tank you

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can someone please explain these answers for me?? :confused:

on #34 on page 134 of lecture 2 30-min, the answer is D, but i put B because it says the rxn is acid-catalyzed, so wouldnt the pH remain the same?

on #128 on page 158 of lecture 6 30-min, the answer is C. but i thought it would be B because the methyl orange changes color but the methyl red does not. the explanation in the back doesnt make any sense.

on #118 on page 156 of lecture 6 30-min, the answer is B, but i put A. what does it mean when it says Ca(OH)2 and Total after the Ksp??

on #141 on page 162 of lecture 7 30-min, the answer is B. but wouldnt it be 6 moles of Fe2+ for every mole of dichromate? the answer says its the other way around, but if u look at the rxn equation, you would think otherwise.
 

stoleyerscrubz

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you are better off going to the EK website and posting in the forums there.
 

nishi

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on #118 on page 156 of lecture 6 30-min, the answer is B, but i put A. what does it mean when it says Ca(OH)2 and Total after the Ksp??

i can answer this one b/c i just got it wrong. NaOH dissocates into Na+ and OH-. OH- is a spectator ion so it will also influence the Ksp. therefore the answer must reflect the [OH-]. if you reread the passage, it says that choice A includes the [OH-] due to Ca2OH only.
 
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you are better off going to the EK website and posting in the forums there.
I never find those forums particularly helpful.


I'm confused about #118 as well. If we used total [OH-] to calculate Ksp, then adding NaOH to the rxn would *increase* the value of Ksp, wouldn't it? And that doesn't make sense.

The common ion effect decreases the solubility of Ca(OH)2. The new Ksp can be calculated using: Ksp = 4X^3, where x is the new solubility (in M) of Ca(OH)2. This *only* takes into account the [OH-] in solution that arose from Ca(OH)2.


Is my reasoning correct? I think the answer should be A.