TyroCity: Chemistry 12 Notes

Zinc (Zn)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

The element Zn, Cd and Hg forms group IIB of the periodic table. These elements do not have partially filled d. orbitals both in metal and metal ion. So, they do not exhibit general properties of transition metals and are called non- typical transition metal.

Occurrence:

Zinc occurs in nature only in combined state. The main ores of zinc are:

Heat Treatment Of Steel

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Steel can be given desire property by heat treatment there are three different heat treatment.

1. Annealing:
This method is done to obtain soft steel. When steel is heated to red hot (about 11000c) and then cooled & lowly, steel becomes soft and the process is called annealing. In annealed steel, carbon is present in free state.

2. Quenching or Hardening:
This process is done to obtain hard steel and brittle steel. When steel is heated to red not and then cooled rapidly by plunging into water or oil, gives hard and brittle steel and the process is called Quenching. In quenched steel, carbon is present in combined form as iron carbide (Fe3C) or Cementite.

3. Tempering:
This process is done to obtain hard and malleable steel Quenched steel is heated below red hot (about 7000c ) and then cooled slowly to obtain mild steel and the process is called tempering. In tempered steel, carbon is present in both combined and free state.

Enthalpy (H)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is the sum of internal energy and product of pressure and volume.

i.e. H=E+PV…..(1)
Here, E, P & V all are state function so H is also the state function.
Being a state function it depends upon initial and final state and also its absolute value cannot be determined however change can be measured.
Now, ∆H=Hp-Hr…………(2)
Where, Hp= enthalpy of product
Hr= Enthalpy of reactant
∆H at constant pressure
We have, from first law of thermodynamics;
Q=∆E+W
Q=∆E+P∆V….(1)
Also, H=E+PV……..(2)
At constant pressure, Q=Qp
So, equation (1) becomes,

Qp=Ep-Er+P(Vp-Vr)
Qp=Ep+PVp-(Er+PVr)
Qp=Hp-Hr
Qp=∆H
It means, heat of reaction at constant pressure is equal to change in enthalpy of reaction.

Determination Of Order Of Reaction By Initial Concern Method

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

For the reaction,

2NO + Cl2 → 2NOCl

Following datas were obtained:

Determine the order of the reaction with respect to NO, Cl2 and overall order. Write the rate law expression and determine the value of rate constant.

Soln:

Let the order w.r.t. NO and Cl2 be in and n. The rate low expression will be,

Dividing eqn (ii) by (i) we get,

Dividing eqn (iii) by (ii), we get,

order w.r.t. NO = 2

order w.r.t. Cl2 = 1

Overall order of r × n = 2 + 1 = 3

Then, the rate law expression,

Rate = k [NO]2 [Cl2]

Putting the value of m and n in equation (i), we get,

The experimental data for the reaction

Determine the order of the r × n wrt A and B and overall r × n. Write the rate law expression and determine the value of rate of constant.

Solution:

Let the order w.r.t. A and B be m and n. The rate law expression will be,

Dividing eqn (ii) by (i) we get,

Hess’s Law Of Constant Heat Summation

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Hess’s law of constant heat summation states, “The total amount of heat involved in a physic-chemical process is same whether the process is done in single step or multiple steps involving intermediates.”

A can be converted to B into two ways:

Method I: A I directly converted to B

A = B + Q

Method II: A is first converted to C, then to D and finally to B

According to Hess’s Law,

Q = Q1 + Q2 + Q3

This law can be verified by taking the conversion of carbon to carbon dioxide.

Method I: Carbon is directly oxidized to carbon dioxide.

Method II: Carbon is first converted to carbon monoxide and then to carbon dioxide.

This result verifies Hess’s law of constant heat summation.

Application of Hess’s law:

This law can be used to determine heat of transition of allotropes.
This law can be used to determine heat of reaction of those reactions which cannot be performed in lab.

Chemistry XII

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

General

Define Hydrogen Bond. How Is It originated?

General & Physical Chemistry (Section A)
Volumetric Analysis

Energetics of Chemical Reactions

Chemical Thermodynamics

Chemical Kinetics

Inorganic Chemistry (Section C)
Heavy Metals

Coinage Metal

Heavy Metals: Copper

Heavy Metals: Zinc

Heavy Metals: Mercury

Heavy Metals: Iron

Heavy Metals: Silver

Other titles

Pseudo Unimolecular Reaction

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

In a chemical reaction if two or more reactants are involved but the rate of reaction depends only upon the concentration of one of the reactant and independent of other reactants then it is said to be pseudo unimolecular reaction.

Example:

Acid Catalyzed Hydrolysis of ester
Acid Catalyzed hydrolysis of sucrose

For the reaction, A (g) + B (g) → C(g) + D (g) . It is found that Rate = k [A]2 [B]

How many times does the rate of reaction increase or decrease if

The partial pressure of both A and B are double.
The partial pressure of A doubles but of B remains constant.
The volume of reacting vessel is doubled.
An inert gas is added which doubles the overall pressure whilist the partial pressure of A and B remains constant.
The temperature rises by 300C.

Soln:

Let the rate of reaction be R. Then,

R = k [A]2 [B]

1. Molar Concentration is directly proportional to partial pressure so if partial pressure of A and B is doubled their concentration is doubled.

2. The concentration of a is doubled while that of B is constant

Rate of reaction increases by 4 times.

3. When volume of vessel is doubled the concentration of both A and B is halved.

So,

Rate of reaction decreases by 8 times.

4. The concentration of A and B remains constant so rate of r ×n is also constant.

5. We know increase in temperature by 10 0c causes increases in rate of reaction by 2-3 times.

For 300C (100C + 100C 100C). The rate increases by 8 (2 ×2×2) to 27 ( 3 ×3×3) times

For the reaction;
A + B → products, following data were obtained.

Let rate law exp. be,

We have,

Order Of Reaction

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Let’s consider a reaction,
A + B → product

The rate of reaction of above reaction is given by rate law expression,

Rate:

where k is constant called rate constant and is rate of reaction when concentration of all reactants is unit molarity (1m). Here m is order of reaction with respect to A, n is order of reaction w.r.t B and (m +n) is overall order of reaction. So, order of a reaction is the sum of the power to which the concentration of reactants is raised in the experimental rate law expression.

Unit of rate constant

Let’s consider a reaction,

A → product

The unit of rate constant depends upon the order of reaction.

For a reaction,

A → product

The rate law expression is,

when n = 0 The reaction is said to be a zeroth order reaction and for such reaction the rate of reaction is independent of concentration of reactant.

E.g.

Enzyme catalysed bio-chemical reaction.
Decomposition of HI on the surface of gold.
Reaction between H2 and Cl2 to give HCl in presence of light.

When, n =1,
The reaction is said to be a first order reaction and for such reaction the change rate is equal to the change in concentration of reactant.

Cuprous Oxide Or Red Oxide Of Cupper (Cu2O)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It occurs in nature as cuprite. It is obtained by heating copper in air above 11000c.

4Cu+o2 above 11000c → 2Cu2o.

If can also be obtained by reducing alkaline Cuso4. (fehling’s solutional with reducing agents like glucose.

CuSO4+2NaOH → Cu(OH)2+Na2SO4
Cu(OH)2 → CuO+H2O
2CuO + C6H12O6 → Cu2O + C6H12O7

Properties

It is a red amorphous solid insoluble in water.
It dissolves in conc. HCl giving cuprous chloride.

Cu2O + 2Conc.HCl → Cu2Cl2 + H2O

It dissolves in conc. H2SO4 giving copper sulphate and metallic copper

Cu2O + H2OSO4 → CuSO4 + H2O + Cu

Uses

It is used in making ruby-red glass.
It is used in making anti-rust paints.
It is used in preparation of Cu2Cl2.

Introduction To Thermodynamics

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Energy is the capacity of doing work and it has different forms. Energy can neither be created nor be destroyed but can be transferred from one form to another.
Thermodynamics is a branch of science that deals with the inter-conversion of one form of energy into another. In another word, it is the relation between energy change and chemical reaction.
Different terms used in thermodynamics:
System
The part of universe which is our observation is called system.
Surrounding
The part of our universe beyond the system is called surrounding.
Boundary
The part of universe that separates system from surrounding is called boundary.

Types of system
Open system
The system which can exchange both matter and energy to the surrounding is called open system.eg water kept in open vessel.
Closed system
The system which can exchange energy but not matter to the surrounding is called closed system.eg water kept in closed vessel.
Isolated system
The system which can neither exchange energy nor matter to the surrounding is called isolated system.eg water kept in thermos.

Free Energy Change And Net Useful Work

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Work other than pressure volume work (PΔV) is net useful work. So, total work of a process is,

W = Wnet + PΔV

Wnet = W – PΔV

From Gibb’s helmuntz equation,

ΔG = H – TΔS ……………. (i)

We have,

H = E + PΔV
S = Q /T

TΔS = Q

Putting the values of H and TS in eqn (i), we get
ΔG = ΔE + PΔV – Q

From first law of thermodynamics
Q = ΔE + W

Putting the value of Q in above enq we get,
G = Δ E + PΔV – ΔE – W
G = PΔV – W
G = – (W – PΔV)
G = – Wnet
Wnet is – ΔG
Thus, the net useful work is the amount of decrease in free energy of a system under constant temperature and pressure.

Relation between free energy change and cell potential

The net work done by galvanic cell in carrying charge is

W = charge × potential difference = nf Ecell

We have,
ΔG = -Wnet
ΔG = -nfEcell

Relation between G and equilibrium constant

The variation of G is given by Nernst equation as,
G = ΔG + RT in Q

Where, Q = reaction quotient

Where, the reaction is at equilibrium
g = k (equilibrium constant)
ΔG = O
O = G° + RT in k
ΔG° = -RT InK
ΔG = -2.303 RT logK

The overall reaction for corrosion of iron by oxygen is,

4Fe (s) + 3O2 (g) → 2Fe2O3 (s) Rust

Calculate the free energy change and equilibrium constant for this reaction at 250°c.

Given,

ΔS° and ΔH° = -543 JK-1 and -1652 KJ mol-1
= -1652000 Jmol-1

Δ G° = Δ H° – TΔS°
= 1652000 – 298 × (-543)
= -1490186 J

Again,

ΔG° = -RTInK
= -2.303 RTlogK
1490186 = – 2.303 × 8.314 × 298 × log K
logK = 261.17
K = 10261.17
K = 1.48 × 10261.17

Calculate the free energy at standard condition for galvanic cell having following cell reaction.

2Al (s) + 3 Cu ++ (aq) → 2Al+++ (aq) + 3Cu (s)

E° Cu++/Cu = 0.34 V → E° Al+++/A1 = -1.66V

So, the standard cell potential,

E°cell = E°cathode – E°anode

= E°cu++/cu – E°Al+++/A1
= 0.4 – (-1.66)
= 2V

Again, Δ G = -nfEcell
= – 6 × 96500 × 2
= 1.158 × 106J

Ferric Chloride (FeCl2 or Fe2Cl6)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Preparation:

Anhydrous FeCl3 is obtained by passing dry Cl2 gas over red hot iron.
2Fe + 3Cl2 → 2FeCl3

Hydrated ferric chloride is obtained by dissolving iron in aquaregia or by dissolving Fe2O3 or Fe (OH)3 in HCl. On crystallization FeCl3 solution gives yellow crystals of FeCl3 6H2O.
2Fe + 9HCl + 3HNO3 → 2FeCl3 + 3NOCl + 6H2O
Fe2O3 + 6HCl → 2FeCl3 + 3H2O
Fe (OH)2 + 6HCl → FeCl3 + 3 H2O

FeCl3 (ag) crystallization → FeCl3.6H2O
Yellow crytals

Properties:

Anhydrous FeCl3 is black amorphous solid while hydrated FeCl3 is yellow crysaline solid.
At lower temperature (4000c) the vapor density of ferric chloxde corresponds to the molecular formula Fe2Cl6. Fe2Cl6 is chlorine bridged dimeric structure.

At higher temperature (7000c), Fecl3 decompose forming ferrous chloride.
FeCl3 above 700 → 2FeCl2 + Cl2

Hydrolysis
The aqueous solution of FeCl3 is acidic due to hydrolysis to form weak base and strong acid.
FeCl3 + 3H2O → Fe(OH)3 + 3HCl
Weak base strong acid
Reaction with potassium Ferro cyanide:
Ferric chloride reacts with potassium ferro cyanide forming a prussiara blue colouration of ferric ferro cyanide.
4FeCl3 + 3 K4 [Fe (CN)6]0 → Fe4 [Fe (CN)6]3 + 12KCl
Prussian blue ferroc ferro cyanide
Reaction with ammonium thiocyanate:
Ferric chloride gives a blood red coloration of Ferric thiocyanate with ammonium thiocyanate.
FeCl3 + 3 NH4CNS → [Fe (CNS)3] + 3NH4Cl
Ferric thiocyanate
Blood red
Reaction with ammonium hydroxide:
Ferric chloride gives a reddish brown ppt of ferric hydroxide with Ammonium Hydroxide solution.
FeCl3 + 3NH4OH → Fe (OH)3 + 3NH4Cl
Ferric hydroxide
Reddish brown

Uses:

It is used in medicine as astrigents and antiseptic.
It is used as mordant in dying.
It is used as a catalyst in friedal craft’s reaction.
It is used to etch metals like Cu, Ag, during making block.