Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: williec on April 08, 2008, 11:25:34 AM
-
the aq NaOH has an approximate concentration of 2 moldm-3. i think it is to use a pH meter but it said it should involve chemical reactions. What other methords are there to find out the concentration?
-
Your application isn't perfectly clear, but titration seems necessicary for any accuracy. What else is in solution, how accurately do you need the value, what other instruments do you have, that sort of info is needed for a better answer.
-
there is only NaOH in the solution and you have to find the concentration as accuratly as possible, but it cant be a titration and the this method i am looking for have to involve chemical reaction. you are allowed to use any instruments.
-
Could you measure a density of solution?
-
So the game is, unique ways to determine concentration? OK, I'll play. Can you evaporate a known volume, and mass? Or evaporate, roast to NaO, and then mass, and calculate backwards?
Using a pH meter, on this solution, won't give you a useful answer, do you know why? *Hint* Can you figure out the pH of a 2 M, 2.5 M, 2.25 M, and 1.13 M, or 1.0, or 0.98 M NaOH solution. How can you fix it so you can get useful info from a pH meter?
Notice, you still haven't answered my question, how accurately do you need the answer. What is the likely value -- 2, 2.25, 2.5, or is it far away like 3 or 1.1. And do you need the answer as -- 2, 2.2, 2.20, or 2.213 M. This is info you need to know first.
-
the question says find the concentartion as accuratly as possible but it is probably 2.d.p
-
As I understand your original question, you want to use just a pH meter, to determine the concentrations of 2.?? M NaOH, without titrating. Can you see anything wrong with your plan? Did you try it, what pH did you get? Have you looked up what pH you're likely to get?
-
no i havent try it yet. But if I use a pH meter to find the concentration can it involve some kind of chemical reactions?
-
As I study your posts, I still find it hard to understand what the question really is. The title says you don't want a titration, you've said you want to use a pH meter, and a reaction. You can use a pH meter, to determine the concentration of NaOH, by a chemical reaction with an acid, watching for the endpoint with a pH meter. But that is called -- a titration.
-
are ther any other ways without using a pH meter?
-
Gravimetric analysis.
-
Gravimetric analysis.
Yep. Like AWK: said, weigh the liquid, or like I said, dry it and weigh it, or dry it, roast it, and weigh it.
-
Dose NaOH reacts with Al and gives Hydrogen gas? if yes what are the conditions?
-
Start with this experiment here: http://www2.uni-siegen.de/~pci/versuche/english/v44-10.html
And work with it to see what's appropriate for your application.
-
i dont really get this. so Al reacts with water to produce hydrogen??? and how do i work out the concentration of the NaOH from the whose equations if i have got the volume of hydrogen of gas produced? Or can i react it with zinc
thank you v much
-
Dear Williec;
If you feel confident that all Na+ is only from NaOH, you can use: "Uranyl Zinc Acetate (http://en.wikipedia.org/wiki/Uranyl_zinc_acetate)”.
Good Luck!
ARGOS++
-
Hi,
I'm doing this paper too; basically ... just to clear up as some posts seem to be a little irrelevant to what we are trying to figure out! ... we've been given the NaOH solution with an "approximate concentration of 2mol dm-3". We have to find the conc "as accurately as possible" BOTH methods have to include chemical reactions (ie so cant use a pH meter) and only one is allowed to use a titration.
To me this is as close to my thinking as I've seen:
Gravimetric analysis.
and
If you feel confident that all Na+ is only from NaOH, you can use: "Uranyl Zinc Acetate (http://en.wikipedia.org/wiki/Uranyl_zinc_acetate)”.
but the thing is the whole uranyl zinc acetate thing is a bit far fetched I think ... they want us to use substances that we use in a college lab.
Does anyone know of anything else that's insoluble in NaOH because I don't really know how you figure that out! (it does have to be insoluble doesn't it in order to form a precipitate and then weigh it?)
Also ... once you have the precipitate ... what exactly would it be and how do you calculate the conc of NaOH from it?
Am fine with calculating it from a titration but this bit loses me!
Thanks muchly for any help given!
x
ps. sorry for the loooong post!
-
If you feel confident that all Na+ is only from NaOH, you can use: "Uranyl Zinc Acetate (http://en.wikipedia.org/wiki/Uranyl_zinc_acetate)”.
but the thing is the whole uranyl zinc acetate thing is a bit far fetched I think ... they want us to use substances that we use in a college lab.
So perhaps you should try to assume that all OH- is only from NaOH and look for hydroxide that can be precipitated and filtered out?
-
So perhaps you should try to assume that all OH- is only from NaOH and look for hydroxide that can be precipitated and filtered out?
okay, so would
NaOH + FeCl3 work forming a precipitate of Fe(OH)3 ... or am I making that up???
-
Nice try :)
Now try to use Google for a general idea about how to do it...
http://www.google.com/search?q=iron+gravimetric+determination
-
Ok i have this paper too and yes alot of the answers so far have been helpful for a degree standard however, the best solution for a second experiment supposably is an enthalpy change. You use hydrochloric acid and measure ethalpy of neutralisation or something, can anyone tell me how you can use this to work out concentrations of NaOH. I know you can do an enthalpy experiment neutralise the NaOH with a certain amount of HCL, but how can u do the calculations?. Any detailed answer about what you would do be grateful ty.
-
enthlapy change? do they want you to do it calometrically maybe and use molar bond energies of formation of NaCl and water to calculate how much naoh...but hcl also releases heat when placed in water so you would have to look up the amount of heat released and precisesly measure out the amount of water and then subtract the amount of heat that would be evolved ...but you would have errors due to the fact that the naoh changed the volume of the water...
after that you'd have to compare the heat of formation of naoh and nacl/water to compare how much energy went where and by calculating the total diffrence in temprature and coverting it to joules you should be able to calculate the amount of naoh present...sorry if this wasnt clear im having a hard time explaining what was going through my head
and
sorry this was just a stab in the dark..