31.
Ellingham diagram represents change of A
$$\Delta G$$ with temperature
B
$$\Delta H$$ with temperature
C
$$\Delta G$$ with pressure
D
$$\left( {\Delta G - T\Delta S} \right)$$ with temperature
Answer :
$$\Delta G$$ with temperature
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32.
Brine is electrolysed by using inert electrodes. The reaction at anode is _________ . A
$$Cl_{\left( {aq} \right)}^ - \to \frac{1}{2}C{l_{2\left( g \right)}} + {e^ - };E_{{\text{cell}}}^ \circ = 1.36\,V$$
B
$$2{H_2}{O_{\left( l \right)}} \to {O_{2\left( g \right)}} + 4{H^ + } + 4{e^ - };$$ $$E_{{\text{cell}}}^ \circ = 1.23\,V$$
C
$$Na_{\left( {aq} \right)}^ + + {e^ - } \to N{a_{\left( s \right)}};E_{{\text{cell}}}^ \circ = 2.71\,V$$
D
$$H_{\left( {aq} \right)}^ + + {e^ - } \to \frac{1}{2}{H_{2\left( g \right)}};E_{{\text{cell}}}^ \circ = 0.00\,V$$
Answer :
$$Cl_{\left( {aq} \right)}^ - \to \frac{1}{2}C{l_{2\left( g \right)}} + {e^ - };E_{{\text{cell}}}^ \circ = 1.36\,V$$
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Although reduction potential of $$C{l^ - }$$ ion is higher than that of $${H_2}O,$$ yet oxidation of $$C{l^ - }$$ ions occurs in preference to $${H_2}O$$ due to overvoltage of $${O_2}$$ ( i.e., water needs greater voltage for oxidation to $${O_2}$$ as it is a kinetically slow process ).
33.
$$XC{l_2}{\text{(excess)}} + YC{l_2} \to $$ $$XC{l_4} + Y \downarrow ;$$ \[YO\xrightarrow[>{{400}^{\circ }}]{\Delta }\frac{1}{2}{{O}_{2}}+Y,\] Ore of $$Y$$ would be : A
Siderite
B
Cinnabar
C
Malachite
D
Hornsilver
Answer :
Cinnabar
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\[\begin{align}
& \underset{\left( XC{{l}_{2}} \right)}{\mathop{SnC{{l}_{2}}}}\,+\underset{\left( YC{{l}_{2}} \right)}{\mathop{HgC{{l}_{2}}}}\,\to \underset{\left( XC{{l}_{4}} \right)}{\mathop{SnC{{l}_{4}}}}\,+\underset{\left( Y \right)}{\mathop{Hg}}\, \\
& HgO+\frac{\Delta }{>{{400}^{\circ }}C}Hg+\frac{1}{2}{{O}_{2}} \\
& HgS\text{ : Cinnabar} \\
\end{align}\]
34.
Calcination is the process in which : A
ore is heated above its melting point to expel $${H_2}O$$ or $$C{O_2}$$ or $$S{O_2}$$
B
ore is heated below its melting point to expel volatile impurities
C
ore is heated above its melting point to remove $$S, As$$ and $$Sb$$ as $$S{O_2},A{s_2}{O_3}$$ and $$S{b_2}{O_3}$$ respectively
D
ore is heated below its melting point to expel $${H_2}O$$ or $$C{O_2}$$
Answer :
ore is heated below its melting point to expel $${H_2}O$$ or $$C{O_2}$$
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Calcination is a process of heating a substance to a high temperature but below the melting or fusion point, causing loss of moisture, reduction or oxidation and dissociation into simpler substances.
35.
Which of the following is not a method of refining of metals? A
Electrolysis
B
Smelting
C
Poling
D
Liquation
Answer :
Smelting
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Smelting is a process used for reduction of oxide to convert it into metal.
36.
Zone refining is based on the principle that ___________. A
impurities of low boiling metals can be separated by distillation
B
impurities are more soluble in molten metal than in solid metal
C
different components of a mixture are differently adsorbed on an adsorbent
D
vapours of volatile compound can be decomposed in pure metal
Answer :
impurities are more soluble in molten metal than in solid metal
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37.
Pyrolusite is a/an A
oxide ore
B
sulphide ore
C
carbide ore
D
Not an ore
Answer :
oxide ore
38.
Which of the following is used as a method of purification for silicon? A
Electrolytic refining
B
Liquation
C
Zone refining
D
Distillation
Answer :
Zone refining
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Elements such as $$Si,Ge,Ga,$$ etc. which are used as semiconductors are refined by zone refining method.
39.
Calgon used as a water softner, is A
$$N{a_2}\left[ {N{a_4}{{\left( {P{O_3}} \right)}_6}} \right]$$
B
$$N{a_4}\left[ {N{a_2}{{\left( {P{O_3}} \right)}_6}} \right]$$
C
$$N{a_4}\left[ {N{a_4}{{\left( {P{O_4}} \right)}_5}} \right]$$
D
$$N{a_4}\left[ {N{a_2}{{\left( {P{O_4}} \right)}_6}} \right]$$
Answer :
$$N{a_2}\left[ {N{a_4}{{\left( {P{O_3}} \right)}_6}} \right]$$
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Sodium polymetaphosphate is used to remove the permanent hardness of water. The commercial name of sodium polymetaphosphate is calgon meaning calcium gone. The molecular formula of calgon is $$N{a_2}\left[ {N{a_4}{{\left( {P{O_3}} \right)}_6}} \right].$$
40.
Heating pyrites to remove sulphur is called A
smelting
B
calcination
C
liquation
D
roasting
Answer :
roasting
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Pyrites are sulphur ores and are converted into oxide by roasting.