NEET Questions Solved


In the preparation of hydrogenated oil the chemical reaction involving hydrogen is called:

(a) hydrogenation

(b) reduction

(c) dehydration

(d) oxidation

(a)

  1. Necessity for Hydrogenation • Hydrogenated fat is basically a substitute to butter fats. • High costs of butter fat and its poor storage stability were detrimental factors that led to the investigation of alternative sources of hard fats. • This investigation led to the invention of catalyzed H2 addition across unsaturated sites of oils and fats and was quickly commercialized. • Conversion of liquid oils to solid and semi-solid fats having wide spectrum of physical & chemical characteristics of products were thus obtained.
  2.  What is Hydrogenation? • Hydrogenation is a process that reduces unsaturated fatty acid content of triglycerides by attaching hydrogen atoms at the point of unsaturation in the presence of catalyst, usually Nickel. • Hydrogenation accomplishes two things-: • 1.It increases the melting point of the oil or fat. • 2.Resistance to oxidation and flavor deterioration. • Hydrogenation process depends on several parameters: • Pressure, Temperature, Type of catalyst, Speed of agitation etc.
  3.  MECHANISM • The mechanism involved in fat hydrogenation is believed to be the reaction between unsaturated liquid oil and atomic hydrogen adsorbed on a metal catalyst. • It is similar to hydrogenation of alkenes.

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The most abundant isotope of hydrogen is:

(a) tritium

(b) deuterium

(c) protium

(d) para-hydrogen

(c) Protium is 1H1.

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Hydrogen is evolved by the action of cold dilute HNO3 on:

(a) Fe

(b) Mg or Mn

(c) Cu

(d) Al

(b) Only Mg and Mn react with cold dil. HNO3 to give H2.

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Hydrogen is not obtained when zinc reacts with:

(a) cold water

(b) dil. H2SO4

(c) dil HCl

(d) hot 20% NaOH

(a) Elements having reduction potential of -0.41V or below can liberate hydrogen from cold water. Such as alkali metals Ba, Sr and Ca.

Also Zn-Cu and Al-Hg couples liberate hydrogen with cold water.

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Very pure hydrogen (99.9%) can be made by which of the following processes ?

(a) Mixing natural hydrocarbons of high molecular weight

(b) Electrolysis of water

(c) Reaction of salt like hydrides with water

(d) Reaction of methane with steam

(c) Hydrogen of high purity is obtained by electrolysing aqueous barium hydroxide in presence of Ni electrodes.

             2e + 2H3O+          2H2O + 12H2            2OH-           H2O + 12O2 + 2eAlso pure metal hydrides give pure H2 NaH + H2O            NaOH + H2

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Which of the following pairs will not produce dihydrogen gas ?

(a) Cu + HCl (dil.)

(b) Fe + H2SO4

(c) Mg + steam

(d) Na + alcohol

(a) Cu has E°OP lesser than H.

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The metal that does not displace hydrogen from an acid is:

(a) Hg

(b) Zn

(c) Al

(d) Ca

(a) Hg is placed below H in electrochemical series.

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The catalyst used in Bosch process of manufacture of H2 is:

(a) finely divided Ni

(b) V2O5

(c) Pd

(d) Fe2O3 + Cr2O3

(d)

In this process water gas (CO + H2, prepared from coal and water at 1270 K) is mixed with two times its volume of steam passed over catalyst Fe2O3, in the presence of promoter Cr2O3 or ThO2 at 773 K giving products CO2 and H2.

CO2 is dissolved in water under pressure (20 to 25 atm) and is removed leaving behind un dissolved H2.



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In which reaction hydrogen is not formed ?

(1) Copper and hydrochloric acid

(2) Iron and sulphuric acid

(3) Magnesium and steam

(4) Sodium and alcohol

(1) Copper is placed below hydrogen in electrochemical series. Hence it does not librate hydrogen gas with hydrochloric acid.

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Hydrogen will not reduce-

(A) heated cupric oxide                                 

(B) heated ferric oxide

(C) heated stannic oxide                               

(D) heated aluminium oxide

(D).  Al-O bond is very strong.

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