Topic 14 Introductions to Organic Chemistry

14.1 Bonding of the carbon atoms: the shapes of ethane, ethene, ethyne and benzene molecules

What is a hybrid orbital in chemistry?

Hybrid orbitals are the result of a model which combines atomic orbitals on a single atom in ways that lead to a new set of orbitals that have geometries appropariate to form bonds in the directions predicted by the VSEPR model. The VSEPR model predicts geometries that are very close to those seen in real molecules.

How do you determine hybrid orbitals?

 

How to naming? Know how to draw structural formula?

Draw structural formula of 3-methyl-1-butene.

Count sigma and pi bond, how many? Calculate sigma and pi bond? 

Give the number and shape of hybridised orbital for sp, sp2 and sp3?

the mixing of 1s orbital and 1p orbital to form two new equivalent orbitals.

sp = 1s + 1p hybridised orbital, linear, 180°.

sp2 = 1s + 2p hybridised orbital, trigonal planar, 120°.

sp3 = 1s + 3p hybridised orbital, tetrahedral 109.5°.

 

How to know carbon atoms has a three dimensional geometry?

Carbon has 4 valence electrons will form 4 sp3 hybrid orbital and the shape is tetrahedron.

In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners.

Two p orbital can overlap to give either a sigma bond or a pi bond.

(a) draw the orbital overlap diagram for the formation of a sigma bond and a pi bond.

(b) draw the orbital overlap diagram for the ethene molecule, C2H4?

Ethene consists of two sp​2-hybridized carbon atoms, which are sigma bonded to each other and to two hydrogen atoms each. The remaining unhybridized p orbitals on the carbon form a pi bond, which gives ethene its reactivity.

(c) which is stronger, a sigma bond or a pi bond?

sigma bond.

(d) what is the approximate C-C-C bond angle in CH3CH=CH2?

Explain benzene regarding of arene series, draw the kekule and resonance structure?

benzene is the first member of arenes series, C6H6.

explain the concept of delocalisation of electrons in benzene ring.

How many sigma and pi bonds are there in one molecule of benzene and how to calculate it?

sigma bonds (C-C, C=C, C-H) = 12

pi bonds (C=C) = 6 (there are only 3 double bond, but with resonance structure of benzene ring will add more 3 pi bond, total is 3+3= 6 pi bonds).

For each of the following compounds, state the type of hybridisation of each carbon atom and estimate the bond angles.
CH3C=OH, C6H5-CH=CH2, CH3-CCH.

sp3 109.5° tetrahedral 
sp2 120° trigonal planar
sp 180° linear 

14.2 General, empirical, molecular and structural formulae of organic compounds

Calculate ratio/ stoichiometric? Calculate % stoichiometry?

Compound X (molar mass = 54.0 g/ mol has the following composition by mass C: 89% , H: 11%. What is the molecular formula of X?

C2H3,

Compound X has the followimg composition by mass. C: 60.0%, O: 26.8%, H: 13.2%.
Calculate its empirical formula?

An organic compound, Y, contains carbon, hydrogen and oxygen only. When 6.0g of Y is burned completely in excess oxygen, 13.2 g of carbon dioxide and 7.2g of water is produced. Determine the empirical formula of Y.

An organic compound, X has the following composition by mass: C: 35%, H: 6.6%, Br: 58.4%. When 1.36 g of X is vaporised, it occupies a volume of 389.2 cm3 at 200°C and 101 kPa. 

(a) determine the empirical and moleculat formula of X.

(b) draw and name all possible isomers for X and determine which of them (if any) is/ are chiral.

Compound X is produced from catalytic oxidation of an alkene. It has the percentage composition by mass: Carbon 38.7%, hydrogen 9.70%, oxygen 51.6%. When 0.890 g of X is heated at 400K, the vapor produced occupies a volume of 477 cm3 at 100 kPa. [the gas constant, R is 8.31 J/K / mol]

Find the empirical formula of X? What is molecular formula? What is the compound produced (oxidation of alkene)? What is the uses of diol?

Empirical formula: CH3O, Mr: 61.8 g/mol, molecular formula: C2H6O2, 1,2-ethanediol. used as antifreeze in car radiator.

14.3 Functional groups: classification and nomenclature

Functional groups? How do we determine the homologous series of a functional groups related to its chemical properties, physical states, general formula, and its preparations?

What is a functional group simple definition?

Functional groups are groups of one or more atoms of distinctive chemical properties no matter what they are attached to. The atoms of functional groups are linked to each other and to the rest of the molecule by covalent bonds.

What is the priority order of functional groups?

Priority Functional group

1 Cations e.g. Ammonium NH4+

2 Carboxylic acids –COOH

3 Carboxylic acid derivatives

Esters –COOR

Acyl halides –COX

Amides –CONH2

4 Nitriles –CN

5 Aldehydes –CHO

6 Ketones =O

7 Alcohols –OH

8 Hydroperoxides

Sulfenic acid -SOH

9 Amines –NH2

1°, 2°, 3° carbon atom.

What is type of classification of primary, secondary and tertiary in organic chemistry?

Certain functional group may behave differently when bonded to different crbon atom in a chain. Primary (1º) = carbon atom is attached to only ONE other carbon. Secondary (2º) = carbon atom is attached to only TWO other carbons. Tertiary (3º) = carbon atom is attached to THREE other carbons.

Draw skeletel formula, state the name and classify these alcohols compounds as primary (1°), secondary (2°) or tertiary (3°) alcohols?

1. CH3CH(CH3)CH2OH
2. CH3CH(OH)CH2CH3
3. (CH3)3COH

What are the rules for naming organic compounds?

In summary, the name of the compound is written out with the substituents in alphabetical order followed by the base name (derived from the number of carbons in the parent chain). Commas are used between numbers and dashes are used between letters and numbers. There are no spaces in the name.

How the nomenclature of classes of organic compounds named according to IUPAC names or systematic names?

In the IUPAC system, the chemical name of an organic compound has three (3) parts: prefix, parent or root and suffix.

Parent or root gives the number of carbon atoms in the longest continuous chain in the molecues.

Prefix identifies a substituent group attached to the main chain and the carbon atom to which it is attached.

Suffix gives the functional group of organic compound the molecule represents.

Draw the structural formula of the following compounds?

Alkane

methane, CH4, ethane, CH3CH3, 2-methyl propane, CH3CH(CH3)2.

 

Alkene

ethene, C2H4, phenyl ethene,

 

Alkyne

ethyne, C2H2,

 

Arene

benzene, C6H6, methyl benzene,

 

Haloalkane

chloromethane, CH3Cl, bromobenzen, C6H5Br.

 

Alcohol, phenol

methanol, CH3OH, ethanol, CH3CH2OH, 2-methyl propan-1-ol, butan-2-ol, phenol, C6H5OH.

 

Carbonyl compound (Ketone, Aldehyde)

propanon, CH3COCH3, ethanal, CH3COH.

 

Carboxylic acid

ethanoic acid, CH3COOH, benzoic acid, C6H5COOH.

 

Acyl Chloride

ethanoyl chloride, CH3COCl, benzoyl chloride, C6H5COCl.

 

Amide, -CONH2.

ethanamide, CH3CONH2, benzamide, C6H5CONH2.

 

Ester, ROOR.

ethyl ethanoate, CH3COOCH2CH3, phenyl benzoate, C6H5COOC6H5.

 

Amine, -NH2.

methanamine or methylamine, CH3NH2, phenyl amine, C6H5NH2.

 

Amino acid (-NH2 and -COOH)

aminiethanoic acid.

 

14.4 Isomerism: structural and stereoisomerism

Types of isomerism? Isomerism, how to differentiate?

Optical stereo isomer differ in the arrangement if atoms in 3D space which create miror images of each other. has chiral carbon which is optically active compound.

Optically active?

Cis-trans isomerism, structural, geometrical.

Chiral carbon?

What is isomers and what is the type of isomerism?

For chain isomerism, C5H12, draw the structure of pentane, 2-methylbutane, 2,2-dimethyl propane.

For positional isomerism, draw the structure of but-2-ene, but-1-ene, 2-methylphenol, 3-methylphenol, 4-methylphenol.

For functional group isomerism, draw the structure of:

hexene, cyclohexane.

ethanol, methoxymethane.

propanal, propanone.

propanoic acid, methyl ethanoate.

Draw the structure of: butanone, butanal, 2-methylpropanal, propan-1-ol, propan-2-ol, methoxyethane.

Draw the structural formula and state the names of all the structural isomers of the hydrocarbon C4H8.

but-2-ene, but-1-ene, 2-methylpropene, cyclobutane, methylcyclopropane.

What is stereoisomerism?

What is cis-trans isomerism, double bond, give the difference in their physical properties?

What is optical isomerism? Optically active? What is asymmetric, chiral carbon atom, C*, what is enantiomers?

 

14.5 Free radicals, nucleophiles and electrophiles

What is free radicals, nucleophiles and electrophiles?

Free radical reaction mechanism: 3 steps, initiation, propagation, termination.

What is nucleophilic?

(of a molecule or group) having a tendency to donate electrons or react at electron-poor sites such as protons.

What is electrophilic?

(of a molecule or group) having a tendency to attract or acquire electrons.

How do you tell if a reaction is electrophilic or nucleophilic? What is electrophilic and nucleophilic addition?

Electrophilic addition is where the group being added accepts an electron pair while nucleophilic addition is where the group being added donates an electron pair.

What type of reaction is free radical substitution?

Free radical reactions Free radicals are atoms or groups of atoms which have a single unpaired electron. A free radical substitution reaction is one involving these radicals. Free radicals are formed if a bond splits evenly – each atom getting one of the two electrons. The name given to this is homolytic fission.

Which of the following species are radicals, CO2, HNO3, NO2 ?

NO2

What are the type of bond fission?

Two types of bond fission are possible, homolytic fission and heterolytic fission. These are very important principles, used throughout organic chemistry.

Homolytic fission

In the example above, a covalent bond breaks so that one of the bonding electrons goes to each of A and B. Homolytic fission forms two free-radicals.

Heterolytic fission

In the example above, a covalent bond breaks so that both the bonding electrons go to either A or B.
Heterolytic fission forms oppositely-charged ions.
NOTE:
Homolytic fission → free radicals
Heterolytic fission → ions

14.6 Molecular structure and its effect on physical properties

Molecular structure and its effect on physical properties. Arrange? 

What happens when a particular homologous series as the same size of the molecules increases, regarding to its volatality, boiling point, melting point and enthalphy of vaporisation?

14.7 Inductive and resonance effect.

Acidity and pKa. Acidic/ basidic pKa, pKb how to determine?

Electron withdrawing/ donating group.

What is pka in chemistry? What does pKa mean in chemistry?
The pKa value is one method used to indicate the strength of an acid. pKa is the negative log of the acid dissociation constant or Ka value. A lower pKa value indicates a stronger acid.
What is the difference between pH and pKa?
The pH is a measure of the concentration of hydrogen ions in an aqueous solution.
pKa (acid dissociation constant) and pH are related, but pKa is more specific in that it helps you predict what a molecule will do at a specific pH.
The pKa is the pH value at which a chemical species will accept or donate a proton.
The lower the pKa, the stronger the acid and the greater the ability to donate a proton in aqueous solution. The Henderson-Hasselbalch equation relates pKa and pH (The equilibrium between the weak acid and its conjugate base allows the solution to resist changes to pH when small amounts of strong acid or base are added. The buffer pH can be estimated using the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA])). However, it is only an approximation and should not be used for concentrated solutions or for extremely low pH acids or high pH bases. pH and pKa Once you have pH or pKa values, you know certain things about a solution and how it compares with other solutions: The lower the pH, the higher the concentration of hydrogen ions [H+]. The lower the pKa, the stronger the acid and the greater its ability to donate protons. pH depends on the concentration of the solution. This is important because it means a weak acid could actually have a lower pH than a diluted strong acid. For example, concentrated vinegar (acetic acid, which is a weak acid) could have a lower pH than a dilute solution of hydrochloric acid (a strong acid). On the other hand, the pKa value is constant for each type of molecule. It is unaffected by concentration. Even a chemical ordinarily considered a base can have a pKa value because the terms “acids” and “bases” simply refer to whether a species will give up protons (acid) or remove them (base). For example, if you have a base Y with a pKa of 13, it will accept protons and form YH, but when the pH exceeds 13, YH will be deprotonated and become Y. Because Y removes protons at a pH greater than the pH of neutral water (7), it is considered a base.
What factors that affect acidity?
There are several factors that affect acidity:
1) Electronegativity: Acidity increases as you go left to right across the periodic chart.
2) Anion size: Acidity increases as you go from top to bottom in a group of the periodic chart.
3) Resonance: Anions that have resonance structures will be more acidic than anions that don’t.
4) Hybridization: acidity follows sp > sp2 > sp3
5) Inductive effect: Electron withdrawing substitution will increase the acidity of a compound.

 

 

 

 

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15.1, 3 steps, initiation, propagation, termination.

Application of organic compounds? Cracking process, refining of crude oil, fractional distillation, air pollution, photo chemical smog, engines of vehicles, what gases produced, how to reduce, what catalyst used. Catalytic converter.

Refining of crude oil. Fractional distillation, Catalytic cracking process –> product?
Refining, reforming. Reagent to convert ethene –> ethane-1,2-diol.
alkylbenzene, react with CH3Cl/ FeCl3, mechanism.

15.2 Common names, toluene, phenol vs phenyl?

Alkene: Chemical test. Reaction of organic compounds? How to produce/ reaction/ test (final comparisons, perbandingan)? [selected] In general?

Distinguish between cycloalkanes and alkene?

How to distinguish cycloalkane form alkene?
Add separately bromine dissolved in tetrachloromethane to the cycloalkane and alkene. Alkene – decolourises the reddish-brown colour of bromine. Cycloalkane – does not decolourise the bromine.
Reaction alkyl benzene with CH3Cl/ FeCl3?
Methyl is added to C number 4.

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https://docs.google.com/document/d/116HRoPny7vvjoHO46-FgSbNZryMzgFWucUumS0X5CA8/edit?usp=sharing

 

14 Introductions to Organic Chemistry

14.1 Bonding of the carbon atoms: the shapes of ethane, ethene, ethyne and benzene molecules

Candidates should be able to:

(a) use the concept of sp3, sp2 and sp hybridisations in carbon atoms to describe the bonding and shapes of molecules as exemplified by CH4, C2H4, C2H2 and C6H6;

(b) explain the concept of delocalisation of electrons in benzene ring.

14.2 General, empirical, molecular and structural formulae of organic compounds

Candidates should be able to:

(a) state general, empirical, molecular and structural formula of organic compounds;

(b) determine empirical and molecular formulae of organic compounds.

14.3 Functional groups: classification and nomenclature

Candidates should be able to:

(a) describe the classification of organic compounds by functional groups and the nomenclature of classes of organic compounds according to the IUPAC rules of the following classes of compounds:

(i) alkanes, alkenes, alkynes and arenes,

(ii) haloalkanes/ alkyl halide,

(iii) alcohols (including primary, secondary and tertiary) and phenols,

(iv) aldehydes and ketones,

(v) carboxylic acids and their derivatives (acyl chlorides, amides and esters),

(vi) primary amines, amino acids and protein.

14.4 Isomerism: structural and stereoisomerism

Candidates should be able to:

(a) define structural and stereoisomerism (geometrical and optical);

(b) explain the meaning of a chiral centre in optical isomerism;

(c) classify isomers as structural, cis-trans and optical isomers;

(d) identify chiral centres and/or cis-trans isomerism in a molecule of given structural formula;

(e) deduce the possible isomers for an organic compound of known molecular formula.

14.5 Free radicals, nucleophiles and electrophiles

Candidates should be able to:

(a) describe homolytic and heterolytic fissions;

(b) define the terms free radical, nucleophile and electrophile;

(c) explain that nucleophiles such as OH, NH3, H2O, Br, I and carbanion are Lewis bases;

(d) explain that electrophiles such as H+, NO2+, Br2, AlCl3, ZnC12, FeBr3, BF3 and carbonium ion are Lewis acids.

14.6 Molecular structure and its effect on physical properties

Candidates should be able to:

(a) describe the relationship between the size of molecules in the homologous series and the melting and boiling points;

(b) explain the forces of attraction between molecules (van der Waals forces and hydrogen bonding).

14.7 Inductive and resonance effect

Candidates should be able to:

(a) explain inductive effect which can determine the properties and reactions of functional groups;

(b) use inductive effect to explain why functional groups such as NO2, CN, COOH, COOR, >C=O, SO3H, X (halogen), OH, OR, NH2, C6H5 are electron acceptors whereas R (alkyl) is an electron donor;

(c) explain how the concept of induction can account for the differences in acidity between CH3COOH, C1CH2COOH, C12CHCOOH and Cl3CCOOH; between C1CH2CH2CH2COOH and CH3CH2CHClCOOH;

(d) use the concept of resonance to explain the differences in acidity between ethanol & phenol, as well as the differences in basicity between methylamine & aniline.

By writing the equations and state reagents and the conditions, give one example for each of the following mechanism:
1. free radical substitution reaction
2. electrophilic addition reaction
3. electrophilic substitution reaction
4. nucleophilic substitution reaction
5. nucleophilic addition reaction
6. friedel-craft reaction

Chemical Test:
1. for alkenes and unsaturated compounds
2. for phenol
3. to detect the presence of >C=O groups
4. to differentiate between aldehyde and ketone
5. iodoform test

14 Introductions to Organic Chemistry (APPS)

14.1 Bonding of the carbon atoms: the shapes of ethane, ethene, ethyne and benzene molecules

 

 

Candidates should be able to:

(a) use the concept of sp3, sp2 and sp hybridisations in carbon atoms to describe the bonding and shapes of molecules as exemplified by

sp3
sp2
sp

CH4,

C2H4,

C2H2 and

C6H6;

QUIZ

sp3
sp2
sp

 

 

 

CH4

 

C2H4

 
 

C2H2 and

 

 
C6H6 ;

 

(b) explain the concept of delocalisation of electrons in benzene ring.

 

 

14.2 General, empirical, molecular and structural formulae of organic compounds

Candidates should be able to:

(a) state general, empirical formulae, molecular formulae and structural formulae of organic compounds;


state general,

empirical formulae,

 

3.3 molecular formulae and

 

structural formula of organic compounds;

 

(b) determine empirical and molecular formulae of organic compounds.

empirical formulae

molecular formulae

 

 

14.3 Functional groups: classification and nomenclature

Candidates should be able to:

(a) describe the classification of organic compounds by functional groups and the nomenclature of classes of organic compounds according to the IUPAC rules of the following classes of compounds:

(i) alkanes, alkenes, alkynes and arenes,

(ii) haloalkanes/ alkyl halide,

(iii) alcohols (including primary, secondary and tertiary) and phenols,

(iv) aldehydes and ketones,

(v) carboxylic acids and their derivatives (acyl chlorides, amides and esters),

(vi) primary amines, amino acids and protein.

(i) alkanes, alkenes, alkynes and arenes ,

(ii) haloalkanes / alkyl halide,

(iii) alcohols (including primary, secondary and tertiary) and phenols,

(iv) aldehydes and ketones,

(v) carboxylic acids and their derivatives (acyl chlorides, amides and esters),

(vi) primary amines, amino acids and protein.

 

14.4 Isomerism: structural and stereoisomerism

Candidates should be able to:

(a) define structural and stereoisomerism (geometrical and optical (enantiomer)); chirality, optically inactive active

 

structural
stereoisomerism (geometrical and optical (enantiomer));
chiralitychiral centre,
optically inactive activeoptical isomers

 

(b) explain the meaning of a chiral centre in optical isomerism; chirality

(c) classify isomers as structural, cis-trans and optical isomers;

structural,

cis-trans and

optical isomers;


(d) identify chiral centres and/ or cis-trans isomerism in a molecule of given structural formula;

(e) deduce the possible isomers for an organic compound of known molecular formula.

 

14.5 Free radicals, nucleophiles and electrophiles

Candidates should be able to:

(a) describe homolytic and heterolytic fissions;


(b) define the terms free radical, nucleophile and electrophile;

free radical,

 

 


Free radicals are atoms or groups of atoms with an odd (unpaired) number of electrons and can be formed when oxygen interacts with certain molecules. Once formed these highly reactive radicals can start a chain reaction, like dominoes.

nucleophile

A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction. All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.

electrophile;

in organic chemistry, an electrophile is a reagent attracted to electrons. Electrophiles are positively charged or neutral species having vacant orbitals that are attracted to an electron rich centre. It participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile.

SO3 is the electrophile in the reaction with benzene ring


(d) explain that electrophiles such as H+, NO2+, Br2, AlCl3, ZnC12, FeBr3, BF3 and carbonium ion are Lewis acids.

H+,

NO2+,

Br2,

AlCl3,

ZnC12,

FeBr3,

BF3

carbonium ion

14.6 Molecular structure and its effect on physical properties

Candidates should be able to:

(a) describe the relationship between the size of molecules in the homologous series and the melting and boiling points;

 

 

(b) explain the forces of attraction between molecules (van der Waals forces and hydrogen bonding).

van der Waals forces

hydrogen bonding

14.7 Inductive and resonance effect

Candidates should be able to:

(a) explain inductive effect which can determine the properties and reactions of functional groups;


(b) use inductive effect to explain why functional groups such as NO2, CN, COOH, COOR, >C=O, SO3H, X (halogen), OH, OR, NH2, C6H5 are electron acceptors whereas R(alkyl) is an electron donor;

NO2,

 


CN,


COOH,

COOR,
>C=O,
SO3H,
X (halogen),
OH,
OR,
NH2,
C6H5

are electron acceptors whereas R (alkyl) is an electron donor

(c) explain how the concept of induction can account for the differences in acidity between CH3COOH, C1CH2COOH, C12CHCOOH and Cl3CCOOH; between C1CH2CH2CH2COOH and CH3CH2CHClCOOH;

acidity

Cl3CH2COOH > Cl2CHCOOH > ClCH2COOH > CH3COOH

CH3CH2CHClCOOH > ClCH2CH2CH2COOH

(d) use the concept of resonance to explain the differences in acidity between CH3CH2OH (ethanol) and C6H5OH (phenol), as well as the differences in basicity between CH3NH2 (methylamine) and C6H5NH2 (aniline).

acidity between ethanol & phenol

basicity methylamine & aniline



An organic compound T that contains only carbon, hydrogen and oxygen is found to contain 52.2% carbon and 13.0% hydrogen by mass on analysis. Calculate the empirical formula of T?

% of oxygen in T = 100 – 52.2 -13 = 13.8%

C; 52.2%/12 = 4.35 mol, H; 13.0%/1 = 13.0 mol, O; 34.8%/16 = 2.18 mol

Simplest ratio; 4.35/2.18 = 2, 13.0/2.18 = 6, 2.18/2.18 =1

the empirical formula of T is C2H6O.

A compound V consisting of carbon, hydrogen and oxygen is analysed. 14.4 g of the compound burns completely in oxygen to form 31.7 g of carbon dioxide and 17.3 g of water. Determine the empirical formula of V?

Mr of CO2 = 44.0, 44.0 g of CO2 contains 12.0 g of C,

Mass of C in 14.4 g of V = 31.7 x 12.0/44.0 = 8.65 g.

Mr of H2O = 18.0, 18.0 g of H2O contains 2.0 g of H.

Mass of H in 14.4 g of V = 17.3 x 2.0/18.0 = 1.92 g of hydrogen.

Mass of O in 14.4 g of V = 14.4 – 8.65 – 1.92 = 3.83 g.

C; 8.65 g/12.0 = 0.72 mol, H; 1.92 g/1 = 1.92 mol, O; 3.83 g/ 16 = 0.24 mol.

Simplest ratio; C; 0.72/0.24 = 3, H; 1.92/1 = 8, O; 0.24/0.24 = 1.

the empirical formula of V is C3H8O.

A volatile organic compound W has the percentage composition of carbon, 65.7%; hydrogen, 15.1%; nitrogen, 19.2%. At 96°C and 100 kPa, the volume of 0.30 g of W is 126 cm3. Determine the empirical formula and molecular formula of W?

C; 65.7%/12 = 5.48 mol, H; 15.1%/1 = 15.1 mol, N; 19.2%/14 = 1.37 mol.

Simplest ratio; C; 5.48/1.37 = 4, H; 15.1/1.37 =11, O; 1.37/1.37 = 1.

the empirical formula of W is C4H11N.

Using the ideal gas equation, PV = nRT

PV = (m/Mr) RT. Mr = mRT/(PV) = [0.30×8.31x(273+96)]/ [100x126x10^-3]

= 73.0, n(C4H11N) = 73.0, n = 73.0 / (4×12.0+11×1.0+1×14.0) = 1.

the molecular formula of W is C4H11N.

0.81 g of an organic compound burnt completely in oxygen to yield 1.55 g of carbon dioxide and 0.99 g of water. If the compound contains carbon, hydrogen and oxygen only, determine the empirical formula of the compound?

Mr of CO2 = 44.0, 44.0 g CO2 contains 12.0 g C, Mass of C in the compound = 1.55 x 12.0/44.0 = 0.42 g.

Mr of H2O = 18 gmol-1. 18.0 g H2O contains 2.0 g H.

Mass of H in the compound = 0.99 x 2.0/18.0 = 0.11 g.

Mass of O in the compound = 0.81 – 0.42 – 0.11 = 0.28 g.

C; 0.42/12 = 0.035 mol, H; 0.11/1 = 0.11 mol, 0.28/16 = 0.018 mol.

Simplest ratio = C2H6O.

A mixture of 10 cm3 of methane and 10 cm3 of ethane is ignited in excess oxygen. After being cooled, the remaining gas is bubbled through an aqueous solution of KOH. Determine the volume of gas that would be absorbed by the alkali?

CH4 + 2O2 –> CO2 + 2H2O

C2H6 + 3½ O2 –> 2CO2 + 3H2O

1 mol CH4 forms 1 mol CO2, 10cm3 CH4 forms 10 cm3 CO2.

1 mol C2H6 forms 2 mol CO2, 10 cm3 C2H6 forms 20 cm3 CO2.

Total volume of CO2 absorbed by the alkali = 10 + 20 = 30 cm3.

When 8 cm3 of hydrocarbon P was burnt in 60 cm3 oxygen, the volume of the gaseous products occupied 44 cm3. After absorption by KOH, the residual gas occupied 12 cm3. What is the molecular formula of the hydrocarbon?

Volume of O2 gas reacted = 60 – 12 = 48 cm3.

Volume of CO2 gas liberated (absorbed by KOH) = 44 – 12 = 32 cm3.

CxHy + (x + y/4)O2 –> xCO2 + y/2H2O

8 cm3 CxHy formed 32 cm3 CO2, x = 4.

8 cm3 CxHy reacted with 48 cm3 O2•(x+y/4) = 48/8, y = 8.

The molecular formula of P is C4H8.

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