Practical 1a - University of KwaZulu-Natalcheminnerweb.ukzn.ac.za/Files/CHEM261/CHEM261 Prac...
Transcript of Practical 1a - University of KwaZulu-Natalcheminnerweb.ukzn.ac.za/Files/CHEM261/CHEM261 Prac...
SCHOOL OF CHEMISTRY and Physics
HOWARD COLLEGE CAMPUS
UNIVERSITY OF KWAZULU-NATAL
I, the undersigned (please print your full name):
_____________________________________________________________________
Student No.: ____________________
do hereby acknowledge having read and understood the documents headed
“Occupational Health and Safety” and “Laboratory Rules and Regulations”.
Furthermore, I accept that contravention of these rules and regulations may lead to
my expulsion from the laboratory class, or classes, with subsequent loss of my Duly
Performed (DP) certificate.
I agree to abide by any additional laboratory regulations or safety rules presented in
writing in this laboratory manual or issued verbally by the lecturer-in-charge, or
other responsible member of staff, during pre-laboratory lectures or in the
laboratory.
In addition, I understand that I must attend at least 80% of the scheduled laboratory
classes and that failure to do so, irrespective of the reasons, may result in the loss of
my DP certificate.
DATE: __________________
SIGNATURE: ___________________________
It is a legal requirement that
SAFETY GLASSES, LABORATORY COATS AND CLOSED SHOES
are worn in this room at ALL times.
Sunglasses (normal or prescription) are NOT to be worn as a substitute for safety glasses.
Prescription glasses (except sunglasses) are acceptable PROVIDED THEY COVER THE EYES COMPLETELY.
Some types of contact lens should not be worn in the laboratory. Check with your lens supplier.
All shoes MUST be closed. No high heels are allowed.
All headgear such as hats and scarves must be made safe. Long hair MUST be tied back.
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General Fire Orders
Fire-fighting instructions are exhibited in each laboratory, but the following orders must
always be obeyed.
In the event of a fire
Attack it at once using the appropriate fire-fighting equipment and SHOUT for help.
On hearing a fire evacuation alarm
Stop normal work immediately.
Make safe any apparatus and material in use, shutting off any local gas taps/valves,
electricity and other potentially dangerous services under your control.
Immediately leave the building.
Go to the Fire Evacuation Area outside the main entrance to the building; unless you have been given any other instructions.
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Occupational Health and Safety (OHS)
YOU are warned that all substances handled and all operations performed in a laboratory
can be hazardous or potentially hazardous. All substances must be handled with care and
disposed of according to laid down procedures. All operations and manipulations must be
carried out in an organized and attentive manner.
In order to assist you in developing good and safe laboratory techniques, a set of Laboratory
Rules and Regulations is attached. You are required to read these and acknowledge that
you have read and understood them. Additionally, in the laboratory manuals and/or pre-
practical lectures your attention will be drawn to the correct and safe handling of specific
chemicals/reagents/solvents, and to the correct/safe manner in which specified laboratory
operations must be carried out. These specific instructions and/or warnings must never be
ignored.
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Laboratory Rules and Regulations
Students must be present before the start of each scheduled practical session.
Latecomers will be refused entry to the laboratory.
No student will be permitted to work in the laboratory outside of practical hours.
Do not put anything into your mouth while working in the laboratory. NEVER taste a
chemical or solution. Eating and drinking is PROHIBITED in all laboratories.
All students are required to wear a laboratory coat. No student will be permitted to
work in a laboratory without one.
All students who do not wear conventional spectacles must wear eye protection.
These must be worn throughout all practical sessions
All students must wear closed shoes while in the laboratory.
All students must have a laboratory towel to dry apparatus and clean bench-tops.
No entry is allowed into preparation and issue rooms.
Apparatus and chemicals are not to be removed from the laboratory.
Students will find the laboratory benches clean on arrival in the laboratory. The bench
at which you work must be left clean when you leave the laboratory at the end of the
practical session. Bench tops must be wiped clean. Glassware and other apparatus
should be left clean and dry, unless otherwise indicated or instructed. Sinks and
basins must be cleaned after each practical.
Work areas must at all times be kept clean and free from chemicals and apparatus
that are not required. All glassware and equipment must be returned to its proper
place, clean and dry and in working condition, unless otherwise indicated or
instructed.
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All solids must be discarded into the bins provided in the laboratory. Never throw
matches, paper, or any insoluble chemicals into the sinks. Solutions and chemicals
that are emptied into sinks must be washed down with water to avoid corrosion of the
plumbing. Waste solvents must be placed into the special waste solvent bottles
provided.
Before leaving the laboratory at the end of the practical session, make sure that all
electrical equipment is switched off, and that all gas and water taps are shut off.
Students who break or lose equipment allocated to them will be required to pay for
replacements. All breakages or losses must be reported to the technician in charge.
Do NOT heat graduated cylinders or bottles.
Any apparatus or glassware, which has to be heated, must be heated gently at first,
with heating gradually increased thereafter.
Balances must be treated with care and kept clean and tidy at all times.
Fume-hoods must be used when handling toxic and fuming chemicals. Other
operations, such as ignitions, are also carried out in fume-hoods. The only parts of the
body that should ever be in the fume-hood are the hands - never put your head inside
a fume-hood!
Never leave a laboratory experiment unattended!!
Reagent bottles must be re-stoppered immediately after use. It is ABSOLUTELY
FORBIDDEN to introduce anything into reagent bottles - not even Pasteur pipettes!
Solutions and reagents taken from bottles must NEVER be returned to the bottles. Do
not place the stopper of a reagent bottle onto an unprotected bench top.
Laboratory reagents and chemicals must be returned to their correct places
immediately after use. Spillage must be cleaned off bottles/containers.
Liquids - whether corrosive or not - must be handled with care and spillage on the
bench or floor should be avoided. Any spillage should be cleaned up at once. If the
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liquid is corrosive (acids or bases), call your demonstrator or staff member in charge.
Never hold a container above eye level when pouring a liquid.
When carrying out a reaction, or boiling a liquid in a test tube, point the mouth of the
test tube away from yourself and others in the laboratory.
Beware of hot glass and metal. Never handle any item that has been in a flame, hot
oven, or a furnace without taking precautions. Use leather/asbestos gloves/tongs, or
ask for advice.
Report all accidents, cuts, burns, etc., HOWEVER MINOR, to your demonstrator or the
staff member in charge. Eyewash stations are located in various places in the
laboratory. Ensure that you know where the nearest one to your bench is located.
A chemical laboratory is not a place for horseplay. Do not attempt any unauthorised
experiments. Do not play practical jokes on your classmates - transgressors will be
banned from the laboratory, with consequent refusal of a Duly Performed (DP)
Certificate.
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Instructions to Students
Read the following instructions CAREFULLY. Make sure you understand the instructions and
sign the declaration at the front of the manual.
Fire Extinguishers are provided in the laboratory. Make sure you know where they are
situated and how to use them. N.B. A SHOWER is situated in front of the lecturer's
desk, as well as in the corridor outside. Make sure you know where they are!
Gas is highly flammable. It can form dangerous explosive mixtures with air when not
controlled. GAS TAPS MUST BE TURNED OFF WHEN GAS IS NOT IN USE. Slow leaks
can lead to dangerous concentrations.
Burners: Students must provide their own matches or lighters. The use of paper spills
is FORBIDDEN as it poses a fire hazard.
Flammable solvents such as ether, alcohol, hexane, benzene, acetone, etc. are used in
the organic laboratory. Students must take care when handling these solvents. The
following rules are important:
Inflammable solvents are NOT TO BE HEATED IN OPEN CONTAINERS OVER A FLAME.
These should be heated over a steam bath or under reflux conditions.
Solvents, such as chloroform, hexane, ether, which are immiscible with water must
be disposed of by carefully pouring them into the WASTE SOLVENT bottles located
in the fume cupboards. They may NOT be poured down sinks or troughs.
Solvents that are miscible with water (e.g..alcohol and acetone) may be poured into
the sinks, provided they are washed away with an ample volume of water.
Glassware with ground glass joints is expensive and must be treated with care. After
use, glassware must be carefully cleaned, dried, and ground surfaces must be lightly
smeared with petroleum jelly. This prevents the "freezing together" of the joints. The
process of "freezing" is accelerated by the presence of any alkaline solid or solution
left on the surfaces. The joints should NEVER be forced or heated with a flame.
Disassemble ALL joints before leaving the laboratory.
Students must be careful when using balances. ALL SPILLAGES MUST BE CLEANED UP
and balances must be left clean.
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Laboratory benches must be looked after. Acid spillages must be neutralised with
sodium bicarbonate and cleaned up immediately. Bunsen burners, hot glassware and
steam baths must be placed on asbestos mats.
Refuse Bins are for SOLIDS only. No burning or smoldering materials may be placed in
bins.
Sinks and troughs are for liquids only. Solid material will cause blockage of the
drainage system.
Use of Fume Cupboards: The careless use of certain chemicals makes working in the
laboratory extremely unpleasant. Brominations must be done in the fume cupboard.
Always check warnings on the reagent bottles BEFORE using.
Practical Preparation: Before the practical class you are required to:
Familiarize yourself with the experimental procedures you are about to perform.
Read up the relevant section in your textbook.
Fill in specific information, as requested.
Reactions will be discussed in lectures, practical work being examinable in your
examination.
All SOLID products prepared and derivatives of unknowns must be submitted in neatly
labeled sample tubes. Liquid products may not be handed in, but must be shown to
your demonstrator for verification and then poured into the appropriate bottle on the
demonstration bench.
Report sheets for a particular practical MUST be handed in at the conclusion of that
practical session. They will then be marked and returned to you at the start of the
following laboratory.
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Schedule of Practical Work
Page No
Practical 1A Preparation of the “double salt”
Ammonium copper sulphate 11
Practical 1B Preparation of the “coordination complex”
tetraamine- copper(II) sulphate 11
Practical 2 Preparation of [Co(NO2)6]3- 12
Practical 3 Preparation of [Co(acac)3] 13
Practical 4 Preparation of copper(I) chloride 14
Practical 5 Preparation of chromium metal by the
Thermite Reaction 15
Practical 6 Construction of model crystals 16
Preparation of the “double salt” ammonium coppersulphate
Procedure
Dissolve copper(II) sulphate pentahydrate (2 g) and ammonium sulphate (1 g) in hot water
(5 mL). Cool the solution, and filter the crystals at the pump. Dry between pads of filter
papers. Evaporate the filtrate to about 5 mL, cool, filter, and dry the second crop of crystals.
Record the total weight of product but keep the two samples separate. Calculate the
percentage yield.
Preparation of the “coordination complex”tetraamine- copper(II) sulphate
CuSO4 + 4NH3 [Cu(NH3)4]SO4.H2O
Procedure:
Dissolve four grams (4 g) of copper(II) sulphate pentahydrate in a mixture of 6 mL of
concentrated ammonia and of 4 mL water. Cool the resulting deep-blue solution in ice,
stirring continuously while 15 mL of alcohol is added drop-wise using a dropper. Allow the
mixture to stand in the cold for at least 4 hours, preferably overnight; the supernatant liquid
should be almost colourless. Filter the crystalline product, wash first with 10 mL of a cold
equal volume mixture of alcohol and concentrated aqueous ammonia, and then with 10 mL
each of 95% alcohol and ether. Dry the salt in air and calculate the percentage yield.
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Practical 1A
Practical 1B
Preparation of [Co(NO2)6]3
Co(NO3)2 + 5NaNO2 + NO2− Na3[Co(NO2)6] + 2NaNO3
Procedure:
12 g of pure potassium-free sodium nitrite are dissolved in 12 mL of hot water. The solution
is cooled to 50C, and 4 g of cobalt nitrate hexahydrate are dissolved in the liquid. With
continuous stirring, 4 mL of 50% acetic acid are added dropwise from a burette and the dark
brown solution is transferred to a filter flask fitted with a stopper and an inlet tube leading
almost to the bottom of the vessel. A steady stream of air is drawn through the solution for
30 minutes to remove excess oxides of nitrogen; some product may crystallize out during
the aeration. The liquid and any solid that has formed (the more vigorous the air current
the more material tends to settle out) are now placed in a beaker and surrounded by an ice
bath. Add 20 – 30 mL of 95% alcohol slowly with agitation, and the mixture is then allowed
to crystallize in the cold for 30 minutes. The orange-brown product is filtered by suction
and the mother liquor is set aside. The material is washed three times with 10 mL of
alcohol; the final washing should be almost colourless. The crystals are dried in air.
Calculate the percentage yield.
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Practical 2
Preparation of [Co(acac)3]
Procedure:
Slurry 2.5 g powdered cobalt(II) carbonate and 20 mL acetylacetone in a 125 mL Erlenmeyer
flask. Heat the mixture to 100C on a steam bath. Transfer the flask immediately onto a
white tile and add 15 mL of 10% H2O2 at a rate of to 2 mL/min while stirring. Reheat the
reaction mixture to incipient boiling, then add 15 mL more of H2O2 as before. After addition
is complete, heat to boiling.
Cool the mixture in an ice-salt bath for half an hour and filter the green-black sludge with
suction. Wash with water followed by small (3 x 5 mL) amounts of cold ethanol. The yield
should be about 6 g of raw product. Recrystallize from toluene. If any of the raw product
cannot be dissolved in hot toluene, filter the hot solution by gravity to eliminate the
insoluble impurities. Dry at 110C. The yield of purified dark green crystals is expected to be
4.0 to 4.5 g pure. Calculate the percent yield.
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Practical 3
Preparation of Copper(I) chloride
Procedure:
Copper(I) chloride is prepared by reducing copper(II) ions with sulphur dioxide or sulphite
ions in the presence of chloride ions. The copper(I) ions once formed, react with chloride
ions to form the insoluble copper(I) chloride.
Prepare three solutions:
(a) Dissolve sodium sulphite (3.3 g) in 50 mL of water,
(b) Dissolve copper(II) chloride (4.8 g) in 25 mL of water,
(c) Prepare a sulphurous acid solution by dissolving sodium sulphite
(1 g) in 10 mL of water and add 12 mL of 2 M hydrochloric acid.
Add slowly, with constant stirring, the sodium sulphite solution to the copper(II) chloride
solution. Dilute the suspension of copper(I) chloride so formed with about half the
sulphurous acid solution, allow the precipitate to settle, and decant most of the supernatant
solution. Filter the solid by suction on a sintered glass disc, wash the precipitate on to the
sinter by means of sulphurous acid solution. Take care that the copper(I) chloride is always
covered by a layer of solution. Finally wash the product with portions of glacial acetic acid,
alcohol, and ether. Dry the product in a warm oven. Calculate the percentage yield.
Copper(I) chloride is slowly oxidized by moist air to give the basic copper(II) chloride,
CuCl2.3Cu(OH)2, so it must be stored in stoppered containers.
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Practical 4
Preparation of chromium metal by the Thermite Reaction
2Al + Cr2O3 = Al2O3 + 2Cr
Procedure:
Fuse potassium dichromate (1 g) in a porcelain crucible. Cool, and grind to a fine powder.
Ignite hydrated chromium(III) oxide (4 g), (note that the bottle may be labelled chromic
hydroxide), in a porcelain crucible until the green anhydrous chromium(III) oxide is
obtained. Prepare a mixture containing chromium(III) oxide (2 g), fused potassium
dichromate (0.5 g), and aluminium powder (1 g). The reaction will proceed without the
potassium dichromate but the temperature may not be sufficiently high to fuse the
chromium metal produced. This makes recovery more difficult.
Fill a crucible (4 cm x 7 cm o.d.) to within 1 cm of the rim with powdered calcium fluoride,
and make an indentation about 2 cm in depth in the centre of the powder with the end of a
boiling tube. Place the prepared mixture in this indentation in the calcium fluoride. Prepare
an ignition charge of barium peroxide (1 g) and aluminium powder (0.1 g) and place this on
the surface of the reaction mixture. Insert a short length of magnesium ribbon into the
ignition charge to act as a fuse. Place the crucible in a fume cupboard, surround it vertically
on four sides with asbestos board and fasten another asbestos board horizontally above the
asbestos ‘walls’. During the firing of the charge wear safety goggles or a face mask. Ignite
the magnesium ribbon using a micro burner. There will be some sparking initially but this
will quickly cease and the charge will continue to react quite smoothly. Allow the product to
cool, and carefully transfer it to a mortar. Grind the product and remove the bead (or
beads) of chromium metal. Weigh the chromium and calculate the yield.
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Practical 5
Construction of model crystals (by Prof M Laing)
This laboratory exercise is derived from those used in the Department of Chemistry, Purdue University, USA for Course 115 (Profs Robinson and Bodner) and 241 (Prof Davenport).
You are given a model consisting of 5 sheets of transparent plastic each of which has drilled in it 25 holes. The coordinates of the sheets in fractions of z are:
0, ¼, ½, ¾, 4/4and within the z sheets, the coordinates of theholes in the fractions of x are:0, ¼, ½, ¾, 4/4and in fractions of y are:0, ¼, ½, ¾, 4/4
The x, y coordinates of the hole marked *are x = ¾, y = ¼; its z = 4/4.
The coordinates for the positions of the spheres will be given as number of quarters: with x being given before y, followed by z. The coordinates of the hole marked * thus are: 3,1,4.
Models of crystal structures are made by placing Styrofoam spheres at the appropriate positions in the framework.
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Practical 6
1 Simple cubic
Place atoms at:z = 4 : 0.0; 4.0; 0.4; 4.4z = 0 : 0.0; 4.0; 0.4; 4.4
(a) What fraction of the atom at the corner of the cell (0, 0, 0) is within the unit cell?
_______________
(b) How many unit cells share the atom at the corner (0, 0, 0)?
_______________
(c) How many atoms are there per unit cell?_______________
(d) How many atoms are in contact with an atom at (0, 0, 0)?
_______________
(e) If the atoms are in contact along the cell edges, what is the relationship between the length of the cell edge (ao) and the radius (r) of the atom?
________________
(f) Given that the volume of the atom is 4/3r3 and the volume of the cell is ao3,
calculate what fraction of the unit cell volume is occupied by the atoms.
________________
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2 Body-centred cubic
Place atoms at:z = 4 : 0.0; 0.4; 4.0; 4.4z = 2 : 2.2z = 0 : 0.0; 0.4; 4.0; 4.4
(a) What fraction of the atom at (1/2, 1/2, 1/2) is within the cell?
_______________
(b) What fraction of the atom at (0, 0, 0) = (1, 1, 1) is within the cell?
_______________
(c) How many atoms are there per unit cell?
_______________
(d) How many atoms are in contact with the atom at (1/2, 1/2, 1/2)?
_______________
(e) The atoms at (0, 0, 0), (1/2, 1/2, 1/2), (1, 1, 1) are in contact along the body diagonal, b; i.e. b = 4r. Calculate the volume of the cell in terms of r.
_______________
(f) What fraction of the unit cell is occupied by atoms?
_______________
(This structure is adopted by pure iron at room temperature, and by brass of composition CuZn at 300C when all the Cu and Zn atoms are scrambled between (0, 0, 0) and (1/2, 1/2, 1/2).
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3 Face-centred cubic
Place white atoms at:z = 4 : 0.0; 0.4; 4.0; 4.4; 2.2z = 2 : 0.2; 2.0; 4.2; 2.4z = 0 : 0.0; 0.4; 4.0; 4.4; 2.2
(a) What fraction of the atom at the centre of the face is within the cell?
________________
(b) What is the nett number of atoms per face-centred cubic unit cell?
________________
(c) What is the coordination number of an atom in this face centred cubic unit cell?
________________
(d) The atoms are in contact along the face diagonal, d, of the unit cell, i.e. d = 4r. What is the value of ao, the unit cell edge, in terms of r?
________________
(e) What is the volume of the unit cell in terms of r?
________________
(g) What is the volume of the cell occupied by atoms (in terms of r)?
________________
(h) What fraction of the unit cell volume is occupied by the atoms?
________________
(many metals have this structure)
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4 Diamond (FCC)
Retain the FCC structure from part 3;add white atoms at:z = 3 : 3.1; 1.3z = 1 : 1.1; 3.3
These atoms are now in the diamond structure.
(a) How many atoms are there per unit cell? ________________
(b) The atom at (0, 0, 0) is covalent bonded to the atom at (1/4, 1/4, 1/4), with C C = 1.54 Å (equal to 1/4 of the body diagonal). Calculate ao, the unit cell edge.
______________Å
(c) What is the coordination number of each atom?_______________
(Silicon, germanium and tin (below 0C), have this structure).
N.B. Retain this model for part 5.
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5 Zinc sulphide : blende
Replace all the white atoms at z = 3, andz = 1 by red atoms.This is the cubic zinc blende (ZnS) structure.
(a) What is the coordination number of the atom at (1/4, 1/4, 1,4)?
________________
(b) What is the coordination number of the atom at (0, 0, 0)?
________________
(c) Assume the Zn atom is at (1/4, 1/4, 1/4) and the S atom is at (0, 0, 0);
(i) how many S atoms are there per unit cell?
________________
(ii) how many Zn atoms are there per unit cell?
________________
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6 Sodium chloride (NaCl)
Remove the red atoms from the layers z = 1and z = 3. The standard FCC array remains.Now add red spheres at the following positions.z = 4 : 0.2; 2.0; 2.4; 4.2z = 2 : 0.0; 0.4; 4.0; 4.4; 2.2z = 0 : 0.2; 2.0; 2.4; 4.2
The pattern is the sodium chloride structure, face-centred cubic. Assume that the red spheres are Na+, and that the white spheres are Cl.
(a) How many Cl are in contact with each Na+? ________________
(b) How many Na+ are in contact with each Cl? ________________
(c) How many Cl are there per unit cell? ________________
(d) How many Na+ are there per unit cell? ________________
(e) Calculate the shortest distance between each pair of Cl ions in terms of the cell edge ao.
________________
(f) Assume all the white spheres (Cl) are in contact, i.e. the face diagonal is 4 x r. What is the radius, R, of the cation in terms of r if it just touches the six anions arranged around it in an octahedron?
________________
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7 Caesium chloride structure, CsCl, primitive cubic
Clear all spheres from the model.Place one red sphere at : z = 2 : 2.2;and 8 white spheres atz = 0 : 0.0; 0.4; 4.0; 4.4z = 4 : 0.0; 0.4; 4.0; 4.4
Note: there are two types of atom.(a) How many red atoms are there per unit cell?
________________
(b) How many white atoms are there per unit cell? ________________
Compare this with the BCC structure. In this CsCl structure, the atom at (1/2, 1/2,1/2) differs chemically from the atoms at the corners of the cubic cell.(The atoms of brass of composition CuZn take up this ordered arrangement at room temperature).
(c) Assume that the Cl ions are at the corners of the cube and touch along the edges of the cube; i.e. ao = 2r. Assume that the Cs+ at (1/2, 1/2,1/2) is in contact with the 8 Cl ions at the corners of the cube.
Calculate the ratio : radius of Cs+ ion to radius of Cl ion.
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8 Rutile (TiO2)
This structure is common for metal oxides of formula MO2.Place red spheres (M4+) at:z = 3 : 0.0; 0.4; 4.0; 4.4z = 2 : 2.2z = 1 : 0.0; 0.4; 4.0; 4.4and white spheres (O=) atz = 3 1.1; 3.3z = 2 3.1; 1.3z = 1 1.1; 3.3
(a) How many O= are in contact with the M4+ at (1/2, 1/2, 1/2)?
________________
(b) How many M4+ are in contact with each O= at (3/4, 1/4, 1/2)?
________________
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9 Fluorite (CaF2)
Put 14 white spheres into the model to give a FCC arrangement (as per part 3).
Now add red spheres at:
z = 3 : 1.1; 3.1; 1.3; 3.3z = 1 : 1.1; 3.1; 1.3; 3.3
The white spheres represent Ca2+ cations, and the red spheres represent F anions.
(a) How many Ca2+ ions are in contact with each F ion?
_______________
(b) How many F ions touch each Ca2+ ion?_______________
(c) How many F ions are there per unit cell?_______________
(d) How many Ca2+ ions are there per unit cell?_______________
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