Q  1. Name the functional group present in propanone, CH₃COCH₃.

Solution

Ketonic group is present in the propanone.
Q  2. (i) Why coal or charcoal burns with just a glow red and gives out heat without flame while LPG burns with flame?(ii) When we light a Bunsen burner it burns with blue flame, but sometimes we get yellow sooty flame. Why?

Solution

(i) A coal or charcoal burns with just a glow red and gives out heat without flame however LPG burns with flame, this is because a flame is produced only when gaseous substances burn. When wood or charcoal is ignited, the volatile substance present in it vapourizes and burns with a flame in the beginning. A luminous flame is seen when the atoms of the gaseous substance are heated and start to glow. (ii) When the air holes of Bunsen burner are open, sufficient amount of oxygen rich air is available and it burns with blue flame. Sometimes when these holes get blocked, due to the lack of oxygen rich air we get yellow sooty flame.
Q  3. Why are covalent compounds generally poor conductors of electricity?

Solution

Covalent compounds are generally poor conductors of electricity because they do not produce ions in solution or on melting.
Q  4. Give a chemical test to distinguish between saturated and unsaturated hydrocarbons.

Solution

On adding few drops of bromine water, if brown colour of bromine disappears quickly then the compound is an unsaturated hydrocarbon.
Q  5. How is scum formed?

Solution

When soap reacts with hard water, the minerals present in water react with soap and form a white curdy substance known as scum. It reduces the cleaning ability of soap.
Q  6. What are aromatic hydrocarbons?

Solution

Hydrocarbons which contain benzene and its derivative compounds are called aromatic hydrocarbons.
Q  7. Both carbon and silicon belong to group 14 of the periodic table. But the tendency to exhibit catenation in carbon is much more than in silicon. Explain.

Solution

The size of carbon atom is small as compared to that of silicon. Therefore, C-C bond is smaller and stronger than Si-Si bond. As a result, any number of carbon atoms can be linked to each other resulting in a large number of carbon compounds.
Q  8. Why is alcohol mixed with copper sulphate for industrial purposes?

Solution

Alcohol mixed with copper sulphate for industrial purposes to make it unfit for drinking purposes. 
Q  9. Give the names for the suffixes of the following functional groups: -COOH; -CHO; -OH; -CO-

Solution

The suffix names for the functional groups are:1. -COOH is -oic acid2. -CHO is -al3. -OH is -ol4. -CO- is -one
Q  10. How do cyclic hydrocarbons differ from aromatic hydrocarbons?

Solution

Aromatic hydrocarbons have the typical benzene ring or in other words alternate double bonds while in cyclic hydrocarbons the terminal carbon atoms bond with each other to form a closed cyclic structure.
Q  11. Why is ethanol used as an additive to petrol?

Solution

Alcohol (ethanol) is used as an additive in petrol since it is a cleaner fuel which gives rise to only carbon dioxide and water on burning in sufficient air (oxygen). C₂H₅OH  +  3O₂ →  2CO₂  +  3H₂O
Q  12. Differentiate between addition reaction and substitution reaction shown by hydrocarbons.

Solution

The reactions in which an unsaturated hydrocarbon combines with simple substances to form a single saturated product are addition reactions. Those reactions in which one or more hydrogen of a saturated hydrocarbon is replaced by an atom or a group of atoms are substitution reactions.
Q  13. How ethanoic acid got its name as glacial acetic acid?

Solution

The melting point of ethanoic acid is 290 K and hence it often freezes during winter and forms ice like flakes.
Q  14. (a) State the role of concentrated sulphuric acid in the esterification reaction. (b) Write one use of esters.

Solution

(a) Sulphuric acid being a strong dehydrating agent removes water from the reaction mixture of ethanoic acid and ethanol. As a result, the reaction proceeds only in the forward direction to form ester. (b) Esters are used in making artificial perfumes.
Q  15. Write the name and structure of an aldehyde with 5 carbon atoms.

Solution

Pentanal, CH₃CH₂CH₂CH₂CHO
Q  16. Define:(i) Addition reaction(ii) Substitution reaction(iii) Combustion reaction

Solution

(i) Addition reaction:- A reaction involving addition of atoms(s) or molecules to the double or the triple bond of an unsaturated compound to give a saturated product is known as addition reaction.(ii) Substitution reaction:- A reaction in which one atom of a molecule is replaced by another atom(or group of atoms) is called a substitution reaction.(iii) Combustion reaction:- Carbon in all its allotropic forms, burns in oxygen to give carbon dioxide and water along with the release of heat and light. This reaction is called combustion reaction.
Q  17. Why carbon forms strong bonds with other carbon atoms, hydrogen, oxygen, nitrogen or sulphur?

Solution

Due to small size and presence of four valence electrons, carbon forms strong bonds with other carbon atoms, hydrogen, oxygen, nitrogen or sulphur.
Q  18. Give reasons for the following: (a) Unsaturated hydrocarbons show addition reactions but saturated hydrocarbons do not. (b) Carbon only forms covalent compounds.

Solution

(a) Unsaturated hydrocarbon contains either double or triple bonds, which are reactive, so they break easily and convert into single covalent bonds hence they easily undergo addition reactions. While saturated hydrocarbons have only single bonds which are strong hence they do not show addition reactions. (b) Carbon cannot lose its 4 valence electrons as large amount of energy is required for that process. It cannot gain 4 electrons as 6 protons can’t hold 10 electrons therefore, it only shares electrons to form covalent compounds.
Q  19. What are alkanes? Name an alkane which has three carbon atoms.

Solution

Alkanes are saturated hydrocarbons with carbon atoms bonded to each other with single bonds. They have a general formula C_nH_2n+2. Propane is a hydrocarbon with 3 carbon atoms and has the formula C₃H₈.
Q  20. Name the property of carbon element responsible for a large number of compounds having carbon. Give an example of a compound illustrating this property.

Solution

Catenation is the property of carbon to combine with itself. Example: ethane.
Q  21. Name the functional group present in each of the following organic compounds: (i) CH₃COCH₃    (ii) C₂H₅COOH

Solution

(i) Ketone (ii) Carboxylic acid
Q  22. Write the molecular formula of cyclohexane and benzene. How are they different?

Solution

Molecular formula : i) Cyclohexane : C₆H₁₂ ii) Benzene : C₆H₆
Though both contain six carbon atoms but cyclohexane is a saturated hydrocarbon and benzene is an unsaturated hydrocarbon.       
Q  23. (a) What is the difference in the molecular formulae and masses of any two adjacent homologues? (b) Separate the given compounds of same homologous series. Name the series.  
      HCHO, CH₃OH, C₂H₅CHO, C₃H₇OH, C₂H₅OH, CH₃CHO

Solution

(a) Two adjacent homologues differ by a CH₂ group in their molecular formulae. The difference in the molecular masses of any two adjacent homologues is 14u.   (b)   Aldehyde homologous series – HCHO, CH₃CHO, C₂H₅CHO        Alcohol homologous series – CH₃OH, C₃H₇OH, C₂H₅OH
Q  24. (a) Soaps are not effective for washing woolen garments. Why? (b) Detergents are called “soap less” soaps. Why? (c) Why is common salt added in soap making process?

Solution

(a) Soaps being basic in nature reacts with the acidic dyes of woolen garments and hence are not effective for washing woolen garments. (b) Detergents are called “soap less” soaps because though they act like soaps  with cleansing properties, they do not contain  sodium stearate etc. (c) Common salt is added in soap making process to precipitate out all the soap from the aqueous solution.
Q  25. Why fuels such as coal and petroleum are major pollutants in air?

Solution

Fuels such as coal and petroleum have some amount of nitrogen and sulphur in them. Their combustion results in the formation of oxides of sulphur and nitrogen which are major pollutants in the environment.
Q  26. What are oxidizing agents?

Solution

An oxidizing agent is one which oxidizes other substances by providing oxygen or removing hydrogen.
Q  27. (a) Write two points of difference in the structures of diamond and graphite. (b) Explain why, graphite can be used as a lubricant but diamond cannot.

Solution

(a) Diamond Graphite (i) Each carbon atom is linked to four other carbon atoms. (ii) A diamond crystal has a tetrahedral arrangement of carbon atoms. (i) Each carbon atom is joined to only three other carbon atoms. (ii) A graphite crystal has flat hexagonal rings structure. (b) Due to its softness, powdered graphite can be used a lubricant whereas diamond being extremely hard cannot be used as a lubricant.
Q  28. Write the next higher homologue of the following: (i)C₃H₆ (ii)C₅H₈

Solution

(i) The next higher homologue of C₃H₆ is C₄H₈. (ii) The next higher homologue of C₅H₈ is C₆H₁₀.
Q  29. Discuss the drawback of using soaps over detergents for cleansing process.

Solution

Soaps form an insoluble substance called scum with hard water while detergent do not form any scum with hard water. Soap reacts with the calcium and magnesium salts which are responsible for the hardness of water to form scum. Thus, a larger amount of soap needs to be used.
Q  30. What is the reason for the non-biodegradable nature of detergents?

Solution

The reason is the presence of branching in the hydrocarbon chains that are attached to the sulphonic acid group or its sodium salt. These chains break with difficulty by the micro-organisms that are present in sewage discharge, septic tanks or other water bodies and make the detergents non-biodegradable.
Q  31. How is coal formed?

Solution

Coal is formed from biomass which has been subjected to various biological and geological processes.
Q  32. Give the IUPAC name of valeric acid.

Solution

Valeric acid is saturated five carbon carboxylic acid.CH₃CH₂CH₂CH₂COOH  pentanoic acid
Q  33. List two differences between saturated and unsaturated hydrocarbons.

Solution

Saturated hydrocarbons Unsaturated hydrocarbons (i) Hydrocarbons have single bonds between carbon atoms (i) Hydrocarbons have one or more multiple (double or triple) bonds between carbon atoms. (ii) Gives a clean flame on burning. (ii) Gives yellow flame with lots of black smoke on burning.
Q  34. How will you distinguish between sodium chloride and carbon tetrachloride?

Solution

Sodium chloride is an ionic compound; it is soluble in water and a good conductor of electricity. On the other hand, carbon tetrachloride is a covalent compound; it is insoluble in water and poor conductor of electricity.
Q  35. What type of intermolecular force helps water and ethanoic acid to mix?

Solution

Both in water and ethanoic acid, hydrogen bonds are present between their atoms. Hence, they can easily form hydrogen bonds with each other.
Q  36. Name the following compound according to IUPAC:CH₃CH(OH)CH₃

Solution

The IUPAC name of this compound is propan-2-ol or 2-propanol.
Q  37. Give the IUPAC name of the following compound. Give reasons to support your answer.CH₃CH₂CH₂C(=O)OH

Solution

This compound is butanoic acid. (i) This compound has functional group -COOH, which is a carboxylic acid, therefore suffix “-oic acid” will be used.(ii) The carbon chain is a hydrocarbon structure with all single bonds between carbon atoms therefore, an alkane and a suffix “-ane”.(iii) The longest continuous chain is C₄ therefore, root name will be “but-“.
Q  38. Classify following into alkanes, alkenes and alkynes: CH₄, C₂H₂, C₄H₆, C₂H₄, C₃H₆, C₂H₆, C₃H₈, C₃H₄ Give reasons.

Solution

(i) CH₄, C₂H₆, and C₃H₈ are alkanes as they have each carbon bonded to four other atoms through single covalent bonds and follow general formula C_nH_2n+2. (ii) C₂H₄, C₃H₆ are alkenes since they contain a single carbon-carbon double bond and follow general formula  C_nH_2n. (iii) C₃H₄, C₂H₂ and C₄H₆ are alkynes as they contain a single carbon-carbon triple bond and follow the general formula C_nH_2n-2.
Q  39. Why do covalent compounds have low boiling and melting point?

Solution

Covalent compounds are made up of electrically neutral molecules. So, the force of attraction between the molecules of a covalent compound is very weak. Only a small amount of heat energy is required to break these weak molecular forces, due to which covalent compounds have low melting and boiling points.

Q  40. Identify the functional group in the following compounds: (i) CH₃CH₂COCH₃   (ii) CH₃CHO

Solution

(i) Ketone group (or Keto group) (ii) Aldehyde group