Chem 高手請答~~

With reference to the ionic equation below:
CO32- (s) + 2H+ (aq) → CO2 (g) + H2O (l)
1 mole of carbonate can give 1 mole of carbon dioxide gas.
So in 10 g of the impure calcium carbonate sample, there should be 2.5/24 = 0.104 moles of carbonate ions in total.
Compared to 10 g of pure calcium carbonate which contains 0.1 moles of carbonate ions, we can say that:
no. of moles of carbonate ions in 10 g of impure calcium carbonate > 10 g of pure calcium carbonate
So, in other words:
Average molar mass of impure calcium carbonate < Molar mass of pure calcium carbonate
Looking all choices, the only possible substance that will lower the average molar mass of calcium carbonate is magnesium carbonate since molar mass of calcium carbonate is 100 g/mol.

首先 10g pure架calcium carbonate molar mass100.1g 即係有10g/100.1=2.4/24
a similar experiment using 10g of impure calcium carbonate 2.5dm^3 CO2出左黎
設 mass of impurity is a metallic carbonate is X
mass of calcium carbonate is y
昂係要2.5/24= 10-x/ x架molar mass + y/100.1
之後可以計吧...
其實不用計的.. 因為出黎架CO2係2.5dm^3 比 pure calcium carbonate 多
而且仲有10g 所以個 impurity 架molar mass 一定要細過100.1g 所1 ans一定係A 其實3個molar mass 太大