standardized NaOH

[Sassi]

Hi everyone,

I am slightly confused today and i need your help please. I was just asked for standardized 0.100M NaOH solution for a titration prac, in the request she said this 'the 0.100 M NaOH needs to be standardised and you need to use a solution of HCl to do this'. Off course she has now left and I can't ask her what she means. I dont know what she means with using a solution of HCl to do that, if she expects me to so some titration she can get stuffed. I hate titrations and vowed when I completed my last chem sunject at uni that I would never do it again... Please shed some light on this, so confused

Sass

[Sassi]

Just got an email from her and she now asked for this

'it may be a good idea to give me a heap of HCl say 200 mL per girl (and another indicator) so the girls can practise titrating, before doing the aspirin titration.
Make the HCl up to be a concentration so that 21.5 mL of 0.100 NaOH (in the burette), neutralises the 25 mL of HCl in the flask.

(Can this be the HCl that you use to standardise the NaOH - then you can kill two birds with one stone!)'

I dont want to titrate, please help me and tell me I don't, there must be some other way

[sunray18]

this is crazy! sorry - but ...
You NEVER standardise a soltuion like this! The HCL you buy is NOT accurately made UNLESS you purchase expensive ones that come like that.. goodness me - I buy my HCl from Bunnings to save money! And I sure wouldnt use that to standardise a solution.....
You standardise it against a known weight of a solid chemical [eg Oxalic Acid] that is dissolved in an accurate amount of distilled water. You then titrate the Oxalic acid using the NaOH in the burette.. you must do it at least in triplicate!
THEN calculate the concentration.....

[Judy R]

Sassi,
The other method is to make up a standard solution of 0.1M sodium carbonate which has been dried in a drying oven and titrate this against a 0.1M solution of HCl.
I can fax you the calculations for this as it is not 1ml for 1ml.
If you purchase your HCl from Labtek or equivalent supplier they are reliable and your 0. 1M solution will be accurate.Then make a 0.1M solution of sodium hydroxide and titrate one against the other....should be around 23 to 25mls of each.That is accurate enough for any school titration.
For many years I made solutions at PLC for the titration competition and they worked fine.
Don't stress go for the practical option.Given the techniques of the teachers and students you don't need to be that particular.

[lada]

Dear Sassi, if you want enought solution for all the girls, sounds like bucket chemistry to me. Make up in 1L volumetric flask o,1M NaOH by dissolving 4g of pellets in 1L distilled H2O. I make it up 5x and keep it in 5L container. Then make 1L of HCl by diluting 10M conc solution. Use 8.5 ml of conc HCL in 1L volumetric flask .That will give you around 0.085M HCl which will titrate around 21.5 ml of NaOH. It is not accurate, because none of those chemicals are primary standards, but girls can knock themselves out by working out their own titrations. So there. I refuse to pamper my teachers. The kids need to practice, I garantee you, that nobody will get identical results. So your NaOH will be 0.1 M and HCl will be 0.085M.

To work it out
M1xV1=M2xV2

Good luck
lada

[Ross]

Hi everyone,

I read through the thread and wondered if I should put my 2 cents worth into the discussion.

Sassi, I think your teacher needs some education about volumetric methods - not using any primary standards! The fumes on top of the HCl is HCl so the concentration is changing (granted - slowly) and NaOH sucks in the water from the atmosphere at a great rate of knots. NaOH in the bottle varies quite a but depending on how often the bottle is opened and how good the seal is.

Normally, someone will make a solution that is approximately the concentration required, then find out what the concentration is by titrating against a standard (standardising) and write that concentration on the bottle. So in other words, generally for schools where the kiddies titrate acid and base it does not matter what the concentration is as long as everybody uses the same solutions.

When I do pracs where they are using a lot of approx 0.1M HCl or NaOH, I will make up 20 to 25L of solution at a time and they can come and grab what they need. At the end, I just throw whats left out. If they want it standardised, I have been known to write and concentration that is close to what is in the bottle and the teachers are none the wiser. They have learnt there are times when its important to have a known concentration (eg for titating with asprin) and times when its not important.

To follow on with this standising theme, I even make up lots of the bulk solutions with tap water if they are going to just titate with them. (Can almost hear the gasps in horror now!) I find it amusing when they are titrating, or doing a dilution for their titration solutions and they insist in using distilled water... if they only knew.

Sorry for the rant, must be having one of those weeks where the lack of knowledge of the teaching staff has gotten to me.

Cheers
Ross

[lada]

I agree with Ross. I too, use tap water for bucket chemistry. To make up 10 l of HCl or NaOH, why waste distilled water. I always say, the kids must bathe in it, they use it up soo fast.
Lada

[Robb]

Hi All,

For standarisation of NaOH we need to make sure you have the primary standard KHP or Potassium Hydrogen Phthalate. This is then measured against the prepared NaOH.

If you need the calcs let me know, this could benefit most people. I don't have a problem with sharing this information... Good Luck!

Cheers,

Robb.....

[Sassi]

Well thanks for all your help guys, I knew I could count on you

I have spent the entire day titrating and I survived! For someone who thoroughly HATES titrations it went surprisingly well and I feel quite calm and because of that I am very proud of myself

this is what happened; Firstly the teacher DEMANDED that i standardized it, she did not want to hear anything about 'bucket chemistry' so grrrr, there went the easy option

So then I started it using oxalic acid as the primary standard and it did not go well at all, thought I was doing something wrong since after all last time I did a titration was back in 2002, but eventually, after a lot of wasted time, I discovered that the 'oxalic acid' was not oxalic acid after all. Despite the very large label stating it was oxalic acid, there was a miniscule little formula on the side of the bottle saying that it was sodium oxelate.... Believe you me, there was a lot of very loud swearing going on at this stage, all in Swedish off course, and a bit of Italian too, and I was not very impressed with the lady that was here before me, although I guess accidents happen.

After a calming tea (wishing it was wine) I started again, but cause we had no KHP I had to use Na2CO3 to standardize HCL and then using that to standardize the NaOH, pheeeew! A lot of work for something the kids are gonna mess up anyways. I think I got the calculations right fingersx please, very surprised at how much I remembered from uni, specially since I thought I had put that in the 'I will permanently forget this, because if I have to do it again I will kill myself" part of my brain. Anyways I hope i was right... if not I dont give a rat's a...

Robb I would love a copy of the calcs, so that I could check myself if I did it right and also for future reference My email is Saberg@wenona.nsw.edu.au

Sass

[ird]

Gday All.
These attached files may be of some help!!
We purchase the Volumetric Standards produced by AJAX. (1M HCl, 1M H2SO4 & 0.02M KMnO4)
Then we buy cheapest stock and titrate against the above standards to find thier true Molarity.

Tip for ease of titrating:
Use burette, magnetic stirrer, beaker, stirring bar. This takes the rub your tummy while you pat your head out of doing titrations.

Hope this helps.
ian.davies@brisbanegrammar.com

[Xenon]

0.100M? It is meaningless if she wants standardised solution to 3 decimal points unless you have an analytical balance capable of weighing the primary standard to at least 3 decimal points. Even if you have such a balance, schools aren't analytical laboratories and if the students end up working in this area, they'll find titration skills are redundant. They will need to know instrumental techniques: HPLC, GC/MS, spectrophotometry etc.

[Sassi]

Well what do you know...

After all of that, she didn't have time to use it!!! They ran out of time, and now they wont do it again I am so pissed off, bloody was forced to do titration and it was a complete waste of time, wasted my entire day yesterday and this morning setting it all out for the kids. But at least she was very sorry about it and she actually gave me some flowers for my troubles They can be human after all

Sass

[dime]

Holy Moly!!! I think I would have killed her. Most of us labbies haven't been to uni so she is particularly fortunate to have you to understand in the first place! Remember we don't get paid to think that much, the teachers do!

[rae]

Oh Sassi
I feel for you !! They really have no idea sometimes. I'm sure they think they are brain surgeons who are saving lives or trying to produce a class of brain surgeons.
At least the flowers may help but it doesn't bring back all that time you wasted. Imagine if all the teachers expected us to do that!!!

OMG!!!

Lorrae

[Xenon]

Flowers? Flowers? Bribery & Corruption!

[labbassistant]

Hi all,
Can someone explain making a primary standard to me? I do not understand this at all.
We have some made up from the previous labbie but she retired and I'll need to make more.
We used 0.1m oxalic as the primary standard and 0.1 NaOH (unknown conc to the students), but do I just make up 0.1m oxalic and call it primary standard? Or do I need to titrate it? So confused....

[Marama T]

Taken from Google. It's not about the concentration, it's about the properties of the solid chemical.
Standards are used in analytical chemistry. Here, a primary standard is typically a reagent which can be weighed easily, and which is so pure that its weight is truly representative of the number of moles of substance contained. Features of a primary standard include: High purity. Stability (low reactivity)

Primary standard - Wikipediahttps://en.wikipedia.org › wiki › Primary_standard
Image result for what is a primary standard in chemistry

[Merilyn1]

Hi all,
Can someone explain making a primary standard to me? I do not understand this at all.
We have some made up from the previous labbie but she retired and I'll need to make more.
We used 0.1m oxalic as the primary standard and 0.1 NaOH (unknown conc to the students), but do I just make up 0.1m oxalic and call it primary standard? Or do I need to titrate it? So confused....

If you don't know what to do, ask the chemistry teacher. I have never standardised a solution in over ten years. I had a Chem teacher once who would go to the trouble of doing this. I love my chem teacher here - he just makes up a number as long as my solution is close to 0.1M. He only wants the students to learn the process, doesn't matter if the answer isn't accurate.

[shaz.H]

Year 12 Chemistry in Focus page 196 explains primary standard solutions. The students usually make their own when performing a titration. If the teacher is trying to save time then yeah make it up as analytical as you can, label primary standard solution and the students will titrate this solution against the 0.1 NaOH that you have made(unknown to the students).You do not need to titrate (unless you love it and want to have some fun)

[labbassistant]

Thanks so much!! I spoke to the chem teacher too and they clarified it too.