F.5 Chem MC

2008-03-06 7:16 pm

1)
When 10g of PURE CaCO3 (molar mass = 100.1g) reacted with excess HCl, 2.40 dm3 of CO2 was obtained at rm t and pressure.
However, in a similar experiment using 10g of IMPURE CaCO3, 2.50 dm3 of CO2 was obtained. Assuming that the impurity is a metallic carbonate, what would this impurity be?

A. MgCO3 (molar mass = 84.3 g)
B. ZnCO3 (molar mass = 125.4 g)
C. FeCO3 (molar mass = 115.8 g)
D. CuCO3 (molar mass = 123.5 g)

The answer is A but I don't know how to calculate.
Please show me the steps.

2)
1st: Molten sulphur is a good conductor of electricity
2nd: Sulphur molecules are mobile in molten sulphur

Correct/Wrong...
Please tell me the answer and explain.

Thanks a lot!!

回答 (1)

用戶7369

2008-03-06 7:30 pm

✔ 最佳答案

1. A is the correct answer.

the molar mass of MgCO3 is 84.3g which is smaller than

that of CaCO3. that means the number of moles of MaCO3

is present. so more CO2 will be released.

2. the first statement is wrong because molten sulphur

does not contain any mobile ion

the sulphur molecules are mobile in molten sulphur because it is

liquid form.

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