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### Topic: Chemical reactions/acid base reactions help on questions i got wrong, please  (Read 3854 times)

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#### sam12103

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##### Chemical reactions/acid base reactions help on questions i got wrong, please
« on: October 13, 2009, 02:12:51 AM »
1. If an aqueous solution ____ is added to a mixture of Ba^2+ and Fe^3+, the barium ion will precipitate, but the iron ion will remain in solution

a.NaOH
b.Na2SO4
c.K3PO4
d.KCl
e.Pb(NO3)2

but how and why did they get that answer, I don't understand. Can you please explain to me how they got the answer.

2. Aspirin (C9H8O4) is produced by the reaction of salicylic acid (M=138.1 g/mol) and acetic anhydride (M=102.1 g/mol)

C7H6O3 (s) + C4H6O3 (l)  ->  C9H8O4 (s) + C2H4O2 (l)

If you mix 2.00 g grams if each reactant, what mass of aspirin (M=180.2 g/mol) can theoretically be obtained?

a. 2.00 g
b. 2.61 g
c. 2.71 g
d. 3.53 g
e. 4.00 g

the answer is 2.61 g, can you please explain how to get this answer, what steps to take etc. I am very confused on how to solve this problem too.

#### Borek

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##### Re: Chemical reactions/acid base reactions help on questions i got wrong, please
« Reply #1 on: October 13, 2009, 03:26:09 AM »

2. Basic stoichiometry & limiting reagent:
http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations
http://www.chembuddy.com/?left=balancing-stoichiometry&right=limiting-reagents
(basic assuming you know how to convert between masses and moles).
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### djiang87

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##### Re: Chemical reactions/acid base reactions help on questions i got wrong, please
« Reply #2 on: October 14, 2009, 06:23:59 PM »
Im pretty sure the first one has something to do with solubility rules.

For the second question, first work out the moles of the limiting reagent (i think thats the term i should be using). Then use the formula n=mass / molar mass. Using the value u get for n, sub it into the same formula again except this time using the molar mass of aspirin. This should give you a value of 2.61