Equivalent weight is expressed as the ratio of atomic weight or molecular weight or formula weight (or molar mass) to the valency.
Equivalent weight of a substance is the number of parts by weight or amount of a substance, which will combine with or displace 1 part by weight of hydrogen, or 8 parts by weight of oxygen or 35.5 parts by weight of chlorine. It is expressed in amu.
In simple words, equivalent weight of a species is its combining capacity with other standard species under given conditions.
If the element reacts directly with H2 or O2 or Cl2 then equivalent of element is calculated as (both masses are in same unit):
Formula
Equivalent weight of different substances is given by:
Equivalent weight of element = Atomic weight / valency
Equivalent weight of base = Molecular weight/ acidity (ionizable OH− ions)
Equivalent weight of salt = Molecular weight/ no of positive charge on cation
Equivalent weight of oxidant = Molecular weight/ no. of electrons gained (change in oxidation no.)
Equivalent weight of reductant = Molecular weight/ no. of electrons lost(change in oxidation no.)
Equivalent weight of radical = Formula weight/valency
Gram Equivalent
Equivalent weight of a substance expressed in gram is called Gram equivalent weight or One gram equivalent.
For example;
One gram equivalent of Na = 23 g
One gram equivalent of Ca = 20 g
One gram equivalent of Al = 9 g
One gram equivalent of HCl = 36.5 g
One gram equivalent of H2SO4= 49 g
Equivalent weight of CO32− = 12+48/2 = 60/2= 30
Equivalent weight of KMnO4 in acidic medium = 39+55+64/5 = 158/5= 31.6
Equivalent weight of Acids
Equivalent weight of an acid is the number showing how many parts by weight of an acid contains one part by weight of replaceable hydrogen i.e.
For example
1. Equivalent weight of HCl = 36.5/1= 36.5
2. Equivalent weight of HNO3 = 63/1 = 63
3. Equivalent weight of CH3COOH = 60/1 = 60
4. Equivalent weight of H2SO4 = 98/2 = 49
5. Equivalent weight of H2C2O4.2H2O = 126/2 =63
Equivalent weight of an acid is the number showing how many parts by weight of an acid neutralizes one gram equivalent an alkali (base)
For example
equivalent weight of H2SO4 can be calculated as follows:
Equivalent weight of Base
Equivalent weight of a base is the number showing how many parts by weight of a base contains one part by weight of replaceable OH− ion i.e.
For example
1 Equivalent weight of NaOH = 40/1 = 40
2 Equivalent weight of KOH = 56/1 = 56
3 Equivalent weight of NH4OH = 35/1 = 35
4 Equivalent weight of Ca(OH)2 = 74/2 = 37
Equivalent weight of a base is the number showing how many parts by weight of an alkali neutralizes one gram equivalent an acid.
For example
Equivalent weight of NaOH can be calculated as follows:
Equivalent weight of Compounds (salts)
Equivalent weight of a compound (salt) is the number showing how many parts by weight of a compound (salt) contains one, two or three positive charge on its cation. i.e.
For example
1. Equivalent weight of Na2CO3 = 106/2 = 53 amu
2. Equivalent weight of K2CO3 = 138/2 = 69 amu
3. Equivalent weight of CaCO3 = 100/2= 50 amu
4. Equivalent weight of NaHCO3 = 84/1 = 84 amu
2. Equivalent weight of a compound (salt) is the number showing how many parts by weight of a compound (salt) interacts with the known chemical equivalent an element or a compound (whose equivalent weight is known).
For example
Equivalent weight of Na2CO3 can be calculated as follows:
Equivalent weight of Oxidizing agent
The equivalent weight of an oxidizing agent or oxidant is that weight of it which gains one electron. It is obtained by dividing molecular weight by no of electrons gained per mole.
For example
1. Equivalent of an oxidant KMnO4 in acidic medium can be calculated as:
2KMnO4 + 3H2SO4 →K2SO4 + 2MnSO4 + 3H2O + 5[O]
Equivalent weight of KMnO4 in acidic medium = 158/5 = 31.6
2.Equivalent of an oxidant KMnO4 in basic medium can be calculated as:
2KMnO4 + H2O→ 2KOH + 2MnO2 + + 3[O]
Equivalent weight of KMnO4 in basic medium = 158/3 = 52.66
Equivalent weight of reducing agent
The equivalent weight of a reducing agent or reductant is that weight of it which donates one electron. It is obtained by dividing molecular weight by no of electrons lost per mole.
For example
1). Equivalent of a reducing agent FeSO4.7H2O can be calculated as:
Equivalent weight of FeSO4.7H2O = 278/1 = 278
2). Equivalent of a reducing agent Mohr’s salt (FeSO4. (NH4)2SO4.6H2O can be calculated as:
Model Test Questions on Chapter # 7, chemistry of Benzene Test # 6
Q1. How will you prepare a sample of benzene from petroleum (coal tar or n-hexane or n-heptane)?
Q2. How will you obtain benzene from the following? (i). Aliphatic sources (n-hexane or n-heptane or ethyne) (ii). Aromatic sources (phenol or sodium benzoate or toluene)
Q3.Define Aromaticity. How will you explain the stability of benzene?
Q4. Define Resonance. Draw all the possible structures of benzene.
Q5. Give two reactions in which benzene ring is not retained. (Hydrogenation and halogenation in sunlight)
Q6. Under what conditions benzene reacts with chlorine to form (i) Monochlorobenzene (ESR with chlorine in dark) (ii) hexachlorocyclohexane (Halogenation with chlorine in sunlight)
Q7. Starting from benzene or toluene how will you prepare the following?
(i) Acetophenone [acylation with acetyl chloride ]
(ii) Benzenesulphonic acid [sulphonation with oleum]
(iii) Cyclohexane [Hydrogenation]
(iv) Carbolic acid or Phenol [Chlorination, hydrolysis, acidification]
(v) Bromobenzene/Halobenzene [Bromination or halogenation in dark]
(vi) Cumene (isopropylbenzene) [alkylation or isopropylation with isopropyl chloride]
(ix) Ortho & para nitrotoluene [Alkylation + Nitration(methylation)]
(x) Chlorine derivatives of toluene [Halogenation in sunlight]
Q8. Benzene acts as Saturated as well as unsaturated compound. Support your answer by two chemical reactions for each type of behavior.
Q9. What is ESR? Why benzene undergoes ESR? Explain general pattern of mechanism of ESR.
Q10. Why does benzene give E.S.R? Give only one step equation of acylation of benzene. Explain 4 equations showing mechanism of isopropylation of benzene.
Q11. Explain Nitration & Acylation in Benzene with mechanism.
Model Test Questions on Chapter # 7, Chemistry of Benzene Test # 7
Q1. Indicate the main product in each of the following reactions (write only equation with proper condition)
Xylene is chemically dimethylbenzene having three positional isomers namely ortho, meta and para xylene. acidified potassium tetraoxomanganate(VII) or KMnO4 being an oxidizing agent always oxidizes alkyl group of any length into one carboxylic group. Since there are two methyl groups on adjacent, alternate and opposite carbons, they are oxidized to give two carboxylic groups on respective positions forming phthalic acid, isophtalic acid and Terephthalic acid respectively.
ii). Toluene+ oleum
Toluene is methylbenzene containing methyl group which is o,p-directing group. Toluene reacts with oleum or fuming sulphuric acid containing SO3 as a Sulphonating agent to form ortho and para toluenesulphonic acid due to the presence of ortho-para directing CH3- group.
iii). Toluene+ methyl chloride (catalyzed by aluminum (III) chloride)
Toluene is methylbenzene containing methyl group which is o,p-directing group. Toluene reacts with methyl chloride in the presence of Lewis acid catalyst aluminum (III) chloride (AlCl3) undergoing Friedel-Craft alkylation (methylation) to form two isomeric dimethylbenzenes called ortho and para xylene.
iv). Toluene+ concentrated nitric acid
Toluene is a benzene with a methyl substituent. The methyl group activates the ortho and para positions for electrophilic aromatic substitution (EAS). In order to obtain TNT from toluene, we must add NO2 groups to these three positions which are already activated via nitration using nitrating mixture of HNO3 and H2SO4. However, each NO2 that is added greatly increases the energy needed for the next substitution to occur. The third substitution requires a massive input of energy to occur.
TNT is synthesized in a three-steps process. First, toluene is nitrated with a mixture of sulfuric and nitric acid to produce mono-nitrotoluene (MNT) which is renitrated to produce dinitrotoluene (DNT) which is further nitrated to tironitrotoluene (NT). At low temperatures, the mononitrotoluenes are made, and as the reaction temperature is increased the dinitro compounds are formed, until eventually TNT is formed.
TNT is a yellow, odorless material that does not occur naturally in nature. TNT is a kind of explosive that is extensively employed in military shells, bombs, and grenades, as well as industrial and undersea blasting. TNT is an abbreviation for trinitrotoluene. The IUPAC name is 2-methyl-1,3,5-trinitrobenzene. The International Union of Pure and Applied Chemistry (IUPAC) nomenclature of organic chemistry is a system of naming organic chemical compounds. Other names include 2,4,6-trinitromethylbenzene, as it contains a benzene ring with methyl group, 2,4,6-trinitrotoluol TNT, trinitrotoluol, tritolol, trinol, triton, tritolo, trotol, and tritone.
v). Toluene + chlorine in sunlight
In the presence of sunlight, toluene (or any alkyl benzene) react with Cl2 or Br2 by a free radical photochemical substitution reaction to substitute hydrogen of methyl (alkyl) group rather than the H of benzene ring forming all the three possible products. In this reaction, hydrogen atoms from side chain get replaced by chlorine giving benzyl chloride on monochlorination, benzal chloride on dichlorination and benzochloride on trichlorination.
Q2. Starting from benzene or phenol how the following compounds can be prepared:
i. Bakelite (Reaction of phenol with formaldehyde)
ii. m-nitrotoluene (Alkylation + Nitration)
iii. p-nitrobenzoic acid (Alkylation + Nitration + Oxidation)
iv). cyclohexanol (Hydrogenation of phenol)
(v) Picric acid (Nitration of phenol with conc. Nitric acid)
In presence of dilute base, phenol reacts with formaldehyde to produce a mixture of ortho and para-methylol phenols which are polymerized into a condensation polymer, Bakelite (first synthetic plastic), a thermo-setting plastic, once moulded, it cannot be remoulded and remelted.
The reaction may be summarized as: (according to book)
ii. m-nitrotoluene
To prepare m-nitrotoluene, we first perform nitration of benzene using nitrating mixture of HNO3 and H2SO4 to produce nitrobenzene which is then alkylated using methyl chloride in the presence of Lewis acid catalyst AlCl3 to produce the required compound. Nitro group being meta-directing group, direct the second group i.e. methyl group to meta position.
iii. p-nitrobenzoic acid
p-nitrobenzoic acid can be produced (along with its ortho isomer; o-nitrobenzoic acid) from nitration of toluene using nitrating mixture of HNO3 and H2SO4 to produce two isomeric nitrotoluenes followed by their oxidation using acidified potassium permanganate to get the required compound (along with o-nitrobenzoic acid)
iv). Cyclohexanol
Phenol is reduced to cyclohexanol when hydrogen gas is bubbled through phenol at 150-200°C in the presence of finely divided nickel catalyst. Cyclohexanol is used in the manufacture of nylon.
(v) Picric acid
Phenol undergoes nitration with concentrated nitric acid on heating in such a way that all the active position have been substituted by nitro group yielding 2,4,6-trinitrophenol (TNP) or picric acid which is quite a strong acid (Ka = 10–1 ) and can liberate CO2 from Na2CO3 solution, as the acidity of a phenol is increased when electron-attracting substituents (like –NO2) are introduced into the aromatic ring. [The dry solid picric acid is highly explosive compound but solutions have been used as an antiseptic and as yellow dye, and it was probably the first artificial dye (1849)].
(vi) Bromol
Phenol reacts with bromine water (or chlorine water) very rapidly in such a way that substitution in all available ortho and para-positions take place to yield white precipitate of 2,4,6-tribromophenol or TBP or bromol (or 2,4,6-trichlorophenol). This reaction is used as a test for phenol. tribromophenol also called bromol is a soft-white needles like solid with a sweet taste and penetrating bromine odour. trichlorophenol simply called 2,4,6-T is a yellow flakes with strong phenolic odour used as fungicide and herbicide.
Q3. How will you convert phenol into following?
(i) Cyclohexanol (Catalytic hydrogenation)
(ii) Benzene (Reduction)
(iii) picric acid (Successive nitration)
(iv) Phenoxide (Neutralization)
Answer
(i) Cyclohexanol (Catalytic hydrogenation)
Phenol is reduced to cyclohexanol when hydrogen gas is bubbled through phenol at 150-200°C in the presence of finely divided nickel catalyst. Cyclohexanol is used in the manufacture of nylon.
(ii) Benzene from Phenol (Reduction)
The removal of oxygen from compound is called reduction. Phenol is reduced to benzene when its vapours are passed over red hot with zinc dust (as zinc being a reducing agent removes oxygen from phenol). The new hydrogen atom in benzene is derived from – OH group of phenol.
(iv) Phenoxide (Neutralization)
Phenol forms salt called Phenoxide or phenate or Phenolate with aqueous strong alkalis like sodium hydroxide. Phenol is fairly acidic in nature and it is stronger acid than alcohols and hence it can neutralize alkalis.
Phenoxide may be prepared from phenol either by its neutralization with NaOH or by displacement reaction with Na in which hydroxylic hydrogen of phenol is displaced by sodium to form sodium phenoxide liberating H2 gas
(iii) Picric acid (Successive nitration)
Phenol undergoes nitration with concentrated nitric acid on heating in such a way that all the active position have been substituted by nitro group yielding 2,4,6-trinitrophenol (TNP) or picric acid which is quite a strong acid (Ka = 10–1 ) and can liberate CO2 from Na2CO3 solution, as the acidity of a phenol is increased when electron-attracting substituents (like –NO2) are introduced into the aromatic ring. [The dry solid picric acid is highly explosive compound but solutions have been used as an antiseptic and as yellow dye, and it was probably the first artificial dye (1849)].
Q4. How do you convert ethanol into benzene?
Q5. How do you convert ethene into benzene?
Ethene is first converted into 1,2-dibromoethane by the action of bromine, tetrachloromethane. Then it is treated with alc. KOH to form bromoethene which will further react with NaNH2/liq.NH3 to form ethyne. After that ethyne is heated in the red-hot iron tube at 873 K, benzene is obtained.
