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ScienceClass 10CBSE

1. In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level? Grass → Grasshopper → Frog → Snake → Hawk (a) 5 k J (b) 50 k J (c) 500 k J (d) 5000 k J

Soln: Answer is (d) 5000 k J Explanation: Available energy level at a particular trophic level is 10 times the energy level at next tropic level. Hence, energy at third level trophic level is 50kj. Second level trophic has 500 KJ energy and 1st level trophic level (Producer) has energy of 5000 KJ.

ScienceClass 10CBSE

1. An ecosystem includes (a) all living organisms (b) non-living objects (c) both living organisms and non-living objects sometimes living organisms and sometimes non-living objects

Soln: Answer is (c) both living organisms and non-living objects Explanation: An ecosystem is a complex of living and nonliving organisms and their interactions.

ScienceClass 10CBSE

1. In a food chain, the third trophic level is always occupied by (a) carnivores (b) herbivores (c) decomposers producers

Soln: Answer is (a) carnivores Explanation: First trophic level are producers, second tropic level are herbivores, third trophic level is occupied by carnivores.

ScienceClass 10CBSE

1. Which one of the following is an artificial ecosystem? (a) Pond (b) Crop field (c) Lake (d) Forest

Soln: Answer is (b) Crop field Explanation: Crop field is a man made ecosystem.

ScienceClass 10CBSE

1. An organic compound A on heating with concentrated H2 SO4 forms a compound B which on addition of one mole of hydrogen in presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of CO2 and 3 moles of H2O. Identify the compounds A, B and C and write the chemical equations of the reactions involved.

Soln: Compound A is Ethanol Compound A = CH3CH2OH CH3CH2OH conc. H2SO4 CH2-CH2+ H2O Compound B is Ethane Compound B = CH2= CH2 CH2=CH2 Ni C2H6 Compound C = CH3 — CH3 2C2H6+7O2 4CO2 +6H2O

ScienceClass 10CBSE

1. Explain the given reactions with the examples (a) Hydrogenation reaction (b) Oxidation reaction (c) Substitution reaction (d) Saponification reaction (e) Combustion reaction

Addition of Hydrogen to unsaturated Hydrocarbons to convert into saturated Hydrocarbons is called as Hydrogenation. This process is used in the conversion of unsaturated vegetable oil into saturated fats. R2C+CR+H2 Ni R2C-CR2 H H When oxygen is added to alcohol to form carboxylic acid the process is known as Ex: CH3CH2CH2OH Alk KMnO4/ acidified K2Cr2O7 CH3CH2COOH Saturated hydrocarbons are fairly But in the presence of sunlight chlorine substitutes Hydrogen one by one. Ex: CH4+Cl2 CH3Cl+HCl( In presence of sunlight) When Ester is treated with alkali, the reaction gives ethanol and Sodium This reaction is called saponification. Ex: CH3COOC2H5+NaOH CH3COONa+C2H5OH Combustion is the burning of a substance in presence of Ex: CH4+O2 CO2+H2O+ heat and Light

ScienceClass 10CBSE

1. How would you bring about the following conversions? Name the process and write the reaction involved. (a) ethanol to ethene. b) propanol to propanoic acid. Write the reactions.

Soln: Ethene is formed when ethanol is heated at 443 K with excess of concentrated sulphuric CH3CH2OH Con H2SO4 CH2=CH+H2O Propanol is treated with alkaline Potassium permanganate or acidified Potassium-di-chromate to obtain propanoic acid. CH3CH2CH2OH Alk KMnO4/ acidified K2Cr2O7 CH3CH2COOH

ScienceClass 10CBSE

1. A compound C (molecular formula, C2H4O2 ) reacts with Na - metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in presence of an acid forms a sweet smelling compound S (molecular formula, C3H6O2 ). On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved.

Compound C is Ethanoic acid[Acetic acid] It reacts with sodium metal to form a compound called R . R is Sodium Ethanoate. 2CH3COOH +2 Na 2CH3COONa+H2 conc, H2SO4 CH3COOH +C2H5OH CH3COOC2H5 + H20 so compound S is Ester or Ethyl ethanoate and compound A is Ethanol 3)CH3COOC2H5+NaoH CH3COONa + C2H5OH. so compound R is again Sodium Ethanoate. So compound C is Ethanoic acid A is Ethanol S is EsterR is sodium Ethanoate.

ScienceClass 10CBSE

1. a) What are hydrocarbons? Give examples. (b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each. (c) What is a functional group? Give examples of four different functional groups. Soln:

(Compounds of Carbon and hydrogen are called as Ex: Ethane, Methane All the bond in saturated Hydrocarbons are single bonds whereas bonds in the unsaturated Hydrocarbons are either double or triple bonds. Saturated Hydrocarbon Ex: Ethane, Methane Unsaturated Hydrocarbons-Ethyne, Ethene Functional groups are set of atoms joined in a specific manner which are responsible for characteristic chemical property of the compound.Ex: CHO-Aldehyde, OH-Hydroxyl , COOH- Carboxylic acid.

ScienceClass 10CBSE

1. Match the reactions given in Column (A) with the names given in column (B). Column A Column B (a) CH3OH + CH3COOH CH3COOCH3 + H2O (i) Addition reaction (b) CH2 = CH2 + H2 CH3 — CH3 (ii) Substitution reaction (c) CH4 + Cl2 Sunlight CH3Cl + HCl (iii) Neutralisation reaction (d) CH3COOH+NaOH CH3COONa+H2O (iv) Esterification reaction

Soln: Column A Column B (a) CH3OH + CH3COOH CH3COOCH3 + H2O (iv) Esterification reaction (b) CH2 = CH2 + H2 CH3 — CH3 (i) Addition reaction (c) CH4 + Cl2 Sunlight CH3Cl + HCl (ii) Substitution reaction (d) CH3COOH+NaOH CH3COONa+H2O (iii) Neutralisation reaction

ScienceClass 10CBSE

Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.

Soln: Saturated Hydrocarbons burns with clean flame and produce no soot where as non-saturated Hydrocarbons burns with yellow flame and produces lot of soot. Ethane is saturated hydrocarbon and it burns with clean flame with no soot. Ethene is unsaturated hence it burns with yellow flame producing lot of soot.

ScienceClass 10CBSE

1. Carbon, Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with (a) chlorine (Group 17 of Periodic Table) oxgygen (Group 16 of Periodic Table)

Sulphuric acid acts as a catalyst and a dehydrating agent in the formation of ethene. Soln: CCl4- Carbon Tetra chloride Carbon-di-oxide- CO2

ScienceClass 10CBSE

A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

When ethanol reacts with sodium it gives Sodium ethoxide with the liberation of Hydrogen gas. 2CH₃- CH₂-OH +2Na——>2 CH₃- CH₂- ONa + H₂

ScienceClass 10CBSE

.      Intake of small quantity of methanol can be lethal. Comment.

Methanol gets converted to Methanal and liver and kills all the cells. Methanol also affect the optic nerves and causes blindness. Hence intake of small quantity of methanol can be lethal.

ScienceClass 10CBSE

How is ethene prepared from ethanol? Give the reaction involved in it.

Ethanol is heated at 443k along with excess Sulphuric acid to obtain Ethene. CH3-CH2OH------- >CH2=CH2 +H2O (ethanol) (H2SO4) (ethene)

ScienceClass 10CBSE

Name the functional groups present in the following compounds (a) CH3COCH2 CH2 CH2 CH3 (b) CH3CH2CH2COOH (c) CH3CH2 CH2 CH2 CHO (d) CH3CH2OH

Soln: Ketone Carboxylic acid Aldehyde Alcohol

ScienceClass 10CBSE

Why detergents are better cleansing agents than soaps? Explain.

Soln: Detergents are better than soaps because detergents are ammonium or sulphonate salts of long chain carboxylic acids. Charged ends of theses will not for precipitate with calcium and magnesium present in hard water. On the other hand soaps will form precipitate with calcium and magnesium ions present in the hard water.

ScienceClass 10CBSE

1. The first member of alkyne homologous series is (a) ethyne (b) ethene (c) propyne methane

Soln: Answer is (a) ethyne

ScienceClass 10CBSE

1. Which of the following represents saponification reaction? (a) CH3COONa + NaOH CH4 + Na2CO3 (b) CH3COOH + C2H5OH CH3 COOC2H5 +H2O (c) 2CH3COOH + 2Na → 2CH3 COONa + H2 (d) CH3COOC2H5 + NaOH → CH3 COONa + C2 H5OH

Soln: Answer is (d) CH3COOC2H5 + NaOH → CH3 COONa + C2 H5OH Explanation: Saponification is a reaction in which ethanol and sodium ethanoate are produced upon treatment of ester with an alkali.

ScienceClass 10CBSE

1. The heteroatoms present in CH3 — CH2 — O — CH2— CH2 Cl are (i) oxygen (ii) carbon (iii) hydrogen (iv) chlorine a) (i) and (ii) (b) (ii) and (iii) (c) (iii) and (iv) (i) and (iv)

Soln: Answer is (d) (i) and (iv) Explanation: Oxygen and chlorine are not among essential components of Hydrocarbon hence they are heteroatoms.

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