METALS: NICKEL Nickel, which is relatively rare in the Earth's crust (0.008%), is usually found as a sulfide (e.g., in the ore millerite). This element is a typical transition metal, as evinced by its high melting point (1535°C), high density (8.91 g cm-³), variable oxidation states [e.g., Ni(II) and Ni(III)], formation of coloured compounds (which are often green), and catalytic activity (e.g., it is used in the hydrogenation and dehydrogenation of organic compounds). [.. K > Cs > Ca > Na > Mg > Al > Fe > Ni > Sn > (H) > Cu > Hg > Ag ..]
1. Suggest how nickel can be extracted from nickel(II) oxide, which is obtained by roasting its sulfides in air. _____________________________ _______________________________________________________________________  2. Perhaps coincidentally, the thermal stabilities of nitrates appear to parallel the reactivity series. For example, mercury(II) nitrate decomposes on very gentle heating, to give a silvery liquid, nitrogen dioxide, and dioxygen: whereas, nickel(II) nitrate decomposes only on moderately strong heating, to give a black solid, nitrogen dioxide, and dioxygen: and, typical of Group 1 nitrates, caesium nitrate decomposes only on very strong heating, to give a pale-yellow solid and dioxygen. (a) Construct the symbol equation for each of these decompositions. _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________  (b) The volume (V1) of one mole of any gas at room temperature (25°C = 298 K; T1) and pressure (100 kPa; P1) is 24000 cm³; furthermore, the following relationship holds true for gases: P1 × V1 P2 × V2 ¾¾¾¾¾ = ¾¾¾¾¾ T1 T2 Determine the volume (V2) of nitrogen dioxide, at room temperature and low pressure (5 kPa; P2), obtained from the thermal decomposition of 3.66 g of nickel(II) nitrate - as follows. Calculate the molar mass of nickel(II) nitrate. _______________________ _______________________________________________________________________ Calculate the number of moles of nickel(II) nitrate in 3.66 g of the compound. _____________________________________________________________ Using the symbol equation, determine the number of moles of nitrogen dioxide obtained from this number of moles of nickel(II) nitrate. _____ _______________________________________________________________________ Calculate the volume (V1) of gas obtained at room temperature (T1) and pressure (P1). ________________________________________________________ And finally, using the above relationship, calculate the volume (V2) of gas at the decreased pressure (P2). ___________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________  3. When powdered nickel is added to aqueous mercury(II) nitrate, the grey solid rapidly dissolves, the colourless solution changes to green, a silvery liquid forms, and the temperature of the solution increases. Construct the net ionic equation for this redox reaction, complete with a qualitative indication of the heat energy change. ___________________ _______________________________________________________________________  4. Suggest one reason why aqueous solutions of metal nitrates should not be discharged into the environment. _______________________________ _______________________________________________________________________ 
5. Shown below is a diagram of an electrolytic cell used to nickel- plate an aluminium object.
[Q = n × z × F and Q = I × t, where: Q, measured in coulombs (C), is the quantity of electricity; n is the number of moles of substance evolved at the electrode; z is the charge on the ion; F is a constant, with a value of 96500 C mol-¹; I, measured in amps (A), is the current; and t, measured in seconds (s), is the time.]
(a) The mass (m) of the object increased by 0.383 g in 20 minutes. Write an ionic equation for the reaction which occurs at the cathode. _______________________________________________________________________ Calculate the number of moles (n) of nickel deposited at the cathode. _______________________________________________________________________ Calculate the quantity of electricity (Q) required to deposit this number of moles. ______________________________________________________ And finally, calculate the current (I) that flowed in the circuit. ____ _______________________________________________________________________  (b) State and explain what would be observed for each of the following, if the polarities of the above circuit were reversed. Nickel strip __________________________________________________________ _______________________________________________________________________ Aluminium object ______________________________________________________ _______________________________________________________________________ Electrolyte ___________________________________________________________ _______________________________________________________________________  6. Nickel's use as a catalyst is exemplified by the dehydrogenation of ethylbenzene to phenylethene. [This alkene, better known as styrene, is the monomer in the manufacture of poly(phenylethene).]
Suggest and explain two advantages in using a high temperature in the above reaction. _______________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ 
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