EXAMPLE: Solid calcium bromide is slowly added to 75.0 mL of a potassium fluorid
ID: 1009743 • Letter: E
Question
EXAMPLE:
Solid calcium bromide is slowly added to 75.0 mL of a potassium fluoride solution until the concentration of calcium ion is 0.0305 M. The maximum amount of fluoride remaining in solution is M Incorrect When calcium bromide is added to potassium fluoride, calcium fluoride, CaF can precipitate (all other salts are soluble) At equilibrium: CaF2 (s) Ca (aq) 2F (aq) 2+ 0.0305 M M Some Solve for [F] at equilibrium from the Ksp expression: Kgp 2+. [F 12 11 from the table (1/2) 11 (1/2) 3.6x10 M Faq) (0.0305)Explanation / Answer
The regiochemistry of an electrophilic aromatic substitution (EAS) reaction, that is, where on the ring the new group is attached, is determined by the other functional groups already attached to the ring. These may be ortho-para directing (electron donating), or meta directing (electron withdrawing). Ortho substituents Meta substituents Para substituents . In addition to their directing effect, electron donating groups also activate the aromatic ring to electrophilic substitution. Resonance structures placing a negative charge at the ortho and para positions can be drawn and are shown below. The positively charged electrophiles more likely to react at a center that is more negatively charged and substitution occurs at the ortho and para positions. Conversely, electron withdrawing groups deactivate the ring to electrophilic substitution. In this case, the resonance structures drawn below show a positive charge at the ortho and para positions of the aromatic ring. These are now unattractive sites for the positively charged electrophile to react. The uncharged meta positions are more reactive.
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