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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Morphic flip on January 26, 2018, 03:14:06 PM

Title: determining concentration of caustic soda in solution.
Post by: Morphic flip on January 26, 2018, 03:14:06 PM

What would be the easiest way of determining the concentration of caustic soda in a solution that also contains sulphated castor oil? Both are low concentrations.
Any help appreciated.

Title: Re: determining concentration of caustic soda in solution.
Post by: chenbeier on January 26, 2018, 05:58:17 PM

Using a pH-probe and a titration.

Title: Re: determining concentration of caustic soda in solution.
Post by: Morphic flip on January 27, 2018, 02:36:01 PM

titration against what strength HCl?

Title: Re: determining concentration of caustic soda in solution.
Post by: chenbeier on January 27, 2018, 09:07:36 PM

You have to check to use 1 m or 0,1 m HCl.

Title: Re: determining concentration of caustic soda in solution.
Post by: Arkcon on January 28, 2018, 06:21:34 AM

You can check a pharmacopeia, if it specifies how to determine adulterants in sulfated castor oil.  You'll be required to do that, if you expect to sell this castor oil, as a pharmaceutical.   There may also be ASTM testing protocols available.   A purchaser may expect you to follow such testing protocols, especially if you claim to be doing so.

Quote from: chenbeier on January 27, 2018, 09:07:36 PM

You have to check to use 1 m or 0,1 m HCl.

If you're just curious, you can design a titration on your own, as was described here.  You start with a balanced reaction.  You make a guess as to how much caustic there is.  You consider how big of a sample you can handle, and determine which concentration will keep the reaction volume reasonable.  You can test that it works, by spiking some caustic into water.  And again, by spiking some into some sulfated castor oil that you know is clean.  You can also test your precision.

Title: Re: determining concentration of caustic soda in solution.
Post by: Morphic flip on January 28, 2018, 08:57:54 AM

OK, thanks.

So if it takes say 25ml of 0.1M of HCl to neutralise 50ml of the caustic solution, the equation would be

25.00 ml x 0.1M / 50.00 ml

=0.05M ?

What would 0.05M be as a percentage in 100 litres of the caustic solution?

Thanks, but I'm new to this.

Title: Re: determining concentration of caustic soda in solution.
Post by: chenbeier on January 29, 2018, 04:12:42 AM

What does 0,05 M means? Please express in a different unit. If you know that change this to mass value. Then you need the specific gravity of the solution. The ratio of your result devided to the mass of the solution will guide you to the percentage.

Title: Re: determining concentration of caustic soda in solution.
Post by: Morphic flip on January 29, 2018, 11:15:19 AM

0.05M is molar strength result.

Title: Re: determining concentration of caustic soda in solution.
Post by: chenbeier on January 30, 2018, 06:59:33 AM

No I mean what can you write instead of M. Which unit?

Title: Re: determining concentration of caustic soda in solution.
Post by: Morphic flip on January 30, 2018, 01:51:15 PM

do you mean grams?

Title: Re: determining concentration of caustic soda in solution.
Post by: chenbeier on January 31, 2018, 04:32:40 AM

You have to calculate to the mass (gram),

But it doesnt answer what M is in a correct unit.

Title: Re: determining concentration of caustic soda in solution.
Post by: Morphic flip on January 31, 2018, 12:09:39 PM

What are the equations to do so please?

Title: Re: determining concentration of caustic soda in solution.
Post by: Borek on January 31, 2018, 01:53:37 PM

It is a simple stoichiometry.

http://www.titrations.info/titration-calculation

Title: Re: determining concentration of caustic soda in solution.
Post by: chenbeier on February 01, 2018, 02:17:58 AM

Quote from: Morphic flip on January 31, 2018, 12:09:39 PM

What are the equations to do so please?

M = mol/l convert to g/l  convert to g/kg convert to %

Title: Re: determining concentration of caustic soda in solution.
Post by: Morphic flip on February 02, 2018, 02:33:44 PM

OK, thanks. I'll have a go, but never been any good with formula's