CE Molar Volume question

Ian Langley

2012-03-02 3:54 am

When 10g of PURE calcium carbonate (molar mass = 100.1 g/mol) reacted with excess hydrochloric acid, 2.4dm^3 of carbon dioxide was obtained at room temperature and pressure. However, in a similar experiment using 10g of IMPURE calcium carbonate, 2.5dm^3 of carbon dioxide was obtained. Assuming that impurity is a metallic carbonate, what would this impurity be?
(Molar masses: MgCO3 = 84.3g/mol , ZnCO3 = 125.4 g/mol, FeCO3 = 115.8g/mol, CuCO3 = 123.5 g/mol)

Thank you very much.

回答 (1)

知識就是力量

2012-03-02 7:35 am

✔ 最佳答案

In fact, this is a qualitative analysis instead of quantitative analysis.
Since more carbon dioxide is produced when the mass of metal carbonate used remains constant, the no. of moles of metal carbonate used is higher due to a lower molar mass of metal carbonate used.

Hence the impurity among the options is MgCO3, which has a lower mass than CaCO3.

2012-03-01 23:35:54 補充：
Last line: which has a lower molar mass than CaCO3.

2012-03-01 23:39:00 補充：
Is it a MC in CE 2007? The questions of this year are the most difficult among the past decade.

參考: Knowledge is power.

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