can help me to do this CHEM 問題

Question

如題:
The mass of a sample of copper powder contaminated whit copper(2)oxide is known. Describe how you would conduct an experiment to determine the percentage by mass of copper powder in the sample. State the expected observation of the experiment.
(Hint: You may use an acid in the experiment)

P.S. 如可以告知小弟是何年HKCEE題和第幾題.

Answer 1

1. Using an electronic balance, weigh the sample of copper powder contaminated with copper(II) oxide.

2. Add the weighed sample to a beaker containing excess 2 M hydrochloric acid and stir the mixture well. Brown solid of copper does not react, but black solid of copper(II) oxide dissolves in the hydrochloric acid to give a blue solution of copper(II) chloride.
CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(l)
If necessary, warm the reaction mixture to speed up the reaction, and ensure that all copper(II) oxide is reacted.

3. Filter the reaction mixture. The copper residue is then washed with distilled water (or ionized water) to remove all impurities. Draw the copper obtained in a oven. After cooled, the mass of copper is weighed.

4. % by mass of Cu = [(Mass of Cu) / (Mass of sample)] x 100%



2007-03-19 22:27:36 補充：
唔知邊年，識做就得。

Answer 2

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