LiTw 發問於 科學及數學化學 · 9 年前

6 MC question

For 1~3, refer to the following experiment

25cm^3 of NaOH is diluted to 250cm^3 with distilled water. Then, 25cm^3 of the portion of the diluted NaOH is titrated with 16.4cm^3 sulphuric acid(0.25 mol dm^-3)

1) What is the concentration of undiluted NaOH?

A. 1.64 mol dm^-3

B. 2.05 mol dm^-3

C. 3.28 mol dm^-3

D. 4.10 mol dm^-3

2) Which of the following apparatus are required for the dilution?

(i) burette

(ii) pipette

(iii) volumetric flask

A. i and ii only

B. i and iii only

C. ii and iii only

D. i, ii and iii

3) Which of the following statement(s) concerning the experiment is/are correct?

(i) the colour of phenolphthalein change from pink to colourless at the end point

(ii) the conical flask for holding diluted NaOH should be washed with the same diluted NaOH solution before titration

(iii) the solution mixture in conical flask could not conduct electricity at the end of the experiment

A. i only

B. ii only

C. i and iii only

D. ii and iii only

4) For a simple chemical cell, which of the following will there be electron flow in the external wire?

A. Electrodes: Iron and copper; solution connecting two metals: vinegar

B. Electrodes: Copper and copper; solution connecting two metals: vinegar

C. Electrodes: Copper and iron; solution connecting two metals: wine

D. Electrodes: Iron and copper; solution connecting two metals: sugar solution

5) In a simple chemical cell, a current flow from metal X to metal Y in the external circuit, and the electrolyte is dilute sulphuric acid.

Which of the following statements concerning the experiment are correct?

(i) the electrode made of metal X is the cathode

(ii) electron move free in the dilute sulphuric acid

(iii) chemical energy is converted to electrical energy

A. i and ii

B. i and iii

C. ii and iii

D. i, ii and iii

6) Which of the following dry cells is a secondary cell?

A. Zinc-carbon cell

B. Nickel metal hydride cell

C. Silver oxide cell

D. Alkaline manganese cell

更新:

其實我係想對答案,

我的答案: C,C,A,A,C,B

1 個解答

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  • 最愛解答

    1) No. of moles of H2SO4 used = 16.4/1000 x 0.25 = 0.0041

    Hence no. of moles of NaOH = 2 x 0.0041 = 0.0082

    Conc. of diluted NaOH = 0.0082/0.025 = 0.328 M

    Conc. of original NaOH = 3.28 M

    2) C, since burette is used only during titration.

    3) A

    (i) is true. Phenolphthalein is colourless when acidic and pink when alkaline.

    (ii) is false. If washed with the same diluted NaOH, no. of moles of NaOH actually present in the conical flask will be more than actual no. of moles in 25 cm3 of solution.

    (iii) is incorrect. Na2SO4 in aqueous state still can conduct electricity by the mobile ions.

    4) A. Iron and copper have different position in ECS and also vinegar is an electrolyte.

    5) B

    (i) is true since X accepts electrons, meaning that reduction occurs around it (cathode)

    (ii) is false since electrons cannot freely exist in electrolyte

    (iii) is true since in cell action, chemical energy is consumed to push current flow which is the electrical energy.

    6) B, since it is rechargeable.

    2012-01-06 20:58:08 補充:

    All you ans are correct except that Q5 should be B as I explained.

    資料來源: 原創答案
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