russbost
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| posted on 16/4/09 at 01:19 PM |
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"A" level chemistry question
Don't know if anyone can help, but surely one of you must have done this fairly recently, it's on the OCR/Salters syllabus
My daughter for her coursework has been titrating sodium hydroxide into various different water samples until the pH reaches 8.3 & similarly with
sulphuric acid until pH 8.3 is reached (coming down from an alkaline sample) & then pH 4.5 is reached.
She's been given the question why are the values of 8.3 & 4.5 used?
I've been thro' all her course info with her, we've searched the internet & asked her brother who did chemistry "A"
level only last year & got an A grade (different syllabus) & can't come up with any answers, to us they appear arbitrary values???
Any ideas on answers or where we might find the info??
Come on guys, don't let the infallability of Locostbuilders down!!!
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
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stevebubs
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| posted on 16/4/09 at 01:28 PM |
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Probably down to the indicator they use - perhaps this are the points where it changes colour?
Going to google now...
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damajin
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| posted on 16/4/09 at 01:30 PM |
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This is the best I can come up with, but I'll warn you I gave up Chemistry as soon as I could and stuck with physics!
- PH neutral is 5.5
- The natural PH of the human body is 7.3
- This would make the values in your question about 1.0 more acidic / alkaline than these so might constitute some sort of safe limits to be
handled?
I'm sure someone will give you the real answer tho! Good luck to you both.
D
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stevebubs
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| posted on 16/4/09 at 01:31 PM |
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phenolphthalein changes at 8.3 and methyl orange @ 4.5 ....
clickety click
[Edited on 16/4/09 by stevebubs]
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damajin
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| posted on 16/4/09 at 01:32 PM |
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See, told you there'd be a propper answer
D
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Dangle_kt
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| posted on 16/4/09 at 01:33 PM |
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quote:
Originally posted by stevebubs
phenolphthalein changes at 8.3 and methyl orange @ 4.5 ....
clickety click
[Edited on 16/4/09 by stevebubs]
just beaten to it.....
OH, OK I WASN'T! I'm just trying to look clever. 
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cd.thomson
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| posted on 16/4/09 at 01:35 PM |
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second stevebubs, i didnt know the exact change pHs of phenolphthalein and methyl orange but know they are used in A-level chemistry for these exact
titrations (or at least they were when i did it!)
another suggestion would be that theyre using EDTA buffer (pH 8.3) also used in A-level chem and bio but not for titrations.
Craig
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Mr Whippy
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| posted on 16/4/09 at 01:36 PM |
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something to do with gobbldygook stuff -
linky if you can follow it
what the feck is acid doing away? dissolving things...is it just breaking bonds between molecules?? How does it do that??????
[Edited on 16/4/09 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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madmandegge
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| posted on 16/4/09 at 01:36 PM |
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Having received an E grade I was surprised I knew this 
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smart51
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| posted on 16/4/09 at 01:41 PM |
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quote:
Originally posted by damajin
- PH neutral is 5.5
I believe it is 7.
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Mr Whippy
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| posted on 16/4/09 at 01:42 PM |
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quote:
Originally posted by madmandegge
Having received an E grade I was surprised I knew this
I was put off chemistry because the teacher set her hair on fire, didn't seem a very safe class...so I did craft & design doing wood turning
and welding instead
Fame is when your old car is plastered all over the internet
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mr_pr
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| posted on 16/4/09 at 01:43 PM |
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quote:
Originally posted by smart51
quote:
Originally posted by damajin
- PH neutral is 5.5
I believe it is 7.
Yeah your right, 5.5 is the skins natural ph.
.JPG)
My Build Progress
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damajin
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| posted on 16/4/09 at 01:44 PM |
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I warned you, I gave up Chem when I was about 13 which was quite a while ago.
D
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JoelP
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| posted on 16/4/09 at 02:39 PM |
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depressing what you can forget in 15 years 
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hobzy
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| posted on 16/4/09 at 02:40 PM |
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pH is a measure of the concentration of H+ ions in solution; its a logorithmic scale. pH 7 has 1x10 to the power of -7 hydrogen Ions per litre.
Alkalis have less Hydrogen ions and more hydroxide ions. Put the 2 together and you get water, hence the "neutral" state at pH7.
Been teaching it all flippin' year for GCSE coursework - HTH! 
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tomprescott
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| posted on 16/4/09 at 04:06 PM |
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God A level chemistry, I remember doing that and wishing I hadn't, much harder than maths, the only things I remember was how to name
hydrocarbons, free radicals and molar masses!
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stevebubs
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| posted on 16/4/09 at 04:22 PM |
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quote:
Originally posted by tomprescott
God A level chemistry, I remember doing that and wishing I hadn't, much harder than maths, the only things I remember was how to name
hydrocarbons, free radicals and molar masses!
Remember the indicators well - mainly because I messed up the titration in my practical (still got a good grade overall, though)
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trogdor
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| posted on 16/4/09 at 04:22 PM |
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yes maths was easier in that you could work out the answers
whereas with chemistry you had to know so much stuff.
Have forgotten alot of it now tho,
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russbost
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| posted on 16/4/09 at 05:23 PM |
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Well done guys! Knew you wouldn't fail!!
Is there a question that someone on here can't answer???
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
|
NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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stevebubs
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| posted on 16/4/09 at 05:42 PM |
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quote:
Originally posted by russbost
Is there a question that someone on here can't answer???
That may be the stumbler...
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Confused but excited.
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| posted on 16/4/09 at 05:46 PM |
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quote:
Originally posted by JoelP
depressing what you can forget in 15 years
Wait until you are my age.........It's amazing what you can forget in 15 minutes!
Tell them about the bent treacle edges!
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JoelP
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| posted on 16/4/09 at 07:01 PM |
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Liam
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| posted on 16/4/09 at 07:01 PM |
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quote:
Originally posted by russbost
...My daughter for her coursework has been titrating sodium hydroxide...
You said titrating!
Huh huh
Huh huh
Huh huh huh
[Edited on 16/4/09 by Liam]
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Richard Quinn
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| posted on 16/4/09 at 07:06 PM |
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quote:
Originally posted by stevebubs
quote:
Originally posted by tomprescott
God A level chemistry, I remember doing that and wishing I hadn't, much harder than maths, the only things I remember was how to name
hydrocarbons, free radicals and molar masses!
Remember the indicators well - mainly because I messed up the titration in my practical (still got a good grade overall, though)
Apparently I
messed mine up too (but didn't get a good grade either!). I realised that filling a burette that stopped above head level probably wasn't
the safest thing so used my initiative (commendable!) but instead of lowering the burette and stand onto the stool so that you were filling it below
your head height I elected to stand on the stool instead (apparently not so commendable!)
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