AAMC Sample Test Question

[CJhooper123]

Hi everyone.... quick question regarding AAMC sample test.

Section: Chemical/Physical Foundations
Passage: 3, Question #11

I think this is relatively easy... but I am clearly missing something.

The final paragraph of the passage states:
"A researcher attempted to identify an unknown AOm(OH)n compound. The compound completely dissolved in water and weakly conducted electricity. The hydrogen ion concentration of the unknown aqueous solution was 1x10^-5M.

Q) The unknown compound was probably a:

a) weak base
b) strong acid
c) weak acid
d) strong acid

Answer was "c"

I was under the assumption that the definition of a strong acid is one that completely dissociates in water. I was also under the assumption that a strong acid is considered to have a pKa<1 or Ka>1. What is the justification for this being a weak acid. Also... assuming that dissolving and ionization or two separate entities.

I think this is relatively easy... but I am clearly missing something lol.

Thanks.

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[laczlacylaci]

Hi everyone.... quick question regarding AAMC sample test.

Section: Chemical/Physical Foundations
Passage: 3, Question #11

I think this is relatively easy... but I am clearly missing something.

The final paragraph of the passage states:
"A researcher attempted to identify an unknown AOm(OH)n compound. The compound completely dissolved in water and weakly conducted electricity. The hydrogen ion concentration of the unknown aqueous solution was 1x10^-5M.

Q) The unknown compound was probably a:

a) weak base
b) strong acid
c) weak acid
d) strong acid

Answer was "c"

I was under the assumption that the definition of a strong acid is one that completely dissociates in water. I was also under the assumption that a strong acid is considered to have a pKa<1 or Ka>1. What is the justification for this being a weak acid. Also... assuming that dissolving and ionization or two separate entities.

I think this is relatively easy... but I am clearly missing something lol.

Thanks.

You are confusing dissolving with dissociating. A weak acid can dissolve in water, but cannot completely dissociate in water.
From the aqueous solution (1E-5), you know the pH=5 (I believe this was the previous question) you can deduce this is an acid. If you didn't know that that number represents a weak acid, you go to the weakly conducted electricity, and that tells you that it is a weak acid.

A strong acid will completely dissolve and completely dissociate while acting as a strong electricity conductor.
A weak acid will completely dissolve and partially dissociate while acting as a weakly electric conductor.
vs. for strong/weak base.

Let me know if this helps.

 

[CJhooper123]

You are confusing dissolving with dissociating. A weak acid can dissolve in water, but cannot completely dissociate in water.
From the aqueous solution (1E-5), you know the pH=5 (I believe this was the previous question) you can deduce this is an acid. If you didn't know that that number represents a weak acid, you go to the weakly conducted electricity, and that tells you that it is a weak acid.

A strong acid will completely dissolve and completely dissociate while acting as a strong electricity conductor.
A weak acid will completely dissolve and partially dissociate while acting as a weakly electric conductor.
vs. for strong/weak base.

Let me know if this helps.

Much appreciation. Cheers.