Wednesday 3 December 2014

Electrochemistry Class XII (chapter3)







d & f block elements (Chapter 8) class XII

d- and f- block elements
d-block elements represent change in properties from most electropositive s-block elements to least electropositive p-block elements. So, these are called transition metals.
Transition elements are those elements which have partially filled d-subshells in their elementary state or in their commonly occurring oxidation states.
General configuration = (n-1) d1-10 ns1-2
There are four transition series:
3d – Sc        Ti         V        Cr         Mn           Fe         Co        Ni      Cu       Zn
4d – Y          Zr        Nb     Mo        Tc            Ru          Rh       Pd      Ag      Cd
5d – La        Hf        Ta       W         Re           Os            Ir        Pt       Au      Hg
6d – Ac        Ku       Ha
Cu = 3d10 4s1. But in its most common oxidation state (+2), it contains one unpaired electron in its d-orbital. So, it is a transition element. Cu2+ = 3d9 4s0. Similarly, Ag and Au are also transition elements.
Physical Properties –
1) Atomic radii – Across the period (series), atomic radii of elements of a particular series decrease with increase in atomic number and then  become constant in mid-way and at last, there is an increase in atomic radius.
Reason – With increase in atomic number, nuclear charge goes on increasing and force of attraction between nucleus and valence electrons increases due to which atomic radius decreases with increase in atomic number in the beginning.
But as the electrons are increased in d-orbitals. These electrons screen the outermost s-electrons. So, as the d-electrons increase, screening effect increases which neutralises the effect of increased nuclear charge and hence, atomic radius remains almost unchanged after chromium.
At the end of the series, there is slight increase in the atomic radii due to increased electron-electron repulsions between electrons in same orbitals due to which electron cloud expands and size increases.
Down the group, atomic radii increase due to increase in number of shells. But atomic radii of elements of 4d-series and 5d-series are nearly same due to Lanthanide Contraction.
2) Metallic character - All transition elements are metals. They have high density, hardness, high melting point and boiling point, malleable, ductile, conduct electricity and heat.
Reason – Metallic character is due to their low ionization energies and number of vacant orbitals in outermost shell. Greater the number of unpaired d-electrons, greater is the number of bonds and greater is the strength of metallic bonds. E.g. Cr, Mo and W (tungsten) have maximum number of unpaired electrons and are very hard metals.
Zn, Cd and Hg do not have any unpaired electrons. So, they are not hard (nd10). They are also known as non-transition metals.
3) Density – All metals have high density. Osmium has the highest density.
4) Melting point and boiling point – They have high melting point and boiling point due to strong metallic bonds between atoms of elements.
Metallic bond is formed due to the interaction of electrons in outermost orbitals. Greater the number of valence electrons, stronger is the metallic bonding and higher is the melting point. In a particular series, metallic strength increases upto middle with increasing availability of unpaired electrons upto d5 configuration (Sc =1, Ti =2, V =3, Cr =4, Mn =5) and then decreases with decreasing availability of unpaired electrons in d-orbital. Therefore, melting point decreases.
5) Ionization enthalpy – Energy required to remove an electron from valence shell of an isolated gaseous atom. First ionization enthalpy is higher than those of s-block elements and lesser than p-block elements.
Reason – Due to increase in nuclear charge and force of attraction between nucleus and valence electrons. Hence more energy is required to remove an electron from outermost shell.
Also, the effect of increasing nuclear charge is opposed by additional screening effect of nucleus and hence, ionization enthalpy increases but quite slowly among d-block series.
First ionization enthalpy of 5-d series is higher than those of 3d- and 4d- series due to poor shielding effect of 4f-orbitals. As a result, outer electrons have greater nuclear charge acting on outer valence electrons.
Consequences: a) Ni (II) compounds are thermodynamically more stable than Pt(II) compounds. Pt(IV) compounds are more stable than Ni(IV) compounds. E.g. K2PtCl6 exist but not K2NiCl6.
6) Oxidation state – Transition metals exhibit variable oxidation states.
Reason- This is due to the participation of inner (n-1) d-electrons in addition to outer n electrons because energies of ns- and (n-1) d subshells are almost equal. They contain many unpaired electrons.
Highest oxidation state is shown by Osmium(Os) and Rhuthenium(Ru) of +8.
Few transition metals also form compounds in low oxidation states like +1, 0, -1. E.g. [Ni(CO)4], [Fe(CO)5] in which Ni and Fe have zero oxidation states.
7) Formation of coloured ions – s and p-block elements are white in colour while d-block elements are coloured in solid or solution form.
Reason- It occurs due to the presence of unpaired electrons. The energies of five d-orbitals in the same subshell do not remain equal during the formation of complexes or compounds of transition metals. Under the influence of approaching ions towards the central metal ion, d-orbitals split into different energy levels. This phenomenon is known as crystal field splitting (CFS).
In case of transition metal ions, electrons are excited from one energy level to another in same d-subshell. These are known as d-d transitions. The amount of energy required to excite unpaired electrons to higher excited states within the same d-subshell corresponds to energy of certain colours of visible light and the observed colour of substance is always complementary colour of colour absorbed by the substance.
Zn, Cd and Hg compounds are generally white in colour because of completely filled d-orbitals i.e. they do not have any unpaired electron (d10).
8) Magnetic properties – Most of the compounds of transition elements are paramagnetic due to the presence of unpaired electrons in the d-orbitals of metal ion. Unit of magnetic moment (μ) = Bohr Magneton.              μ =    n ( n + 2 )        where n = number of unpaired electrons
Iron oxide = Ferromagnetic substance (highly magnetic).
Zn2+, Cd2+, Hg2+, Cu+ compounds = Diamagnetic (no unpaired electron).
9) Tendency to form complexes – Transition elements form large number of coordination compounds. The transition metal ions bind to number of anions or neutral molecules (ligands) in the complexes like [Ni(NH3)6]2+, [Co(NH3)6]3+, etc.
Reason- due to small size of transition metal atoms or ions, high nuclear charge, presence of vacant d-orbitals of suitable energy are available to accept lone pair of electrons donated by ligands.
10) Formation of interstitial compounds – Transition metals form interstitial compounds with elements like B, C and N i.e. they get trapped in vacant spaces of lattices of these metals.
Reason-  Transition metals can easily accommodate the vacant spaces of these non-metals due to their small size, defects in structures and their variable oxidation states.
11) Catalytic properties – Many transition metals and their compounds act as good catalyst for many reactions like Ni, Pt, Pd, V2O5, MnO2, etc.
Reason- (i) due to the presence of vacant orbitals and their tendency to show variable oxidation states, (ii) Transition metals provide large surface area on which reactants may be absorbed for the reaction to occur. E.g. in Contact process, solid VO5 adsorbs SO2 for reaction.
12) Alloy formation - Transition metals form large number of alloys.
Reason- Transition metals are quite similar in size and atoms of one element in its crystal lattice substitute atoms of other metal in its crystal lattice. E.g. Brass = Cu + Zn, Bronze = Cu + Sn, Stainless steel = Fe + Cr + Ni (high melting point, hard, more resistant to corrosion).
13) First row transition metals – Oxides- General formulae: MO, M2O3, M3O4, MO2, M2O5, MO3 .
Acidic character increases as oxidation state increases.
Oxide :                   MnO        Mn2O3          Mn3O4          MnO2       Mn2O7
Oxidation:               +2               +3               +8/3               +4             +7
Reducing character of oxides –Across the period, reducing character first increases then decreases as oxidation state. Lower oxidation state is more stable in 3d-series i.e. +2 state. V2O5 and CrO are strong reducing agents.
 As we move down the group, higher oxidation states become more stable. E.g. Osmium(VIII) oxide (OsO4) is known but iron (VIII) oxide is not known. Similarly, hexafluorides of 4d- and 5d-series exist.
K2Cr2O7  (potassium dichromate):
Preparation: from chromite ore
(i) 4FeCrO4 + 16NaOH + 7O2 → 8Na2CrO4 + 2 Fe2O3 + 8H2O
(ii) 2Na2CrO4 + H2SO4 → Na2Cr2O7  + Na2SO4 + H2O.  Na2SO4 can be removed by crystallization.
(iii) Na2Cr2O7  + 2KCl → K2Cr2O7  + 2NaCl. So, orange crystals of K2Cr2O7  are obtained.
Properties: (i) It is orange red crystalline solid, soluble in water.
(ii) Action of heat: 4 K2Cr2O7     →  4 K2Cr2O4 + 2 Cr2O3 + 3O2
(iii) K2Cr2O7  + 2 KOH → 2 K2Cr2O4 + H2O
2 K2CrO4 + H2SO4 → K2Cr2O7  + K2SO4 + H2O
(iv) Chromyl chloride test – used to test the presence of chloride ions.
K2Cr2O7 + 4NaCl + 6H2SO4 → 2KHSO4 + 4NaHSO4 + 3H2O + 2Cr2O2Cl2 (chromyl chloride red vapours)
(v) K2Cr2O7 + 4HCl → 2KCl + 2CrCl3 + 7H2O + 3Cl2
(vi) Oxidising character- K2Cr2O7 is a powerful oxidizing agent.
K2Cr2O7 + 4H2SO4 → K2SO4 + Cr2(SO4)­3­ + 4H2O + 3[O]
Strong oxidizing agent in acidic medium:
Cr2O72- + 14 H+ + 6e- → 2Cr3+ (green) + 7 H2O
Uses: a) in volumetric analysis of Fe2+, I-.    b) in photography for hardening gelatin film.  c) in dyeing.
Note: a) 2I- → I2 + 2e-           b) Fe2+ → Fe3+  + e-                 c) H2S → S + 2H+ + 2e-
d) H2C2O4 → 2CO2 + 2H+ + 2e-                e) SO32- + H2O  → SO42- + 2e- + 2H+ 

KMnO4 = Potassium permanganate
Preparation: 1) a) 2MnO2 + 4KOH + O2 →2K2MnO4 + 2H2O
b) 3MnO42- + 4H+ → 2MnO4- + MnO2 + 2H2O   [Disproportionation reaction]
2) Commercial process:  KMnO4 is prepared by the alkaline oxidative fusion of MnO2 followed by electrolytic oxidation of manganite (VI)
Properties: a) It is dark violet crystalline solid.
b) It is fairly soluble in water.
c) 2KMnO4                K2MnO4 + MnO2 + O2
d) 4KMnO4 + 4KOH → 4K2MnO4 + 2H2O + O2
e) It is powerful oxidising agent in neutral, alkaline or acidic solutions. MnO4-  + e-  → MnO42-,
MnO4- + 4H+ +3e-  → MnO2 + 2H2O,                MnO4- + 8H+ +5e-  → Mn2+ + 4H2O.
Uses: as an oxidizing agent in labs and industries, used as disinfectant for water, in quantitative and qualitative analysis.
E0 values (standard electrode potential) become less negative across the series is related to the general increase in sum of the first and second ionization enthalpies.
More the ionization enthalpy is, more is the reduction potential and lesser is the oxidation potential. So, E0 value (reduction potential) becomes more negative.
Exception: a) E0 for Mn, Ni and more (-) than expected from the trend. This is due to the stability of the half-filled d subshell in Mn2+ and completely filled d10 configuration in Zn2+, whereas E0 for Ni is related to the highest negative ΔhydH0 (hydration energy).
b) Cu2+ = 3d9 4s0,   Cu+ = 3d10 4s0
Cu2+ is exceptionally more stable than Cu+ in aqueous solutions because of more negative ΔhydH0 of Cu2+ (aq) than Cu+ , which is more than compensates for the second ionization enthalpy of Cu. So, Cu+ undergoes disproportionation in aqueous solution. 2 Cu+ (aq) → Cu2+ + Cu. E0 = + 0.34V (favourable E0 value).
c) All Cu2+ halides are known except the iodide. In this case, Cu2+ oxidises I-  to I2.
2 Cu2+ + 4 I- → Cu2I2 (s) + I2
Stable d-configurations – d3 = stable half-filled t2g configuration, d5 = half-filled d-orbital, d6 = fully-filled t2g level, d10 = fully-filled d-orbital.
f-block elements: Elements in which last electron enters the f-orbital of their atoms are called f-block elements. They are known as inner transition elements.        
 General Configuration: (n-2)f1-14 (n-1)d0-10 ns1-2      (n-2) = Anti-penultimate shell,   (n-1) = Penultimate shell,   n = main ( valence ) shell.
They consist of two series of elements placed at the bottom of periodic table by filling of electrons in 4f- and 5f-orbitals.
(i) Lanthanoids or lanthanides-  The series involving the filling of 4f-orbitals following Lanthanum (Z=57), Cerium (Z=58) to Lutetium (Z=71).
They occur very rarely and are known as rare earth metals.
Z=57 = La (Lanthanum) = 5d1 6s2,    Z=58 = Ce (Cerium) = 4f1  5d1 6s2,     Z=59 = Pr (Praseodymium) = 4f2  6s2,      Z=63 = Eu (Europium) = 4f7 6s2     ,        Z=64 = Gd  (Gadolinium) = 4f7  5d1 6s2,                            Z=71 = Lu (Lutetium) = 4f14  5d1 6s2.
(ii) Actinides - The series involving the filling of 5f-orbitals following Actinium (Z=89), Thorium (Z=90) to Lawrencium (Z=103).
Actinium (Z=89) = Ac = 6d1 7s2,  Thorium (Z=90) = Th = 6d2 7s2, Curium (Z=96) = Cm = 5f7 6d1 7s2, Lawrencium (Z=103) = Lr = 5f14 6d1 7s2
The Lanthanoids- All Lanthanoids have common oxidation state of +3 with +2 and +4 also by attaining stable f0, f7, f14 configurations.
Physical Properties: All lanthanides are soft, malleable, and ductile with low tensile strength, bad conductors of heat and electricity.
General Charcteristics:  1) Trivalent ions of lanthanides are coloured in solid state as well as in solution due to the absorption in visible light of spectrum by unpaired electrons resulting in f-f transitions.
2) They are paramagnetic. All lanthanides are highly electropositive metals and have almost similar reactivity due to the fact that lanthanides differ only in number of 4f electrons. Since these electrons are very effectively shielded from interaction by 6s, 5p electrons, hence they show little differences in their chemical reactivity. So, they are difficult to separate.
f0 and f14 are colourless and diamagnetic [La3+ and Lu3+]
3) Atomic radii- The steady decrease in atomic sizes and ionic sizes of lanthanides with increasing atomic number is known as lanthanide contraction.
Reason: As atomic number increases across the series, nuclear charge increases by one unit. The new electrons are added to same inner 4f-subshells. But 4f electrons shield each other from nuclear charge quite poorly because of very diffused shapes of f-orbitals.

Consequences of lanthanide contraction:  
a) Elements of 4f- and 5f- transition series resemble each other due to similar sizes.
b) It is difficult to separate these elements in pure state. Fractional crystallization method is done repeatedly to separate them.
c) Due to lanthanide contraction, size of lanthanide ions decrease with increase in atomic number due to which the covalent character between Lanthanide ion and OH- ions increase from La3+ to Lu3+. Therefore, basic strength of hydroxides decreases with increase in atomic number across the series. Thus, La(OH)3 is most basic and Lu(OH)3 is least basic.
The actinoids-
General Characteristics: 1) These metals are all silvery in appearance.
2)Antinoid contraction- The steady decrease in atomic sizes and ionic sizes of antinoids with increasing atomic number is known as actinide contraction.
Reason: As atomic number increases across the series, nuclear charge increases by one unit. The new electrons are added to same inner 5f-subshells. But 5f electrons shield each other from nuclear charge quite poorly.
3) They are radioactive elements and earlier members have relatively long half lives, the latter ones have half lives ranging from a day to 3 minutes for Lawrencium (Z=103). The latter members are prepared only in nanogram quantities. These facts render their study more difficult.
Lanthanoids
Actinoids
1) Tendency to form complexes is less.
1) More tendency to form complexes.
2) Non-radioactive except promethium.
2) All are radioactive.
3) All show +3 oxidation state and few show +2 and +4 also.
3) All show +3, +4, +5, +6 and +7 oxidation state.
4) They are less basic.
4) They are more basic.

Misch Metall- An alloy of a lanthanoid metal (95%) and iron (5%) with traces of S, C, Ca and Al. It is used in Mg-based alloy to produce bullets, shell and lighter flint.
Uses of Lanthanoids: (i) For production of alloy steels for plates and pipes. (ii) Mixed oxides of lanthanoids are used as catalysts in petroleum cracking.
Reactions of Lanthanoids:
2Ln + 3X2 → 2LnX3 ,        2Ln + 6H2O →  2Ln(OH)3 + 3H2 ,
Ln + O2 → Ln2O3 ,              Ln + S →Ln2S3 ,                Ln + N2 → LnN,                         Ln + C  →  LnC2  

  

Chemistry in everyday life (Chapter 16) Class XII

Chemistry in everyday life
Drugs – are the chemicals of low molecular mass (100-500u) which interact with macromolecular targets and produce a biological response i.e. can act as medicines or as poisons.
Chemotherapy - Branch in medicine where we use chemicals to cure the diseases or reduce suffering from pains (for therapeutic effect).
Classification of drugs: a) On the basis of pharmacological effect – analgesics for pain killing effect, antiseptics for killing or arresting the growth of micro-organisms.
b) On the basis of drug action – It is based on the action of a drug on a particular biochemical process. E.g. all antihistamines inhibit the action of the compound, histamine which causes inflammation in the body.
c) On the basis of chemical structure – on the basis of common structural features and similar pharmacological activity. E.g. sulphonamides have common structure:
d) On the basis of molecular targets – Drugs possessing some common structural features may have the same mechanism of action on targets. (most useful classification).
Consideration of drug designing – Two considerations are essential: (i) Choice of drug target – Drugs usually interact with biological macromolecules known as targets, (ii) Drug metabolism – A drug travels through the body in order to reach the target. So, its design should be such that it reaches the target without being metabolised in between and also, after its action, it should be excreted without causing harm to the body.
Drugs are designed by lead compounds (Sources = plants, trees, bushes, metabolites of microorganisms)
Q. How do drugs interact with targets?
Drugs interact with biological macromolecules like proteins, carbohydrates, lipids and nucleic acids. E.g. Enzymes are the proteins which perform the role of biological catalysts. They hold the substrate for a chemical reaction and they provide functional group (-OH, -NH2, -COOH) that will attack the substrate and carry out chemical reaction (by H-bonding, ionic bonds, Vander Waal’s forces, dipole-dipole interactions). Drugs are designed to inhibit any of the above activities of enzymes and are known as enzymes inhibitors which can block the binding site and prevent the binding of substrate with enzyme.
Drugs compete with the natural substrate for active site. Such drugs are called as competitive inhibitors. Some drugs do not bind to the active site but bind to the different site of enzyme known as allosteric site. This changes the shape of active site such that substrate cannot recognize it.
Receptors – are the proteins that are crucial to the body’s communication process which are embedded in cell membrane (made up of phospholipid bilayer). Two chemical messengers which help the receptor to transfer message into the cell are:
a) Hormones – are released from endocrine glands. These enter into the blood stream and travel in the body, activating all the receptors which recognize them for message transfer (that helps in the growth and development of the body). E.g. Adrenaline (epinephrine) is a hormone released from adrenal medulla in the situation of stress or danger.
b) Neurotransmitters – like acetylcholine, dopamine and serotonin. Nerves transfer message through them.
Drugs are categorised as – a) Antagonists : drugs that bind to receptors site and inhibits its natural function by blocking the active site.
b) Agonists : Drugs that mimic the natural messenger by switching on the receptor. These are useful when there is lack of natural chemical messenger in the body.
Side effects are caused when drugs bind to more than one type of receptor or are taken in excess.
Therapeutic action of different classes of drugs:
 a) Antacids – Chemical substances which can reduce or neutralise the acidity of stomach which occurs due to release of excess of gastric acid (HCl) in stomach. E.g. Ranitidine (Zantac), Cimetidine. They are better than NaHCO3 and Mg(OH)2 as they prevent interaction of histamine with receptors (or anti-allergic action) in stomach and helps in quick healing of ulcers as they  are mild bases.
b) Antihistamines (or anti-allergic drugs)- Drugs which combat or prevent the effects of histamine, a chemical released by certain cells of body (mast cells) during an allergic reaction. E.g. Dimetapp and seldane.
Histamine is a potent vasodilator. It contracts smooth muscles in bronchi and gut and relaxes other muscles of blood vessels. It is also responsible for nasal congestion associated with common colds and allergic response to pollen grains. 
Antihistamines do not affect the secretion of acid in stomach because antiallergic and antacid drugs work on different receptors.
c) Neurologically active drugs
(i) Tranquilizers or sedatives – drugs given to patients suffering from anxiety and tension. These relieve anxiety, stress, irritability or excitement. Antipsychotic tranquilizers are the major tranquilizers while sedative tranquilizers are used during intense anxiety or panic. These are used for making sleeping pills like Barbituric acid, lyminal and seconal. Non-adrenaline is a neurotransmitter that plays role in mood changes. If level of non-adrenaline is low, the person suffers from depression. So, anti-depressant drugs are required like Iproniazid, Nardil (phenelzine).
(ii) Analgesics – Chemical substances which are used for relieving pains in the body. Two types of analgesics are: Non-narcotic drugs (non-addictive) – Salicylates (for e.g. aspirin and paracetamol) belong to this class. Aspirin inhibits the synthesis of chemicals known as prostaglandins which stimulate inflammation in tissue and cause pain. These drugs are effective in reducing fever (antipyretic) and preventing platelet coagulation. Because of its anti-blood clotting action, aspirin finds its use in prevention of heart attacks.(Aspirin = 2-Acetoxy benzoic acid).                                                                  Narcotic analgesic drugs – such as morphine and many of its homologous, when administered in medicinal doses, relieve pain and produce sleep and cause addiction. Morphine narcotics are sometimes referred to as opiates, since they are obtained from the opium poppy.  
d) Antibiotics – Chemical substances produced by micro-organisms (bacteria, fungi, moulds) that inhibit the growth or even destroy other micro-organisms. First antibiotic was discovered by Alexander Fleming and it was penicillin (for malaria). The complete range of micro-organisms which can be killed by a particular antibiotic is called its spectrum. There are two types of antibiotics-: Broad – spectrum antibiotics: antibiotics which can kill different types of micro-organisms. They can cause several infections. E.g. Tetracyclines, chloramphenicol. Narrow – spectrum antibiotics: antibiotics which can kill only few micro-organisms. E.g. Penicillin, streptomycin, chloromycetin.
Two major classes of antibiotics: Bactericidal is an antibiotic which kills the micro-organisms in the body. E.g. Penicillin, ofloxacin. Bacteriostatic is an antibiotic which inhibit or control the growth of micro-organisms. E.g. tetracycline, chloramphenicol.
e) Antiseptics – can kill or prevent the growth of micro-organisms. They do not harm the living tissue and can be applied to the skin. They are used for dressing wounds, ulcers and in treatment of diseased skin. E.g. Dettol (a mixture of chloroxylenol and terpineol), Tincture of iodine (2-3% iodine solution of alcohol-water)
Disinfectants – can kill micro-organisms. They are toxic to living tissues. So, it cannot be applied to the skin. These are used for disinfecting floors, toilet drains, instruments, etc. E.g. DDT (Dichloro Diphenyl Trichloroethane), BHC (Benzene hexachloride).
Phenol 1-2% solution is used as disinfectant while 0.2% solution of phenol is used as antiseptic.
f) Antifertility drugs – are hormonal contraceptives and are available for females only. Birth control pills are derivatives of synthetic oestrogen and progesterone. E.g. Norethindrone (progesterone derivative), novestrol (oestrogen derivative).
Chemicals in food: a) Artificial sweetners – Natural sweetners sucrose adds to calorie intake and therefore many people prefer to use artificial sweetners. Its use is of great value to diabetic persons. E.g. Aspartame (unstable at cooking temperature as it contains peptide linkages), Saccharine(low quality), Sucrulose, Alitame (high potency sweetner).  
b) Preservatives – They prevent the spoilage of food due to microbial growth. They are classified into two groups: Class 1 preservatives contain table salts, sugars and vegetable oils and Class 2 preservatives contain sodium benzoate (CH5COONa).
c) Antioxidants – Substances which when added to the fats and fat containing food prevents their  oxidation (rancidity) and thus prolong their life. Example : Butylated  Hydroxy Anisole (BHA), Butylated Hydroxy Toluene (BHT), Vitamin C.
 Chemistry of Cleansing agents :
SOAPS  ::  are sodium and potassium salts of long chain fatty acids. Soaps are formed  by treating NaOH with fatty acids. This process is known as saponification.
The soap obtained is in colloidal form which is precipitated by adding NaCl and is obtained by fractional distillation. Cleansing action of soaps –
Hydrophobic tail and Hydrophilic head forming micilles.
Soaps do not work in hard water (disadvantage): Hard water contains calcium and magnesium ions which form insoluble salts with soaps as scum which are useless as cleansing agent.
2C17H35COONa  +  CaCl2 (in hard water)     è     2NaCl  +  (C17H35COO)2Ca    (insoluble)
Soaps can be biodegraded.
Advantage of detergents :  They do not form scum with hard water.
 Disadvantage of detergent: They are non-biodegradable.
STRUCTURE :
Sodium palmitate :  C15H31COONa
Sodium oleate : C17H31COONa
Types of synthetic detergents:
a) Anionic detergents – are sodium salts of sulphonated long chain alcohols. They are effective in acidic solutions. Their larger part of molecule is anion. E.g. ABS (alkyl benzene sulphonate) CH3(CH2)16OSO3Na and Sodium lauryl sulphonate  CH3(CH2)10CH2OSO3Na.
b) Cationic detergents – are chlorides or bromides of quarternary amines. Cationic part possesses a long hydrocarbon chain and a positive charge. E.g. Cetylmethylammonium bromide(non-biodegradable). They have germicidal properties but have high cost.

c) Non-ionic detergents – Liquid dishwashing detergents are of non-ionic type. They have same mechanism of cleansing action as of soaps.
HO-CH2-CH2-OH   +   n  CH2-CH2     →     HO(CH2CH2O)nCH2CH2OH (polyethylene glycol)
Q. Why medicines or sleeping pills should not be taken without consulting doctors?
Ans. Because most drugs are potential poisons if taken in doses higher than the dose recommended.
Q. What is biothionol? Give its use.
Ans. Biothionol is an aromatic compound containing sulphur and it is added to soaps to impart antiseptic  properties.
Q. What are hypnotics? Give an e.g.
Ans. Hypnotics are drugs which produce sleep. They are habit forming. E.g. Luminal, Seconal.
Q. What kind of medicines are given to agitated and violent patient?
Ans. Tranquilizers or sedatives or anti-depressant drugs.
Q. Low level of non-adrenaline is the cause of depression. What type of drugs are needed to cure this problem? Name two drugs.
Ans. Psychotherapeutic drugs or tranquilizers. E.g. Luminal, Equanil.
Q. Why aspirin should not be taken empty stomach?

Ans. It decreases pH and causes ulcer. 

Chemistry Class XII syllabus

Name Reactions (Organic Chemistry) Class XII







CBSE Chemistry Sample Paper 2014-15 Class XII