What is [HCl(aq)] in the following scenario?

A 1.12*L volume of carbon dioxide was collected under standard conditions from the reaction between HCl(aq) and EXCESS "calcium carbonate"?

1 Answer
anor277
Mar 26, 2016

We assume conditions of 1 atm, and a temperature of 298K. The normality of HCl is approx. 1*mol*L^-1.

Explanation:

We always start these sorts of problems with a balanced equation:

CaCO_3(s) + 2HCl(aq) rarr CaCl_2(aq) + H_2O(l) + CO_2(g)uarr

From the stoichiometric equation, it is clear that whatever quantity of carbon dioxide gas is collected, this is HALF the molar quantity of acid added.

Now, the molar volume of an ideal gas at 298K is 24.5*L.

So "moles of "CO_2" collected" = (1.12*cancelL)/(24.5*cancel(L)*mol^-1) = 0.0457*mol

To generate this quantity of gas, there MUST have been TWICE this molar quantity of HCl in the 100 mL volume initially added to the carbonate.

So "Concentration of acid" = (0.0457*molxx2)/(100xx10^-3L) = ??mol*L^-1. A more accurate answer would be obtained if we included "SVP", the saturated vapour pressure of water under the given conditions (i.e. a gas collected under water, will always include the "SVP").

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