Official SAT Chemistry Practice Question

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  • #1
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The answer provided to this question is disturbing me:

The set of lettered choices below refers to multiple questions. Select the one lettered choice that best fits each statement or answers each question. A choice may be used once, more than once, or not at all in each set.

Is weakly acidic

(A) 0.1 M H Cl
(B) 0.1 M Na Cl
(C) 0.1 M H C_2 H_3 O_2
(D) 0.1 M C H_3 O H
(E) 0.1 M K O H

Methanol is a weaker acid than acetic acid. Choice (D) fits in the weakly acidic category. The answer provided is (C).
Who is correct?
 

Answers and Replies

  • #2
Borek
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Select the one lettered choice that best fits each statement
Acetic acid fits the category much better than methanol does. C is the correct answer. Your thinking would be OK if you were to select all choices that fit the category.
 
  • #3
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Actually I have studied throught out the year that methanol is a very weak acid, even weaker than water. So that made me select it. I still find it ridiculuous to select acetic acid when methanol is there in the choices.
 
  • #4
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Actually I have studied throught out the year that methanol is a very weak acid, even weaker than water. So that made me select it. I still find it ridiculuous to select acetic acid when methanol is there in the choices.
You mean acidity is very weak, but is it really a acid? Just like ammonia has higher pH than any weak acid, but you can not say it is an acid.
 
  • #5
Borek
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Just like ammonia has higher pH than any weak acid, but you can not say it is an acid.
Care to elaborate? Higher pH of solution means something is basic.
 
  • #6
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Care to elaborate? Higher pH of solution means something is basic.
I think he was trying to say that just because something has a higher pH than a really weak acid, doesn't make it an acid.

So you couldn't say something pH 8 was a weaker acid than something pH 6.

Well, that's how I read it anyway.

Would I be right in saying 7 is neutral and that is the decider if it's acidic or basic?
 
  • #7
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Would I be right in saying 7 is neutral and that is the decider if it's acidic or basic?
Yeah, pH7 is defined as neutral which is about the pH of distilled water at room temperature IIRC.

http://en.wikipedia.org/wiki/PH
 
  • #8
Borek
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OK, I think I see what confused me in the ZealScience's post.

To clarify/add to what you posted:

pH 7 solution is not necessarily neutral, it depends on the temperature. Solution is neutral if [H+] = [OH-], it happens that at 25 °C that means pH = 7.00, but for temperatures between 0°C and 100°C neutral pH varies from 7.47 to 6.14. See water ion product page.

pH is a property of a solution and is a function of both acid concentration and acid strength, so comparing strength of acids just by comparing solutions pH can be misleading - you have to be sure both solutions have the same acid concentrations. In such a case (and additionally assuming you compare monoprotic acids) solution with lower pH will mean stronger acid, but if solution is neutral substance is not acidic at all, and if pH is above 7, substance is basic, not acidic. I think this is more or less what ZealScience posted?
 

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