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(EAMCET 2001 M)
1) NaH2PO2
2) P2O5
3) Na2PO3
4) P2O3
Logic and Solution:
When phosphorus dissolves in caustic soda (NaOH), phosphine (PH3) gas is liberated along with formation of sodium hypophosphite (NaH2PO2).
3NaOH + P4 + 3H2O ---------> 3NaH2PO2 + PH3
Conclusion:
The correct option is '1'.
(EAMCET 2005 M)
1) SiO2, Na
2) Fused NaOH, C
3) Mg, B2O3
4) Mg, CO2
Logic & solution:
1) There is no reaction between silica, SiO2 and sodium metal, Na.
2) Fused NaOH reacts with carbon to liberate dihydrogen gas.
6NaOH + 2C ----------> 2Na2CO3 + 3H2
3) Magnesium reduces boric anhydride to give boron.
3Mg + B2O3 ----------> 3MgO + 2B
4) Magnesium reduces carbon dioxide to carbon.
2Mg + CO2 ---------> 2MgO + C
Conclusion:
The correct option is: 2.
(EAMCET 1992 M)
1) Zn(OH)2
2) ZnO
3) Na2ZnO2
4) all the above
Logic & solution:
In excess of sodium hydroxide, Zn2+ forms sodium zincate, Na2ZnO2 that is soluble in water. It is a complex salt and should be represented by the formula: Na2[Zn(OH)4].
Zn2+ + 2NaOH (excess) ----------> Na2ZnO2 + 2H+
or
Zn2+ + 4NaOH (excess) ----------> Na2[Zn(OH)4] + 2Na+
However, when small amount of sodium hydroxide is added, a while gelatinous precipitate of Zn(OH)2 is formed.
Zn2+ + 2NaOH (little) ----------> Zn(OH)2 + 2Na+
Conclusion:
The correct option is: 3.
(EAMCET 1992 M)
1) Iron
2) Carbon
3) Mercury
4) Nickel
Logic & solution:
In the Castner-Kellner cell, used to manufacture sodium hydroxide, a bunch of iron rods is used as cathode in the central compartment.
In the side compartments, graphite rods are used as anodes.
Mercury acts as cathode in side compartments and as anode in the middle compartment.
Conclusion:
The correct option is: '1'.
(EAMCET 2001 M)
1) Iron
2) Carbon
3) Mercury
4) Nickel
Logic & solution:
'A' is: NaClO3. The oxidation number of Cl is +5.
Calculation:
Na + Cl + 3O = 0
(+1) + Cl + 3(-2) = 0
Cl = +5
Conclusion:
The correct option is: '1'.
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Author: Aditya vardhan Vutturi