9 MC questions

2012-01-05 11:20 pm
7)Which of the following combinations is correct for a zinc-carbon cell?
A. Positive electrode: carbon; negative electrode: zinc; electrolyte:manganese(IV) oxide
B. Positive electrode: carbon; negative electrode: zinc; electrolyte: ammoniumchloride
C. Positive electrode: zinc; negative electrode: carbon; electrolyte:manganese(IV) oxide
D. Positive electrode: zinc; negative electrode: carbon; electrolyte: ammoniumchloride 8)Which compound does iodine have oxidation state of +3?
A. HIO3
B. NaI3
C. CrI3
D. NaIO2 9)Which of the following pairs of substances are the oxidation numbers of sulphurand nitrogen the same?
A. sulphuric acid and nitric acid
B. H2SO3 and NO2
C. Na2S and NO
D. FeS and NH4Cl

10) In which of the following reaction does nitrogen have the greates change inoxidation number?
A. N2 + 3H2 --> 2NH3
B. 4NH3 + 5O2 --> 4NO + 6H2O
C. 2NO + O2 --> 2NO2
D. 3NO2 + H2O --> 2HNO3 + NO 11)For the following reaction, which of the following is correct?
9H2SO4 + 8KI --> H2S + 8KHSO4 + 4H2O + 4I2
A. Species being reduced: H2S; species being oxidized: I2
B. Species being reduced: I2; species being oxidized: H2S
C. Species being reduced: H2SO4; species being oxidized: KI
D. Species being reduced: KI; species being oxidized: H2SO4

12) Which of the following reactant in bracket is NOT a reducing agent?
A. PbO + [CO] --> Pb + CO2
B. [Zn] + 2Ag+ --> Zn2+ + 2Ag
C. Br2 + 2[I-] --> 2Br- + I2
D. [SO2] + H2O --> H2SO3

13) Which of the following are redox reaction?
(i) Li + H2O --> LiOH + H2
(ii) Ag + PtCl4 --> AgCl +Pt
(iii) HClO4 + Ca(OH)2 --> H2O + Ca(ClO)2

14) For the equation
w Zn + x ReO- + y H+ --> w Zn2+ + x Re + z H2O
A. w=4, x=1, y=8 and z=16
B. w=4, x=2, y=16 and z=8
C. w=7, x=2, y=16 and z=8
D. w=7, x=1, y=8 and z=16

15) Which of the substances will react with ammonium iodide?
(i) warm NaOH solution
(ii) aqueous bromine
(iii) silver nitrate solution
A. i and ii
B. i and iii
C. ii and iii
D. i, ii and ii
更新1:

其實我係想對答案, 我的答案: B,D,B,A,C,D,A,C,D

回答 (1)

2012-01-07 6:19 am
✔ 最佳答案
7. correct.
zinc oxidizes to give electrons, so it acts as -ve electrode.
MnO2 is insoluble in water, so it's not an electrolyte.

8. correct.

9. correct. both are +4.

10. wrong.
in B, from ammonia (-3) to nitrogen monoxide (+2), then change is (+)5.
in fact, the 4 choices are the procedures of industrial manufacture of nitric acid from N2.
A: Haber process; changes from 0 to -3.
B: combustion of NH3; changes from -3 to +2.
C: oxidation of NO by air, giving NO2; changes from +2 to +4.
D: dissolution / reaction with water; changes from +4 to +5 (nitric acid) & +2 (NO); this is disproportionation reaction.

11. correct.
C&D are talking about products.

12. correct.
plain dissolution to give acid.

13. ?
none of them are balanced, and some species seem strange (judging from equation and reaction). no choices were given neither.
i) is right, Li from 0 to +1
ii) is right, Ag from 0 to +1
iii) ...? reaction should give Ca(ClO4)2, calcium perchlorate; if it's so, then it isn't redox: Cl keeps at +7.

14. ?
again, I guess the rhenium oxy-anion should be perrhenate / rhenate(VII), ReO4(-).
if it's so, then from ReO4(-) to Re, O.N. change is -7 (from +7 to 0),
where Zn O.N. change is +2 (from 0 to +2),
thus ratio of Zn and ReO4(-) should be 7:2.

if you insisted the equation is correct,
then from ReO(-) to Re, O.N. change is -1 (from +1 to 0),
thus ratio of Zn and ReO(-) should be 1:2.

15. correct.
yielding:
i. ammonia
ii. elemental iodine
iii. silver iodide solid


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