Answer to Question #76689 in Inorganic Chemistry for Arun Rawat

Question #76689
3. a) Give the names of any two alloys of aluminium which have some amount of copper or
magnesium. How are these more advantageous than pure aluminium?
b) Why boric acid is a very weak monobasic acid (pH = 9.25)? Explain with suitable
c) Why iron, cobalt and nickel do not form typical interstitial carbides? Write the type of
carbides they form.
Expert's answer
. Duralumin is 95% aluminium, 4% copper, 0.5% magnesium, and 0.5% manganese - has increased strength and hardness compared to pure aluminum. Magnalium is alloy aluminium (70-95%) with magnesium (30-5%) and few amount copper and nickel - has high corrosion resistance, good weldability, high plasticity compared to pure aluminum.
2.These acids have only one hydrogen atom to donate to a base in an acid base reaction just because they have one replaceable hydrogen they are known as monobasic.If they are capable to donate 2 or 3 hydrogen then it is known as dibasic or tribasic. Boric acid in water, accepts OH-ion acting as lewis acid and water releases H+ions. The reaction is as follows:
B(OH)3 + H2O→ H+ + [B(OH)4]-
3. Interstitial carbides have metallic properties and are refractory. The long-held view is that the carbon atoms fit into octahedral interstices in a close-packed metal lattice when the metal atom radius is greater than approximately 135 pm. Iron, cobalt and nickel form intermediate transition metal carbides. In intermediate transition metal carbides the transition metal ion is smaller than the critical 135 pm, and the structures are not interstitial but are more complex. Multiple stoichiometries are common; for example, iron forms a number of carbides, Fe3C and Fe2C. The best known is cementite, Fe3C, which is present in steels. These carbides are more reactive than the interstitial carbides; for example, the carbides of Fe, Co and Ni are all hydrolysed by dilute acids and sometimes by water, to give a mixture of hydrogen and hydrocarbons. These compounds share features with both the inert interstitials and the more reactive salt-like carbides.

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