10th science activities

Brief procedure:

Activity 4.1 asks us to list the materials we use in daily life and classify them by their source.

 Answer:

In daily life, we see and utilise many materials. We can classify them in many ways like shape and size, composition, colour etc. Based on the composition of the material, we can classify materials like metals, plant products, soil and clay products and so on. Below is the classification of material as metals, clay products and others.

Things made of metal: glass, plate, compass box, pen, bottle, mobile phone, watch, key-ring, fridge, cooler

Items made of glass/clay: Glass, bowl, pitcher, window, glass door.

Example of others: Book, pen, bottle, glass, tiffin box, cooler, washing machine, bag, cloth, wood door, polythene bag etc.

Explanation: 

We use a variety of materials in our daily life. A significant number of objects consist of organic compounds. For example, all plant products like fruits, seeds, paper; all soil products like clay pot; all polythene products like plastic, rubber etc. are organic compounds. This vast presence of organic compound signifies its importance in our life.

Discussion: A large number of things and various food items are made up of only compounds of carbon.

Conclusion: Most of the utilities which we use in our daily life are made up of compounds of carbon. These carbon compounds are called Organic compounds.

Questions based on activity 4.1 Class 10 Science

     1.   Why does carbon form numerous compounds?

Ans. – Carbon forms numerous compounds because of its two main properties – Catenation and Tetravalency.

     2.   Are petroleum and fossil fuels carbon compounds?

Ans. – Yes, petroleum and other fossil fuels are carbon compounds.

Brief procedure:

Activity 4.2 asks us to observe the difference in formulae and molecular masses of various alcohol.

Observation:

Name: Chemical formula: Difference; Molecular weight: Difference

Methanol: CH₃OH       —-        32      —–

Ethanol: C₂H₅OH       -CH₂       46       14

Propanol: C₃H₇OH     -CH₂        60       14

Butanol: C₄H₉OH      -CH₂        74      14

Explanation: 

Carbon contains four electrons in its valance shell. It needs 4 extra valence electrons to complete the octet. It combines with various other molecules like oxygen, nitrogen, hydrogen but also reacts with other carbon atoms as well. We call such property as polymerisation tendency. Here, a carbon atom attaches to another carbon atom and elongates the chain. The various compounds formed show similar property and gradual change (increase or decrease) in the property, e.g. Boling point, melting point, solubility, polarity. We call such groups as homologous series.

Methanol, ethanol, propanol, butanol etc. are similar in structure and molecular weight increases by 14amu (Atomic Mass Unit). Here Melting point and boiling point also increase with the number of carbon atoms. They all show the polar property due to the presence of polar -OH(hydroxy group). With an increase in the bulkiness of carbon atom, higher alcohols are less polar.

We use such a tendency to predict the behaviour of the molecule.

Similarly, the property of other functional groups like Amide (CONH₂), Carboxylic acid (COOH), Primary, secondary, and tertiary Amines (NH) etc. also depend on the number of carbon atoms.

Inference/conclusion: molecules of a homologous series show similar physical and chemical property.

Activity 4.2 Page No. 67

• Question 1. Calculate the difference in the formulae and molecular masses for:
  
  1. CH₃OH and C₂H₅OH
  2. C₂ H₅ OH and C₃ H₇OH
  3. C₃ H₇OH and C₄ H₉OH
• Answer:

  	Molecular formula	Molecular mass	Difference of molecular mass	Difference in molecular formula
  (a)	CH3OH and C2H5OH	32 amu and 46 amu	14U	CH2
  (b)	C2H5OH and C3H7OH	46 amu and 60 amu	14U	CH2
  (c)	C3H7OH and C4H7OH	60 amu and 74 amu	14U	CH2

• Question 2. Is there any similarity in these three?
• Anser:All these three have alcoholic (-OH) function group.
• Question 3. Arrange these alcohols in the order of increasing carbon atoms to get a family. Can we call this family a homologous series?
• Answer: CH₃OH, C₂H₅OH, C₃H₇OH, C₄H₉OH.
  Yes, It is a homologous series of alkane alcohols as each successive member of the series differs by - CH₂ unit from proceeding member
• Generate the homologous series for compounds containing up to
  four carbons for the other functional groups given in Table 4.3.
  

  Hetero atom	Functional group	Formula of functional group
  CL/Br	Halo - (Chloro/Bromo)	- Cl, - Br (substitutes for hydrogen atom)
  Oxygen	Alcohol Aldehyde Ketone Carboxylic acid	-OH H / - C \\ O - C - || O O || - C - OH

• Answer:
Chloro (-CI) --> CH₃CI, C₂H₅CI,C₃H₇CI,C₄H₉CI. Aldehydes --> CH₃CHO,C₂H₅CHO,C₃H₇CHO,C₄H₉CHO. Ketone -->CH₂CO,C₂H₄CO,C₃H₆CO,C₄H₈CO. Carboxylic acids--> CH₂COOH, C₂H₄COOH, C₃H₆COOH, C₄H₉COOH. 

(i) Homologus series having Choloro (-Cl) functional group: CH₃Cl, C₂H₅Cl, C₃H₇Cl, C₄H₉Cl. 

(ii) Homologus series having Aldehydes functional group: CH₃CHO, C₂H₅CHO, C₃H₇CHO, C₄H₉CHO.

(iii)Homologus series having Ketone functional group: CH₂CO, C₂H₄CO, C₃H₆CO, C₄H₈CO. 

(iv) Homologus series having Carboxylic acids functional group:CH₂COOH, C₂H₄COOH, C₃H₆COOH, C₄H₉COOH

Conclusion -  Now from the above discussion, it is clear that the common difference in the molecular formula is -CH₂  and molecular mass is 14u. 

Question-based on activity 4.2 Class 10 Science

1. What is homologous series?

Ans.- A series or group of organic compounds having similar structural formulae, same functional group, and same chemical properties is called a homologous series.

2. What is the importance of a homologous series?

Ans.- (i) It helps in a systematic study of organic compounds.

(ii) We can predict the properties of all the members of a homologous series when we identify the properties of any member.