DAT Destroyer 2014 Questions!

[urbanthread]

Gen Chem:
1. Net ionic equation for reaction between KOH and HI?
K+ + OH- + H+ + I- -> K+ + I- + H2O
OH- + H+ -> H2O (spectators cancel)
Why don't K+ and I- combine to form KI?

23. What would be the approximate pH of 1 x 10^-12M HCl solution?
Answer: solution is extremely dilute so take into account H+ ions from water
1 x 10^-12 + 1 x 1o^-7 = 1 x 1o^-7
How do you know that the solution is dilute?

Biology:
15. What's double pollination? Is it the same as cross pollination..?

O Chem:
24. Which compound is the most basic?
The answer key says that choices B,C,E have electron withdrawing groups which decrease basicity but B has NH2 on benzene and C has NHCOCH3 on benzene which I thought were both electron donating groups? So shouldn't they increase base strength?

Thanks a lot!!

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[SmileDesignersDDS]

1) it does form KI, HOWEVER, KI in solution exists as K+ and I- (follow solubility rules concerning group 1a being soluble) thus you have both K+ and I- on both sides of the equation and therefore they are spectator ions. Remember when you write out net ionic equations you always separate strong electrolytes, strong acids and bases, and things that are soluble obviously.

 

[biomolecmed]

I just have something to say about question #23. If the concentration is as low as 1*10^-12, it is definitely diluted in some kind of a solvent, usually water.

 

[Lambs]

Gen Chem:
1. Net ionic equation for reaction between KOH and HI?
K+ + OH- + H+ + I- -> K+ + I- + H2O
OH- + H+ -> H2O (spectators cancel)
Why don't K+ and I- combine to form KI?

Ionic bonds are weak and disrupted by polar solvents. Ionic bonds form Ions in water.

23. What would be the approximate pH of 1 x 10^-12M HCl solution?
Answer: solution is extremely dilute so take into account H+ ions from water
1 x 10^-12 + 1 x 1o^-7 = 1 x 1o^-7
How do you know that the solution is dilute?

M = mole per liter. HCl is a strong acid. So 1x10^-12 M HCl is 1x10^-12 moles of H+ and 1x10^-12 moles Cl- in water. Water normally has 10^-7 moles of H per liter so the ph would be just 7.

Biology:
15. What's double pollination? Is it the same as cross pollination..?

Cross pollination is pollination from one plant to another. Double pollination or double fertilization is when one male gamete fertilizes the femal gamete and another male gamete fertilizes the polar body making one diploid and one triploid cell.

O Chem:
24. Which compound is the most basic?
The answer key says that choices B,C,E have electron withdrawing groups which decrease basicity but B has NH2 on benzene and C has NHCOCH3 on benzene which I thought were both electron donating groups? So shouldn't they increase base strength?

Withdrawing groups INCREASE acidity. A strong acid forms a WEAK congregate base. NH2 can stabilize the resonance structure and stable bases are weak bases.