Determining the Empirical Formula of Copper Chloride
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Transcript of Determining the Empirical Formula of Copper Chloride
Determining the Empirical Formula of Copper Chloride
Purpose of the Experiment
Determine the empirical formula of a compound containing only
copper and chlorine
The mass in grams of 1 mole of a compound
Molar Mass (Molecular Weight)
H2O MW = 18.0148 g
AlCl3 MW= 133.341 g
Percent Composition
Gives the percentages of a compound’s mass that are due to each of the component elements
C2H5OH
Mass of C = 24.022 gMass of H = 6.048 gMass of O = 15.999 g
Mass of 1 mole of C2H5OH = 24.022 + 6.048 + 15.999 = 46.069
52.144%100%46.069g
24.022g100%
OHHC 1mol of mass
OHHC of mol 1in C of massC ofpercent Mass
52
52=×=×=
Empirical Formula
Represents the simplest whole-number ratio of the various types of atoms in a compound
Examples: CH5N , C2H10N2, C3H15N3
Schematic diagram of the combustion device used to analyze substances for carbon and hydrogen.
A white compound is analyzed and found to contain 43.64% phosphorous and 56.36% oxygen by mass.
What is the empirical formula?
In terms of moles, in 100.00 g of compound we have:
Empirical Formula Example
43.64g P x (1 mol P / 30.97g P) = 1.409 mol P
56.36 g O x (1 mol O / 15.99g O) = 3.523 mol O
Dividing both mole values by the smaller one gives:
O 2.51.4093.523
and P 11.4091.409
This yields the formula PO2.5
Since compounds must contain whole numbers of atoms, the empirical formula should contain only whole numbers.
Empirical Formula = P2O5
Empirical Formula Example, contd.
Mg(s-silvery-white) + O2(g)
limiting reagent
MgxOy(s, white)
(0.353 g)
Atmospheric oxygen in excess
heat
Result: Mass of MgxOy = 0.585 g
Another Empirical Formula Example
60.3%100585.0
353.0100
OMg of mass total
g Mg, of mass% Mg,Percent
yx=×=×=
%7.39100g 0.585
g 0.232100
OMg of mass total
O of mass% O,Percent
yx=×=×=
Mass of O = total mass of compound – mass of Mg = 0.232 g
Another Empirical Formula Example, contd.
Mg = 60.3% and O = 39.7%
Formula masses and percent composition of three theoretical compounds of Mg and O
Formula of Oxide MgxOy %Mg %O
MgO 60.3% 39.7%MgO2
43.2% 56.8%Mg2O 75.2% 24.8%
Mg = 60.3% and O = 39.7%
Today’s Experiment
Al(s, silvery white) + CuxCly(aq, blue) AlCl3(aq) + Cu(s, reddish)
known mass
25 mLLimiting reagent
~0.3 g ea. strip(excess) known mass
Zn(s, silvery white) + CuxCly(aq, blue) ZnCl2(aq) + Cu(s, reddish)
Original
Modified
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Copper is a transition metal, with unfilled d orbitals.
Ground state electron configuration: [Ar].3d10.4s1Shell structure: 2.8.18.1
Transition metals may exhibit multiple oxidation states(+1, +2, +3, etc…).
These are not easily predicted by position in the periodic table.
Transition metals ions in aqueous solutions frequently are brightly colored, also due to d orbitals (e.g. Cu ions are blue).
Zn and Al are both stronger reducing agents than copper. (Note: the redox potentials on next slide)
Because of this either one would work to produce metallic copper from a solution of a copper salt.
These potentials indicate the relative thermodynamic tendency for the indicated half-reaction to occur.
**
*
Zn(s) + 2 HCl(aq) ----> ZnCl2(aq) + H2(g)
2 Al(s) + 6 HCl(aq) ----> 2 AlCl3(aq) + 3 H2(g)
Cu(s) + n HCl(aq) --x--> No Reaction
Other Reactions in the Procedure:
Removal of Excess Reducing Agent
Reagents in Lab
CuClx solution in 4L spigot jugs- take ~25 ml for each run
Record data: (0.08067 g CuClx / ml, d=1.074 g/ml)
10% HCl in 1L wash bottles (take ~5 ml)(N.B. solid NaHCO3 is to be used for acid spills)
Checkout2 pc Al foil (~0.3 g)1-pr Beaker Tongs
25 mL copper chloride, weigh and use exact density to get mass of CuClx
Add Al foil
Stir (takes about 5 min)
Add 5-10 drops of 10% HCl and stir ( HCl will dissolve excess Al)
Decant the supernatant liquid
Cu
Flow Chart for Procedure
waste
Do not overheat to avoid oxidation
Wash with distilled water to remove aluminum chloride
Transfer Cu residue to a pre-heated and pre-weighed
casserole
heat
Determine the mass of Cu
Cu
Flow Chart for Procedure
waste
waste
Procedure NotesRecord all weights to 0.001g
Weigh 25 ml of CuClx solution, use exact density to calculate exact volume, then calculate the mass of CuClx
Do not use metal forceps or spatulas
Add Al foil until blue color is gone, allow excess foil to dissolve also
Allow container to cool before weighing
Speed up cooling by placing in front of hood sash raised 4-6”
The second beaker does not have to be 150 mL
A casserole will also work as an evaporating dish
Hazards10% HCl-strong acid, corrosive
CuClx solution-heavy metal, irritant
Hot surfaces - hotplates, glassware
WasteLiquid Waste: Al+3 / HCl
Cu solids
Results (calculations)Collected data
Mass of CuClxMass of Cu
Mass percent of CuMass of ClMass percent of ClEmpirical formula
Summary of Data & Calculations
Additional background reading for Antacid Analysis/Titrations:
Atkins, “Chemical Principles”, 3rd ed, pp. F67-F72, F85-F88, 415-425
Next Week’s Experiment:
Antacid Analysis (green book)