Sciencemadness Discussion Board

Tests for Boron in Borax

CHRIS25 - 6-7-2014 at 01:50

How would I, if it is possible, be able to determine the amount of boron that is in Borax, or any sodium borate or tetraborate compound? Something here that I can not discover for myself.

sasan - 6-7-2014 at 03:33

Chris it is a hard question.boron compounds like borax and boric acid have easy procedure for producing in industry.the commercial ones are nearly 99% pure.so if you want know the purity of your reagent it is the answere

There are methods for determining the boron in its compunds but I dont think if you can find some data about that

[Edited on 6-7-2014 by sasan]

blogfast25 - 6-7-2014 at 04:51

@ Sasan:

It's not the purity of Borax he's looking at.

@ Chris:

Accurately weigh a sufficient amount of Borax and dissolve it in sufficient water to give a solution of about 0.3 M.

Acidify the solution according to:

Na2B4O7·10H2O(aq) + 2 HCl(aq) ===> 4 H3BO3(s) + 2 NaCl(aq) + 5 H2O(l)

The boric acid (H3BO3) is poorly soluble in cold water, so after this step, chill in a refrigerator or on an ice bath: the boric acid will crystallise out as slightly greasy looking flakes.

Filter these off and wash carefully with small aliquots of iced water to remove the NaCl and any excess HCl.

Dry the boric acid and weigh it. From that weight the w% boron in the Borax can be calculated. This is approximate because boric acid does have limited solubility in cold water, so you will slightly underestimate the boron content.


[Edited on 6-7-2014 by blogfast25]

CHRIS25 - 6-7-2014 at 04:56

Ah, thanks Gert (and Sasan). Not a whimsical question, I need to determine the amount of Boron in samples so much appreciated, I was afraid that it might have been more complex than this, so glad to read it is fairly straightforward.

blogfast25 - 6-7-2014 at 05:03

Quote: Originally posted by CHRIS25  
I need to determine the amount of Boron in samples so much appreciated,


You have reasons to not trust the empirical formula of the product you have bought?

CHRIS25 - 6-7-2014 at 06:42

Getting a product from an Irish farmers shop in a clear bag with no labelling and it simply says "Boron Powder' yes it is difficult to know the source, except that upon questioning he told me the company/manufacturer's name was solubor (USA as I understand) and further hunting revealed a Boron content of 21%, but Solubor is an octaborate tetrahydrate and the 50 kg sack the shop owner showed me had 17.5% sodium borate, not tetraborate otherwise this would be classed as Borax, which the EU seems to be banning slowly with stupid ridiculously invented health warnings. Yes it is all rather hazy this info. I know what wolfram says about Borax being 11.3% Boron, but I do not seem to be able to find it at the moment, very strange indeed.

blogfast25 - 6-7-2014 at 07:25

The octahydrate and decahydrate often referred to may be one and the same. Borax's formula is written in two ways: Na2B4O7•10H2O or Na2[B4O5(OH)4]•8H2O but they are one and the same product (CAS 1303-96-4) with a molar mass of 381.38 g/mol. The latter notation is closer to reality as we understand it today. With the molar mass of boron being 10.81 g/mol:

W% boron = (4 x 10.81) / 381.38 x 100 % = 11.34 w% boron


[Edited on 6-7-2014 by blogfast25]

CHRIS25 - 6-7-2014 at 08:09

Quote: Originally posted by blogfast25  
The octahydrate and decahydrate often referred to may be one and the same. Borax's formula is written in two ways: Na2B4O7•10H2O or Na2[B4O5(OH)4]•8H2O but they are one and the same product (CAS 1303-96-4) with a molar mass of 381.38 g/mol. The latter notation is closer to reality as we understand it today. With the molar mass of boron being 10.81 g/mol:

W% boron = (4 x 10.81) / 381.38 x 100 % = 11.34 w% boron


[Edited on 6-7-2014 by blogfast25]

Hi, no solubor is OctaBorate with formula: Na2B8013

blogfast25 - 6-7-2014 at 08:36

That's an anhydrate. About 25 w% boron.

The tetrahydrate of that octaborate has MM = 412.48 g/mol and boron w% of 21 w%.

Yep, I think you best get analysing!

[Edited on 6-7-2014 by blogfast25]