Schottky Defect

Introduction
Like the human body, lattice structures (most commonly known as crystals) are far from perfection. Our body works hard to keep things proportional but occasionally our right foot is bigger than our left; similarly, crystals may try to arrange it's ions under a strict layout, but occasionally an ion slips to another spot or simply goes missing. Realistically speaking, it should be expected that crystals will depart itself from order (not surprising considering defects occurs at temperature greater than 0 K). There are
many ways a crystal can depart itself from order (thus experiences defects); these defects can be grouped in different categories such as Point Defects, Line Defects, Planar Defects, or Volume or Bulk Defects [2]. We will focus on Point Defects, specifically the defect that occurs in ionic crystal structures (i.e. NaCl) called the Schottky Defect.
Point Defects

Lattice structures (or crystals) undergoing point defects experience one of two types:
1.) atoms or ions leaving their spot (thus creating vacancies) [3].
2.) atoms or ions slipping into the little gaps in between other atoms or ions; those little gaps are known as interstitials--since atoms or ions in the crystals are occupying interstitials, they inherently become (create) interstitials [3].
By the simplest definition, the Schottky defect is defined by type one. For anyone interested, type two is known as the Frenkel defect.Schottky Defect - ChemWiki:

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Point Defects in Ionic Crystals

Even for the most simple ionic crystals of the type A+B– like LiCl or NaCl, we can, in principle, produce arbitrary concentrations of two kinds of vacancies and two kinds of interstitials as shown on the left.

However, as we already learned in dealing with Schottky defects, global charge neutrality must be maintained. Arbitrary concentrations are thus not really allowed, we must demand that the the sum of the positively charged defects equals the sum of the negatively charged defects. In other words: we have to obey the charge conservation law.
If we also keep the number of atoms constant, we must add an A or B atom to the surface of the crystal for every pure vacancy we produce. In other (fancy) words, we have to obey the mass conservation law.

solid defects

What are crystal defects and how are they classfied?

How do impurities affect the structure and properties of a solid?

What are color centers and how do they affect electric conductivity of solids?

Solid defects

Few, if any, crystals are perfect in that all unit cells consist of the ideal arrangement of atoms or molecules and all cells line up in a three dimensional space with no distortion. Some cells may have one or more atoms less whereas others may have one or more atoms than the ideal unit cell. The imperfection of crystals are called crystal defects.

Crystal defects are results of thermaldynamic equilibrium contributed also by the increase in entropy T S term of the Gibb's free energy:

DG = DH - TDS.

Only at the unatainable absolute zero K will a crystal be perfect, in other words, no crystals are absolutely perfect. However, the degree of imperfection vary from compound to compound.

On the other hand, some solid-like structure called flickering clusters also exist in a liquid. For example, the density of water is the highest at 277 K. The flickering clusters increase as temperature drops below 277 K, and the water density decreases as a result.

Solids are important for many technologies, and this link gives a well organized presentation.

What are crystal defects and how are they classfied?

As mentioned earlier, the missing and lacking of atoms or ions in an ideal or imaginary crystal structure or lattice and the misalignment of unit cells in real crystals are called crystal defects or solid defects. The two terms are interchangeable.

Crystal defects occur as points, along lines, or in the form of a surface, and they are called point, line, or plane defects respectively.

Demonstration of Resonance

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How double indicator titration works

When we have a mixture containing Na2CO3 and NaOH and you titrate it with a standard solution of HCl, you will need to use two indicators; one after another. The video below will explain how double indicators work in titration, using the above mentioned as the example."

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Read more
KWOK The Chem Teacher: Double Indicator Titration: "Double Indicator Titration
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Qualitative Analysis of Some Common Ions Class Notes

Qualitative Analysis of Some Common Ions Class Notes: "Carbonate Ion CO32-

Carbonate Ion CO32-

There are a lot of carbonate ions found in our area in the form of calcium carbonate (limestone). Carbonate ions are also found in the common household products of baking soda and baking powder. When the carbonate ion reacts with an acid, gaseous carbon dioxide is produced. These gas bubbles of carbon dioxide causes bread and cakes to rise.

In the test for the carbonate ion the formation of bubbles when an acid is added indicates the presence of the carbonate ion.

Sulfate Ion SO42-

The sulfate ion is found in a common drugstore product called Epsom Salts, which is used to prepare soothing baths. The sulfate ion is found in the bath salts found in the drugstore. When BaCl2 is added to a solution containing the sulfate ion, a fine white. powdery precipitate of BaSO4 is formed.

In the test for the sulfate ion, when BaCl2 is added, the formation of a white powdery precipitate indicates the presence of the sulfate ion.

Phosphate Ion PO43-

The phosphate ion is one of the common ingredients found in laundry detergent and wall washing compounds. The phosphate ion is also the principle intracellular anion. It is present in bones where it combines with calcium and it plays an important role in blood plasma.

To test for the phosphate ion, add ammonium molybdate to an acidified solution and upon heating a bright yellow precipitate is formed. This indicates the presence of the phosphate ion.

If you get a bright yellow solution without the precipitate or a pale yellow precipitate you do not have the phosphate ion. You must have the bright yellow precipitate.

Thiocyanate Ion SCN-

The thiocyanate ion is one of the major constituents of waste water from factories where the gasification of coal occurs. It also occurs where cyanide is used in mining of precious metals. In both of these instances, cyanide which is used is converted to thiocyanate ions by the reaction with sulfur. Thiocyanate ions are toxic but are less toxic than cyanide. Fortunately, there is a bacteria which can convert SCN- ions to a sulfide and ammonia, both of which do not hurt the environment.

Thiocyanate is also found in other things. Some pesticides use thiocyanate as the poison. Your body naturally contains trace amounts of thiocyanate in the blood and body fluids. It has been found that smoking increases the level of thiocyanate in the body. Thiocyanate is the product formed by the bodies metabolism of some drugs used to treat hypertension.

The test for the thiocyanate ion is to add iron (III) nitrate to a solution. If the solution turns blood-red upon the addition of iron(III) nitrate this indicates the presence of the thiocyanate ion.

Chloride Ion

We are using sodium chloride, table salt, to provide the chloride ion. The chloride anion is the principle anion of plasma and the fluids in the spaces between the cells of our body. The chloride ion is needed to maintain the electrolyte balance of the body fluids involved in blood transport of oxygen and carbon dioxide.

When a chloride ion reacts with silver nitrate it produces a white (lacy or snowflake looking) precipitate of silver chloride. In the test for chloride ion, a white precipitate is formed upon the addition of silver nitrate indicating the presence of the chloride ion.

Aluminum Ion Al3+

Aluminum is the most abundant metal and the third most abundant element in the earth's crust after oxygen and silicon. Aluminum is too reactive to exist as a free metal. You cannot walk around a pick up pure aluminum from the ground. The most common form of aluminum is bauxite. Aluminum is found combined in over 270 different minerals. The aluminum ion is used to lower the pH of soils by hydrolysis. Aluminum in the soil is leached out by acid rain, going into the water and then into plants. It has been found that tea grown in acid soil, when mixed with lemon is a significant source of aluminum ingestion and may be the primary cause of osteoporosis ( bone softening, crushing and breaking) and dementia in the elderly. It has also been found that when milk is added to tea, the milk detoxifies the tea by binding with the aluminum ion. There is NO BIOLOGICAL ROLE for aluminum in vertebrate life forms.

To test for the presence of aluminum a gelatinous precipitate of Al(OH)3 is formed when ammonia is added to the aluminum ion. Upon dissolving the precipitate with acetic acid and adding cathecol violet, the solution turns pale blue. You must have the gelatinous precipitate for aluminum to be present.

Copper Ion Cu2+

Copper is a micronutrient in our body. An average weight man or woman requires approximately 1.5 mg of copper daily. It occurs naturally in water and is found in drinking water when copper pipes are used to transport drinking water in houses. Copper occurs widely in our food, particularly in nuts, raisins, liver, and legumes. A person who is deficient in copper will suffer anemia, skeletal defects and degeneration of nerve cells. Copper is also used to destroy algae and bacteria in water.

In the test for the presence of copper the clear light blue solution of copper(II) sulfate will change to a milky light blue and then to a clear, deep blue when ammonia is added.

Iron Ion Fe3+

Iron is the most important transition metal in living systems, transporting oxygen in the blood. The average adult requires approximately 10 mg of iron daily. Very high concentrations of iron in the blood apparently renders an individual more susceptible to infections. The lack of iron in the blood causes anemia. Iron is present in the water when there are reddish brown stains in tubs, toilets, sinks, on dishes, glassware, and the laundry.

To test for the presence of iron (III) ion add potassium thiocyanate (KSCN) to the solution to get a blood red color.

THE ADVANCED STUDY ASSIGNMENT EXAMPLE

An unknown that might contain any of the eight ions studied in this experiment (but no other ions) has the following properties:

a. On addition of 1 M HCl, bubbling occurs.

b. When 0.1 M BaCl2 is added to the acidified unknown, a clear solution results.

c. When 0.1 M Fe(NO3)3 is added to the unknown, a deep red color appears.

On the basis of the preceding information, classify each of the following ions as present (P), absent (A), or undetermined (U) by the tests described:

CO32- SO42- PO43- SCN- Cl- AL3+ Cu2+ Fe3+

HINT
What ion do you use the HCl to test for? Is the indicator for that ion present? What ion has a test where you add barium chloride and what is the indicator for that test? What ion uses Fe(NO3)3 to test for it and what is the indicator for that ion to be present? Are you doing any other tests for ions? Is the Fe3+ ion initially present if you had to add Fe(NO3)3?

ANSWER

If 1 M HCl causes bubbling, then carbonate ion must be present. If a clear solution results when barium chloride is added, then sulfate ion must be absent. If Fe(NO3)3 is added and a deep red color results, then SCN- must be present. Since SCN- is present and the solution was not originally red and you had to add iron (III) then iron (III) must have been absent. All the other ions are undetermined because there was no tests run for the other ions.

Determination of Water Hardness By Complexometric Titration Class Notes

Determination of Water Hardness By Complexometric Titration Class Notes: "Why Be Concerned About Hard Water?

The determination of water hardness is a useful test that provides a measure of quality of water for households and industrial uses. Originally, water hardness was defined as the measure of the capacity of the water to precipitate soap. Hard water is not a health hazard. People regularly take calcium supplements. Drinking hard water contributes a small amount of calcium and magnesium toward the total human dietary needs of calcium and magnesium. The National Academy of Science states that consuming extremely hard water could be a major contributor of calcium and magnesium to the diet.

Hard water does cause soap scum, clog pipes and clog boilers.

Soap scum is formed when the calcium ion binds with the soap. This causes an insoluble compound that precipitates to form the scum you see. Soap actually softens hard water by removing the Ca2+ ions from the water.

When hard water is heated, CaCO3 precipitates out, which then clogs pipes and industrial boilers. This leads to malfunction or damage and is expensive to remove."

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G. GURDJIEFF : Meetings with Remarkable Men

Unhappiness on earth is from the wiseacring of women.

He is stupid who is 'clever'.

Happy is he who sees not his unhappiness.

The teacher is the enlightener, who then is the ass?

Fire heats water, but water puts out fire.

Genghis Khan was great, but our policeman, so please you, is still

greater.

If you are first, your wife is second; if your wife is first, you had better be zero: only

then will your hens be safe.

If you wish to be rich, make friends with the police.

If you wish to be famous, make friends with the reporters.

If you wish to be full—with your mother-in-law.

If you wish to have peace—with your neighbour.

If you wish to sleep—with your wife.

If you wish to lose your faith—with the priest.

To give a fuller picture of my father's individuality, I must say

something about a tendency of his nature rarely observed in

contemporary people, and striking to all who knew him well. It was

chiefly on account of this tendency that from the very beginning, when

he became poor and had to go into business, his affairs went so badly

that his friends and those who had business dealings with him

considered him unpractical and even not clever in this domain.

And indeed, every business that my father carried on for the purpose

of making money always went wrong and brought none of the results

obtained by others. However, this was not because he was unpractical or

lacked mental ability in this field, but only because of this tendency.

This tendency of his nature, apparently acquired by him when still a

child, I would define thus: 'an instinctive aversion to deriving personal

advantage for himself from the naivete and bad luck of others'.

In other words, being highly honourable and honest, my father could

never consciously build his own welfare on the misfortune of his

neighbour. But most of those round him, being typical contemporary

people, took advantage of his honesty and deliberately tried to cheat

him, thus unconsciously belittling the significance of that trait in his

psyche which conditions the whole of Our Common Father's

commandments for man.

Indeed, there could be ideally applied to my father the following

paraphrase of a sentence from sacred writings, which is quoted at the

present time by the followers of all religions everywhere, for describing

the abnormalities of our daily life and for giving practical advice:

Strike—and you will not be struck.

But if you do not strike—they will beat you to death, like Sidor's

goat.

In spite of the fact that he often happened to find himself in the midst

of events beyond the control of man and resulting in all sorts of human

calamities, and in spite of almost always encountering dirty

manifestations from the people round him—manifestations recalling

those of jackals—he did not lose heart, never identified himself with

anything, and remained inwardly free and always himself.

The absence in his external life of everything that those round him

regarded as advantages did not disturb him inwardly in the least; he was

ready to reconcile himself to anything, provided there were only bread

and quiet during his established hours for meditation.

What most displeased him was to be disturbed in the evening when

he would sit in the open looking at the stars.

I, for my part, can only say now that with my whole being I would

desire to be able to be such as I knew him to be in his old age.

Owing to circumstances of my life not dependent on me, I have not

personally seen the grave where the body of my dear father lies, and it

is unlikely that I will ever be able, in the future, to visit his grave. I

therefore, in concluding this chapter devoted to my father, bid any of my sons, whether by blood or in spirit, to seek out,

when he has the possibility, this solitary grave, abandoned by force of circumstances ensuing chiefly from that human scourge called the herd instinct, and there to set up a stone with the inscription:

I AM THOU,

THOU ART I,

HE IS OURS,

WE BOTH ARE HIS.

SO MAY ALL BE

FOR OUR NEIGHBOUR.

How Cu reacts with NH3

An equilibrium involving copper(II) ions

Students add ammonia to a solution of copper(II) sulfate, observe the colour changes taking place, and then reverse the reaction by the addition of sulfuric acid.

Read our standard health & safety guidance

Lesson organisation

This experiment is best carried out by students working individually. It takes about 15 - 20 minutes.

Apparatus and chemicals

Each student or working group will require:

Eye protection
Test-tubes, 3
Test-tube rack
Test-tube holder
Dropping pipettes, 2

Copper(II) sulfate solution, 1.0 mol dm^-3 (Harmful at this concentration), about 3 cm³ (see note 1)
Ammonia solution, 1.0 mol dm^-3 (Low hazard at this concentration), about 10 cm³
Dilute sulfuric acid, 1.0 mol dm^-3 (Irritant at this concentration), about 10 cm³

Technical notes

Copper(II) sulfate solution (Harmful at concentration used) Refer to CLEAPSS Hazcard 27C
Ammonia solution (Low hazard at concentration used) Refer to CLEAPSS Hazcard 6 and Recipe Card 4
Dilute sulfuric acid (Irritant at concentration used) Refer to CLEAPSS Hazcard 98A and Recipe Card 69

1 The copper(II) sulfate solution is most conveniently supplied in a bottle fitted with teat pipette.

Procedure

a Put 10 drops of copper(II) sulfate solution into each of two test-tubes.

b Add ammonia solution drop-by-drop to the first test-tube. Shake the tube gently from side to side after adding each drop. What happens as you add a few drops of the solution?

c Add more drops of ammonia solution. What happens? Continue until you have a clear blue solution.

d Divide the solution from c into two test-tubes. Add dilute sulfuric acid drop-by-drop to one of the solutions from c. Shake the tube gently from side to side after adding each drop. Do you get back to where you started – compare the three test-tubes?

e Can you repeat the whole process by adding ammonia again to the acidified solution?

Teaching notes

If this experiment is being carried out with pre-A-level students, the reactions occurring can simply be explained by reference to the addition of an alkali (containing hydroxide ions) being added to a solution of a copper compound, producing copper(II) hydroxide initially and later a complex compound of ammonia. The reversal of the process is easy to explain since sulfuric acid is capable of neutralising the alkaline ammonia and causing the reaction to reverse back to the start:

CuSO₄(aq)(pale blue solution) + 2NH₃(aq) + 2H₂O(l) → Cu(OH)₂(s) + (NH₄)₂SO₄(aq)(pale blue precipitate)

Cu(OH)₂(s)(pale blue precipitate) + ammonia → complex copper compound (dark blue solution)

A rather more advanced treatment in terms of complexes and ligand exchange would involve the following explanation:

1 Ammonia is a weak base and forms a few ammonium and hydroxide ions in solution

NH₃(g) + H₂O(l) ⇌ NH₄⁺(aq) + OH^-(aq)

2 The hexaaquacopper(II) ions react with hydroxide ions to form a precipitate. This involves deprotonation of two of the water ligand molecules:

[Cu(H₂O)₆]²⁺(aq)(pale blue) + 2OH^-(aq) → [Cu(H₂O)₄(OH)₂](s)(pale blue precipitate) + 2H₂O(l)

3 The copper(II) hydroxide precipitate reacts with ammonia molecules to form tetraamminediaquacopper(II) ions This involves ligand exchange:

[Cu(H₂O)₄(OH)₂](s)(pale blue precipitate) + 4NH₃(aq) ⇌ [Cu(NH₃)₄(H₂O)₂)]²⁺(aq)(dark blue solution) + 2OH^-(aq) + 2H₂O(l)

4 Thus the overall reaction, combining 2 with 3, gives:

[Cu(H₂O)₆]²⁺(aq) + 4NH₃(aq) ⇌ [Cu(NH₃)₄(H₂O)₂)]²⁺(aq) + 4H₂O(l)

5 Addition of dilute sulfuric acid introduces H⁺ ions, which react with NH₃ molecules to form NH₄⁺ ions, and this draws the equilibrium in 4 back to the left-hand side, regenerating the hexaaquacopper(II) ions in the process.

Health & Safety checked, August 2008

Web Links

This link describes how to obtain a solid sample of a salt containing the dark blue tetraamminediaquacopper(II) ions:
http://firstyear.chem.usyd.edu.au/LabManual/E16.pdf

(Websites accessed August 2008)

GuruPrakashAcadmy

Schottky Defect

Point Defects in Ionic Crystals

solid defects

Demonstration of Resonance

How double indicator titration works

Qualitative Analysis of Some Common Ions Class Notes

Determination of Water Hardness By Complexometric Titration Class Notes

G. GURDJIEFF : Meetings with Remarkable Men

The Photoelectric Effect - explanation of the photoelectric effect

Quantum Double Slit Experiment

Physics 20 Note-A-Rific

How Cu reacts with NH3

An equilibrium involving copper(II) ions

Lesson organisation

Apparatus and chemicals

Technical notes

Procedure

Teaching notes

Web Links

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