The heat liberated when 1.89 g of benzoic acid is burnt in a bomb

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 Multiple Choice QuestionsMultiple Choice Questions

271.

Arrange the following in the decreasing order of their melting points:
I. Heptane      II. Octane
III. Nonane     IV. Decane

  • IV > II > III > I

  • IV > III > I > II

  • I > II > IV > III

  • II > III > I > IV


272.

The most reactive hydrocarbon is :

  • methane

  • ethane

  • ethylene

  • acetylene


273.

Which of the following is not a cumulated diene?

  • Hexa - 2 , 3 - diene

  • Penta - 1 , 3 - diene

  • Hexa - 1 , 2 - diene

  • Penta - 2 , 3 - diene


274.

What is the product P ?

  • Both (a) and (b)


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275.

In the eclipsed conformation of ethane, the dihedral angle between the hydrogen atoms of adjacent methyl groups is :

  • 60°

  • 120°

  • 180°


276.

The major product of the addition of water molecule to propyne in the presence of mercuric sulphate and dilute sulphuric acid is :

  • ethanal

  • 2-propanol

  • propane

  • propanone


277.

Which of the following statements is not an essential feature of an optically active molecule ?

  • It will rotate the plane of polarised light

  • It will have a non-superimposable mirror image

  • It will have no element of symmetry

  • It will have an asymmetric carbon atom


278.

The reagent which could distinguish between 1-hexyne and 1-hexene is :

  • Ag(NH3)2+

  • KMnO4

  • Br2 in CCl4

  • H2SO4


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279.

Choose the correct reagent required to carry out the transformation :

  • Zn + conc. HCl

  • conc. H2SO4

  • Li then H2O

  • H2/Pt


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280.

The heat liberated when 1.89 g of benzoic acid is burnt in a bomb calorimeter at 25°C and it increases the temperature of 18.94 kg of water by 0.632°C. If the specific heat of water at 25°C is 0.998 cal/g-deg, the value of the heat of combustion of benzoic acid is

  • 881.1 kcal

  • 771.2 kcal

  • 981.1 kcal

  • 871.2 kcal


B.

771.2 kcal

Weight of benzoic acid = 1.89 gm

Temperature of bomb calorimeter = 25°C = 298 K

Mass of water (m) = 18.94 kg = 18940 gm

Increase in temeperature (t) = 0.632°

Specific heat of water (s) = 0.998 cal/g-deg.

We know that heat gained by water or heat liberate by benzoic acid (Q) = mst = 18940 × 0.998 × 0.632 = 11946.14 cal

Since, 1.89 gm of acid liberates 11946.14 cal of heat.

Therefore heat liberated by 122 gm of acid ( mol. wt. of benzoic acid)

11946.14 × 1221.89 = 771126.5 cal = 771.12 kcal.


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