8 Mc question

2012-01-06 1:22 am

20) In a hydrogen-oxygen fuel cell, oxygen isinjected from the right and hydrogen is injected from the left. The electrolyteis concentrated NaOH solution.Which of the following is correct?Chemical change occurs at the left-hand-sideelctrode and direction of OH- ion move to areA. O2 + 2H2O + 4e- --> 4OH- and XB. 4OH- --> O2 + 2H2O + 4e- and XC. 4OH- --> O2 + 2H2O + 4e- and YD. O2 + 2H2O + 4e- --> 4OH- and Y 21) Where does reduction occur in chemical cell andelectrolytic cell?A. Anode in bothB. Cathode in bothC. Anode in chemical cell and cathode in electrolyticcellD. Cathode in chemical cell and anode inelectrolytic cell 22) Which of the following substance will NOT bedecomposed by electricity?A. Molten silverB. Dilute sulphuric acidC. Concentrated sodium chloride solutionD. Silver nitrate solution 23) Which ion will be reduced during electrolysisof molten AgCl?A. Ag+B. Cl-C. H+D. OH- 24) What is the function of a rheostat?A. To measure electric currentB. To supply energyC. To increase electrical conducting wireD. To vary the electric current 25) Which of the following combinations concerningthe electrolysis of dilute sulphuric acid is correct?A. Positive electrode: 2H+ + 2e- --> H2;negative electrode: 4OH- --> 2H2O + O2 + 4e-B. Positive electrode: 2H+ + 2e- --> H2;negative electrode: 4H+ + SO4 2- + 2e- --> SO2 + 2H2OC. Positive electrode: 4OH- --> 2H2O + O2 + 4e- ;negative electrode: 2H+ + 2e- --> H2D. Positive electrode: 4H+ + SO4 2- + 2e- -->SO2 + 2H2O; negative electrode: 2H+ + 2e- --> H2 26) Which of the following statements concerningthe electrolysis of 0.05M NaCl solution is correct?A. Bubble of hydrogen appear at the positiveelectrodeB. Bubble of oxygen appear at the negativeelectrodeC. pH of the solution near the anode increaseD. After electrolysis carried out for some time, sodiumchloride solution become more concentrated

更新1:

其實我係想對答案，我的答案: D,B,A,A,D,C,D

回答 (1)

胡雪8°

2012-01-14 9:37 am

✔ 最佳答案

20)
There is no answer.
The left is the anode :
H2(g) + 4OH^-(aq) → 4H2O(l)+ 4e^-
The right is the cathode :
O2(g) + 2H2O(l) + 4e^- → 4OH^-(aq)
The OH^- ions move from right to left, because OH^-(aq) ions are produced onthe right while consumed on the left.

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21)
correct
In both chemical cell and electrolytic cell, reduction occurs at cathode.

22)
correct
Silver is a metal, which conducts electricity without decomposition in bothliquid or solid states.
The other three are electrolytes, which conducts electricity withdecomposition.

23)
correct
In molten AgCl, there are mobile only Ag^+ and Cl^- ions, but no H^+ or OH^-ions.
Ag^+ ions are reduced to Ag metal, while Cl^- ions are oxidized to Cl2.

24)
correct
A rheostat is a variable resistor.
The electric current can be varied by adjusting the resistance of the rheostat.

25)
correct
Hydroxide and sulphate ions migrate to the positive electrode. Hydroxide ionsare preferentially discharged at the positive electrode to form oxygen gas becausesulphate ions are oxidized much less readily than hydroxide ions.
Only hydrogen ions migrate to the negative electrode. Hydrogen ions aredischarged at the negative electrode to form hydrogen gas.

26)
correct
Chloride and hydroxide ions migrate to the positive electrode. As the concentrationof NaCl of low, hydroxide ions are preferentially discharged because hydroxideions are oxidized much readily than chloride ions.
4OH^-(aq) → 2H2O(l) + O2(g) + 4e^-
Sodium and hydrogen ions migrate to the negative electrode. Hydrogen ions arepreferentially discharged because sodium ions are reduced much less readilythan hydrogen ions.
2H^+(aq) + 2e^- → H2
The net change is the electrolysis of water.
2H2O(l) → 2H2(g) + O2(g)
After electrolysis carried out for some time, a certain amount of water is consumed.Thus, NaCl solution becomes more concentrated.

參考: 胡雪

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