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 
(1535C), high density (8.91 g cm-), 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. _____________________________ _______________________________________________________________________ [1] 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. _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ [6] (b) The volume (V1) of one mole of any gas at room temperature (25C = 298 K; T1) and pressure (100 kPa; P1) is 24000 cm; furthermore, the following relationship holds true for gases: P1 V1 P2 V2 = 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). ___________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ [9] 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. ___________________ _______________________________________________________________________ [3] 4. Suggest one reason why aqueous solutions of metal nitrates should not be discharged into the environment. _______________________________ _______________________________________________________________________ [1]

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-; 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. ____ _______________________________________________________________________ [7] (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] 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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