Education

Saturday, 29 April 2017

Solid state

Definition

the state of matter in which materials are retain their boundaries without support, the atoms or molecules occupying fixed positions with respect to each other and unable to move freely.
Types of solid:-

1. Crystalline Solid :- Eg:- Metals And Non metals

2. Amorphous Solid :- Eg:- Rubber ,Glass ,Plastic

Difference and Comparison between of characteristics

Crystalline Solid: -

Contain regular arrangement having short range & as well as long range order.

Definite geometric shape, Sharpe melting point, they have definite heat fusion, they undergo clean cleavage, and they are true solid.

Amorphous Solid: -

Containing irregular arrangement having short range order only, irregular shape, melting over range of temp, they do not have definite heat of fusion they undergo an irregular cut they are pseudo solid or super cooled solid.

Classification of crystalline solid:-

1. Ionic Solid

2. Molecular Solid

3. Covalent of network Solid

4. Metallic Solid

1. Ionic solid: -

In these crystalline solids, constituent particle are positive or negative ion held together by columbic or electrostatic forces of attraction.

Eg:-NaCl, Mgo,Cao, kcl

2. Molecular solids:-

These are of three types

1 Non polar molecular solid: - in these the constituent particles are atoms of noble gas or non polar molecules are held by London dispersion forces.

Eg: - Ar, H2.

2- polar molecular solids: - In these solids constituent particles are held together by dipole-dipole attraction forces.

Eg: - Hcl, SO2.

3. Hydrogen bonded molecular solids: - in these types of molecular solids constituent particles are molecule containing hydrogen linked to F, O and N held by hydrogen bonding.

Eg: - H2O (ice), NH3.

3. Covalent or Network Solids: -

Constituent particles are atoms held together by covalent bonds

Eg: - C (diamond), Sio2 (quartz)

4. Metallic solids: -

Constituent particles are positive ions in a sea of mobile electrons held together by metallic bonds.

Eg: - All metals and alloys.

Crystal Lattice: -

Regular arrangement of constituent particles in 3-D is called crystal lattice or space lattice.

Unit cell: -

The smallest three dimensional portion of a complete space lattice which when repeated over and again in different direction produces the complete space lattice is called unit cell.

Bravais lattice: -

The fourteen lattices corresponding to seven crystal system are known as Bravais Lattice.

Coordination number: -

Tthe number of spheres touching to a particular sphere.

No. of atoms per unit cell:-

(a) No. of atoms in simple cubic lattice:- 8 atoms are at corner

8*1/8=1

Simple Cubic Latice

(b) No. of atoms in BCC:

8 atoms are at corner and one in the body

8*1/8+1+2

BCC

8 atoms are at corner and six atoms are at faces (one on each face)

8*1/8+6*1/2=4

FCC

Close packing in crystals:-

(a) Close packing in one dimension : - sphere are touching each other in a row. In this arrangement coordination no. is 2

Close packing in one dimension

(b) Close packing in two dimension:- it is done by two ways-

1. Square close packing: - in this arrangement spheres of second row are exactly above the first row.

Square Close Packing

2. Hexagonal close packing: - in this arrangement the spheres of second row may be placed in the depression of the first row.

Hexagonal Close Packing

1. Three dimensional close packing from two dimensional closed packed layer: - starting from the square close packed layer the second layer and all further layers will be built up such that they are horizontally as well as vertically aligned with each other.

Simple cubic lattice formed by A A A......... arrengment

2. Three dimensional packing from two dimensional hexagonal close packing:- when spheres are arranged in hexagonal close packing in 2-Dthe two types of voids ‘a’& ‘b’ are formed.

‘a’ & ‘b’ voids are triangular when second layer is placed over the void of first layer (only one void is full filled) in hexagonal close packing and these layer form two voids

C – Triangular and D – Octahedral.

A stack of two layers of close packed spheres and voids generated in them. T = Tetrahedral void; O = Octahedral void

Packing efficiency: -

The percentage of the total space filled by the particles is called packing efficiency.

Packing fraction: -

The fraction of the total space filled is called packing fraction.

=>> Calculation of spaces occupied

1. in a simple cubic unit cell:-

Suppose radius of sphere is = r

Edge length of unit cell = a

As sphere are touching each other

a=2r

No. of sphere per unit cell= 8*1/8=1

Volume of sphere = 4/3πr³

Volume of cube =a³= (2r)³ = 8r³

Packing fraction

% occupied = 52.4%

2. in face centered cubic structure (Cubic close packing):- spheres of the face center touching the sphere of the corner,

Then, AC = 4r

in ∆ ABC

% occupied = 74%

3. In body centred cubic structure: - Sphere at the body centred touching the sphere of the corner.

Body diagonal, AD = 4r

Further, face diagonal,

% occupied = 68%

=> Radius (r) of the octahedral void =0.414R

=> Radius (r) of the tetrahedral void = 0.225R

In CCP or HCC. If there are N spheres in the packing.

No. of octahedral voids = N

No. of Tetrahedral voids = 2N

Imperfection and defects in solids

Types of Defects:-

1. Stoichiometric defects

2. Non-Stoichiometric defects

3. Impurity defects

1. Stoichiometric defects:-

In these defects the ratio of anion and cation remains same as the Stoichiometry of the substance not changed.

These are also classified as:

a. Vacancy defects: - These arise when some sites of the crystal lattice are vacant, it decrease density.

b. Interstitial Defects: - When some constituent particles present in the interstitial side, it increase the density of the crystal.

c. Schottky Defects:- If in a ionic crystal +ve or –ve ions missing their lattice sites so that electric neutrality is maintained

Ex: NaCl, KCl, CsCl, AgBr.

d. Frenkel Defect: - If an ion missing their lattice site (causing vacancy or hole their) and comes in the interstitial side, so maintain electric neutrality or Stoichiometry of the crystal is called Frenkel defect.

Ex: ZnS, AgCl, AgBr, AgI.

2. Non-Stoichiometric Defect: -

In this defect ratio of cation & anion became different from the original ratio.

It is of two types:

a. Metal excess: - this may occur in two way-

I. By anion vacancies: A –ve ion may missing their lattice site and leaving a hole which occupied by an electron there by maintaining electrical balance.

II By the presence of extra cation in the interstitial site: - it is extra cation (+ve ion) is occupying the interstitial site.

Anion = -ve ion

Cation = +ve ion

And electric neutrality is maintained by an electron is present in another interstitial site.

b. Metal deficiency:- This defect shows variable vacancy and occurs usually due to the missing of a cation from its lattice site and two monovalent cation is replaced one divalent cation to maintain electric neutrality.

III. Impurity defects :- These defects arises when foreign atoms are present at the lattice site in place of host atoms or in the interstitial sites.

Doping: -

The process of adding impurities to a crystalline substance so as to change its properties is called doping.

Electrical properties of solids

1. Conductors:-

The solids which have conductivity in the range of 10⁴to 10⁷ ohm^-1m^-1 are called conductors.

2. Insulators :-

The solids which have extremely low conductivity ranging between 10^-20 to 10^-10ohm^-1m^-1 are called insulators.

3. Semiconductors:-

The solids which have conductivity between the conductors and insulators, ranging from 10^-6 to 10⁴ ohm^-1m^-1 are called semiconductors.

Band Theory

=> In case of metals (conductors), the atomic orbital’s of the metal atom are so close in energy that they overlap to form a large no. of molecular orbital’s very close in energy. This set of molecular orbital’s is called a band. Two types of band formed then electron can easily flow by gaining energy and conduct electricity.

=> If gap between band is large electron can not jump from valance band to conduction band, so these behave as insulator.

=> If the gap is small then electron may jump and show some conductivity and act as semiconductor.

Band Theory

Magnetic properties of solids: -

1. Diamagnetic Substances: -

Substances which are weakly repelled by the external magnetic field are called diamagnetic substances.

Ex: TiO₂, H₂O, NaCl

2. Paramagnetic Substances: -

Substances which are attracted by the external magnetic field are called paramagnetic substances.

Ex: O₂, Cu²⁺, Fe³⁺

3. Ferromagnetic Substances: -

Substances which show permanent magnetism even in the absence of magnetic field are called ferromagnetic substances.

Ex: Fe, Ni

4. Anti- Ferromagnetic Substances: -

Substances which are expected to posses’ paramagnetism and ferromagnetism on the basis of magnetic moments of the domains but actually they posses Zero magnetic moment are called anti- ferromagnetic substances.

Ex: MnO

5. Ferromagnetic Substances: -

Substances which are expected to posses large magnetism on the basis of magnetic moments of the domains but actually have small net magnetic moment are called ferromagnetic substances.

Ex: Fe₃O₄

electrochemistry for 12th

science study

defination
Electrochemistry is the study of chemical processes that cause electrons to move. This movement of electrons is called electricity, which can be generated by movements of electrons from one element to another in a reaction known as an oxidation-reduction ("redox") reaction
or
we can say that electrochemistry is the branch of science in which we study about the energy relationship between chemical energy and electrical energy produced during redox
voltic cell
reactionElectrochemical cells that use an oxidation-reduction reaction to generate an electric current are known as galvanic or voltaic cells. Because the potential of these cells to do work by driving an electric current through a wire is measured in units of volts, we will refer to the cells that generate this potential from now on as voltaic cells.

Let's take another look at the voltaic cell in the figure below.

Within each half-cell, reaction occurs on the surface of the metal electrode. At the zinc electrode, zinc atoms are oxidized to form Zn²⁺ ions, which go into solution. The electrons liberated in this reaction flow through the zinc metal until they reach the wire that connects the zinc electrode to the platinum wire. They then flow through the platinum wire, where they eventually reduce an H⁺ ion in the neighboring solution to a hydrogen atom, which combines with another hydrogen atom to form an H₂ molecule.

The electrode at which oxidation takes place in a electrochemical cell is called the anode. The electrode at which reduction occurs is called the cathode. The identity of the cathode and anode can be remembered by recognizing that positive ions, or cations, flow toward the cathode, while negative ions, or anions, flow toward the anode. In the voltaic cell shown above, H⁺ ions flow toward the cathode, where they are reduced to H₂ gas. On the other side of the cell, Cl^- ions are released from the salt bridge and flow toward the anode, where the zinc metal is oxidized.

Standard-State Cell Potentials for Voltaic Cells

The cell potential for a voltaic cell is literally the potential of the cell to do work on its surroundings by driving an electric current through a wire. By definition, one joule of energy is produced when one coulomb of electrical charge is transported across a potential of one volt.

The potential of a voltaic cell depends on the concentrations of any species present in solution, the partial pressures of any gases involved in the reaction, and the temperature at which the reaction is run. To provide a basis for comparing the results of one experiment with another, the following set of standard-state conditions for electrochemical measurements has been defined.

All solutions are 1 M.
All gases have a partial pressure of 0.1 MPa (0.9869 atm).

Although standard-state measurements can be made at any temperature, they are often taken at 25^oC.

Cell potentials measured under standard-state conditions are represented by the symbol E^o. The standard-state cell potential, E^o, measures the strength of the driving force behind the chemical reaction. The larger the difference between the oxidizing and reducing strengths of the reactants and products, the larger the cell potential. To obtain a relatively large cell potential, we have to react a strong reducing agent with a strong oxidizing agent.

Example: The experimental value for the standard-state cell potential for the reaction between zinc metal and acid is 0.76 volts.

Zn(s) + 2 H⁺(aq) =Zn²⁺(aq) + H₂(g)

E^o = 0.76 V

The cell potential for this reaction measures the relative reducing power of zinc metal compared with hydrogen gas. But it doesn't tell us anything about the absolute value of the reducing power for either zinc metal or H₂.

We therefore arbitrarily define the standard-state potential for the reduction of H⁺ ions to H₂ gas as exactly zero volts.

2 H⁺ + 2 e^- =H₂

E^o = 0.000... V

We will then use this reference point to calibrate the potential of any other half-reaction.

The key to using this reference point is recognizing that the overall cell potential for a reaction must be the sum of the potentials for the oxidation and reduction half-reactions.

E^o_overall = E^o_ox + E^o_red

If the overall potential for the reaction between zinc and acid is 0.76 volts, and the half-cell potential for the reduction of H⁺ ions is 0 volts, then the half-cell potential for the oxidation of zinc metal must be 0.76 volts.

Zn = Zn²⁺ + ~~2 e~~^-	E^o_ox = 0.76 V
+ 2 H⁺ + ~~2 e~~^- = H+ ------------------------	E^o_red = 0.00 V -------------------

Zn + 2 H⁺ = Zn²⁺ + H₂	E^o = E^o_ox + E^o_red = 0.76 V

Predicting Spontaneous Redox Reactions From the Sign of E^o

The magnitude of the cell potential is a measure of the driving force behind a reaction. The larger the value of the cell potential, the further the reaction is from equilibrium. The sign of the cell potential tells us the direction in which the reaction must shift to reach equilibrium.

Consider the reaction between zinc and acid, for example.

Zn(s) + 2 H⁺(aq) = Zn²⁺(aq) + H₂(g)

E^o = 0.76 V

The fact that E^o is positive tells us that when this system is present at standard-state conditions, it has to shift to the right to reach equilibrium. Reactions for which E^o is positive therefore have equilibrium constants that favor the products of the reaction. It is tempting to describe these reactions as "spontaneous."

What happens to the cell potential when we reverse the direction in which a reaction is written? Turning the reaction around doesn't change the relative strengths of the oxidizing or reducing agents. The magnitude of the potential must remain the same. But turning the equation around changes the sign of the cell potential, and can therefore turn an unfavorable reaction into one that is spontaneous, or vice versa.

Standard-State Reduction Half-Cell Potentials

The standard-state cell potentials for some common half-reactions are given in the table below.

Standard-State Reduction Potentials,

	Half-Reaction	E^o_red
	K⁺ + e^- =K	-2.924	Best
	Ba²⁺ + 2 e^- = Ba	-2.90	reducing
	Ca²⁺ + 2 e^- = Ca	-2.76	agents
	Na⁺ + e^- = Na	-2.7109
	Mg²⁺ + 2 e^- = Mg	-2.375
	H₂ + 2 e^- = 2 H^-	-2.23
	Al³⁺ + 3 e^- = Al	-1.706
	Mn²⁺ + 2 e^- = Mn	-1.04
	Zn²⁺ + 2 e^- = Zn	-0.7628
	Cr³⁺ + 3 e^- = Cr	-0.74
	S + 2 e^- = S^2-	-0.508
	2 CO₂ + 2 H⁺ + 2 e^- = H₂C₂O₄	-0.49
	Cr³⁺ + e^- = Cr²⁺	-0.41
	Fe²⁺ + 2 e^- = Fe	-0.409
	Co²⁺ + 2 e^- = Co	-0.28
	Ni²⁺ + 2 e^- = Ni	-0.23
	Sn²⁺ + 2 e^- = Sn	-0.1364
	Pb²⁺ + 2 e^- = Pb	-0.1263
	Fe³⁺ + 3 e^- = Fe	-0.036
	2 H⁺ + 2 e^- = H₂	0.0000...
	S₄O₆^2- + 2 e^- = 2 S₂O₃^2-	0.0895
Oxidizing	Sn⁴⁺ + 2 e^- = Sn²⁺	0.15
power	Cu²⁺ + e^- = Cu⁺	0.158	Reducing
increases	Cu²⁺ + 2 e^{- =} Cu	0.3402	power
	O₂ + 2 H₂O + 4 e^- = 4 OH^-	0.401	increases
	Cu⁺ + e^- = Cu	0.522
	I₃^- + 2 e^- = 3 I^-	0.5338
	MnO₄^- + 2 H₂O + 3 e^- = MnO₂ + 4 OH^-	0.588
	O₂ + 2 H⁺ + 2 e^- = H₂O₂	0.682
	Fe³⁺ + e^- = Fe²⁺	0.770
	Hg₂²⁺ + 2 e^- = Hg	0.7961
	Ag⁺ + e^- = Ag	0.7996
	Hg²⁺ + 2 e^- = Hg	0.851
	H₂O₂ + 2 e^- = 2 OH^-	0.88
	HNO₃ + 3 H⁺ + 3 e^- = NO + 2 H₂O	0.96
	Br₂(aq) + 2 e^- = 2 Br^-	1.087
	2 IO₃^- + 12 H⁺ + 10 e^- = I₂ + 6 H₂O	1.19
	CrO₄^2- + 8 H⁺ + 3 e^- =Cr³⁺ + 4 H₂O	1.195
	Pt²⁺ + 2 e^- = Pt	1.2
	MnO₂ + 4 H⁺ + 2 e^- = Mn²⁺ + 2 H₂O	1.208
	O₂ + 4 H⁺ + 4 e^- = 2 H₂O	1.229
	Cr₂O₇^2- + 14 H⁺ + 6 e^- = 2 Cr³⁺ + 7 H₂O	1.33
	Cl₂(g) + 2 e^- = 2 Cl^-	1.3583
	PbO₂ + 4 H⁺ + 2 e^- = Pb²⁺ + 2 H₂O	1.467
	MnO₄^- + 8 H⁺ + 5 e^- = Mn²⁺ + 4 H₂O	1.491
	Au⁺ + e^- = Au	1.68
	H₂O₂ + 2 H⁺ + 2 e^- =2 H₂O	1.776
	Co³⁺ + e^{-2 =}Co²⁺	1.842
Best	S₂O₈^2- + 2 e^- = 2 SO₄^2-	2.05
oxidizing	O₃(g) + 2 H⁺ + 2 e^- = O₂(g) + H₂O	2.07
agents	F₂(g) + 2 H⁺ + 2 e^- = 2 HF(aq)	3.03

Balancing Redox Reactions

Method 1: Oxidation Number Method

Step 1: Assign oxidation numbers to each atom.
Step 2: Determine the net change in charge to determine the ratio of atoms
Step 3: Use the ratio to eliminate the net charge change
Step 4: Use the ratio as coefficients for the elements
Step 5: Add H+ (under acidic conditions), OH- (under basic conditions), and H2O to balance charges.

Method 2: Half-Reaction Method

Step 1: Determine oxidation numbers for each atom
Step 2: Use oxidation numbers to determine what is oxidized and what is reduced.
Step 3: Write a half-reaction for reduction
Step 4: Write a half-reaction for oxidation
Step 5: Balance all elements except H and O
- if have acid redox reaction: Balance the O using $H_{2} O$ , balance the $H$ using protons
- if have base redox reaction: Balance O using $O H^{-}$
Step 6: Add up the charge on each side
Step 7: Balance the charges by adding electrons
Step 8: Multiply the half-reactions by factors that cancel out electrons
Step 9: Add the two half-reactions back together to eliminate out intermediate
$\begin{matrix} (1.27) & 6 H^{+} + 2 M n O_{4}^{1 -} + 5 H_{2} C_{2} O_{4} \to 2 M n^{2 +} + 8 H_{2} O + 10 C O_{2} \end{matrix}$

Free elements have an oxidation state of 0. (e.g., He, N2, O2 has an oxidation state of 0)
The oxidation state of one atom ion must equal the net charge. ( Ex: F- oxidation state is -1, K+ oxidation state is +1)
The sum of the oxidation state has to equal the total net charge for a compound. (Ex: MnO4 has a net charge of -1, Mn(+7)O4(-8)= -1)
The alkali metals (Group I elements) have an oxidation state of +1. (EX: Li2O, Li= +1)
The alkaline earth metals (Group II elements) always have an oxidation state of +2. (Ex: CaO, Ca=+2)
Oxygen has an oxidation state of -2 in a compound
Fluorine has an oxidation state of -1 in a compound
Hydrogen has an oxidation state of +1 in a compound.
Transition metals and other metals may have more than one common ionic charge. ( EX: Chromium's common ionic charges are Cr+2 and Cr+3

Terminology

Anode: Electrode in an electrochemical cell on which the oxidation reaction occurs.

Cathode: Electrode in an electrochemical cell on which the reduction reaction occurs<iframe style="width:120px;height:240px;" marginwidth="0" marginheight="0" scrolling="no" frameborder="0" src="//ws-in.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=IN&source=ac&ref=qf_sp_asin_til&ad_type=product_link&tracking_id=technologyi06-21&marketplace=amazon&region=IN&placement=B013I2YJTO&asins=B013I2YJTO&linkId=4951db99a0056fb35f36f4b413e05900&show_border=false&link_opens_in_new_window=false&price_color=333333&title_color=0066C0&bg_color=FFFFFF"> </iframe>

Education

Saturday, 29 April 2017

Solid state

Definition

Difference and Comparison between of characteristics

Crystalline Solid: -

Amorphous Solid: -

Classification of crystalline solid:-

1. Ionic solid: -

2. Molecular solids:-

3. Covalent or Network Solids: -

4. Metallic solids: -

Crystal Lattice: -

Unit cell: -

Bravais lattice: -

Coordination number: -

No. of atoms per unit cell:-

Close packing in crystals:-

Packing efficiency: -

Packing fraction: -

=>> Calculation of spaces occupied

1. in a simple cubic unit cell:-

Imperfection and defects in solids

Types of Defects:-

1. Stoichiometric defects:-

2. Non-Stoichiometric Defect: -

Doping: -

Electrical properties of solids

1. Conductors:-

2. Insulators :-

3. Semiconductors:-

Band Theory

Magnetic properties of solids: -

1. Diamagnetic Substances: -

2. Paramagnetic Substances: -

3. Ferromagnetic Substances: -

4. Anti- Ferromagnetic Substances: -

5. Ferromagnetic Substances: -

Friday, 28 April 2017

electrochemistry for 12th

Balancing Redox Reactions

Terminology

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