Aamc 8, ps#40

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SN2reaction

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Hey guys, I had a question about number 40 on the PS section of AAMC 8.

The passage talks about two solutions, NiSO4-6H20, and Na2CO3-10H20 being mixed together and so on. But there is a question that basically asks what type of gas evolves when HCl is added to Na2CO3. How the hell do you predict that? The answer was CO2, which was the most logical answer choice, but is there a methodical way of predicting the product?

Thanks in advance!
 
k, so u get Na2CO3 + HCl --> H2CO3 + NaCl right??

OH, and then H2CO3 --> H2O + CO2 because its in an aqueous solution??
 
This is a good type of question to make an educated guess on. What are the other answer choices? I bet CO2 is the only one that even remotely makes sense, given the species present in the solution.
 
You can eliminate sulfur dioxide and sulfur trioxide right away cuz there's no sulfur in the reactants. To distinguish btwn CO and CO2 you have recognize that it's a double replacement rxn (like the equation you already wrote) and know from memory the carbonic acid is unstable in water and will tend to form H2O and CO2.
 
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