Question

1. Lithium aluminum hydride is an important reagent in organic chemistry. You are shipping 500 g of LiAlH₄ in ether (ethereal). Which of the following statements is true?

a)The bottle should be labeled as a flammable liquid and dangerous when wet.

b)Lithium aluminum hydride is a marine pollutant.

c)The reportable quantity is 10 g.

d)When shipped by water, it must be stored on deck only.

e)LiAlH₄ cannot be shipped by passenger aircraft.

f)It can only be shipped in PG I.

g)The truck transporting this material must be placarded

2.A mixture of natural gas (which is mostly methane) and oxygen gas shows no apparent reaction at room temperature, yet it explodes when a match is lit. What is the correct explanation for this observation?

a)CO₂ and water are more stable than natural gas and oxygen at room temperature.

b)Unless the concentrations of natural gas and oxygen are mixed with the exact right stoichiometry, no reaction occurs.

c)The reaction is exothermic at higher temperatures, but endothermic at room temperature.

d)The activation energy for this reaction is so high that there is not enough thermal energy at room temperature for reaction to occur.

Answer 1

1. Lithium Aluminium Hydride (LAH) is an extremely reactive reducing agent for organic compounds such as aldehydes, ketones, acyl chlorides and acids. It reduces such compounds by providing reactive hydride ion. This hydride ion can easily pick up any proton to form hydrogen molecule. This reaction is exothermic and explosive if it occurs in unprotected reaction conditions. Water molecules which are the source of proton can readily reacts with LAH leading to the explosion. Hence the bottle should be labeled as flammable and dangerous when wet.

2. The natural gases are mostly stable compunds which need a thermal activation to undergo oxidation reaction to yield CO₂ and H₂O molecules. The reaction is highly exothermic and the heat evolved during the reaction keeps the reaction on till the supply of oxygen or the gas gets over. This is the reason we lit the gas for its burning (oxidation). So the answer is d).