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Class 10 Chemistry Chapter 21 Organic Chemistry Test 7
Chemistry Class 10 Chapter 21 full chapter Test
Prepare for the Punjab Board Class 10 Chemistry Examination 2027 with Chapter 21: Organic Chemistry – Class Test No. 7. This full chapter test, including textbook exercises, is designed to help students revise important concepts and practice exam-oriented questions according to the new Chemistry syllabus issued by PECTAA Punjab. As part of our Punjab Board 2027 Model Papers, Full Unit Model Papers, and Chapter-Wise Test Series, this test helps students assess their understanding of Organic Chemistry, improve problem-solving skills, and prepare effectively for their annual board examinations. Practice regularly to strengthen your concepts and boost your confidence for the Class 10 Chemistry Board Exam 2027.
Full Chapter Test
T-07
CHAPTER # 21
Note:Four possible answers A, B, C and D to each question are given. The choice which you think is correct, fill that circle in front of that question with Marker or Pen ink. Cutting or filling two or more circles will result in zero mark in that question.
1.
What is the IUPAC name for a branched-chain compound where a methyl group is attached to the second carbon of a propane chain?
(a) Butan-1-ol(b) 2,2-Dimethyl propane(c) 2-Methyl propane(d) Cyclopropane
Answer: (c) 2-Methyl propane
2.
Which of the following is the functional group for Carboxylic acids?
(a) –OH(b) –COOH(c) –CHO(d) –NH2
Answer: (b) –COOH
3.
As the number of carbon atoms in a hydrocarbon increases, the number of possible isomers:
(a) Decreases(b) Remains constant(c) Increases very rapidly(d) Becomes zero
Answer: (c) Increases very rapidly
4.
Propanone (Acetone) is the simplest member of which homologous series?
(a) Alcohols(b) Carboxylic Acids(c) Aldehydes(d) Ketones
Answer: (d) Ketones
5.
Hydrocarbons containing only single bonds are called:
(a) Alkenes(b) Alkynes(c) Alkanes(d) Aromatics
Answer: (c) Alkanes
6.
The suffix used for alkanes is:
(a) –ene(b) –yne(c) –ol(d) –ane
Answer: (d) –ane
7.
Formic acid was first isolated from:
(a) Honey bees(b) Red ants(c) Vinegar(d) Plants
Answer: (b) Red ants
8.
Choose the correct IUPAC name for the compound
HC–CH2–CH3
‖
CH2
(a) But-3-ene(b) But-1-ene(c) But-2-ene(d) Butene
Answer: (b) But-1-ene (CH2=CH–CH2–CH3; numbering starts from the end nearest the double bond.)
9.
Identify the aldehyde functional group among the following:
(a)
O‖–C–OH
(b) – OH
(c)
O‖–C–
(d)
O‖–C–H
Answer: (d) –CHO (carbonyl group with a hydrogen attached). (a) is carboxyl, (c) is ketone carbonyl.
10.
Select the general formula of alkyne family.
(a) CnH2n+1(b) CnH2n(c) CnH2n−2(d) CnH2n−1
Answer: (c) CnH2n−2
11.
How many structural isomers will be there for a saturated hydrocarbon having five carbon atoms?
(a) 2(b) 3(c) 4(d) 5
Answer: (b) 3 (n-pentane, isopentane, neopentane)
12.
Which functional group is present in alkenes?
(a) No functional group(b) Carbon-carbon triple bond(c) Carbon-carbon double bond(d) Carbon-carbon single bond
Answer: (c) Carbon-carbon double bond (C=C)
Here is Subjective Part of Question Paper.
Marks: 48
CHEMISTRY (SUBJECTIVE TYPE)
Time: 1:45 minute
Part – I
2.Write short answers to any Five (5) questions:
[5×2=10]
(i)
What is Organic chemistry?
Organic chemistry is the branch of chemistry that deals with the study of carbon compounds, especially hydrocarbons and their derivatives.
(ii)
Which element are commonly present in organic compounds besides carbon?
Hydrogen, oxygen, nitrogen, sulphur, phosphorus and halogens (chlorine, bromine, etc.).
(iii)
What are Aromatic compounds? Give an example.
Aromatic compounds are cyclic compounds that contain a benzene ring (six carbon atoms with three alternate double and single bonds). Example: benzene, C6H6.
(iv)
Define Structural formula and write its importance.
Definition: A structural formula shows how the atoms of a molecule are arranged and joined by bonds.
Importance: it shows the exact structure of the molecule, helps to distinguish isomers having the same molecular formula, and helps to understand the properties of the compound.
Importance: it shows the exact structure of the molecule, helps to distinguish isomers having the same molecular formula, and helps to understand the properties of the compound.
(v)
How do physical properties change within a homologous series as the molecular mass increases?
Physical properties such as melting point, boiling point, density and solubility change gradually and regularly. For example, the boiling points increase steadily as the molecular mass increases.
(vi)
Write any two characteristics of Homologous Series.
(1) All members have the same general formula (e.g. alkanes CnH2n+2) and the same functional group.
(2) Successive members differ by a CH2 group (14 units of molecular mass).
(2) Successive members differ by a CH2 group (14 units of molecular mass).
(vii)
Define Isomerism.
The phenomenon in which compounds have the same molecular formula but different structural formulae is called isomerism. Such compounds are called isomers.
(viii)
How does the number of isomers change with the increase in carbon atoms?
The number of isomers increases very rapidly as the number of carbon atoms increases: C4H10 has 2, C5H12 has 3, C6H14 has 5, C7H16 has 9 and C10H22 has 75 isomers.
3.Write short answers to any Five (5) questions:
[5×2=10]
(i)
Why is the study of functional groups important in Organic Chemistry?
Compounds with the same functional group show similar chemical properties. By studying functional groups we can classify millions of compounds into families, predict their reactions and name them systematically.
(ii)
Phenol and Ethanol both contain the -OH group. Why are they placed in different classes of compounds?
In ethanol the –OH group is attached to an alkyl (aliphatic) carbon, so it is an alcohol. In phenol the –OH group is attached directly to a carbon of a benzene ring (aromatic), so it belongs to the phenols. Their properties differ (phenol is weakly acidic, ethanol is neutral).
(iii)
From where was acetic acid first isolated?
Acetic acid was first isolated from vinegar (Latin acetum).
(iv)
How is the position of hydroxyl group indicated in alcohols?
The carbon chain is numbered from the end that gives the carbon bearing –OH the lowest number, and this number is written before the suffix “ol”. Example: CH3–CH(OH)–CH3 is propan-2-ol.
(v)
What is the difference between cyclohexane and benzene?
Cyclohexane (C6H12) is an alicyclic, saturated ring with only single bonds. Benzene (C6H6) is an aromatic, unsaturated ring with three alternate double and single bonds.
(vi)
Give two examples of branched chain compounds.
(1) Isobutane (2-methylpropane), (CH3)2CH–CH3
(2) Neopentane (2,2-dimethylpropane), C(CH3)4
(2) Neopentane (2,2-dimethylpropane), C(CH3)4
(vii)
Write down the displayed and condensed formulae of pentane.
Displayed formula:
H H H H H
| | | | |
H - C - C - C - C - C - H
| | | | |
H H H H H
Condensed formula: CH3–CH2–CH2–CH2–CH3(viii)
How phenols are different from alcohols?
In phenols the –OH group is attached directly to a benzene (aromatic) ring, e.g. C6H5OH; in alcohols it is attached to an alkyl group, R–OH. Phenols are weakly acidic and react with NaOH, while alcohols are neutral.
4.Write short answers to any Five (5) questions:
[5×2=10]
(i)
Name the following compounds according to IUPAC system of nomenclature.
(a)CH3 – CH2 – CH2 – CH2 – CH3
(b)CH3 – CH2 – CH2 – CH2 – CH2 – CH2 – CH3
(a) Pentane (5 carbons, all single bonds).
(b) Heptane (7 carbons, all single bonds).
(b) Heptane (7 carbons, all single bonds).
(ii)
Condensed structural formulae of some organic compounds are given below. Write down the names of their families.
(a)
CH3-CH-CH3
|
OH(b)
O
||
CH3-CH2-C-CH3(a) Alcohols (functional group –OH); the compound is propan-2-ol.
(b) Ketones (functional group >C=O between two alkyl groups); the compound is butanone.
(b) Ketones (functional group >C=O between two alkyl groups); the compound is butanone.
(iii)
What is the difference between saturated and unsaturated hydrocarbons?
Saturated hydrocarbons contain only single C–C bonds (alkanes, CnH2n+2). Unsaturated hydrocarbons contain at least one carbon-carbon double or triple bond (alkenes CnH2n, alkynes CnH2n−2) and are more reactive.
(iv)
Define structural isomerism.
Structural isomerism is the existence of compounds with the same molecular formula but different arrangement of atoms (different structural formulae). Example: butane and isobutane, both C4H10.
(v)
Why the members of a homologous series have similar chemical properties?
Because all members of a homologous series contain the same functional group, which decides the chemical behaviour.
(vi)
Write down the structural formulae of isomers shown by saturated hydrocarbon containing five carbon atoms.
Pentane (C5H12) has three isomers:
1. n-Pentane: CH3–CH2–CH2–CH2–CH3 2. Isopentane (2-methylbutane):
1. n-Pentane: CH3–CH2–CH2–CH2–CH3 2. Isopentane (2-methylbutane):
CH3-CH-CH2-CH3
|
CH3
3. Neopentane (2,2-dimethylpropane):
CH3
|
CH3-C-CH3
|
CH3(vii)
Write down the structural formulae of the isomers shown by butene.
Butene (C4H8):
1. But-1-ene: CH2=CH–CH2–CH3
2. But-2-ene: CH3–CH=CH–CH3
(A third structural isomer is 2-methylpropene, (CH3)2C=CH2.)
1. But-1-ene: CH2=CH–CH2–CH3
2. But-2-ene: CH3–CH=CH–CH3
(A third structural isomer is 2-methylpropene, (CH3)2C=CH2.)
(viii)
Write down the molecular formula of a carboxylic acid having three carbon atoms.
Propanoic acid: C3H6O2 (structural formula CH3–CH2–COOH).
Part – II
NOTE:- Attempt any two questions.
[9×2=18]
5.
(a) What is an organic compound? How organic compounds are classified based on the type of carbon chain present in them?
Organic compound: a compound of carbon (usually with hydrogen and other elements) in which atoms are joined by covalent bonds.
Classification:
Classification:
- Acyclic (open chain / aliphatic) compounds: straight or branched chains, e.g. CH3–CH2–CH3.
- Cyclic (closed chain) compounds:
- Homocyclic (ring of carbon atoms only): alicyclic (e.g. cyclohexane) and aromatic (e.g. benzene).
- Heterocyclic (ring contains carbon and another atom such as N, O or S): e.g. pyridine.
(b) Define Functional group. Explain any two Functional group briefly.
Functional group: an atom or group of atoms in a molecule that is responsible for its characteristic chemical properties.
1. Hydroxyl group (–OH): present in alcohols, general formula R–OH, e.g. ethanol C2H5OH.
2. Carboxyl group (–COOH): present in carboxylic acids, general formula R–COOH, e.g. acetic acid CH3COOH.
1. Hydroxyl group (–OH): present in alcohols, general formula R–OH, e.g. ethanol C2H5OH.
2. Carboxyl group (–COOH): present in carboxylic acids, general formula R–COOH, e.g. acetic acid CH3COOH.
6.
(a) Write down five characteristics of a homologous series.
- All members have the same general formula (e.g. CnH2n+2 for alkanes).
- Successive members differ by a CH2 group, i.e. 14 units of molecular mass.
- All members contain the same functional group.
- All members have similar chemical properties.
- Physical properties (melting point, boiling point, density) change gradually with increase in molecular mass.
(b) What are Isomers? Describe how the number of isomers varies with the increase in carbon atoms in hydrocarbons.
Isomers: compounds having the same molecular formula but different structural formulae, e.g. n-butane and isobutane (C4H10).
Variation: as the number of carbon atoms increases, the carbon atoms can be arranged in more ways, so the number of isomers increases very rapidly.
Variation: as the number of carbon atoms increases, the carbon atoms can be arranged in more ways, so the number of isomers increases very rapidly.
| Alkane | C4H10 | C5H12 | C6H14 | C7H16 | C8H18 | C10H22 |
|---|---|---|---|---|---|---|
| Isomers | 2 | 3 | 5 | 9 | 18 | 75 |
7.
(a) Give IUPAC rules for naming alcohols.
- Select the longest continuous carbon chain that contains the –OH group.
- Name the chain as the alkane and replace the last “e” with “ol” (alkane → alkanol).
- Number the chain from the end that gives the –OH group the lowest number.
- Write the position number of –OH just before “ol”.
- Name side chains as prefixes with their positions, in alphabetical order.
OH
|
CH3-CH-CH3 → Propan-2-ol(b) What is an alkane? Explain the naming system of organic compound by IUPAC system.
Alkane: a saturated hydrocarbon containing only single bonds between carbon atoms; general formula CnH2n+2; suffix “–ane”.
IUPAC naming: an IUPAC name has three parts:
Prefix (side chains such as methyl, ethyl, chloro, with position numbers) + Root (number of carbons in the longest chain: meth, eth, prop, but, pent, hex) + Suffix (functional group or bond type: –ane, –ene, –yne, –ol, –al, –one, –oic acid).
| Carbons | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| Name | Methane | Ethane | Propane | Butane | Pentane | Hexane |
| Formula | CH4 | C2H6 | C3H8 | C4H10 | C5H12 | C6H14 |
Prefix (side chains such as methyl, ethyl, chloro, with position numbers) + Root (number of carbons in the longest chain: meth, eth, prop, but, pent, hex) + Suffix (functional group or bond type: –ane, –ene, –yne, –ol, –al, –one, –oic acid).
- Select the longest continuous carbon chain (parent chain).
- Number the chain so that the side chain or functional group gets the lowest number.
- Name the side chains as alkyl groups (methyl, ethyl) and write their positions before the root.
- For identical groups use di, tri, etc.; arrange different groups alphabetically.
