a peroxide, or a new
kind.
Background:
Chemists are constantly concerned with the composition of compounds. When a new compound is
found or made for the first time, chemists always ask: (1) what elements are present in the compound?
and (2) what is the ratio of the atoms of the different elements? The chemical formula that shows the
types of elements and the lowest whole number ratio of the different kinds of atoms is called empirical
formula (“empirical” because they are determined through experiments). Determination of empirical
formulas is based on two fundamental laws:
1. Law of Conservation of Mass
2. Law of Constant Composition
In practice, when determining empirical formulas, because the number of atoms (or ions) cannot be
“counted” or determined easily, people almost always conduct experiments to determine the mass
composition (or mass percentage) of each element in a compound first; using the molar mass of the
elements, the mass composition of each element is readily converted to the number of moles for each
element, and the ratio of the moles of the elements is then obtained, which, if written in the simplest
whole numbers, is the empirical formula. An example of this type of problem is: Determine the
empirical formula of a 10.0-g sample of a calcium chloride compound (chemical formula unknown),
found to have 3.60 g Ca and 6.40 g Cl.
In this experiment, when burned in air, magnesium will react with both oxygen and nitrogen to form a
magnesium-oxygen compound (Mg,Oy) and a magnesium-nitrogen compound (Mg, N.). If the Mg, Ny
formed is left untreated, the mass of the final product will be the mass of (Mg,Oy + MgN), rather than
the mass of Mg,Oy. This will certainly cause errors in determining the empirical formula. Fortunately,
Mg.N, is easily converted, by adding water, to magnesium hydroxide (Mg(OH)), which upon further
heating decomposes to the magnesium-oxygen compound. This procedure ensures that all Mg metal
will end up in the final product, the magnesium-oxygen compound (Mg,Oy).
In determining the empirical formula of the magnesium-oxygen compound, a certain amount of me
metal is reacted with oxygen to form the compound (Mg Oy), and the mass of MgO, is determined.
According to the Law of Conservation of Mass, the mass of Mg before the reaction is the same as the
mass of Mg in the final product Mg Oy; further, the difference between the mass of the MgO, and the
mass of the Mg is the mass of oxygen in the compound. The mass of Mg and the mass of O are then
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Date
Experiment/Subject
Lab Partner
Locker/
Desk No.
Course &
Section No.
Exp. No.
Name
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THE HAYDEN-MCNEIL STUDENT LAB NOTEBOOK
Date
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Note: Insert Divider Under Copy Sheet Before Writing
used to determine the moles of Mg and 0, and the mole ratio (Mg : 0) is then calculated and expressed
in the simplest whole number ratio to denote its empirical formula.
General Chemistry concepts: empirical formula, mass composition, Law of Conservation of Mass, Law
of Constant Composition
Techniques:
Laboratory: measuring mass, heating with burners, working with hot crucibles, apparatus setup,
inhalation safety, disposal of solid waste
Computer: Flowchart describing your analysis strategy in PowerPoint, apparatus setup using
ChemSketch.
NOTE: Blackboard has links that can help you with this lab.
Special Apparatus and Chemicals:
Bunsen burner
Tongs
Crucibles and lids
~0.3 g Mg
Wire gauze
Clay triangle
Iron ring and stand
Procedure:
Clean a crucible and lid, dry the crucible and lid over a Bunsen burner with a cool flame for a few
minutes. Let the crucible and lid cool to room temperature and then weigh the crucible and the lid
together to the full limit of precision of your balance. CAUTION: Never weigh hot, wet objects on the
balance. Add approximately 0.3 grams of magnesium metal to the crucible, and weigh the crucible, lid
and magnesium together to get the exact mass of the magnesium added. Heat the magnesium in the
crucible over a Bunsen burner to convert magnesium to magnesium oxide.
After the reaction is complete (a gray-white powder will form), remove the flame and let the crucible
cool slightly. Carefully add a few drops of distilled water (Why? What do you observe?), and heat the
crucible over a low flame for a few minutes, then adjust the flame and heat the crucible with the bottom
glowing red hot for 10 more minutes. (Why?) Shut off the burner, let the crucible cool to room
temperature, and weigh the crucible, the lid, and the final product to a constant weight.
Notes: Hot and cold crucibles should only be handled with tongs. Do not put a hot crucible directly on
the bench; instead, remove the flame and let the crucible sit on the clay triangle to cool off, or set the
crucible on a wire gauze.
Analysis of experimental data through calculations. (Report in table form)
Based on the mass of magnesium measured and the mass of oxygen determined experimentally,
calculate the empirical formula for the new magnesium-oxygen compound formed for each trial. You
may need to refer to your textbook and lecture notes for assistance.
Analysis of data and calculations through discussion. (This belongs in the Discussion section in the lab
report)
Refer back to the project, did you answer the question?
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