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Question-1

What would be the electron dot structure of carbon dioxide which has the formula CO2?

Solution:

 

Question-2

What would be the electron dot structure of a molecule of sulphur, which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)

Solution:


Question-3

How many structural isomers can you draw for pentane?

Solution:
We can draw 3 structural isomers for pentane.

Question-4

What are the two properties of carbon that lead to the huge number of carbon compounds we see around us?

Solution:
Due to its large valency, carbon atoms can form covalent bonds with a number of carbon atoms as well as with a large number of other atoms such as hydrogen, oxygen, nitrogen, sulphur, chlorine and many more atoms. This leads to the formation of a large number of organic compounds.

Question-5

What will be the formula and electron dot structure of Cyclopentane?

Solution:
Formula of Cyclopentane
C5H10

Dot structure

Question-6

Draw the structures for the following compounds.

i. Ethanoic acid
ii. Bromopentane
iii. Butanone
iv. Hexanal

Solution:

i. Ethanoic acid -
 

ii. Bromopentane -


iii. Butanone -



iv. Hexanal -

 

Question-7

How would you name the following compounds?

i. 
ii. 

 
iii.

 


Solution:
i. Ethyl bromide

ii. Formaldehyde

iii. Hexyne

Question-8

Why is the conversion of ethanol to Ethanoic acid an oxidation reaction?

Solution:
The conversion of ethanol into ethanoic acid is called an oxidation reaction because oxygen is added to it during this conversion.

 

Question-9

A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Solution:
When a mixture of oxygen and ethyne is burnt, it burns completely producing a blue flame. This blue flame is extremely hot which produced a very high temperature which is used for welding metals. But the mixture of ethyne and air is not used for welding purposes because burning of ethyne in air produces a sooty flame, which is not enough to melt metals for welding.

Question-10

What are oxidizing agents?

Solution:
Oxidizing agents are the substances that gain electrons in an redox reaction and whose oxidation number is reduced.

Question-11

Explain the nature of the covalent bond using the bond formation of CH3Cl.

Solution:
CH3Cl(methyl chloride) is made up of one carbon atom, three hydrogen atoms and one chlorine atom. Carbon atom has 4 valence electrons, each hydrogen atom has one valence electron, and a chlorine atom has 7 valence electrons. Carbon atom shares its four valence electrons with three hydrogen atoms and 1 chlorine atom to form methyl chloride as follows:

 

From the above reaction, in the dot structure of methyl chloride (CH3Cl) there are four pairs of shared electrons between carbon and other atoms. Each pair of shared electrons constitutes one single covalent bond. So, methyl chloride has four single covalent bonds.


Question-12

Draw the electron dot structures for-

i. Ethanoic acid
ii. H2S
iii. Propanone
iv. F2

 

 

Solution:
i. Ethanoic acid

ii. H2S

iii. Propanone  

 

iv. F2

Question-13

What is a homologous series? Explain with an example.

Solution:
Homologous series is a series of compounds with a similar general formula, possessing similar chemical properties due to the presence of the same functional group, and shows a gradation in physical properties as a result of increase in molecular size and mass. For example, methane has a lower boiling point than ethane since it has more intermolecular forces with neighbouring molecules. This is because of the increase in the number of atoms making up the molecule.

Question-14

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

Solution:
(i) Ethanol has a pleasant smell whereas ethanoic acid has the smell of vinegar.

(ii) Ethanol has a burning taste whereas ethanoic acid has a sour taste.

(iii) Ethanol has no action on litmus paper whereas ethanoic acid turns blue litmus paper red.

(iv) Ethanol has no reaction with sodium hydrogencarbonate but Ethanoic acid gives brisk effervescence with sodium hydrogencarbonate.


Question-15

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

Solution:
Micelle formation takes place when soap is added to water. This is because when soap is added to water in which dirty clothes are soaked, the two parts of the soap molecule dissolves in two different mediums. The organic tail dissolves in the dirt, grime or grease and the ionic head dissolves in water. When the clothes are rinsed or agitated, the dirt gets pulled out of the clothes in the water by the soap molecule. In this way the soap does its cleaning work on dirty and grimy clothes or hands.

 

The soap molecules actually form a closed structure because of mutual repulsion of the positively charged heads. This structure is called a micelle.


Question-16

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

Solution:
Carbon and its compounds are used as fuels for most of the applications because they burn in air releasing a lot of heat energy.

Question-17

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

Solution:
The precipitate form of scum is formed when soap is used for washing clothes. With hard water, a large amount of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate. The precipitate form formed by the action of hard water on soap, sticks to the clothes being washed and interferes with the cleaning ability of the additional soap. This makes the cleaning of clothes difficult.

Question-18

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

Solution:
Soap is the salt of a strong base (NaOH) and a weak acid (carboxylic acid), so a solution of soap in water is basic in nature. Being basic, a soap solution turns red litmus paper blue.

Question-19

What is hydrogenation? What is its industrial application?

Solution:
It is a class of chemical reactions in which the net result is addition of hydrogen (H2) to unsaturated organic compounds such as alkenes, alkynes, etc. Hydrogenation is widely applied to the processing of vegetable oils and fats. Complete hydrogenation converts unsaturated fatty acids to saturated ones.

Question-20

C2H5, C3H8, C3H6, C2H2 and CH4

 

Solution:
Alkenes and alkynes (unsaturated hydrocarbons) undergo addition reactions. From the above hydrocarbons C2H2 is an alkyne, whereas C3H6 is an alkene. So, C3H6 and C2H2 will undergo addition reactions.

Question-21

Give a test that can be used to differentiate chemically between butter and cooking oil.

Solution:
Bromine water test can be used to differentiate chemically between butter and cooking oil. Add bromine water to a little of cooking oil and butter taken in separate test tubes.

a. Decolourising of bromine water by cooking oil (unsaturated compound)
b. Butter (saturated compound) does not decolourise bromine water


Question-22

Explain the mechanism of the cleaning action of soaps.

Solution:
We all know that soap is used to remove dirt and and grime from substances. Generally dirt and grime get stuck because they have an oily component, which is difficult to remove, by plain brushing or washing by water. A soap molecule has two parts, a head and a tail i.e. the long chain organic part and the functional group –COO- Na+.

A soap molecule has a tadpole like structure shown below.

 

The organic part is water insoluble but is soluble in organic solvents or in oil or grease. The ionic part is soluble in water, as water is a polar solvent. When soap is added to water in which dirty clothes are soaked, the two parts of the soap molecule dissolve in two different mediums. The organic tail dissolves in the dirt, grime or grease and the ionic head dissolves in water. When the clothes are rinsed or agitated, the dirt gets pulled out of the clothes, by the soap molecule. In this way soap does its cleaning work on dirty and grimy clothes or hands.

 

The soap molecules actually form a closed structure because of mutual repulsion of the positively charged heads. This structure is called a micelle. The micelle pulls out the dirt and grime more efficiently.

 


Question-23

Would you be able to check if water is hard by using a detergent?

Solution:
We would not be able to check whether a sample of water is hard by using a detergent, this is because a detergent forms lather easily even with hard water.

Question-24

People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat ii with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?

Solution:
It is necessary to shake to get clean clothes because the soap micelles, which entrap oily or greasy particles on the surface of dirty clothes, have to be removed from their surface. When the clothes which are wet by soap solution are beaten, the micelles containing oil or greasy dirt particles get removed from the surface of dirty clothes and go into water and the dirty cloth gets cleaned.




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