Help needed with chem question

[pm123]

Hi,

I was wondering if someone could assist me with this question I have stumbled across.

"0.148g of a metal carbonate exactly reacts with 20.0mL of a 0.100 mol L-1 hydrochloric acid. The formula of the metal carbonate is most likely to be:
A. Li2CO3
B. Na2CO3
Cc. MgCO3
D. SrCO3

I keep on getting A, as through doing stoich, I am getting a molar mass of 74, as I am assuming same moles of HCL (0.002) react with same moles of the unknown.

Looking forward to a reply. Thank You!

[sweetcheeks]

The reaction between an acid and a metal carbonate has a ratio of 2:1 H+ to CO32-. If I am reading correct, you are simply not using the correct stoichiometry.

XCO3(s) + 2H+(aq) --> X2+(aq) + CO2(g) + H2O(l)

[pm123]

That makes a lot more sense.
Thank you!

[keltingmeith]

The reaction between an acid and a metal carbonate has a ratio of 2:1 H+ to CO32-. If I am reading correct, you are simply not using the correct stoichiometry.

XCO3(s) + 2H+(aq) --> X2+(aq) + CO2(g) + H2O(l)

Erm, this ratio only holds for C and D... A and B has metals with oxidation state 1.

[InfinityWen]

I don't think that it is 0.1mol rather than 0.1M(mol/L) in the question .On the one hand ,if HCl is 0.1mol,the condition of 20mL is useless and should not appear.In the other hand,If it is 0.1mol ,none of the option is correct.I had calculated the molar mass of ABCD,the following are 74,106,108,234 g/mol (M)and in A and B ,the ratio of the coefficients in the chemical   equation is 1:2 which is equal to  the ratio of the  amount of substance(n).In this circumstance,the n of HCl is 0.1mol so that the n for XCO3 should be 0.05mol ,use m=M•n and find the mass for option A and B are 3.9g and 5.3g and far away from 0.143g.Then I did C and D using the same method and found the mass are 10.8g and 23.4g .So none of the option is correct.However, If it is 0.1M ,the n for HCl is 0.1M•0.02L=0.002mol ,0.002mol times 74g/mol is 0.148g so the answer is A .

[pm123]

I don't think that it is 0.1mol rather than 0.1M(mol/L) in the question .On the one hand ,if HCl is 0.1mol,the condition of 20mL is useless and should not appear.In the other hand,If it is 0.1mol ,none of the option is correct.I had calculated the molar mass of ABCD,the following are 74,106,108,234 g/mol (M)and in A and B ,the ratio of the coefficients in the chemical   equation is 1:2 which is equal to  the ratio of the  amount of substance(n).In this circumstance,the n of HCl is 0.1mol so that the n for XCO3 should be 0.05mol ,use m=M•n and find the mass for option A and B are 3.9g and 5.3g and far away from 0.143g.Then I did C and D using the same method and found the mass are 10.8g and 23.4g .So none of the option is correct.However, If it is 0.1M ,the n for HCl is 0.1M•0.02L=0.002mol ,0.002mol times 74g/mol is 0.148g so the answer is A .

According to the answers, I was wrong because I forgot about the proper ratio.
It is 1mol/L (M) only, and not 1 mol as stated above.
Sweetcheeks also pointed out that in this equation there is a 2:1 ratio
XCO3(s) + 2HCl(aq) --> XCl2(aq) + CO2(g) + H2O (l)
Firstly- mols reacted for HCl would be 0.02 * 0.1 = 0.002
Thus, A cannot be the right answer as the moles for XCO3 would be 0.5 * 0.002 = 0.001 (According to 2:1 ratio)
If you divide mass of 0.148g with 0.001 mols, you get molar mass of  148.
148 - mrco3(60) = 88, which is molar mass for Sr element. Thus D

Erm, this ratio only holds for C and D... A and B has metals with oxidation state 1.

It holds for all, as the 2 in front of the HCl is required to balance out with H2O, regardless of the oxidation numbers.

Mod Edit: merged post. (keltingmeith)

[keltingmeith]

It holds for all, as the 2 in front of the HCl is required to balance out with H2O, regardless of the oxidation numbers.

I mean, the equation doesn't hold for all. But, it doesn't matter in this case, I focused on the wrong point, my bad.