Brain Drain

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Krysia Lee
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Brain Drain

Post by Krysia Lee »

HI
i have about 1.7L of 0.632M Naoh. I want to make it up to a 1M concentration. How do I work that out? Sorry brains gone to mush.Was trying C=nv and n=m/mr
got myself all fuddled
Thanks Krysia
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dime
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Re: Brain Drain

Post by dime »

I would be just making a fresh batch of NaOH. Its not like it is an expensive chemical really. :D
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smiley
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Re: Brain Drain

Post by smiley »

Well given that NaOH is only 40g per Litre, do you really need the grief of working out how much to add. Seriously, I wouldn't bother! Unless of course it's some sort of weird Senior Science prac? In which case, tell them to find another one! :cheesy:
Cheers, K 8-)
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smiley
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Re: Brain Drain

Post by smiley »

Oh, and just for the academic exercise, the answer is 14.72g/L :D
Cheers, K 8-)
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Graham Kemp
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Re: Brain Drain

Post by Graham Kemp »

Krysia Lee wrote:HI
i have about 1.7L of 0.632M Naoh. I want to make it up to a 1M concentration. How do I work that out? Sorry brains gone to mush.Was trying C=nv and n=m/mr
got myself all fuddled
Thanks Krysia
I'd add 37.0 g and dillute to 2.00 L final volume.
((2.00 L) (1.00 M) - (1.70 L) (0.632 M)) * (39.997 g/mol) = 37.0 g

Just adding sodium hydroxide will change the volume, but if your not so concerned with accuracy* then add 25 g.
((1.7 L) (1.000 M - 0.632 M)) * (39.997 g/mol) = 25 g

(*... and solid NaOH absorbs water so there's no guarantee of accurate weight anyway...).

Basically it's: ( (Target Volume) (Target Concentration) - (Measured Volume)(Measured Concentration) ) * (Molecular Mass)
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Jazz
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Re: Brain Drain

Post by Jazz »

how did youn get such precisse molarity. have you done titration? It is not easy to make up NaOH with such precision. or it just me 8-[
Cheers Jazz
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mtg
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Re: Brain Drain

Post by mtg »

I use old NaOH to clean the sinks and drains.
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Graham Kemp
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Re: Brain Drain

Post by Graham Kemp »

Jazz wrote:how did youn get such precisse molarity. have you done titration? It is not easy to make up NaOH with such precision. or it just me 8-[
It's not just you. NaOH just can't be accurately weighed; it adsorbs moisture too readily. Any precision has to come from calibration after preparation.
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Krysia Lee
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Re: Brain Drain

Post by Krysia Lee »

yes i did do several titrations. I was going to just throw it away but I thought its just as easy to fix it as it is to start again.After a cup of tea the fog cleared and I was able to calculate what I needed. I have a few bottles (all different concentrations) that have been made up incorrectly (not by me) , thanks for all the help anyway.
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