BPSC 70th CCE Re-exam Prelims General Studies · Question 26 of 142

Correct — A, Ni. Vanaspati is made by hardening liquid vegetable oil, and the chemistry behind it is one reaction. Vegetable oils are triglycerides of unsaturated fatty acids: their hydrocarbon chains carry carbon–carbon double bonds, and each double bond puts a kink in the chain that keeps the molecules from packing closely, which is why the oil is liquid at room temperature. Pass hydrogen gas through the hot oil over a catalyst and hydrogen adds across those double bonds, straightening the chains, raising the melting point and turning the oil into a semi-solid fat. The catalyst that makes this happen at industrial scale is finely divided NICKEL, used at roughly 450 to 500 kelvin under a few atmospheres of hydrogen — the process patented by Wilhelm Normann in 1903 and the reason vanaspati exists at all. Nickel wins on economics as much as chemistry: it is an effective hydrogenation catalyst, it can be prepared with an enormous surface area by reducing nickel oxide or by leaching aluminium out of a nickel-aluminium alloy to give Raney nickel, and it is cheap enough to use by the tonne in an edible-oil plant. Note also what the catalyst does not do: it does not appear in the product and is filtered out after the reaction, since a catalyst changes the rate of a reaction by offering a lower-energy path and is recovered unchanged. Because option (a) is right, the escape option (d) cannot stand. One consequence worth knowing is that partial hydrogenation converts some of the remaining cis double bonds into the trans form, and trans fats raise LDL cholesterol while lowering HDL — which is why India's food regulator has progressively capped trans fatty acids in edible oils and fats.

• (b)Pd — Chemically right and economically impossible, which makes it the thinking candidate's mistake. Palladium — usually as palladium on carbon — is an excellent hydrogenation catalyst and is the standard choice in a laboratory or in fine-chemical synthesis, along with platinum. It is a precious metal costing many times what nickel does, and no edible-oil refinery hardening thousands of tonnes a year would use it.
• (c)Fe — Iron is a famous industrial catalyst, but for a different reaction entirely: finely divided iron with promoters such as potassium and aluminium oxide is the catalyst of the Haber process, which combines nitrogen and hydrogen to make ammonia. Seeing 'catalyst' and 'hydrogen' in the same stem and reaching for iron is exactly the association the option is built on.
• (d)None of the above — Fails because nickel is squarely on the list. An escape option is correct only when each of the other three can be shown to be wrong, and here the first of them is the catalyst named in every school and undergraduate account of oil hardening.

A catalyst speeds a reaction by providing a path with a lower activation energy, and emerges chemically unchanged at the end. Heterogeneous catalysts, like the nickel used here, are in a different phase from the reactants — a solid in contact with a liquid and a gas — and they work at their surface: hydrogen molecules adsorb onto the metal and are split into atoms, the double bond of the fatty acid chain adsorbs alongside, the hydrogen atoms add across it, and the saturated chain desorbs. Everything about the catalyst's design therefore aims at surface area, which is why it is used finely divided. The wider family is worth holding as a table: nickel for the hydrogenation of oils, iron for ammonia in the Haber process, vanadium pentoxide for sulphur trioxide in the Contact process, platinum-rhodium gauze for nitric oxide in the Ostwald process, and Ziegler-Natta catalysts for polymerisation.

The route through this question is to ask what each metal is famous FOR, rather than whether it could work. Iron is the ammonia catalyst; palladium and platinum are the laboratory hydrogenation catalysts; nickel is the industrial one for oils. Reasoning by cost gives the same answer independently: an edible-oil plant hardens oil by the tonne, so the catalyst has to be a base metal rather than a platinum-group metal, and nickel is the only base metal on the list that catalyses hydrogenation at all. It is also worth being clear about what changes physically. Hydrogenation does not make the fat 'purer' or richer; it saturates the chains so the product is solid at Indian room temperatures, keeps far longer without going rancid, and can be used for frying at higher temperatures. The nutritional cost is the trans fat produced by partial hydrogenation, which is why the regulatory trend has been to limit it rather than to celebrate the process.

• Hydrogenation of vegetable oil to vanaspati uses finely divided nickel as catalyst at roughly 450 to 500 K under a few atmospheres of hydrogen; the process was patented by Wilhelm Normann in 1903.
• Unsaturated fatty acid chains contain carbon–carbon double bonds that kink the molecule and keep the oil liquid; adding hydrogen across those bonds straightens the chains and raises the melting point.
• Raney nickel, made by leaching aluminium out of a nickel-aluminium alloy, is the standard high-surface-area form of the catalyst.
• Iron with promoters is the catalyst of the Haber process for ammonia; vanadium pentoxide is used in the Contact process for sulphuric acid; palladium and platinum are the laboratory hydrogenation catalysts.
• Partial hydrogenation converts some cis double bonds to the trans form, producing trans fatty acids that raise LDL and lower HDL cholesterol — the reason India's food regulator has capped trans fat content in edible oils and fats.

• Choosing palladium because it is a better catalyst. It is, and it is far too expensive for bulk edible-oil hardening.
• Reaching for iron because the reaction involves hydrogen. Iron is the ammonia catalyst of the Haber process, not an oil-hydrogenation catalyst.
• Thinking the catalyst ends up in the vanaspati. It is filtered out and recovered; a catalyst is not consumed by the reaction it speeds.

BPSC asks applied chemistry through everyday products — which catalyst hardens oil, which gas is used in a particular process, what a household chemical is — with an escape option attached to punish guessing. UPSC has largely stopped asking bare catalyst questions and instead approaches the same chemistry through consumer and health framing, as in its question on what a 'no trans-fats' claim actually signifies.

• practice — not a real PYQ

  The catalyst used in the Haber process for the manufacture of ammonia is

  • (a)Finely divided nickel
  • (b)Finely divided iron with promoters
  • (c)Vanadium pentoxide
  • (d)Platinum-rhodium gauze

  Answer(b) Finely divided iron with promoters such as potassium oxide and aluminium oxide. Vanadium pentoxide belongs to the Contact process for sulphuric acid, platinum-rhodium gauze to the Ostwald process for nitric acid, and nickel to the hydrogenation of oils.

• practice — not a real PYQ

  Hydrogenation converts a liquid vegetable oil into a semi-solid fat because it

  • (a)removes water from the oil
  • (b)adds hydrogen across carbon–carbon double bonds, saturating the fatty acid chains
  • (c)oxidises the fatty acids
  • (d)breaks the triglyceride into free fatty acids and glycerol

  Answer(b) adds hydrogen across carbon–carbon double bonds, saturating the fatty acid chains — which straightens them so that the molecules pack closely, raising the melting point. Breaking a triglyceride into fatty acids and glycerol is hydrolysis, a different reaction.