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1.

The value of`Delta _(f) f^(Ө)` for formation of `Cr_(2) O_(3)` is – 540 kJmol−1and that of `Al_(2) O_(3)` is `– 827 kJmol^(−1)`. Is the reduction of `Cr_(2) O_(3)` possible with Al ?

Answer» chemical equaltion for the foramtion of `Cr_(3)O_(3)` and `Al_(2)O_(3)` are as follows
(a) `(4)/(3) Cr(s) +(3)/(2)O_(2)(g) to (2)/(3) Cr_(2) O_(3) (s) :`
`DeltaG_(f)^(@)` =- 540kj mol^(-1)`
`(b) (4)/(3) Al (s) +(3)/(2) O_(2) (g) to (2)/(3) Al_(2)O_(3) (s) :`
` Delta G_(f)^@)=- 827 Kj mol^(-1)` Substring equcation (a) from equaction (b) ,we get
`(4/93)Al(s) +(2)/(3) Cr_(2)O_(3) (s) to`
`(2)/(3) Al_(2)O_(3) (s) +(4)/(3)Cr(s) DeltaG_(f)^(@)=- 287 kjmol^(-1)`
As can be seen `Delta _(r)G^(@)` is nagative , thius , reducation of `Cr_(2)O_(3)` Al is possible.
Discussion
2.

Why copper matte is put in silica lined converter?

Answer» Copper matte consist of `Cu_(2) S` along with some unchenged FeS when a blast of hot air is passed through milten matte placed in silica inled converter ,FeS present in matte is oxidised to Fe O which combines with silica `(Sio_(2))` to form `FeSiO_(3)` slag .
`2FeS to 2FeO +2SO_(2)`
`FeO+underset("silica")SiO_(2)to underset(Slag") FeSio_(3)`
when whole of iron been removed as slag some of the `Cu_(2)S` undergoes oxidation to form `Cu_(2) O` which then reacts with more `Cu_(2)S` to form copper metal .
`2Cu_(2)S+3O_(2) to 2CU_(2)O+SO_(2)`
`2Cu_(2) O+Cu_(2)S to 6Cu+SO_(2)`
thus copper mette is heated in silica lined coverter to remove FeS present in matte as `FeSiO_(3)` slag.
Discussion
3.

Copper can be extracted by hydrometallurgy but not zinc because

Answer» Correct Answer -
Copper can be extracted by hydrometallury but
not zinc , this is becomes ` E_(2n^(2+)//Zn)^(@) =- 0.76 V` is
lower than that `E_(Cu^(2+)//Cu)^(@)=0.34 V ` Hence , zinc
can displace Cu from solutions of `Cu^(2+)` ions .
`Zn (S) +Cu^(2+) (aq) to An^(2+)(aq) +Cu(s)`
In order to distance zinc solution , a
more reactiv metal is required , such as
`Al(E_(Al^(3+)//Al)^(@) =-1.66 V), Mg (E_(mg^(2+)^(@)=-2.37 V), `
`Ca (E_(Ca^(2+)//Ca)^(@) =-2.87 V),K (E_(K^(+)//K)^(@) =--2.93 V).`
But with water metals `(Al,Mg .Ca and K) forms their corresponding ions with the evolution of `H_(2)` gas . thus ,Al Mg ,Ca ,K etc. cannot be used to distance zinc from zinc solution and only copper can be extracted by hydrometallurgy but not the zinc .
Discussion
4.

Explain: (i). Zone refining (ii). Column chromatography.

Answer» (i) Zone refining . This method is used for produacation of semiconductors and other metals of very high puity e.g. G.e Si. B, Ca and In .
it is based on the prinicple that impurites
are more soluble in the mothen state (Melt ) than in the solid state of the metal .
the impure metal in the form of bar is hearted at one end with a moving circular heater .As - the heater is slowly moved along the length of the rod, the pure metal crystallises out of the melt whereas the impurities pass into the adjacent molten zone Thi.s process is repeated several times till the impurites are completely driven to one end of hte rod which is then cut off and discarded
(ii) chromatogrophy , it is based on the principle that the different components of a misture are absorbed to different extens on an adsorbent .
in column chromatography , an adsorbent , such as alummina `(Al_92)O_(3))` or silica gel is packed in a colunm . this fonns the statioary phase . the mixture to be separated is dissolved in suitable solvent (mobile phase ) and applied to the column . the adsorbed componts are extracted (eluted) from the column with a suitable . solvent (eluent ) . the component which si more strongly adsorbed on the column takes longer time to travel through the colunm than a component which is weakly adsorbed . thus , the various components of the mixture are seperated asthey travel through adsorbent (stationary pase ).
Discussion
5.

Which method of refining will you suggest for an element in which impurities present have chemical properties close to the properties of that elements?

Answer» the statioary phase is selected in such a way that the impurities are more stongly adsorbed or are more soluble In the stationaary phase than component to be purified thus ,when the column is extracted , the impurities will be retained by the statioary phase while the pure component is easily eluted.
Discussion