*SPOILER* AAMC Chemistry Q Pack #12

[Dr. To Be]

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The question asks for the max # of moles of NiCO3 in a precipitation reaction. There is 6.57 g pf NiSO4*6 H2O (MM=262.84) and 7.15g Na2CO3*10 H2O(MM=286.16) dissolved in water. The answer is 0.025 mol which I got. I just want to clarify my reasoning.

I calculated only the # of moles for Ni solution{.025 mol( which is the same for sodium carbonate)] but the AAMC explanation calculated MM for both. Why is that? Is it because we have to take into account that Nickel sulfate is soluble and sodium carbonate is slightly soluble


Thanks!

 

[aldol16]

Well, you would always want to figure out which one is the limiting reagent. Here, there's a 1:1 ratio of NiSO4 and Na2CO3 and the stoichiometry is 1:1 so you don't have that problem but you should always check. If they had given you a different value for grams of Na2CO3, then the latter could be limiting and the answer would no longer be 0.025 mol.

 

[Dr. To Be]

Well, you would always want to figure out which one is the limiting reagent. Here, there's a 1:1 ratio of NiSO4 and Na2CO3 and the stoichiometry is 1:1 so you don't have that problem but you should always check. If they had given you a different value for grams of Na2CO3, then the latter could be limiting and the answer would no longer be 0.025 mol.

Wow! I really over thought this question. Thank you for your response!