Warning: Illegal string offset 'html' in /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php on line 909

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 114

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 127

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 136

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 137

Warning: Cannot modify header information - headers already sent by (output started at /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php:909) in /home/hsn/public_html/forum/admin/sources/classes/output/formats/html/htmlOutput.php on line 141
Acids and Bases question - HSN forum - Page 2

Jump to content


Acids and Bases question


29 replies to this topic

#21 werlop

    Fully Fledged Genius

  • Moderators
  • PipPipPipPipPipPipPip
  • 1,497 posts
  • Location:Cambridge (Term Time), Bearsden (Glasgow) Non Term Time
  • Gender:Male

Posted 12 April 2005 - 09:20 PM

A strong acid is an acid which is 100% dissociated into its ions at equilibrium.

A weak acid is an acid which is not 100% dissociated into its ions at equilibrium.

Don't get confused with concentration. Since pH is dependant on concentration the pH does not really give you much of a clue about the relative strenth of the acid.

pH = -log base1.gif base0.gif [H + ] in mol l -1

Only Ka gives the extent of dissociation:

If you Imagine the hypothetical acid HA this is the formula for its dissociation:

HA ---> H + + A -

Ka = [H + ] x [ A - ] / [HA]

This is advanced higher so don't worry about it, just be aware that pH is not a reliable way of telling the strength of an acid unless both acids have the same concentration.
Click here to visit the Bearsden Academy Website
user posted image


If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!

#22 bred

    Brendan

  • Moderators
  • PipPipPipPipPipPipPipPip
  • 4,215 posts
  • Location:Edinburgh
  • Interests:I have just graduated with a 2:1 in Geography [MA (Hons)] from The University of Edinburgh. I like sports: swimming, cycling, snowboarding, running, football, mountain biking and also travelling and photography.
  • Gender:Male

Posted 12 April 2005 - 09:24 PM

Thanks for clarifying that Werlop. smile.gif
Please vote for me! (Brendan Howard, 5th from bottom, only 1 vote required): http://answers.polld...m/poll/2330393/

#23 werlop

    Fully Fledged Genius

  • Moderators
  • PipPipPipPipPipPipPip
  • 1,497 posts
  • Location:Cambridge (Term Time), Bearsden (Glasgow) Non Term Time
  • Gender:Male

Posted 12 April 2005 - 10:00 PM

no probs!
Click here to visit the Bearsden Academy Website
user posted image


If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!

#24 gary

    Child Prodigy

  • Members
  • PipPipPipPipPipPip
  • 546 posts

Posted 27 April 2005 - 01:47 PM

Well I got my marks back for this question and apparently phosphoric acid is NOT a strong acid.

I got 0 marks for the answer which it was thought to be.

#25 werlop

    Fully Fledged Genius

  • Moderators
  • PipPipPipPipPipPipPip
  • 1,497 posts
  • Location:Cambridge (Term Time), Bearsden (Glasgow) Non Term Time
  • Gender:Male

Posted 27 April 2005 - 03:05 PM

Pure anhydrous phosphoric acid is a white solid that melts at 42.35°C to form a viscous liquid. In solution, phosphoric acid behaves as a triprotic acid, having three ionizable hydrogen atoms. The hydrogen ions are lost sequentially. It is a stronger acid than acetic acid but weaker than sulfuric acid and hydrochloric acid.
Click here to visit the Bearsden Academy Website
user posted image


If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!

#26 gary

    Child Prodigy

  • Members
  • PipPipPipPipPipPip
  • 546 posts

Posted 27 April 2005 - 07:22 PM

So techincally it is a weak acid.

#27 bred

    Brendan

  • Moderators
  • PipPipPipPipPipPipPipPip
  • 4,215 posts
  • Location:Edinburgh
  • Interests:I have just graduated with a 2:1 in Geography [MA (Hons)] from The University of Edinburgh. I like sports: swimming, cycling, snowboarding, running, football, mountain biking and also travelling and photography.
  • Gender:Male

Posted 27 April 2005 - 09:23 PM

Certainly phosphoric acid is much less acidic than triflic acid, but it's apparantly strong enough to be useful in elimination reactions. Phosphoric acid has a pKa of 2.12 (first proton) which makes it stronger than acetic acid (pKa of 4.76), formic acid (pKa of 3.77), and carbonic acid (pKa of 3.6). It's acidity is about the same as o-nitrobenzoic acid (pKa of 2.17). That would put it in the range of "weak" acids - but it's a pretty strong weak acid.
PS - you obviously don't need to know all this stuff for Higher Chemistry, just that sodium hydroxide is a very strong alkali and that phosphoric acid isn't as strong an acid, therefore the balance is tipped towards sodium phosphate solution being alkaline.
Please vote for me! (Brendan Howard, 5th from bottom, only 1 vote required): http://answers.polld...m/poll/2330393/

#28 werlop

    Fully Fledged Genius

  • Moderators
  • PipPipPipPipPipPipPip
  • 1,497 posts
  • Location:Cambridge (Term Time), Bearsden (Glasgow) Non Term Time
  • Gender:Male

Posted 27 April 2005 - 09:41 PM

I would call it a strong weak acid if that makes sense. In my advanced higher investigation it behaved like a strong acid.
Click here to visit the Bearsden Academy Website
user posted image


If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!

#29 Ally

    HSN Legend

  • Moderators
  • PipPipPipPipPipPipPipPip
  • 2,912 posts
  • Interests:Just finished 1st year at uni studying medicine.
  • Gender:Male

Posted 28 April 2005 - 04:26 PM

QUOTE(werlop @ Apr 12 2005, 10:20 PM)
Don't get confused with concentration. Since pH is dependant on concentration the pH does not really give you much of a clue about the relative strenth of the acid.

View Post


Yeah, as werlop said, the PH of a solution isn't enough to show whether an acid is strong or weak. e.g. A solution of an acid which has a pH of 4 might be a very dilute solution of a strong acid or a concentrated solution of a weak acid.

#30 Moral Fabric

    Site Swot

  • Members
  • PipPipPipPip
  • 187 posts
  • Location:Scotland, North Ayrshire, Ardrossan
  • Interests:Well, i love music, I play guitar as a pass time and muck about on drums, I like funk, punk, rock etc etc the list goes on. <br />Hopefully going to Uni this year, Strathclyde Business School, look out for me =P<br />what other interests,... hmm... got lots, but cant remember =D.... later
  • Gender:Male

Posted 14 May 2005 - 10:47 PM

QUOTE(werlop @ Apr 12 2005, 10:13 PM)
QUOTE
Random question: Is caesium hydroxide and hydrofluoric acid the most reactive combination of acid and alkali? I imagine there would be some fireworks.


I think so, HF(aq) is some VERY nasty stuff.

View Post


i would love to see that baby go tongue.gif lol laugh.gif





1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users