# NCERT Solutions

## Class 10 Science

###### carbon and its compounds

Q1) Ethane, with the molecular formula C2H6 has

• (a) 6 covalent bonds
• (b) 7 covalent bonds
• (c) 8 covalent bonds
• (d) 9 covalent bonds

(b) 10, The carbon atoms have 4 atoms in outer most cell and hydrogen atom has one in outer most cell....
the 6 hydrogen atoms will share their electron with carbon atom to form 6 carbon - hydrogen covalent bonds and the two carbon atom will share 1 electron from each to form 1 carbon - carbon covalent bond... thus the ethane have 7 covalent bonds in total.

Q2) Butanone is a four-carbon compound with the functional group

• (a) Carboxylic acid
• (b) Aldehyde
• (c) Ketone
• (d) Alchohol

(C)

##### Butanone

Q3) While cooking, if the bottom of the vessel is getting blackened on the outside, it means that

• (a) the food is not cooked completely.
• (b) the fuel is not burning completely.
• (c)the fuel is wet.
• (d) the fuel is burning completely.

(b) the fuel is not burning completely.

Q4)Explain the nature of the covalent bond using the bond formation in CH3Cl.

Carbon can neither lose four of its electrons nor gain four electrons as both the processes require extra amount of energy and would make the system unstable. Therefore, it completes its octet by sharing its four electrons with other carbon atoms or with atoms of other elements. The bonds that are formed by sharing electrons are known as covalent bonds. In covalent bonding, both the atoms share the valence electrons, i.e., the shared electrons belong to the valence shells of both the atoms.

Here, carbon requires 4 electrons to complete its octet, while each hydrogen atom requires one electron to complete its duplet. Also, chlorine requires an electron to complete the octet. Therefore, all of these share the electrons and as a result, carbon forms 3 bonds with hydrogen and one with chlorine.

Q5)Draw the electron dot structures for

• (a)Ethanoic acid
• (b) H2S
• (c)Propanone
• (d)F2

##### F2
v

Q6)What is a homologous series? Explain with an example.

A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group. For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series.

The general formula of this series is CnH2n+2

• Methane - CH4
• Ethane - CH3CH3
• Propane - CH3CH2CH3
• Butabe - CH3CH2CH2CH3

It can be noticed that there is a difference of ?CH2 unit between each successive compound.

Q7)How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Difference between Ethanol and Ethanoic acid

1. Ethanol has the molecular formula C2H5OH, while ethanoic acid has the molecular formula C2H4O2.
2. Ethanol has an ethyl group while ethanoic acid has a methyl group.
3. Ethanoic acid is a carboxylic acid; this is not the case for ethanol.
4. Ethanol has a hydroxyl group while ethanoic acid has a carboxyl group.
5. Ethanol in a pure state is basic, while ethanoic acid is acidic.
6. Ethanoic acid has a boiling point of 118 to 119oC, while ethanol has a boiling point of 78.5
7. Ethanoic acid has a vinegar smell while ethanol has a perfume type of smell.
8. Ethanoic acid can be formed using Acetobacter bacteria during fermentation; this is not the case with ethanol.
9. Ethanol usually is formed using yeasts such as Saccharomyces cerevisiae or Schizosaccharomyces during fermentation; this is not the case with ethanoic acid.
10. Ethanol is used to make alcoholic beverages while ethanoic acid is used to make vinegar.
11. Ethanol is also referred to as ethyl alcohol while ethanoic acid is also referred to as acetic acid.
12. Ethanol does not react with metal carbonates while, ethanoic acid reacts with metal carbonates to form salt, water and carbon dioxide. For example, $$2CH_{3}COOH + Na_{2}CO_{3}$$ $$\downarrow$$ $$2CH_{3}COONa + CO_{2} + H_{2}O$$
13. Ethanol does not react with NaOH while ethanoic acid reacts with NaOH to form sodium ethanoate and water.
Ex :
Ethanol is oxidized to give ethanoic acid in presence of acidified KMnO4 while, no reaction takes place with ethanoic acid in presence of acidified KMnO4.

Q8)Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. When soap is dissolved in water and clothes are put in the soapy solution, soap molecules converge in a typical fashion to make a structure; called micelle. The hydrophobic ends of different molecules surround a particle of grease and make the micelle; which is a spherical structure. In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. This is why micelle formation takes place when soap is added to water. Since ethanol is not as polar as soap, so micelles will not be formed in other solvents such as ethanol.

Q9)Why are carbon and its compounds used as fuels for most applications?

Carbon and its compounds give large amount of heat on combustion due to high percentage of carbon and hydrogen. Carbon compounds used as fuel have optimum ignition temperature with high calorific values and are easy to handle. Their combustion can e controlled. Therefore, carbon and its compounds are used as fuels.

Q10)Explain the formation of scum when hard water is treated with soap.

Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitate. This precipitate begins floating as an off-white layer over water. This layer is called scum. Soaps lose their cleansing property in hard water because of formation of scum.

Q11)What change will you observe if you test soap with litmus paper (red and blue)?

Since soap is basic in nature, it will turn red litmus blue. However, the colour of blue litmus will remain blue.

Q12)What is hydrogenation? What is its industrial application?