IB Topic 10 Organic Chemistry
Questions and Answers
- 1.
Which of the following is true about alkane? I. they form an homologous series with the general formula CnH2n+2 II. They all have identical physical properties III. They all have similar chemical properties
- A.
I, II and III
- B.
I and III only
- C.
II and III only
- D.
III only
Correct Answer
D. III onlyExplanation
Alkanes are a group of hydrocarbons that have single bonds between carbon atoms. They form an homologous series with the general formula CnH2n+2, which means that the number of carbon atoms in the molecule determines the number of hydrogen atoms. However, alkane molecules with different carbon chain lengths will have different physical properties such as boiling points and melting points. Therefore, statement I is true but statement II is false. Alkanes do have similar chemical properties, as they undergo similar reactions such as combustion and substitution reactions. Therefore, statement III is true.Rate this question:
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- 2.
Which of the following two compounds both belong to the same homologous series?
- A.
CH3COOH and HCOOCH3
- B.
CH3OH and C2H5OH
- C.
C2H4 and C2H6
- D.
C2H5Cl and C2H4Cl2
Correct Answer
B. CH3OH and C2H5OHExplanation
CH3OH and C2H5OH both belong to the same homologous series because they have the same functional group, which is the hydroxyl group (-OH). In both compounds, the hydroxyl group is attached to a carbon atom. The only difference between the two compounds is the number of carbon atoms in the chain. Both compounds are alcohols, with CH3OH being methanol and C2H5OH being ethanol.Rate this question:
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- 3.
How many different isomers of C5H12 exist?
- A.
1
- B.
2
- C.
3
- D.
4
Correct Answer
C. 3Explanation
The correct answer is 3 because C5H12 represents a pentane molecule, which can exist in three different isomeric forms. These isomers include n-pentane, isopentane, and neopentane. Each isomer has a different arrangement of carbon atoms, resulting in distinct chemical and physical properties.Rate this question:
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- 4.
Gave the name for
- A.
2,2-dimethylbutane
- B.
2-methylpentane
- C.
Hexane
- D.
2-methyl-2ethylpropane
Correct Answer
A. 2,2-dimethylbutaneExplanation
The given correct answer, 2,2-dimethylbutane, is the correct name for the compound. This is because it accurately describes the structure of the molecule, which consists of a butane backbone with two methyl groups attached to the second carbon atom. The prefix "2,2-dimethyl" indicates the positions of the methyl groups on the butane backbone.Rate this question:
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- 5.
Which statement is correct about the reaction between methane and chlorine?
- A.
It involves heterolytic fission and Cl- ions
- B.
It involves heterolytic fission and Cl. radicals
- C.
It involves homolytic fission and Cl- ions
- D.
It involves homolytic fission and Cl. radicals
Correct Answer
D. It involves homolytic fission and Cl. radicalsExplanation
The correct answer is "it involves homolytic fission and Cl. radicals." In the reaction between methane and chlorine, homolytic fission occurs, which means that the bond between the carbon and hydrogen atoms in methane is broken equally, resulting in the formation of methyl radicals (CH3•). Similarly, the bond between the chlorine atoms in chlorine (Cl2) is also broken equally, resulting in the formation of chlorine radicals (Cl•).Rate this question:
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- 6.
Which compound is an ester?
- A.
CH3COOH
- B.
C2H5CHO
- C.
CH3OC2H5
- D.
HCOOCH3
Correct Answer
D. HCOOCH3Explanation
HCOOCH3 is an ester because it contains the ester functional group, which is formed by the condensation reaction between an alcohol and a carboxylic acid. In HCOOCH3, the methoxy group (CH3O) acts as the alcohol component, and the formic acid group (HCOO) acts as the carboxylic acid component.Rate this question:
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- 7.
When ethanol is partially oxidized by an acidified solution of potassium dichromate (VI), the product that can be obtained by distillation as soon as it is formed is:
- A.
Ethanal
- B.
Ethanoic acid
- C.
Ethene
- D.
Ethane 1,2 diol
Correct Answer
A. EthanalExplanation
When ethanol is partially oxidized by an acidified solution of potassium dichromate (VI), the product that can be obtained by distillation as soon as it is formed is ethanal. This is because ethanal is an aldehyde that is formed when one hydrogen atom from the alcohol group of ethanol is removed and replaced with a double bond to an oxygen atom. Ethanal has a lower boiling point compared to other products listed, such as ethanoic acid, ethene, and ethane 1,2 diol, allowing it to be easily separated through distillation.Rate this question:
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- 8.
Which formula is that of the secondary halogenoalkane?
- A.
CH3CH2CH2CH2Br
- B.
(CH3)2CHCH2Br
- C.
CH3CHBrCH2CH3
- D.
(CH3)2CBr
Correct Answer
B. (CH3)2CHCH2BrExplanation
The formula (CH3)2CHCH2Br represents the secondary halogenoalkane. This is because it contains a secondary carbon atom (attached to two other carbon atoms) bonded to a halogen (Br). In contrast, the other options either have primary carbon atoms (attached to only one other carbon atom) or tertiary carbon atoms (attached to three other carbon atoms). Therefore, the correct answer is (CH3)2CHCH2Br.Rate this question:
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- 9.
Which compound is converted to butanal by acidified potassium dichromate (VI) solution?
- A.
Butan-1-ol
- B.
Butan-2-ol
- C.
Butanone
- D.
Butanoic acid
Correct Answer
A. Butan-1-olExplanation
Butan-1-ol is converted to butanal by acidified potassium dichromate (VI) solution. This is because acidified potassium dichromate (VI) is a strong oxidizing agent that can oxidize alcohols to aldehydes. In the case of butan-1-ol, the alcohol functional group (-OH) is oxidized to an aldehyde functional group (-CHO), resulting in the formation of butanal.Rate this question:
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- 10.
Which reaction(s) involve(s) the formation of a positive ion? I. CH3CH2CH2Br + OH- II. (CH3)3Br + OH-
- A.
I only
- B.
Both I and II
- C.
II only
- D.
Neither I nor II
Correct Answer
C. II onlyExplanation
The reaction (CH3)3Br + OH- involves the formation of a positive ion. In this reaction, the bromine atom in (CH3)3Br is replaced by the hydroxide ion (OH-), resulting in the formation of (CH3)3OH, which has a positive charge due to the transfer of a lone pair of electrons from the hydroxide ion. On the other hand, the reaction CH3CH2CH2Br + OH- does not involve the formation of a positive ion since the bromine atom is replaced by the hydroxide ion, resulting in the formation of CH3CH2CH2OH, which does not have a positive charge. Therefore, the correct answer is II only.Rate this question:
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- 11.
Which statement about neighbouring members of all homologous series is correct?
- A.
They all have the same empirical formula
- B.
They differ by CH2 group
- C.
They possess different functional groups
- D.
They differ in their degree of unsaturation
Correct Answer
B. They differ by CH2 groupExplanation
Neighbouring members of all homologous series differ by a CH2 group. This means that each member of the series has the same functional group but differs in the number of CH2 units in its molecular structure. This results in an increase in molecular size and mass as you move from one member to the next in the series.Rate this question:
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- 12.
Which compound is a member of the same homologous series as 1-chloropropane?
- A.
1-chloropropene
- B.
1-chlorobutane
- C.
1-bromopropane
- D.
1,1-dichloropropane
Correct Answer
B. 1-chlorobutaneExplanation
1-chlorobutane is a member of the same homologous series as 1-chloropropane because both compounds belong to the alkyl halide family, which is characterized by a halogen atom (in this case, chlorine) bonded to a carbon chain. The only difference between the two compounds is the length of the carbon chain, with 1-chloropropane having three carbon atoms and 1-chlorobutane having four carbon atoms.Rate this question:
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- 13.
Which type of compound must contain a minimum of three carbon atoms?
- A.
An aldehyde
- B.
A carboxylic acid
- C.
An ester
- D.
A ketone
Correct Answer
D. A ketoneExplanation
A ketone is a type of compound that must contain a minimum of three carbon atoms. Ketones have a carbonyl group (C=O) in the middle of the carbon chain, with two additional carbon atoms bonded to it. This structure requires at least three carbon atoms in order to form a ketone. Aldehydes, carboxylic acids, and esters can have fewer than three carbon atoms and are not necessarily required to have a minimum of three carbon atoms.Rate this question:
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- 14.
What is the IUPAC name for CH3CH2CH(CH3)2?
- A.
1,1-dimenthylpropane
- B.
2-methylbutane
- C.
Isopentane
- D.
Ethyldimethylmethane
Correct Answer
B. 2-methylbutaneExplanation
The IUPAC name for CH3CH2CH(CH3)2 is 2-methylbutane. This is because the longest carbon chain in the molecule contains four carbon atoms, making it a butane. The methyl group attached to the second carbon atom is indicated by the prefix "2-methyl." Therefore, the correct IUPAC name for this compound is 2-methylbutane.Rate this question:
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- 15.
How many structural isomers are possible with the molecular formula C6H14?
- A.
4
- B.
5
- C.
6
- D.
7
Correct Answer
B. 5Explanation
The molecular formula C6H14 represents a saturated hydrocarbon with the general formula CnH2n+2. In this case, n is equal to 6, so the general formula becomes C6H14. Structural isomers are compounds with the same molecular formula but different structural arrangements. For C6H14, there are five possible structural isomers: hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. Therefore, the correct answer is 5.Rate this question:
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- 16.
Which compound is a member of the aldehyde homologous series?
- A.
CH3COCH3
- B.
CH3CH2CH2OH
- C.
CH3CH2COOH
- D.
CH3CH2CHO
Correct Answer
D. CH3CH2CHOExplanation
The compound CH3CH2CHO is a member of the aldehyde homologous series. Aldehydes are organic compounds that contain a carbonyl group (C=O) bonded to at least one hydrogen atom. In CH3CH2CHO, the carbonyl group is bonded to a hydrogen atom and an ethyl group (CH3CH2-), making it an aldehyde. CH3COCH3 is a ketone, as it has two alkyl groups bonded to the carbonyl group. CH3CH2CH2OH is an alcohol, as it has a hydroxyl group (-OH) bonded to the carbon atom. CH3CH2COOH is a carboxylic acid, as it has a carboxyl group (-COOH) bonded to the carbon atom.Rate this question:
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- 17.
Which formulas represent butane or its isomer? I. CH3(CH2)2CH3 II. CH3CH(CH3)CH3 III. (CH3)3CH
- A.
I and II only
- B.
I and III only
- C.
II and III only
- D.
I, II and III
Correct Answer
D. I, II and IIIExplanation
The given formulas represent butane or its isomer because all three formulas have the same molecular formula, C4H10, which is the molecular formula for butane. Formula I represents butane, formula II represents 2-methylpropane (an isomer of butane), and formula III represents 2,2-dimethylpropane (another isomer of butane). Therefore, all three formulas represent butane or its isomer.Rate this question:
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- 18.
Which substance(s) could be formed during the incomplete combustion of a hydrocarbon? I. carbon II. hydrogen III. carbon monoxide
- A.
I only
- B.
I and II only
- C.
I and III only
- D.
II and III only
Correct Answer
C. I and III onlyExplanation
During the incomplete combustion of a hydrocarbon, carbon and carbon monoxide can be formed. Incomplete combustion occurs when there is a limited supply of oxygen, resulting in the formation of carbon instead of carbon dioxide. Carbon monoxide is also produced as a byproduct of incomplete combustion. Hydrogen is not formed during incomplete combustion, as it is already present in the hydrocarbon and does not undergo any chemical changes. Therefore, the correct answer is I and III only.Rate this question:
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- 19.
What product results from the reaction of CH2=CH2 with Br2?
- A.
CHBrCHBr
- B.
CH2CHBr
- C.
CH3CH2Br
- D.
CH2BrCH2Br
Correct Answer
D. CH2BrCH2BrExplanation
When CH2=CH2 (ethylene) reacts with Br2 (bromine), it undergoes a halogenation reaction. In this reaction, one bromine atom replaces one hydrogen atom in the ethylene molecule, resulting in the formation of CH2BrCH2Br (1,2-dibromoethane). This product is formed by the addition of one bromine atom to each carbon atom in the ethylene molecule.Rate this question:
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- 20.
What is the final product formed when CH3CH2OH is refluxed with acidified potassiu dichromate(VI)?
- A.
CH3CHO
- B.
CH2=CH2
- C.
CH3COOH
- D.
HCOOCH3
Correct Answer
C. CH3COOHExplanation
When CH3CH2OH is refluxed with acidified potassium dichromate(VI), the final product formed is CH3COOH, which is acetic acid. This reaction is known as the oxidation of ethanol. The acidified potassium dichromate(VI) acts as an oxidizing agent, converting the ethanol into acetic acid.Rate this question:
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