2 marksShort AnswerSection A

(a) Write the molecular formula of the following carbon compounds : (i) Methane (ii) Propane (b) Carbon compounds have low melting and boiling points. Why ?

Carbon and its Compounds

Saturated and Unsaturated Carbon Compounds, Covalent Bonding

Official Answer

(a) The molecular formulas of the given carbon compounds are:

(i) Methane: $\text{CH}_4$

(ii) Propane: $\text{C}_3\text{H}_8$

(b) Carbon compounds are covalent in nature. The intermolecular forces of attraction between these molecules are weak. Consequently, very little thermal energy is required to break these weak forces, resulting in low melting and boiling points.

CH4C3H8covalentweak intermolecular forcesforces of attraction

Marking Scheme

1Writing the correct molecular formula of Methane ( $\text{CH}_4$ ) (0.5 marks)
2Writing the correct molecular formula of Propane ( $\text{C}_3\text{H}_8$ ) (0.5 marks)
3Explaining that carbon compounds have weak intermolecular forces of attraction (1 mark)

Hint

Use the general formula of alkanes $\text{C}_n\text{H}_{2n+2}$ where $n$ is the number of carbon atoms. For part (b), consider the strength of the forces acting between covalent molecules.

Quick Oral Answer

Methane has the formula $\text{CH}_4$ and propane is $\text{C}_3\text{H}_8$ . Carbon compounds have low melting and boiling points because they are covalent molecules held together by weak intermolecular forces, which require very little energy to overcome.

Analysis & Explanation

Methane and propane belong to the alkane family, which follows the general formula $\text{C}_n\text{H}_{2n+2}$ . Since carbon forms covalent bonds by sharing electrons, no ions are formed. The forces holding individual molecules together (intermolecular forces) are weak van der Waals forces, which explains why they have significantly lower melting and boiling points compared to ionic compounds.

Common Mistakes

1Writing incorrect molecular formulas such as $\text{C}_3\text{H}_6$ for propane.
2Confusing strong intramolecular covalent bonds with weak intermolecular forces when explaining melting/boiling points.

Interesting Facts

Methane is the simplest hydrocarbon and is the primary component of Compressed Natural Gas (CNG) and biogas.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2022?

This question carries 2 marks in the CBSE Class 10 Science 2022 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Saturated and Unsaturated Carbon Compounds, Covalent Bonding" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2022 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2022 paper.