precipitates?

[Joker88]

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16.What is the identity of the precipitate that forms in the experiment?

A. BaSO4
A is the best answer. This question tests your memorization skills, but can also be solved quickly using charges. We first must determine the charges of the individual species making up our two aqueous reactants, barium hydroxide and sulfuric acid. We know that the charge on Ba must be 2+, since it is combined with two hydroxide ions (which always have a 1- charge) to form barium hydroxide. The charge on SO4 is 2-, since two hydrogen ions (which always have a 1+ charge) combine with the sulfate ion to form sulfuric acid. Therefore, barium and sulfate combine in a 1:1 ratio. The best answer is A.
B. Ba2SO4
C. BaHSO4
D. Ba(HSO4)

Are precipates usually identified by their charges? If the charges equally cancel out in a solubility problem would they be considered to fall out of the solution? Just some background...the solution contained H2SO4 and BA(OH)2 was added until BaSO4 was precipated out.

 

[whiteshadodw]

16.What is the identity of the precipitate that forms in the experiment?

A. BaSO4
A is the best answer. This question tests your memorization skills, but can also be solved quickly using charges. We first must determine the charges of the individual species making up our two aqueous reactants, barium hydroxide and sulfuric acid. We know that the charge on Ba must be 2+, since it is combined with two hydroxide ions (which always have a 1- charge) to form barium hydroxide. The charge on SO4 is 2-, since two hydrogen ions (which always have a 1+ charge) combine with the sulfate ion to form sulfuric acid. Therefore, barium and sulfate combine in a 1:1 ratio. The best answer is A.
B. Ba2SO4
C. BaHSO4
D. Ba(HSO4)

Are precipates usually identified by their charges? If the charges equally cancel out in a solubility problem would they be considered to fall out of the solution? Just some background...the solution contained H2SO4 and BA(OH)2 was added until BaSO4 was precipated out.

look at barium in the periodic table, it doesn't form a +1 cation, it forms a +2 cation. accordingly, the SO4 is a -2 charged polyatomic ion, and therefore BaSO4 is the right answer (Ba +2, Sulfate -2 = 0) neutral charged salt. pretty much all salts and precipitates will have a neutral charge on the overall solid. the other thing is, none of the other answers work, calculate the individual oxidation states and calculate the total charge of the molecule, none of them have a neutral charge. same thing happens with species in a galvanic cell. the aamc topics list explicitly says to be familiar with common polyatomic ions. i would know the following (i'll let you look up the formula):

phosphate
sulfate
nitrate
carbonic acid (and its conjugate bases)
ammonium/ammonia
http://www.chemistry.wustl.edu/~edudev/LabTutorials/PeriodicProperties/Ions/ions.html

i linked you to a list of more ions you should probably know or be familiar with.


solid anode gets oxidized, loses electrons, becomes charged so it dissolves into solution. charged soluble cathode becomes reduced, so it gains electrons becoming neutral and precipitates out of solution.