10th Science Guide Unit 11 CARBON AND ITS COMPOUNDS

10th Standard Science Chemistry Lesson 11 CARBON AND ITS COMPOUNDS Book Back Answers | Samacheer Kalvi Guide

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10th Science Guide Unit 11 CARBON AND ITS COMPOUNDS

I. Choose the best answer

1. The molecular formula of an open chain organic compound is C3H6. The class of the compound is

__________.

1. alkane
2. alkene
3. alkyne
4. alcohol

Ans ; alkene

2. The IUPAC name of an organic compound is 3-Methyl butan-1-ol. What type compound it is?

1. Aldehyde
2. Carboxylic acid
3. Ketone
4. Alcohol

Ans ; Alcohol

3. The secondary suffix used in IUPAC nomenclature of an aldehyde is __________.

1. ol
2. oic acid
3. al
4. one

Ans ; – al

4. Which of the following pairs can be the successive members of a homologous series?

1. C₃H₈ and C₄H₁₀
2. C₂H₂ and C₂H₄
3. CH₄ and C₃H₆
4. C₂H₅OH and C4H8OH

Ans ; C3H8 and C₄H₁₀

 

5. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O is a __________.

1. Reduction of ethanol
2. Combustion of ethanol
3. Oxidation of ethanoic acid
4. Oxidation of ethanal

Ans ; Combustion of ethanol

6. Rectified spirit is an aqueous solution which contains about __________ of ethanol.

95. 5%
96. 5%
97. 5%
98. 5%

Ans ; 95.5%

7. Which of the following are used as anaesthetics?

1. Carboxylic acids
2. Ethers
3. Esters
4. Aldehydes

Ans ; Ethers

8. TFM in soaps represents ___________ content in soap.

1. mineral
2. vitamin
3. fatty acid
4. carbohydrate

Ans ; fatty acid

9. Which of the following statements is wrong about detergents?

1. It is a sodium salt of long chain fatty acids
2. It is sodium salts of sulphonic acids
3. The ionic part in a detergent is –SO₃–Na+
4. It is effective even in hard water.

Ans ; It is a sodium salt of long chain fatty acids

II. Fill in the blanks

1. An atom or a group of atoms which is responsible for chemical characteristics of an organic compound is called __________. Ans ; Functional group
2. The general molecular formula of alkynes is __________. Ans ; CnH_2n-2
3. In IUPAC name, the carbon skeleton of a compound is represented by __________ (root word / prefix /suffix). Ans ; root word
4. (Saturated / Unsaturated) __________ compounds decolourize bromine water. Ans ; unsaturated
5. Dehydration of ethanol by conc. Sulphuric acid forms __________ (ethene/ ethane). Ans ; ethene
6. 100 % pure ethanol is called __________. Ans ; absolute alcohol
7. Ethanoic acid turns __________ litmus to __________. Ans ; blue, red
8. The alkaline hydrolysis of fatty acids is termed as __________. Ans ; Saponification
9. Biodegradable detergents are made of __________ (branched / straight) chain hydrocarbons.

Ans ; straight

III. Match the following

Functional group –OH     (a) Benzene

Heterocyclic                      (b) Potassium stearate

Unsaturated                      (c) Alcohol

Soap                                    (d) Furan

Carbocyclic                        (e) Ethene

Ans ; 1 – c, 2 – d, 3- e, 4 – b, 5 – a

IV. Answer the following questions using the data given below:

1. A and R are correct, R explains the A.
2. A is correct, R is wrong.

• A is wrong, R is correct.

1. A and R are correct, R doesn’t explains A.
2. 1. Assertion: Detergents are more effective cleansing agents than soaps in hard water.

Reason: Calcium and magnesium salts of detergents are water soluble.

Ans : (i) A and R are correct, R explain the A

2. Assertion: Alkanes are saturated hydrocarbons.

Reason: Hydrocarbons consist of covalent bonds.

Ans : (iv) A and R are correct, R doesn’t explains A

10th Science Guide Unit 11 CARBON AND ITS COMPOUNDS

V. Short answer questions

1. Name the simplest ketone and give its structural formula.

Acetone.

Structure :

CH3 – C – CH3

||

O

2. Classify the following compounds based on the pattern of carbon chain and give their structural formula:

3. i) Propane = CH₃ – CH₂ – CH₃.

Structural formula

A cyclic compound

6. ii) Benzene = C₆ H₆.

Structural formula

Aromatic compound

iii) Cyclobutane = C₄ H₈.

Structural formula :

Alicyclic compound

1. iv) Furan = C₄ H₄ O.

Structural formula

Hetrocyclic compound

3. How is ethanoic acid prepared from ethanol? Give the chemical equation.

Ethanoic acid is prepared in large scale, by the oxidation of ethanol in the presence of alkaline potassium permanganate or acidified potassium dichromate.

CH3CH3OH Ethanol

KMnO4/OH– → 2(O)

CH4COOH + H2O Ethanoic Acid

4. How do detergents cause water pollution? Suggest remedial measures to prevent this pollution?

Detergents also add another problem for aquatic life by lowering the surface tension of the water. Phosphates in detergents can lead to fresh water algal blooms that releases toxins and deplete oxygen in waterways. When the algae decompose, they use up the oxygen available for aquatic life.

Remedial Measures :

• Immediate reduction and evetual eradication of phosphates in detergents.
• Awareness among consumers to select washing products with the least amount of polluting ingredients.
• Prompt promulgation of regulations requiring appropriate labelling of detergent packages listing of the ingredients and information about use of detergents in soft and hard water

5. Differentiate soaps and detergents.

Soap	Detergents
1. It is a Sodium salt of long chain fatty acids.	It is sodium salts of sulphonic acids
2. The ionic part of a soap is –COO–Na+	The ionic part in a detergent –SO3 –Na+
3. It is prepared from animal fats (or) vegetable oils.	It is prepared from hydrocarbons obtained from crude oil.
4. It forms a scum in hard water.	Does not form a scum in hard water.
5. It has poor foaming capacity	It has rich foaming capacity.
6. Soaps are biodegradable.	Most of the detergents are non–biodegradable.

VI. Long answer questions

1. What is called homologous series? Give any three of its characteristics?

Homologous series : is a group or a class of organic compounds having same general formula and similar chemical properties in which the successive members differ by a – CH2 group.

Characteristics of Homologous series :

• Each member of the series differs from the preceding or succeeding member by one methylene group (–CH2) and hence by a molecular mass of 14 amu.
• All members of a homologous series contain the same elements and functional group.
• They are represented by a general molecular formula. e.g. Alkanes, CnH2n+2.
• The members in each homologous series show a regular gradation in their physical properties with respect to their increase in molecular mass.
• Chemical properties of the members of a homologous series are similar.
• All the members can be prepared by a common method.

2. Arrive at, systematically, the IUPAC name of the compound: CH₃-CH₂–CH₂–OH.

Step 1 :

The parent chain consists of 3 carbon atoms. The root word is ‘prop’.

Step 2 :

There are single bonds between the carbon atoms of the chain. So the primary suffix is ‘ane’.

Step 3 :

Since the compound contains –OH group, it is an alcohol. The carbon chain is numbered from the end which is closest to –OH group (Rule 3), C₃H₃ – C₂H₂ – C1H₂ – OH.

Step 4 :

The locant number of –OH group is 1 and thus the secondary suffix is 1–ol. The name of the compound is prop+ane + (1–01) = propan–1–ol.

NOTE :

Terminal ‘e’ of ‘ane’ is removed as per Rule 5.

3. How is ethanol manufactured from sugarcane?

Ethanol is manufactured in industries by the fermentation of molasses, which is a by product obtained during the manufacture of sugar from sugarcane. Molasses is a dark coloured synopy liquid left after the crystallisation of sugar from the concentrated sugarcane juice. Molasses contain about 30% of sucrose, which cannot be separated by crystallisation. It is converted into ethanol by the following steps.

1. i) Dilution of Molasses :

Molasses is first diluted with water to bring down the concentration of sugar to about 8 to 10 percent.

1. ii) Addition of Nitrogen source :

Molasses usually contains enough nitrogenous matter to act as food for yeast during the fermentation process. If the nitrogen content of the molasses is poor, it may be fortified by the addition of ammonium sulphate or ammonium phosphate.

iii) Addition of Yeast :

The solution obtained in step (ii) is collected in large ‘fermentation tanks’ and yeast is added to it. The mixture is kept at about 303K for a few days. During this period, the enzymes invertase and zymase present in yeast, bring about the conversion of sucrose into ethanol.

C12H22O11 + H2O Sugar	invertase →	C6H12O6  +  C6H12O6 glucose      fructose
C6H12O6 glucose or fuctose	zymase →	2C2H5OH + 2 CO2 ethanol

The fermented liquid is technically called wash.

1. iv) Distillation of ‘Wash’ :

The fermented liquid (i.e. wash), containing 15 to 18 percent alcohol, is now subjected to fractional distillation. The main fraction drawn is an aqueous solution of ethanol which contains 95.5% of ethanol and 4.5% of water. This is called rectified spirit. This mixture is then refluxed over quicklime for about 5 to 6 hours and then allowed to stand for 12 hours. On distillation of this mixture, pure alcohol (100%) is obtained. This is called absolute alcohol.

4. Give the balanced chemical equation of the following reactions:

1. i) Neutralization of NaOH with ethanoic acid.

Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.

CH₃ COO H + Na OH → CH₃ COONa + H₂O

1. ii) Evolution of carbon dioxide by the action of ethanoic acid with NaHCO₃

Ethanoic acid reacts with sodium bicarbonate to give salt, water and carbon dioxide gas.

 

CH₃ COO H + Na H CO₃ → CH₃ COONa + CO₂ ↑ + H₂O

iii) Oxidation of ethanol by acidified potassium dichromate.

Ethanol is oxidised to ethanoic acid with alkaline KMnO4 or acidified K2Cr2O7.

C2H5OH Ethyl alcohol

K5Cr5O5 / H+ → 2(O)

CH3 COOH + H2O Acetic acid

1. iv) Combustion of ethanol.

Ethanol is highly inflammable liquid. It burns with oxygen to form carbon dioxide and water.

C2H5OH + 3O2 Ethanol

→

2CO3 + 3H2O Carbon dioxide

5. Explain the mechanism of cleansing action of soap.

A Soap molecule contains two chemically distinct parts that interact differently with water. It has one polar end, which is a short head with a carboxylate group (–COONa) and one non–polar end having the long tail made of the hydrocarbon chain.

The polar end is hydrophilic (water loving) in nature and this end is attracted towards water. The non- polar end is hydrophobic (water hating) in nature and it is attracted towards water. Thus, the hydrophobic part of the group molecule traps the dirt and the hydrophilic part makes the entire molecule soluble in water.

When a soap (or) detergent is dissolved in water, the molecules join together as clusters called micelles. Their long hydrocarbon chains attach themselves to the oil and dirt. The dirt is thus surrounded by the non – polar end of the soap molecules as shown below. The changed carboxylate end of the soap molecules makes the micelles soluble in water. Thus. the dirt is washed away with the soap.

VII. HOT question

1. The molecular formula of an alcohol is C4H10O. The locant number of its –OH group is 2.

1. i) Draw its structural formula.

1        2       3         4

CH3 – CH – CH2 – CH3

|

OH

1. ii) Give its IUPAC name.

2 – butanol.

iii) Is it saturated or unsaturated?

Saturated (C – C single bond).

2. An organic compound ‘A’ is widely used as a preservative and has the molecular formula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound ‘B’.

1. i) Identify the compound ‘A’.

Ethanoic acid.

1. ii) Write the chemical equation for its reaction with ethanol to form compound ‘B’.

Ethyl Ethanoate.

iii) Name the process.

Esterification.

CH2CH2OH + CH3 COOH Ethanol

H+ → Acetic acid

CH3 CH2 COOH3 + H2O Ethyl ethanoate