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July 30, 2014

Homework Help: chem

Posted by polkadot on Friday, April 8, 2011 at 8:46pm.

Can someone please help me by explaining and correcting me?

1) A 0.057M solution of a weak acid has a pH of 4.93. Determine the ionization constant, Ka, of the acid.
a) 2.1 x 10^-4
b) 2.4 x 10^-9
c) 4.1 x 10^-8
d) 2.8 x 10^-7
e) 1.4 x 10^-10
-- To be honest, I skipped this. I know that the Ka = ((H3O^+)(A^-))/(HA), but I didn't know how to find (A^-). Am I approaching this question wrong? Is there a step I missed or can this be solved another way? Perhaps it has something to do with an ICE chart?

2) For the following compound, predict whether the solution is acidic, basic, or neutral and why: NH4Cl.
a) acidic, NH4Cl is the salt of a weak base
b) neutral because there is no hydrolysis
c) acidic, NH4Cl is a strong acid
d) basic, NH4Cl is the salt of a weak acid
e) basic, NH4Cl is a weak base
-- I picked D. I think I may have chosen wrong. I think it dissociates into NH4^+ and Cl^- making an acidic solution... but I'm not so sure

3)
For a reaction where rate = k (A)(B)^2, what factor will NOT change k?
a) raising the temperature
b) increasing concentration of A
c) adding a catalyst
d) none of these
e) lowering the temperature
-- I picked C, although at first I thought it was B...

Thank you for helping, I really appreciate it :)

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